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Visual acuity is the measurement of an individual's ability to recognize details of an object in a space. Visual function measurements in clinical ophthalmology are limited by factors such as maximum contrast and so it might not adequately reflect the real vision conditions at that moment as well as the subjective aspects of the world perception by the patient. The objective of a successful vision-restoring surgery lies not only in gaining visual acuity lines, but also in vision quality. Therefore, refractive and cataract surgeries have the responsibility of achieving quality results. It is difficult to define quality of vision by a single parameter, and the main functional-vision tests are: contrast sensitivity, disability glare, intraocular stray light and aberrometry. In the current review the different components of the visual function are explained and the several available methods to assess the vision quality are described.
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386 Arq Bras Oftalmol. 2013;76(6):386-90
Artigo de Revisão | Review ARticle
INTRODUCTION
Visual acuity measures the ability to recognize object details.
Once it is measured under controlled distance, light and contrast
conditions, visual acuity does not reflect the real quality of vision.
External factors as indirect light can affect this quantitative assess-
ment. Clinical ophthalmology commonly uses visual acuity opto-
types only in order to assess the entire visual function(1).
Several previous epidemiological and clinical studies rely of visual
functions measurements as the primary outcome, despite these
measurements are crucial to understand the real patient’s visual abi-
lity. Visual acuity does not express the real vision conditions and the
subjective aspects of world perception by the patient(2).
The most common vision quantification test is the spatial deter-
mination of visual acuity through the Snellen chart. Letters displayed
have two basic characteristics: size and contrast(3). This test assesses
the smallest identified font, keeping constant the black letters high
contrast relative to the white background on which they are displayed.
The degree of visibility of a given figure may be altered by reducing its
contrast to a level which it is no longer recognized, regardless its size(4).
In view of the fact that excellent visual acuity is expected from
cataract and refractive surgery, the need for measurement of broader
aspects of visual function has increased. Some patients with mode-
rate visual acuity preoperatively might not be prepared to accept a
postoperative visual acuity that, despite being good, is blurred by
troublesome glare or disturbed by loss of contrast sensitivity. When
a patient complains of glare, there are distinct visual phenomena he
might be complaining of(5).
Quality of vision is difficult to define by a single parameter. Some
patients are dissatisfied with their quality of vision after excimer laser
refractive surgery even though their Snellen acuity is 20/20 (1.0) or
better. Higher-order aberrations, image degradation, and contrast
acuity have been implicated as reasons for patient’s dissatisfaction(6).
Glare disability is another parameter that correlates with visual com-
plaints after refractive surgery(7).
The purpose of this review is to explain the different components
of the visual function and to describe available methods to assess the
aspects of quality of vision.
FUNCTIONAL VISION
Functional vision is our everyday vision. Different tasks in our daily
life use different parts of our visual system. It reflects our vision in real-
world situations, where we have to see both smaller high-contrast
images and larger low-contrast ones. Our cognitive perception, the
health of our visual system and our brain processing function, all play
critical roles on how well we see the world(8).
Vision scientists are particularly concerned with how well the eye’s
retina transforms a visual image into neural code. That is how our eyes
work with our brain to translate images into visual perception(9-13).
The retina/brain system also filters the image into different sizes
and levels of contrast(10,11). Many properties come into play at the
cortical level that impacts the final process of the visual information.
These include attention, expectancy, memory, identification and
other cognitive perceptual properties. When examining the comple-
Quality of vision in refractive and cataract surgery, indirect measurers: review article
Qualidade visual em cirurgia refrativa e catarata, medidores indiretos: artigo de revisão
Taís RenaTa RibeiRa PaRede1, andRé augusTo MiRanda ToRRicelli1, adRiana Mukai2, MaRcelo VieiRa neTTo1, saMiR Jacob bechaRa1
Submitted for publication: June 12, 2012
Accepted for publication: July 25, 2013
Study carried out at Universidade de São Paulo - São Paulo (SP), Brazil.
1 Physician, Department of Ophthalmology, Medical School, Universidade de São Paulo - São Paulo
(SP), Brazil.
2 Technician in Ophthalmology, Department of Ophthalmology, Medical School, Universidade de
São Paulo - São Paulo (SP), Brazil.
Funding: No specific financial support was available for this study.
Disclosure of potential conflicts of interest: T.R.R.Parede, None; A.A.M.Torricelli, None; A.Mukai,
None; M.V. Netto, None; S.J.Bechara, None.
Correspondence address: Taís Renata Ribeira Parede. Avenida Doutor Enéas de Carvalho Aguiar,
155 - Instituto Central - 6o andar - Departamento de Oftalmologia / Setor de Cirurgia Refrativa -
São Paulo (SP) - 05403-000 - Brazil - E- mail: taisparede@hotmail.com
ABSTRACT
Visual acuity is the measurement of an individual’s ability to recognize details of an
object in a space. Visual function measurements in clinical ophthalmology are limited
by factors such as maximum contrast and so it might not adequately reflect the
real vision conditions at that moment as well as the subjective aspects of the world
perception by the patient. The objective of a successful vision-restoring surgery lies
not only in gaining visual acuity lines, but also in vision quality. Therefore, refractive
and cataract surgeries have the responsibility of achieving quality results. It is difficult
to define quality of vision by a single parameter, and the main functional-vision tests
are: contrast sensitivity, disability glare, intraocular stray light and aberrometry. In the
current review the different components of the visual function are explained and
the several available methods to assess the vision quality are described.
Keywords: Vision; Refractive surgical procedure; Cataract extraction; Contrast sensi-
tivity; Vision, ocular/physiology; Aberrometry; Vision tests
RESUMO
Qualidade Visual é a medida da capacidade individual de reconhecer detalhes de um
objeto no espaço. Medições de função visual na clínica oftalmológica são limitadas por
vários fatores, tal como máximo contraste e assim podem não refletir adequadamente
as condições visuais reais, bem como os aspectos subjetivos da percepção do mundo
pelo paciente. O sucesso em uma cirurgia está não apenas em restaurar linhas de
visão, mas sim qualidade visual. Portanto, as cirurgias refrativas e de catarata têm a
responsabilidade de alcançar resultados de qualidade. É difícil definir qualidade visual
por um único parâmetro, sendo os principais testes de função visual: sensibilidade ao
contraste; glare; dispersão intraocular da luz e aberrometria. Nesta revisão os diferentes
componentes da função visual são explicados e os diversos métodos disponíveis para
se avaliar a qualidade de visão são descritos.
