
Leon N DaviesAston University · Department of Optometry
Leon N Davies
PhD
About
69
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Introduction
Publications
Publications (69)
Purpose
With the introduction of ChatGPT, artificial intelligence (AI)‐based large language models (LLMs) are rapidly becoming popular within the scientific community. They use natural language processing to generate human‐like responses to queries. However, the application of LLMs and comparison of the abilities among different LLMs with their hum...
Purpose:
ChatGPT is an artificial intelligence language model, which uses natural language processing to simulate human conversation. It has seen a wide range of applications including healthcare education, research and clinical practice. This study evaluated the accuracy of ChatGPT in providing accurate and quality information to answer questions...
Purpose:
To establish whether axial growth and refractive error can be modulated in anisohyperopic children by imposing relative peripheral hyperopic defocus (RPHD) using multifocal soft contact lenses.
Methods:
This study is a prospective, controlled paired-eye study with anisohyperopic children. Axial growth and refractive error were observed...
Presbyopia occurs when the physiologically normal age-related reduction in the eyes focusing range reaches a point, when optimally corrected for distance vision, that the clarity of vision at near is insufficient to satisfy an individual’s requirements. Hence, it is more about the impact it has on an individual’s visual ability to function in their...
Purpose:
To establish whether axial growth and refractive error can be modulated in hyperopic children by imposing relative peripheral hyperopic defocus using multifocal soft contact lenses.
Methods:
A prospective controlled study with hyperopic participants allocated to a control or test group. Control group participants were corrected with sin...
Purpose
To evaluate the efficacy of multifocal soft contact lenses to reduce asthenopic symptoms in myopes with accommodative lag.
Methods
Twenty-four myopic participants, aged 18–35 years, with mean spherical equivalent (MSE) of ≤ -0.75D, were recruited in a randomised, double-blind crossover study. All participants were existing contact lens wea...
The role of accommodation in myopia development and progression has been debated for decades. More recently, the understanding of the mechanisms involved in accommodation and the consequent alterations in ocular parameters has expanded. This International Myopia Institute white paper reviews the variations in ocular parameters that occur with accom...
Purpose: There is evidence that attention can modulate ocular dynamics, but its effects on accommodative dynamics have yet to be fully determined. We investigated the effects of manipulating the capacity to focus on task-relevant stimuli, using two levels of dual-tasking (arithmetic task) and auditory feedback, on the accommodative dynamics at thre...
Introduction:
The standard recommended treatment for neurogenic detrusor overactivity (NDO) is clean intermittent catheterization combined with an antimuscarinic agent. However, the adverse systemic side-effects of oxybutynin, the most widely used agent, are of concern.
Objective:
To evaluate the efficacy and safety of solifenacin in pediatric p...
Significance: The present study may be of relevance in the understanding of the accommodative response depending on the type of optical correction used. Our results are discussed due to its possible implications in myopia progression and visual fatigue.
Purpose: The accommodative response has been investigated due to its possible relationship with...
Presbyopia is a global problem affecting over a billion people worldwide. The prevalence of unmanaged presbyopia is as high as 50% of those over 50 years of age in developing world populations due to a lack of awareness and accessibility to affordable treatment, and is even as high as 34% in developed countries. Definitions of presbyopia are incons...
This study aimed to quantify biometric modifications of the anterior segment (AS) during accommodation and to compare them against changes in both accommodative demand and response. Thirty adults, aged 18–25 years were rendered functionally emmetropic with contact lenses. AS optical coherence tomography (AS-OCT) images were captured along the 180°...
Background:
Hyperopia occurs due to insufficient ocular growth and a failure to emmetropize in childhood. In anisohyperopia, it is unclear why one eye may remain hyperopic while the fellow eye grows toward an emmetropic state. Animal studies have shown that manipulating peripheral defocus through optical means while simultaneously providing correc...
Purpose:
To characterise the anatomical parameters of the porcine eye for potentially using it as a laboratory model of dry eye.
Methods:
Anterior chamber depth and angle, corneal curvature, shortest and longest diameter, endothelial cell density, and pachymetry were measured in sixty freshly enucleated porcine eyeballs.
Results:
Corneal steep...
Aim:
Retrospective analysis of different contact lens wearing groups suggests lens surface lubricity is the main factor influencing contact lens comfort. However, the examined commercially available contact lenses differ in material and design as well as surface properties. Hence this study isolates the contribution of lens surface properties usin...
Purpose:
To investigate non-cycloplegic changes in refractive error prior to the onset of presbyopia.
Methods:
The Aston Longitudinal Assessment of Presbyopia (ALAP) study is a prospective 2.5 year longitudinal study, measuring objective refractive error using a binocular open-field WAM-5500 autorefractor at 6-month intervals in participants age...
Aim
To better understand the phenomenon of dysphotopsia in patients implanted with multifocal intraocular lenses (IOLs).
Methods
Forty-five patients (aged 61.8±8.9 years) implanted bilaterally with Tecnis ZM900 (diffractive multifocal), Lentis Mplus MF30 (segmented refractive multifocal) or Softec-1 (monofocal) IOLs (each n=15) 4–6 months previous...
Background:
The aim was to profile transient accommodative axial length changes from early adulthood to advanced presbyopia and to determine whether any differences exist between the responses of myopic and emmetropic individuals.
Methods:
Ocular biometry was measured by the LenStar biometer (Haag-Streit, Switzerland) in response to zero, 3.00 a...
Purpose To assess the validity and repeatability of the Aston Halometer. Setting University clinic, United Kingdom. Design Prospective, repeated-measures experimental study. Methods The halometer comprises a bright light-emitting-diode (LED) glare source in the center of an iPad4. Letters subtending 0.21° (∼0.3 logMAR) were moved centrifugally from...
Purpose:
To profile accommodative biometric changes longitudinally and to determine the influence of age-related ocular structural changes on the accommodative response prior to the onset of presbyopia.
Methods:
Twenty participants (aged 34-41 years) were reviewed at six-monthly intervals over two and a half years. At each visit, ocular biometry...
To describe and validate bespoke software designed to extract morphometric data from ciliary muscle Visante Anterior Segment Optical Coherence Tomography (AS-OCT) images.
Initially, to ensure the software was capable of appropriately applying tiered refractive index corrections and accurately measuring orthogonal and oblique parameters, 5 sets of c...
Visual search impairment can occur following stroke. The utility of optimal spectral filters on visual search in stroke patients has not been considered to date. The present study measured the effect of optimal spectral filters on visual search response time and accuracy, using a task requiring serial processing. A stroke and control cohort underto...
Purpose: The aim of the study was to determine the effect of optimal spectral filters on reading performance following stroke.
Methods: Seventeen stroke subjects, aged 43–85, were considered with an age-matched Control Group (n = 17). Subjects undertook the Wilkins Rate of Reading Test on three occasions: (i) using an optimally selected spectral fi...
Visual stress is a condition characterised by symptoms of eyestrain, headaches and distortions of visual perception when reading text. The symptoms are frequently alleviated with spectral filters and precision tinted ophthalmic lenses. Visual stress is thought to arise due to cortical hyperexcitability and is associated with a range of neurological...
Purpose. To examine the influence of positional misalignments on intraocular pressure (IOP) measurement with a rebound tonometer. Methods. Using the iCare rebound tonometer, IOP readings were taken from the right eye of 36 healthy subjects at the central corneal apex (CC) and compared to IOP measures using the Goldmann applanation tonometer (GAT)....
To determine the most appropriate analysis technique for the differentiation of multifocal intraocular lens (MIOL) designs by using defocus curve assessment of visual capability.
Four groups of 15 subjects were implanted bilaterally with either monofocal intraocular lenses, refractive MIOLs, diffractive MIOLs, or a combination of refractive and dif...
To demonstrate the application of low-coherence reflectometry to the study of biometric changes during disaccommodation responses in human eyes after cessation of a near task and to evaluate the effect of contact lenses on low-coherence reflectometry biometric measurements.
Ocular biometric parameters of crystalline lens thickness (LT) and anterior...
To study the visual and refractive outcomes after laser-assisted subepithelial keratectomy (LASEK) performed with a 213 nm solid-state laser for a broad range of refractive errors.
Private practice, Jersey, United Kingdom.
Case series.
The LASEK was performed using a Pulzar Z1 213 nm solid-state laser. Manifest refraction and uncorrected (UDVA) and...
The aim of this work was to measure susceptibility to pattern glare within a stroke group, employing a direct method of assessment. Twenty stroke subjects, aged 38-85 years, were recruited, along with an age-matched control group (n = 20). Assessment of pattern glare susceptibility was undertaken using the pattern glare test. An abnormal degree of...
To develop a standardized questionnaire of near visual function and satisfaction to complement visual function evaluations of presbyopic corrections.
Eye Clinic, School of Life and Health Sciences, Aston University, Midland Eye Institute and Solihull Hospital, Birmingham, United Kingdom.
Questionnaire development.
A preliminary 26-item questionnair...
Many practitioners base the prescription of near vision additions on the assertion that only one half or two-thirds of an individual's amplitude of accommodation is sustainable for a prolonged period. To better understand how much eye focus needs to be restored for presbyopic corrections to be adequate, this study investigated the robustness of the...