Descritores: Visão; Procedimentos cirúrgicos refrativos; Extração de catarata; Sensi-
bilidades de contraste; Visão ocular/fisiologia; Aberrometria; Testes visuais
Parede TRR, et al.
387
Arq Bras Oftalmol. 2013;76(6):386-90
xity of our visual system, it is easy to see how the quality of input can
impact the quality of our visual experience(10,11).
A channel model represents how different vision cells, or chan-
nels, handle different aspects of vision, such as color, size, shape,
contrast and motion. Each visual channel collects different bits of
information for these varying aspects of vision and individually
transmits them to the brain to be processed and assembled into a
complete picture(8).
Everything we see is broken down into a range of spatial frequen-
cies, or channels. Channels are size-selective. Our visual system uses
these different channels to see in high- and low-contrast situations.
Our visual perception is the combination of all these channels(8,9).
The channels that are used to see the letters on the 20/20 visual
acuity test might be different from that ones that help us to see ob-
jects in our everyday lives. Because these channels are independent
from each other, we need to test the sensitivity of each channel
separately to determine how well different-size objects are seen(8,14).
FUNCTIONAL VISION PERFORMANCE TESTS
The clinical evaluation of the quality of vision performance before
and after an ophthalmologic surgery includes: the ability to detect
contrasts; vision in different light levels; aberrations.
Contrast sensitivity(8,9,11)
Contrast sensitivity refers to the ability of the visual system to
dis tinguish between an object and its background. According to
the channel model of vision, size-selective contrast cells are used to
detect the differences between light and dark parts of an object and
the background against which it is seen.
There are different available tests for the evaluation of contrast
sensitivity. The main difference among them is the target type.
Charts that use letters, numbers or symbols in decreasing con-
trast are usually called low-acuity contrast tests, while those that
use circles with bars or waves are called contrast sensitivity tests. For
each kind of test, the least amount of contrast that can be perceived
by an observer is displayed in graphs created by the manufacturers
themselves, giving rise to the “line of contrast sensitivity” for each
patient and the patient’s ability to distinguish contrast sensitivity in
relation to the normal range.
In some tests, depending on the logarithmic scale of contrast
sensitivity, the patient might be classified as having normal vision,
visual impairment or low vision.
There are two kinds of contrast sensitivity tests presently em-
ployed: grating tests and letter contrast sensitive.
Sine-wave gratings tests(8-10)
Sine-wave gratings (Figure 1) are used to create and test the con -
trast sensitivity curve. A sine-wave grating is a repeated number of
fuzzy dark and light bars, or cycles. The number of grating cycles over
a specified visual angle determines its spatial frequency.
A small number of cycles over a specified visual angle are defined
as having a low spatial frequency. A large number of them over the
same visual angle are defined as having a high spatial frequency. Con-
trast is the difference between the grating’s brightness and darkness.
The visual system filters the images we see into independent
ranges of sizes, or spatial frequencies. In vision testing, sine-waves of
varying spatial frequencies (sizes) and contrast are needed to test the
visual channels involved in functional vision.
The most commonly used tests are: Vision Contrast Test System
(VCTS 6500 e 6000) (Vistech, Dayton, OH), Contrast Sensitivity Vision
(CSV 1000 E) (VectorVision, Greenville, OH) and Functional Acuity
Contrast Test (FACT) (Vision Science Research Corporation, Walnut
Creek, California).
Environment conditions considerations to grating tests are shown
on table 1.
Letter contrast sensitivity(8,9,13)
Letter contrast sensitivity (Figure 2) is similar to low-contrast
acuity in that the patient’s task is to read as many letters as possible
from a chart. Although in the contrast sensitivity test all letters have
the same size and are large enough to be legible whenever they can
be seen at all, their contrast is progressively reduced, from near 100%
at the top of the chart, to near 0% at its bottom.
The ability to see low-contrast letters is important for reading
signs and identifying low-contrast objects that are similar in size
to the test letters. However, letter contrast sensitivity test results
may not be inferred to real life situations that involve detection and
recognition of objects that are either much larger or much smaller
than the chart letters.
The most commonly used tests are: Test Bailey-Lovie Chart or
Regan (The National Vision Research Institute, Australia), that use
Early Treatment Diabetic Retinopathy Study (ETDRS) Chart (Precision
Vision) and Pelli-Robson (Haag-Streit, Mason, OH, USA).
Environment considerations to letter tests are also shown on table 1.
WhiCh Contrast sensitivity test is the best?
A comparison of Contrast Sensitivity Tests Research shows that
the “Contrast Sensitivity Curve” provided by sine-wave grating tests
is more sensitive and informative than the results obtained from low-
contrast letter-acuity systems(8).
Some investigators believe grating tests of contrast sensitivity
are superior to letter contrast sensitivity charts. Their arguments em-
phasize that, in clinical research, it is important to assess the broad
contrast sensitivity function from low to high spatial frequencies,
as this function reflects the visual system’s multiple spatial filters(15).
A number of authors have concluded that test-retest reliability
of the sine-wave grating tests may be problematic for their intended
purpose of screening and tracking change(15-18). The good test-retest
reliability of the letters chart, relative immunity from varying test
conditions, ease the brevity of administration (3-5 minutes), and
availability of published normative data(19), have led to its frequent
choice for epidemiological studies(20-23).
vision in different light levels - “glare test
Disability glare
It refers to the temporary loss of visual function in the presence of
a bright adjacent light source. Common sources of disability glare for
Figure 1. FACT sine-wave grating chart tests ve spatial frequencies (sizes) and nine levels
of contrast. The patient determines the last grating seen for each row (A, B, C, D and E)
and reports the orientation of the grating: right, up or left. The last correct grating seen
for each spatial frequency is plotted on a contrast sensitivity curve.
Quality of vision in refractive and cataract surgery, indirect measurers: review article
388 Arq Bras Oftalmol. 2013;76(6):386-90
drivers are the sun and headlights from oncoming cars. Susceptibility
to glare sources varies greatly from person to person, depending on
the amount of light that is scattered into the retina from the crystalli-
ne lens and other eye structures. A clinical test that could accurately
predict the effects of glare and light-scattering sources on driving
performance should be a valuable diagnostic tool for evaluating new
medical products that physically produces the light scatter or affects
how one realizes the intraocular light scatter. Several disability glare
tests have been developed for clinical use(24-25).
In most tests, especially those that involve measuring contrast
sensitivity or visual acuity in the presence of a continuous, static glare
source, its light may cause the pupil to constrict enough to affect the
results of the glare measurement(26).
Advantage of these tests is that they eliminate the needs to control
the levels of room light and can be used in a small space (Table 1)(27).
Available tools to measure disability glare are: Optec 6500 P
(Stereo Optical Company, Inc, Chicago, Illinois, USA), CST 1800 digital
(Vision Sciences Research Corporation, Walnut Creek, California) and
CSV 1000HGT (VectorVision, Greenville, OH).
Intraocular stray light
A different approach to assess the effects of disability glare on
visual function is to obtain a direct measurement of the amount of
stray light in the eye produced by a glare source. Oculus Instruments
(Oculus, Optikgeräte, Wetzlar- Dutenhofen, German) have recently
marketed the C-Quant Stray light Meter® (Figure 3) developed by van
den Berg and Ijspeert(28-30).
The device, currently marketed in the United States, effects a tem-
poral variation in the stray light from a flickering glare source, which
is nullified by a superposed light flickering out of phase with the stray
light. The amount of added light that just cancels out the stray light
flicker is a direct measurement of the stray light. The test is fast, easy for
the patient, and accurate. However, the correlation between the stray-
light results from this test and the results of contrast sensitivity with
glare tests and the real life conditions, have not been established(2).
aberrometry(31)
Aberrometry allows the objective evaluation of visual quality. It is
a technological modality that studies the propagation of light from
the physical optic analysis. In an optical homogeneous system the
Table 1. Comparison of Contrast Sensitivity test and Glare test methodologies
Methodology Tests Pros Cons
Contrast sensitivity
Sine-waves grating tests VCTS 6500
VCTS 6000
CSV 1000E
FAC T
Assesses the whole contrast sensitivity function
from lowest to highest spatial frequencies
Time consuming; results are more variable
than standard acuity test results
Letter contrast sensitivity
(ETDRS Charts)
BAILEY-LOVIE
REGAN
Quick, easy, good predictor of performance for
high resolution tasks under bright
and low light conditions
If photopic conditions: Poor predictor of performance under low
contrast conditions. If mesopic condition: Test conditions difficult to
control and results are more variable than photopic results
Letter contrast sensitivity PELLI-ROBSON Assesses performance for
reading low contrast signs
May not provide an accurate assessment of performance detecting
and recognizing objects with sizes different than the chart letters
Glare test
Disability glare OPTEC 6500
CST 1800
CSV 1000HGT
Adding glare testing to vision tests adds
information about the effects of intraocular light
scatter on visual performance
Time consuming; results are more variable
than standard acuity test results
Intraocular straylight C- QUANT Fast, easy for the patient, and accurate Correlation between straylight results and other vision tests with
glare, and driving performance not yet established
VCTS= vision contrast test system; CSV= standardized contrsts sensitivity; FACT= functional acuity contrast test; ETDRS= Early Treatment Diabetic Retinopathy Study; CST= contrast
sensitivity tester; C-Quant= cataract-quantifier.
Figure 2. Pelli-Robson test measures contrast sensitivity using a single large letter size
(20/60 optotype), with contrast varying across groups of letters. Specically, the chart uses
letters (6 per line), arranged in groups whose contrast varies from high to low. Patients
read the letters, starting with the highest contrast, until they are unable to read two or
three letters in a single group. Each group has three letters of the same contrast level,
so there are three trials per contrast level. The subject is assigned a score based on the
contrast of the last group in which two or three letters were correctly read. The score,
a single number, is a measure of the subject’s log contrast sensitivity. Thus a score of 2
means that the subject was able to read at least two of the three letters with a contrast of
1 percent (contrast sensitivity = 100 percent or log 2). A Pelli-Robson score of 2.0 indicates
normal contrast sensitivity of 100 percent. Scores less than 2.0 signify poorer contrast
sensitivity. Pelli-Robson contrast sensitivity score of less than 1.5 is consistent with visual
impairment and a score of less than 1.0 represents in visual disability.
Parede TRR, et al.
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Arq Bras Oftalmol. 2013;76(6):386-90
light propagates uniformly from a point of light, at the same speed
in all directions. When this wavefront hits on an ideal lens, it creates
a single focal point. In real lenses, the spread of the wavefront is
modified, so paracentral and peripherals rays propagate in several
wavefronts, not coinciding in a single focal point. This phenomenon
is known as monochromatic aberration.
The human eye is not a perfect optical system, but the aberrations
can be partially compensated due to the aspherical corneal shape
and the asphericity of the lens, that bring an attenuation of optical
aberrations.
The wavefront analysis measures the difference between the
aberrations of a real wavefront, measured in an optical system and
an ideal wavefront, through an ideal optical system. These differences
are the characteristic of each optical system, of each human eye.
The optical aberrations that can be corrected are the monochro-
matic ones (which have a single wavelength of visible light), and
these can be quantitatively schematized in Zernike Polynomial. This
polynomial describes the wavefronts in three dimensions: x, y and z.
Thus, the final wavefront of an optical system is the sum of Zernike
Polynomials that represents all strains of this system.
In the Polynomial, the aberrations are decomposed in lower order
aberrations (zero until second order) and higher order aberrations
(third until tenth order).
Lower order aberrations, denominated tilt, defocus and astigma-
tism, represent 85% of the total ocular aberrations in normal eyes
and are able to be corrected by spherocylindrical optical systems or
conventional refractive surgery.