To evaluate the accuracy of an open-field autorefractor compared with subjective refraction in pseudophakes and hence its ability to assess objective eye focus with intraocular lenses (IOLs).
Objective refraction was measured at 6 m using the Shin-Nippon NVision-K 5001/Grand Seiko WR-5100K open-field autorefractor (five repeats) and by subjective r...
Citation information: Armstrong RA, Davies LN, Dunne MCM & Gilmartin B. Statistical guidelines for clinical studies of human vision. Ophthalmic Physiol Opt 2011, 31, 123–136. doi: 10.1111/j.1475-1313.2010.00815.x
Statistical analysis of data can be complex and different statisticians may disagree as to the correct approach leading to conflict betwe...
To quantify changes in crystalline lens curvature, thickness, equatorial diameter, surface area, and volume during accommodation using a novel two-dimensional magnetic resonance imaging (MRI) paradigm to generate a complete three-dimensional crystalline lens surface model.
Nineteen volunteers, aged 19 to 30 years, were recruited. T(2)-weighted MRIs...
To use anterior segment optical coherence tomography (AS-OCT) to analyze ciliary muscle morphology and changes with accommodation and axial ametropia.
Fifty prepresbyopic volunteers, aged 19 to 34 years were recruited. High-resolution images were acquired of nasal and temporal ciliary muscles in the relaxed state and at stimulus vergence levels of...
To investigate the mechanism of action of the Tetraflex (Lenstec Kellen KH-3500) accommodative intraocular lens (IOL).
Thirteen eyes of eight patients implanted with the Tetraflex accommodating IOL for at least 2 years underwent assessment of their objective amplitude-of-accommodation by autorefraction, anterior chamber depth and pupil size with op...
High levels of corneal astigmatism are prevalent in a significant proportion of the population. During cataract surgery pre-existing astigmatism can be corrected using single or paired incisions on the steep axis of the cornea, using relaxing incisions or with the use of a toric intraocular lens. This review provides an overview of the conventional...
To assess the effect of ageing on in vivo human ciliary muscle morphology and contractility during accommodation.
Seventy-nine subjects, aged 19-70 years were recruited. High-resolution images were acquired of nasal and temporal ciliary muscle in the relaxed state, and at stimulus vergence levels of -4 and -8 D, using anterior segment optical coher...
The correction of presbyopia and restoration of true accommodative function to the ageing eye is the focus of much ongoing research and clinical work. A range of accommodating intraocular lenses (AIOLs) implanted during cataract surgery has been developed and they are designed to change either their position or shape in response to ciliary muscle c...
To assess the stability of the Akreos AO intraocular lens (IOL) platform with a simulated toric design using objective image analysis.
Six hospital eye clinics across Europe.
After implantation in 1 eye of patients, IOLs with orientation marks were imaged at 1 to 2 days, 7 to 14 days, 30 to 60 days, and 120 to 180 days. The axis of rotation and IOL...
Despite numerous investigations, the aetiology and mechanism of accommodation and presbyopia remains equivocal. Using Gaussian first-order ray tracing calculations, we examine the contribution that ocular axial distances make to the accommodation response. Further, the influence of age and ametropia are also considered. The data show that all chang...
A clinical evaluation of the Grand Seiko Auto Ref/Keratometer WAM-5500 (Japan) was performed to evaluate validity and repeatability compared with non-cycloplegic subjective refraction and Javal-Schiotz keratometry. An investigation into the dynamic recording capabilities of the instrument was also conducted.
Refractive error measurements were obtai...
To evaluate the hypothesis that objective measures of open- and closed-loop ocular accommodation are related to systemic cardiovascular function, and ipso facto autonomic nervous system activity.
Sixty subjects (29 male; 31 female) varying in age from 18 to 33 years (average: 20.3 +/- 2.9 years) with a range of refractive errors [mean spherical equ...
The aim of the study was to determine, objectively and non-invasively, whether changes in accommodative demand modify differentially the peripheral refraction in emmetropic and myopic human eyes.
Forty subjects (19 male, 21 female) aged 20-30 years (mean 22.7 (SD 2.8) years), 21 emmetropes (mean spherical equivalent refractive error (MSE) -0.13 (SD...
A new commercially available optical low coherence reflectometry device (Lenstar, Haag-Streit or Allegro Biograph, Wavelight) provides high-resolution non-contact measurements of ocular biometry. The study evaluates the validity and repeatability of these measurements compared with current clinical instrumentation.
Measurements were taken with the...