Higher order aberrations represent 15% of ocular aberrations in nor-
mal eyes. There are aberrations that limit vision, and can not be corrected
with spherocylindrical lenses or conventional refractive surgeries. The
most relevant are coma, spherical aberration, trefoil and tetrafoil.
It is believed that higher order aberrations are responsible for a
number of visual complaints present even in patients with normal
visual acuity in the tables for high contrast. Complaints include the
presence of halo, glare, double vision and star burst symptoms, es-
pecially at night when the dilated pupil provides greater incidence of
high order aberrations in the optical system of the eye(32).
Higher-order aberrations can be expressed numerically by the
root mean square (RMS), which measures the difference between a
wavefront in a real optical system and an ideal optical system. The
RMS represents a reliable measurement of the amount of aberration
of an optical system, is generic and does not specify the qualitative
characteristics of each aberration found.
There are, however, other aberrometric indices that measure
the quality of the images generated by an optical system, such as
Point spread function (PSF), Strehl ratio, and Modulation transfer
function (MTF).
Point spread function
Measure how the retina views the point image after traversing
the optical system of the eye. It is graphically represented as a distor-
tion of a point on the retina varying with the captured area and the
pupilary diameter.
Strehl ratio
Contrast measurement defined by the ratio between the PSF of
an optical system and the PSF of a perfect optical system (limited only
by diffractions). The Strehl ratio value greater than or equal to 0.8 is
considered to be perfect, representative of an optical system without
aberrations. However, in the normal population, influenced by pupil
size, their values are close to zero.
Modulation transfer function
Attempts to measure image contrast. It evaluates the ability of a
system to convert an object contrast to the image plane, at a specific
resolution. In other words, it analyzes the image contrast as a function
of frequency.
SYSTEMS OF WAVE FRONT ANALYSIS
The system of wavefront analysis can be ingoing or outgoing. The
ingoing system studies the aberrations of the light beams projected
on the retina. The outgoing system evaluates the wave front coming
out of the eye from a light beam projected toward the retina and
reflected back. Thus, aberrometers can be classified according to their
standard operation: outgoing and ingoing system(28).
outgoing system(33)
- Hartmann-Shack Sensor (Zywave - Baush & Lomb; WaveScan -
VISX; Wasca Analyser - Carl Zeiss-Meditec; KR-9000PW - Topcon;
Maxwel - Ziemer Ophthalmology).
ingoing system(33)
Retinal imaging systems
- System of Tschening (WaveLight Wavefront Analyser - WaveLight;
ORK Wavefront Analyser-Schwind)
- Ray Tracing (Trace VFA; i- Trace- Tracey)
Double pass system
- Slit retinoscopy (OPD- Scan - Nidek; OQAS- Visopmetrics S.L.)
The quantitative and qualitative information provided by the
study of the wavefront of each human eye, can help to decode each
optical system separately and proceed surgically to reduce the high
order aberrations, providing better visual quality to the patient. It is
the custom refractive surgery, based on aberrometrical discrimina-
tion, in the wavefront analysis of each human eye(34).
FINAL CONSIDERATIONS
Our cognitive perception, the health of our visual system, and
the processing function of our brain all play critical roles on how well
we see the world. Vision researchers are still developing better tests
to analyze visual system and to understand all variables involved in
the visual acuity(8).
The current objective of a successful vision-restoring eye surgery
is not only to gain lines in visual acuity, but also to achieve quality of
vision. Therefore, refractive and cataract surgeries aim higher quality
standards for their results.
Figure 3. Example of a patient’s view of a straylight test, modied from van den Berg et
al.(24). The patient is presented with two alternative forced choices and asked to choose
between the stronger of two ickers presented in controlled background lights. The
test duration is one to two minutes per eye. The straylight test has an internal analysis
procedure that yields a reliability estimate called the expected standard deviation (ESD),
which was developed to control and increase the internal reliability of the test. Only
reliable test results (ESD ≤0.08 log units) should be accepted.
Stray light source:
Flickering annulus
Test elds
1 - Stray light only
2 - Stray light + variable
counterphase ickering light
Quality of vision in refractive and cataract surgery, indirect measurers: review article
390 Arq Bras Oftalmol. 2013;76(6):386-90
A detailed patient’s clinical history, his visual demands and oph -
thalmological characteristics at the preoperative clinical examination
are important in planning a successful surgery. Besides the diagnosis
of lens opacity or refractive error to be corrected, contrast sensitivity,
glare and wavefront analysis (aberrometry) should also be conside-
red when planning a surgical procedure.
When evaluating the safety and effectiveness of medical pro-
ducts, it is important to assess their effects on the performance of
“real-world” visual tasks. However, tests of visual performance are not
yet standardized, and no consensus has been reached on the ability
of existing clinical vision tests to predict real-world performance(28).
Most currently available clinical vision tests were developed as
general-purpose diagnostic tests for visual system disorders. Spe-
cific validation studies are still needed to identify individual tests or
combinations of them that might accurately and consistently predict
visual performance.
Assessment of visual performance is often important in evalua-
ting the safety and effectiveness of new drugs and medical devices,
but it is typically complex, expensive and burdensome for subjects
and investigators. Identification of clinical tests that could serve as
acceptable reference for visual-performance tests in clinical trials
would yield major savings of time, effort, and expense in the evalua-
tion of new products.
Studies that isolate the visual aspects of performance should
increase the chances of revealing their true correlations with clinical
measures of visual function(28).
Given all the technology available today to achieve excellence in
visual quality, such as customized refractive surgery, aspheric, toric
and intraocular phakic lens, should it be satisfactory to rely on just
one visual acuity, high-contrast test, without further relevant infor-
mation about the optical system of each patient? So how to take
advantage of all current available technology?
Perhaps spending more time on patient evaluation, using tests
that provide valuable information on the particular characteristics
of each optical system, and so improving our clinical and surgical
decisions to meet the patient’s expectations.
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... All participants were verbally screened during initial contact to exclude individuals that were unable to descend a seven-step staircase in a step-over-step walking pattern without a walking aid. Participants were also excluded if they scored worse than 1 logMAR on the administered Early Treatment Diabetic Retinopathy Study (ETDRS) visual acuity test (indicative of severe vision impairment (WHO, 2017),) or 1.0 logCS on the Pelli-Robson contrast sensitivity test (below visual contrast disability threshold of 1.0 (Parede et al., 2013)). The study was approved by the institution's research ethics board (REB#16-5938) and all participants provided informed consent prior to participation. ...
... Moderate visual impairment was represented by scoring higher than 0.46 logMAR (WHO, 2017) for visual acuity. A Pelli-Robson contrast sensitivity score of less than 1.5 is consistent with visual impairment, with a score of less than 1.0 representing visual disability (Parede et al., 2013). Demographic data is summarized in Table 1. ...
Article
Falls during stair descent are dangerous and costly. Contrasting tread edge highlighters improve measures of stair safety, however the necessary contrast level of these interventions has not been investigated. Thirteen older adults (67.7 ± 5.5 years) completed stair descent trials under normal (300lx) and low (30lx) lighting conditions, blurred and normal vision, and four different contrast levels (0%, 30%, 50%, 70%) between the tread edge highlighter and the neighbouring tread surface. Cadence and heel clearance decreased for 0% contrast compared to 50% and 70% contrast conditions, but contrast had no effect on foot overhang. Blurred vision was observed to be a greater factor influencing biomechanical measures of fall risk than low ambient lighting. Results suggest higher contrast highlighters improve measures of safety, even more so during simulated vision impairment, and that at least 50% contrast difference provides adequate visual information for safer stair ambulation.
... Contrast sensitivity measurement provides information about the capabilities of the visual system in real life conditions and more accurate information about the patient's visual quality. [9,10] Patients with cataracts often complain of impaired visual function in situations where high contrast visual acuity is not reduced. Complaints are about dazzling and generally impaired vision. ...
Conference Paper
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Purpose: Neurosensory vision tests can be an additional test to define the progression of cataract. Contrast vision tests can be a useful method to determine if the surgery is needed and the tests help to understand patient complaints about daily life tasks like driving. Our aim was to estimate the contrast vision sensitivity at different background levels and compare light scattering in patients before and after cataract surgery. Methods: Our research investigated 82 patients (73 eyes) with cataract and 56 (112 eyes) control group patients. The contrast sensitivity was measured with alternative forced choice test design (AFC) before and two weeks after Femto laser cataract surgery. The objective scattering index (OSI) was measured with HD Analyzer (Version 2.7.0.0). Contrast vision measurements were performed under mesopic conditions at different background brightness levels: 60 cd/m2 ; 85 cd/m2 ; 100 cd/m2 , and spatial frequencies:4 cpd; 6 cpd; 12 cpd; 18 cpd. Results: At the background brightness level 60, 85 and 100 cd/m2 there was statistically significant difference in all the spatial frequencies results, between all the groups (p<0.0001). The average OSI before the cataract surgery was 3.75 ± 1.62 units and OSI had a negative correlation with visual acuity (r=0.80) Conclusion Cataract-induced light scattering significantly decreased contrast sensitivity at all spatial frequencies There were no statistically significant differences between the Weber constants at the different background lighting levels, between all the groups. At a lighting level of 60 cd/m2 , cataract surgery provided significant improvement at the average spatial frequencies.
... The assessment can include contrast sensitivity, disability glare, intraocular stray light, and aberrometry. 14 For example, contrast sensitivity has been found to correlate well with various aspects of visual ability, including orientation and mobility, 8,11,15 reading speed, 16 and driving. 15 For keratoconus, the improvement of monocular highcontrast visual acuity with CLs is well-established, but fewer reports are available on the improvement of quality of vision with different CL modalities, all relative to spectacles, and do not necessarily compare different CL designs. ...
Article
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Purpose: To analyze the visual performance in contact lens wearers with keratoconus. Methods: A retrospective study including contact lens (CL) wearers was performed. The current best-corrected visual acuity with contact lens (BCVA-CL) and with spectacles (BCVA-S) correction, contrast sensitivity (CS) (by Metrovision-MonPack3 ®), analysis of light scattering in the retina and vision break-up time (HD Analyzer ®), and corneal tomo-graphy (Oculus Pentacam ® HR) were evaluated. Results: This study included 96 eyes of 59 patients with Keratoconus. Rigid gas permeable contact lenses (RGPCL), hybrid contact lenses (HCL), and silicone hydrogel/hydrogel contact lenses (HGCL) were fitted in 67, 17, and 12 eyes, respectively. Dynamic objective scatter index (OSI) (p = 0.024), minimum OSI (p = 0.037) and maximum OSI (p = 0.040) were significantly better with RGPCL and worse with HGCL. Mean CS in photopic conditions was significantly worse with HGCL and better with HCL (p = 0.006), without differences in mesopic conditions (p = 0.121). RGPCL wearers showed a higher mean K (p = 0.020), and a lower corneal thickness at the thinnest point (p=0.011). Conclusion: Visual quality varied significantly with different types of CL. Although RGPCL was fitted in patients with worse Pentacam tomographic parameters, RGPCL was associated with a better dynamic visual quality.
... It has been suggested that the scoring on the Pelli-Robson test would be more reliable if the number of all letters correctly seen was used [17,18]. However, the test's instruction for scoring is to find the last triplet of letters at which at least 2 letters are correctly seen [17,19,20]. ...
Article
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Purpose: The aim of this study was the evaluation of different plastic optical materials and determination of their behaviour in front of the eye. The study was not for clinical screening but mainly for material determination purposes, where the contrast sensitivity function is inefficient and difficult to interpret. Methods: Thirty male and female subjects with no ocular or reported systemic abnormality were selected. Twenty-two lenses of +6.00D power, made from 8 different plastic materials following requested: specifications; were edged to round shape and decentred in order to produce a 9 ∆ prism in front of the subjects' eye. Measurements of every subject were repeated four times on Bailey-Lovie and Pelli Robson charts, for each lens used in the experiment Results: A significant decline of visual acuity in correlation to higher index plastic lenses was observed. Also we observed a similar visual acuity decline concerning aspheric design lenses, but with a little better performance than non-aspheric design lenses of the same index material. Conclusion: The hypothesis of this work was that the higher the index the more the chromatic aberration. The conclusion is that this hypothesis is quite correct. However, the measurement of visual performance is not a very easy task. The wearer may simply experience blur through the periphery of the lens without realising the cause, and therefore the symptoms described to the optician can be confusing.