To evaluate theoretically three previously published formulae that use intra-operative aphakic refractive error to calculate intraocular lens (IOL) power, not necessitating pre-operative biometry. The formulae are as follows: IOL power (D) = Aphakic refraction x 2.01 [Ianchulev et al., J. Cataract Refract. Surg.31 (2005) 1530]; IOL power (D) = Apha...
The binocular Esterman visual field test (EVFT) is the current visual field test for driving in the UK. Merging of monocular field tests (Integrated Visual Field, IVF) has been proposed as an alternative for glaucoma patients.
To examine the level of agreement between the EVFT and IVF for patients with binocular paracentral scotomata, caused by eit...
http://www.amazon.com/Central-scotomata-driving-Safety-Research/dp/1904763804
EXECUTIVE SUMMARY
Background
There is no question that, once binocular scotomata in certain locations within the visual field reach a critical size, they must affect driving performance. The difficulty is determining the level at which binocular visual field loss in the presence of good visual acuity begins to impact on driving safety. The majority...
We assess the accuracy of the Visante anterior segment optical coherence tomographer (AS-OCT) and present improved formulas for measurement of surface curvature and axial separation. Measurements are made in physical model eyes. Accuracy is compared for measurements of corneal thickness (d(1)) and anterior chamber depth (d(2)) using-built-in AS-OCT...
Imaging of the eye is critical to improving the diagnosis, assessment of severity and progression, and evaluation of management of eye disease. Advances have been rapid, with improvements in hardware (such as light sources and imaging chips), optics (such as adaptive aberration compensation) and software (such as image tracking). The technology and...
To develop a questionnaire that subjectively assesses near visual function in patients with 'accommodating' intraocular lenses (IOLs).
A literature search of existing vision-related quality-of-life instruments identified all questions relating to near visual tasks. Questions were combined if repeated in multiple instruments. Further relevant questi...
Imaging of the crystalline lens and intraocular lens is becoming increasingly more important to optimize the refractive outcome of cataract surgery, to detect and manage complications and to ascertain advanced intraocular lens performance. This review examines recent advances in anterior segment imaging.
The main techniques used for imaging the ant...
To evaluate the reliability and repeatability of intraocular pressure (IOP) measurements using a new rebound tonometer.
Intraocular pressure was measured in 42 healthy human eyes of subjects aged 18-30 years (mean +/- standard deviation [SD] 21.5 +/- 3.2 years) using the ICare Rebound and Goldmann tonometers in two separate sessions.
Intraocular pr...
Age-related macular degeneration (ARMD) is the leading cause of visual disability in people over 60 years of age in the developed world. The success of treatment deteriorates with increased latency of diagnosis. The purpose of this study was to determine the reliability of the macular mapping test (MMT), and to investigate its potential as a screen...
To investigate objectively and noninvasively the role of cognitive demand on autonomic control of systemic cardiovascular and ocular accommodative responses in emmetropes and myopes of late-onset.
Sixteen subjects (10 men, 6 women) aged between 18 and 34 years (mean +/- SD: 22.6 +/- 4.4 years), eight emmetropes (EMMs; mean spherical equivalent [MSE...
The prevalence of myopia is known to vary with age, ethnicity, level of education, and socioeconomic status, with a high prevalence reported in university students and in people from East Asian countries. This study determines the prevalence of ametropia in a mixed ethnicity U.K. university student population and compares associated ocular biometri...
We describe a non-invasive phakometric method for determining corneal axis rotation relative to the visual axis (beta) together with crystalline lens axis tilt (alpha) and decentration (d) relative to the corneal axis. This does not require corneal contact A-scan ultrasonography for the measurement of intraocular surface separations. Theoretical in...
To assess repeatability and reproducibility, to determine normative data, and to investigate the effect of age-related macular disease, compared with normals, on photostress recovery time measured using the Eger Macular Stressometer (EMS).
The study population comprised 49 healthy eyes of 49 participants. Four EMS measurements were taken in two ses...
To determine the feasibility of taking intra-ocular pressure (IOP) readings with Goldmann-type applanation tonometer probe covered with cling film to avoid transmission of Creutzfeldt-Jakob disease (CJD).
Data were collected on two occasions from the right eyes of 30 healthy subjects using a Perkins applanation tonometer. On each occasion, a single...
A clinical evaluation of the Shin-Nippon NVision-K 5001 (also branded as the Grand Seiko WR-5100K) autorefractor (Japan) was performed to examine validity and repeatability compared with subjective refraction and Javal-Schiotz keratometry.
Measurements of refractive error were performed on 198 eyes of 99 subjects (aged 23.2 +/- 7.4 years) subjectiv...