... The test score was recorded by the faintest triplet, of which atleast two letters are read correctly. The three letters have the same contrast hence allowing the patient three trials for each contrast [8]. The log CS value for this triplet is provided by the number which is nearest to the triplet on the scoring pad, either on the left or right side. ...
Article
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Objective: The objective of our study was to assess the variations in contrast sensitivity values of normoglycemic subjects and that of type II diabetic subjects of the same age group. It was also aimed at finding the visual acuities and study the associations of it with contrast sensitivity if any. Methods: It was a hospital-based comparative cross-sectional descriptive study conducted in the out-patient department of the Department of Ophthalmology, Saveetha Medical College, Hospital, Chennai. Visual Acuity and Contrast Sensitivity of 50 Type II Diabetic individuals and 50 age-equivalent control group subjects were measured using the Snellen’s chart and Pelli-Robson chart, respectively, during the months of January to March 2020. Results: Contrast Sensitivity measurements from 50 subjects with Non-Insulin dependent Diabetes Mellitus (NIDDM) were obtained. The subjects were the ones who had minimal or no diabetic retinopathy. It was observed that there is a significant association between reduced contrast sensitivity and Diabetes (P value<.00008). We also noted that CS may be reduced without corresponding loss of Visual Acuity. Hence, both visual acuity and contrast sensitivity measurements are helpful in the assessment of visual impairment due to diabetic eye disease. Conclusion: The contrast sensitivity can be seen as an early marker for visual impairment in diabetic eye care.
... Will it affect people's daily activities and be associated with a risk of injury, such as while driving and engaging in ball games? To gain a comprehensive and functional assessment of vision for those PCO eyes and to find new indicators for YAG treatment other than SVA would help physicians make the correct treatment decision [25]. ...
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Purpose To investigate the characteristics of dynamic visual acuity (DVA) and contrast sensitivity (CS) in pseudophakic patients with posterior capsular opacification (PCO). Methods Fifty-four eyes (36 patients) with PCO planned for laser capsulotomy were recruited. They underwent examinations of static visual acuity (SVA), DVA, CS and optical quality analysis (OQAS) before and one week after the laser treatment. Improvements in each index after laser treatment were analyzed. The visual quality of patients with good initial vision was studied separately. Results SVA, DVA and CS all significantly increased after capsulotomy (P < 0.05). Postoperative improvements in DVA were higher than in SVA, but they decreased when the speed increased. DVA at 15 dps gained the most improvement after capsulotomy. DVA at all analyzed speeds was significantly lower than SVA (P = 0.000). There was a significant speed-dependent decrease in DVA at lower speeds compared with higher speeds. The postoperative improvements in CS decreased when the spatial frequency was increased. The CS at the lower frequencies of 3 cpd and 6 cpd was the most improved after capsulotomy. CS was much lower at high frequencies (p < 0.05). There was a significant decrease in CS at higher spatial frequencies compared with lower frequencies. DVA improvements were correlated with CS improvements at medium spatial frequencies and with objective scattering index and Strehl ratio. The CS at all frequencies significantly improved for patients with good initial vision. Conclusion PCO could impair dynamic vision function, but CS was a more sensitive indication of visual complaints in patients with slight PCO.
... The greater the level of intraocular light scattering, the higher the level of OSI. Light scatter can be caused by tear film instability, lens opacities, microvacuoles or material defects of an implanted IOL, posterior capsule opacification (PCO) and by vitreous floaters [33]. The quality of the tear film has a prominently important role in the post-operative outcome after phacoemulsification with IOL implantation. ...
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Background The aim of our case control study was to evaluate the impact of glistening and tear film quality on visual performance after implantation of two different hydrophobic acrylic intraocular lenses (IOLs). Materials and methods In our retrospective study we included cataract patients operated between January 1, 2011 and December 31, 2012, with follow-up controls between January 2016 and December 2019. Z-Flex 860FAB (Medicontur) and AcrySof IQ SN60WF (Alcon) monofocal IOLs were implanted during standard phacoemulsification. Best corrected distance visual acuity (BCDVA) and contrast sensitivity were monitored over the post-operative period of up to 6 years. Glistening was evaluated semi-quantitatively with slit-lamp biomicroscopy and quantitatively using Pentacam HR (Oculus). Using HD Analyzer OQAS (Visiometrics), total intraocular light diffusion was interpreted with the objective scatter index (OSI) and tear film quality was evaluated with the tear film related objective scatter index (TF-OSI). Results 26 eyes implanted with the Z-Flex and 25 eyes with the AcrySof IQ IOLs were included in the analysis. The slit-lamp evaluation of patients with the Z-Flex IOL (0.57 ± 0.60) revealed significantly less glistening (p<0.0001), compared to the AcrySof IQ group (1.82 ± 0.90), and these observations were confirmed by the Pentacam HR analyses, as well (Z-Flex group: 35.1 ± 1.63, Acrysof IQ: 39.6 ± 3.69, p<0.0001). TF-OSI differed between the two sets of patients remarkably (1.53 ± 1.03 vs. 2.51 ± 1.76 for AcrySof IQ and Z-Flex groups, respectively, p = 0.043). Both groups of patients provided similar results of BCDVA and contrast sensitivity. Conclusion Glistening and tear film quality both contribute to visual performance outcomes after cataract surgery. In our study the advantage of less glistening in the Z-Flex IOL might have been masked by the adverse effects of the more pronounced tear film insufficiency of these patients, compared to the AcrySof IQ group. Among other factors, tear film quality should also be taken into consideration when comparing the impact of glistening on visual quality of patients implanted with different IOLs.
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This study investigated the reliability and correlation of two contrast sensitivity test (CST) devices in young adults with normal visual acuity, with or without refractive surgery. 57 patients aged 20–39 years who received both manual (OPTEC-6500) and automated CST (CGT-2000) examinations from June 19 to July 24, 2021 were retrospectively enrolled. Patients with corrected visual acuity under 20/20 or history of ocular surgery other than refractive surgery were excluded. 82 eyes of 41 patients (40 eyes with and 42 without history of refractive surgery) were enrolled. Mean time taken to complete each examination was 396.4 ± 20.4 and 286.8 ± 2.3 s using manual and automated CST, respectively (P < 0.001). Patients who underwent refractive surgery had significantly decreased area under the log contrast sensitivity formula (AULCSF) in mesopic compared with photopic conditions in automated CST examinations (AULCSF difference 0.415 vs. 0.323 in patients with and without refractive surgery, P < 0.001), but there was no significant difference in manual CST examinations. Patients who reported decreased subjective night vision had significantly decreased AULCSF in automated CST examinations, but there was no significant difference in manual CST examinations. Compared with manual CST, automated CST was quicker and correlated well with decrease in subjective night vision.
Article
Introduction Tripping on stairs results from insufficient foot to step edge clearance and can often lead to a fall in older adults. A stair horizontal-vertical illusion is suggested to increase the perceived riser height of a step and increase foot clearance when stepping up. However, this perception-action link has not been empirically determined in older adults. Previous findings suggesting a perception-action effect have also been limited to a single step or a three-step staircase. On larger staircases, somatosensory learning of step heights may be greater which could override the illusory effect on the top step. Furthermore, the striped nature of the existing stair horizontal-vertical illusion is associated with visual stress and may not be aesthetically suitable for use on public stairs. These issues need resolving before potential future implementation on public stairs. Methods Experiment 1. A series of four computer-based perception tests were conducted in older (N = 14: 70 ± 6 years) and young adults (N = 42: 24 ± 3 years) to test the influence of different illusion designs on stair riser height estimation. Participants compared images of stairs, with horizontal-vertical illusions or arbitrary designs on the bottom step, to a plain stair with different bottom step riser heights and selected the stair they perceived to have the tallest bottom riser. Horizontal-vertical illusions included a previously developed design and versions with modified spatial frequencies and mark space ratios. Perceived riser height differences were assessed between designs and between age groups. Experiment 2. To assess the perception-action link, sixteen older (70 ± 7 years) and fifteen young (24 ± 3 years) adults ascended a seven-step staircase with and without horizontal-vertical illusions tested in experiment 1 placed onto steps one and seven. Foot clearances were measured over each step. To determine whether changes in perception were linked to changes in foot clearance, perceived riser heights for each horizontal-vertical illusion were assessed using the perception test from experiment 1 before and after stair ascent. Additional measures to characterise stair safety included vertical foot clearance, margins of stability, foot overhang, stair speed, and gaze duration, which were assessed over all seven steps. Results Experiment 1. All horizontal-vertical illusion designs led to significant increases in the perceived riser height in both young and older adults (12–19% increase) with no differences between age groups. Experiment 2. On step 7, each horizontal-vertical illusion led to an increase in vertical foot clearance for young (up to 0.8 cm) and older adults (up to 2.1 cm). On step 1 significant increases in vertical foot clearance were found for a single horizontal-vertical illusion when compared to plain (1.19 cm increase). The horizontal-vertical illusions caused significant increases in the perceived riser height (young; 13% increase, older; 11% increase) with no differences between illusion design, group or before and after stair ascent. No further differences were found for the remaining variables and steps. Conclusion Results indicate a perception-action link between perceived riser height and vertical foot clearance in response to modified versions of the horizontal-vertical illusion in both young and older adults. This was shown with no detriment to additional stair safety measures. Further evaluating these illusions on private/public stairs, especially those with inconsistently taller steps, may be beneficial to help improve stair safety for older adults.
Article
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OBJETIVO: Comparar os resultados obtidos após o Lasik personalizado utilizando duas plataformas diferentes. MÉTODOS: Estudo prospectivo, randomizado com 50 pacientes míopes submetidos a cirurgia refrativa em ambos os olhos. Foram selecionados para o estudo, pacientes com equivalente esférico semelhante entre os olhos. Todos foram submetidos a Lasik bilateral e simultâneo, sendo que um olho foi operado pela plataforma CustomCornea® e o outro pela Zyoptix®. Acuidade visual sem e com correção, refração dinâmica e estática, medida das aberrações oculares, teste de sensibilidade ao contraste foram realizados no período pré-operatório e pós-operatório de 1, 3 e 6 meses. RESULTADOS: No período pré-operatório a média do equivalente esférico era de -3,29 ± 1,56 D no grupo CustomCornea® e de -3,22 ± 1,50 D no Zyoptix® (p=0,267). No sexto mês de pós-operatório, a média do equivalente esférico no grupo CustomCornea® era de -0,077 ± 0,23 D e -0,282 ± 0,30 D no Zyoptix® (p<0,001*). Acuidade visual sem correção > 20/20 foi alcançada em 86% dos olhos no grupo CustomCornea® e 70% no grupo Zyoptix® (p=0,094). Nenhum paciente perdeu duas ou mais linhas da melhor acuidade visual corrigida. Cem por cento dos olhos CustomCornea® e 88% dos Zyoptix® ficaram entre ± 0,50 D da emetropia (p=0,014*). Melhora da sensibilidade ao contraste em todas as frequências espaciais testadas foi observada em ambos os grupos. A aberração esférica apresentou aumento em ambos os grupos, porém este foi estatisticamente maior na plataforma Zyoptix® (p<0,001). CONCLUSÃO: Não foram observadas diferenças entre os grupos quanto à eficácia e segurança. O tratamento com a plataforma Zyoptix® consumiu menor quantidade de estroma. Melhor previsibilidade da correção cirúrgica foi obtida pelo grupo CustomCornea®, bem como menor indução de aberração esférica.
Article
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1. The contrast thresholds of a variety of grating patterns have been measured over a wide range of spatial frequencies.2. Contrast thresholds for the detection of gratings whose luminance profiles are sine, square, rectangular or saw-tooth waves can be simply related using Fourier theory.3. Over a wide range of spatial frequencies the contrast threshold of a grating is determined only by the amplitude of the fundamental Fourier component of its wave form.4. Gratings of complex wave form cannot be distinguished from sine-wave gratings until their contrast has been raised to a level at which the higher harmonic components reach their independent threshold.5. These findings can be explained by the existence within the nervous system of linearly operating independent mechanisms selectively sensitive to limited ranges of spatial frequencies.
Book
There have been greater advances in our knowledge of the visual function and its disabilities in the past 50 years than had accumulated in all of the previous years. This applies not only to the basic science of biochemistry, physiology, physiopathology, and cytopathology but also to the diagnosis and treatment of visual dysfunction and ocular disease. These advances have been aided by a proliferation of ingenious instruments. When I began my residency in ophthalmology at The Wilmer Institute in 1938, one was supposed to learn not only the physiology of vision but also how to diagnose and treat all phases of ophthalmology including disabilities of the orbit, sclera, retina, lens, and cornea. In addition he or she was supposed to understand neuro-ophthalmology, ophthalmic genetics, and so-called uveitis. It soon became evident that no one could adequately comprehend all of these areas and, therefore, most young trainees today take a year or two of fel­ lowship in a specialized area following their three-to five-year residency train­ ing. Following this they join a group of other ophthalmologists and specialize. Thus, they become more expert in the diagnosis and treatment in a limited area in ophthalmology. When I returned to The Wilmer Institute in 1955 as Head of the Department I was the only full-time member of the staff. To date we have some 28 full-time ophthalmologists working in highly specialized areas of our institution.
Chapter
In the treatment of visual disorders and eye disease, it is obviously useful to assess the patient’s visual abilities. In principle, a great number of abilities could be tested (e.g., perception of motion, depth, color, faces, etc.). In practice, however, the first and often the only aspect of vision to be tested is spatial vision in or near the fovea. As used here, the term spatial vision refers to the ability to see achromatic, two-dimensional patterns. The most common clinical measures of spatial vision are visual acuity measures. In recent years there has been increasing awareness of the limitations of acuity measures and a corresponding rise in interest in other measures of visual function, in particular, contrast sensitivity.
Article
This book presents an integrated view of how we perceive the spatial relations in our visual world, covering anatomical, physiological, psychophysical, and perceptual aspects. The book discusses the visual system primarily in terms of spatial frequency analysis using a linear systems approach. It reviews evidence supporting a local, patch-by-patch spatial frequency filtering of visual information rather than the global Fourier analysis other researchers have proposed. A separate chapter addresses the special issues surrounding color vision, and a brief, nonmathematical introduction to linear systems analysis is included.
Article
Objectifs : Comparer la sensibilité à l’éblouissement mesurée par la lumière diffractée intra-oculaire entre photo-kératectomie réfractive (PKR) et LASIK guidés par front d’onde à un an de suivi et évaluer sa corrélation aux symptômes des patients. Patients et méthodes Nous avons mené une étude prospective randomisée sur 13 patients traités par PKR guidée par front d’onde, sur 13 patients par LASIK guidé par front d’onde et sur un groupe contrôle de 35 patients. La lumière diffractée a été mesurée par le C-QUANT (Oculus®) à 1 an de suivi dans les groupes PKR et LASIK, en préopératoire pour le groupe contrôle. La sensibilité aux contrastes photopique et mésopique ainsi que les symptômes des patients ont été reportés avant et après chirurgie. Résultats Les valeurs de lumière intra-oculaire diffractée étaient normales chez 79 % des patients après LASIK et PKR et chez 86 % des contrôles avec des valeurs moyennes de 1,03Log, 1,05Log et 0,99Log (p > 0,05). Tous les patients symptomatiques d’éblouissements nocturnes avaient des valeurs anormales contre 31,5 % des patients asymptomatiques. L’acuité aux contrastes photopique et mésopique, et la symptomatologie en termes d’éblouissements étaient améliorées 1 an après PKR et LASIK par rapport à l’état préopératoire (pas de différence entre les groupes). Conclusion PKR et LASIK guidés par front d’onde sont des procédures sécurisantes et équivalentes en termes de qualité de vision postopératoire. La mesure de la lumière diffuse intra-oculaire semble être un test discriminant pour évaluer les plaintes des patients en termes d’éblouissements après chirurgie réfractive.
Article
The earliest studies on 'disability glare' date from the early 20(th) century. The condition was defined as the negative effect on visual function of a bright light located at some distance in the visual field. It was found that for larger angles (>1degree) the functional effect corresponded precisely to the effect of a light with a luminosity equal to that of the light that is perceived spreading around such a bright source. This perceived spreading of light was called straylight and by international standard disability glare was defined as identical to straylight. The phenomenon was recognized in the ophthalmological community as an important aspect of the quality of vision and attempts were made to design instruments to measure it. This must not be confused with instruments that assess light spreading over small distances (<1 degree), as originating from (higher order) aberrations and defocus. In recent years a new instrument has gained acceptance (C-Quant) for objective and controllable assessment of straylight in the clinical setting. This overview provides a sketch of the historical development of straylight measurement, as well as the results of studies on the origins of straylight (or disability glare) in the normal eye, and on findings on cataract (surgery) and corneal conditions.
Article
provide[s] a theoretical basis for the spatial-filtering concept with a tutorial treatment of linear systems theory and Fourier analysis physiological data are presented that suggest a biological basis for the existence of spatial filtering in the mammalian visual system attempts to clarify the relationship between spatial filtering, contrast sensitivity, and visual channel theory shown how spatial filters can accurately predict perceptual phenomena described by Gestalt laws of organization relate the concept of spatial filtering to the perception of texture and visual illusions considers the properties of a multichannel model aspects of form perception the assessment of visual performance (PsycINFO Database Record (c) 2012 APA, all rights reserved)
Article
When evaluating how a medical product affects vision, it is important to assess how that product affects the ability to function in real life, not only the ability to read letters on a vision chart. Nevertheless, the measurement of visual acuity with a vision chart remains the primary test of the effects of medical products on vision. Here, we review efforts to identify reliable, cost-effective clinical tests to serve as surrogate measures of functional visual performance.Section editor:Janet Woodcock – Food and Drug Administration, Rockville, MD, USA