Edward A H Mallen

• PhD
• Head of Department at University of Bradford

Background/Objectives: Perceptions and barriers to myopia management (MM) in childhood have not been fully explored within some countries, including the UK, where there is minimal public health education on myopia. Methods: The aim of this mixed-methods study was to explore perceptions of myopia and MM interventions using focus groups and a survey...

Introduction This work aimed to establish the largest UK and Ireland consensus on myopia management in children and young people (CYP). Methods A modified Delphi consensus was conducted with a panel of 34 optometrists and ophthalmologists with expertise in myopia management. Results Two rounds of voting took place and 131 statements were agreed,...

Introduction In the UK, prescribing contact lenses (CLs) for children is undertaken by two groups of Eyecare Practitioners (ECPs): optometrists and contact lens opticians (CLOs). Aims To explore the attitudes and prescribing habits of UK ECPs for fitting CLs in patients under 18 years of age. Methods An online survey was conducted with UK registe...

Introduction Though myopia management options are available within the UK, many myopic children are still prescribed single vision correction. Aims The aim was to ascertain factors which may be limiting the implementation of myopia management into UK clinical practice and its uptake by patients. This was investigated through the attitudes and pers...

Objective Many children with progressive myopia are still prescribed single-vision correction. An investigation into UK eyecare practitioners’ (ECPs) perceptions of myopia management was carried out to ascertain factors which may be limiting its implementation and uptake within clinical practice. Methods and analysis Online focus groups were held...

Myopia typically starts and progresses during childhood, but onset and progression can occur during adulthood. The goals of this review are to summarize published data on myopia onset and progression in young adults, aged 18 to 40 years, to characterize myopia in this age group, to assess what is currently known, and to highlight the gaps in the cu...

In the first of two articles discussing blur sensitivity, Professor Edward Mallen explains what it is and how it differs from blur discrimination and blur adaptation. (C103286, suitable for logging as one provider-led distance learning CPD point for optometrists and dispensing opticians)

Purpose To determine whether accommodative microfluctuations (AMFs) are affected by the image resolution of the display type being observed. The effect of refractive error is also examined. Methods Twenty participants, (10 myopes and 10 emmetropes) observed a target on four different displays: paper, smartphone, e‐reader and visual display unit sc...

Purpose The purpose of this study was to extend the knowledge of peripheral biometric component and its relationship to refractive status in healthy individuals by determining the correlation between peripheral ocular length to peripheral corneal radius ratio and the refractive error. Methods This prospective study was conducted on thirty-three he...

The human visual system is amenable to a number of adaptive processes; one such process, or collection of processes, is the adaptation to blur. Blur adaptation can be observed as an improvement in vision under degraded conditions, and these changes occur relatively rapidly following exposure to blur. The potential important future directions of thi...

Previous studies have shown cognition to have an influence on accommodation. Temporal variation in the accommodative response occurs during the fixation on a stationary target. This constantly shifting response has been called accommodative micro-fluctuations (AMFs). The aim of this study is to determine the effects of increasing task cognitive dem...

When fixating on a stationary object, the power of the eye's lens fluctuates. Studies have suggested that changes in these so-called microfluctuations in accommodation may be a factor in the onset and progression of short-sightedness. Like many physiological signals, the fluctuations in the power of the lens exhibit chaotic behaviour. A breakdown o...

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: Many studies have assessed the visual impact of astigmatism by inducing it using loose trial lenses at set axes. There are conflicting opinions and some confusion about the results, but the reduction in vision is typically least with lens-induced with-the-rule astigmatism. In this study, we determined whether a participant's habitual asti...

Purpose: Blur adaptation occurs when an observer is exposed to continuous defocus. However, it is unclear whether adaptation requires constant defocus, or whether the effect can still be achieved when the adaptation period is interrupted by short periods of clear vision. Methods: The study included 12 emmetropes and 12 myopes. All observers wore...

Purpose: The purpose of this study was to compare retinal thickness and biometric parameters between highly myopic eyes with and without tilted optic discs. Methods: A total of 60 eyes from 60 highly myopic individuals (defined as a mean spherical equivalent refraction of -6.00 D or greater and axial length ≥26 mm) underwent detailed ophthalmic...

In this study, we investigated whether reading influences contrast adaptation differently in young adult emmetropic and myopic participants at the spatial frequencies created by text rows and character strokes. Pre-adaptation contrast sensitivity was measured for test gratings with spatial frequencies of 1cdeg(-1) and 4cdeg(-1), presented horizonta...

Purpose: We determined whether human ocular lens position is influenced by gravity. Methods: Anterior chamber depth (ACD) and lens thickness (LT) were determined with a Haag-Streit Lenstar LS900 for right eyes of participants in two age groups, with a young group of 13 participants aged 18 to 21 years (mean, 21 years; SD, 1 year) and an older gr...

This is a comprehensive study of a large range of biometric and optical parameters in people with type 1 diabetes. The parameters of 74 people with type 1 diabetes and an age matched control group were assessed. Most of the people with diabetes had low levels of neuropathy, retinopathy and nephropathy. Marginal or no significant differences were fo...

To estimate refractive indices used by the Lenstar biometer to translate measured optical path lengths into geometrical path lengths within the eye. Axial lengths of model eyes were determined using the IOLMaster and Lenstar biometers; comparing those lengths gave an overall eye refractive index estimate for the Lenstar. Using the Lenstar Graphical...

Purpose: Race appears to be associated with myopiogenesis, with East Asians showing high myopia prevalence. Considering structural variations in the eye, it is possible that retinal shapes are different between races. The purpose of this study was to quantify and compare retinal shapes between racial groups using peripheral refraction (PR) and peri...

The eye rotation approach for measuring peripheral eye length leads to concern about whether the rotation influences results, such as through pressure exerted by eyelids or extra-ocular muscles. This study investigated whether this approach is valid. Peripheral eye lengths were measured with a Lenstar LS 900 biometer for eye rotation and no-eye rot...

We used adaptive optics to determine the effect of monochromatic aberration dynamics on the level of chaos in the accommodation control system. Four participants viewed a stationary target while the dynamics of their aberrations were either left uncorrected, defocus was corrected, or all aberrations except defocus were corrected. Chaos theory analy...

The accommodative response (AR) to changes in dioptric accommodative stimulus (AS) during the latency period and onset of accommodation was investigated. Participants monocularly observed one period of a square wave in AS, with a 2-D baseline and mean, and amplitude 1 D or 2 D; the period of the square wave ranged from 0.10s to 1.00s; both increase...

Visual suppression of low-spatial frequency information during eye movements is believed to contribute to a stable perception of our visual environment. While visual perception has been studied extensively during saccades, vergence has been somewhat neglected. Here, we show that convergence eye movements reduce contrast sensitivity to low spatial f...

This study examined the effect of myopic defocus on visual acuity (VA) over time, with attention being paid to the first point at which blur adaptation had a significant and measurable effect on defocused VA. Visual acuity was sampled at a higher rate than previous studies in order to assess the time course of blur adaptation processes in myopic an...

Objetivo Comparar el rendimiento visual central y periférico en ojos miopes y emétropes. Métodos Se seleccionaron treinta pacientes emétropes (de -0,50 a +0,50 D) y 60 miopes (de -2,00 a -9,62 D). Se evaluó la agudeza de resolución central y en 12 localizaciones retinianas periféricas (±10°, ±20°, ±30° a lo largo del meridiano horizontal, y ±10°,...

We used a binocular Shack–Hartmann sensor to measure the aberration dynamics of six participants at a rate of 21 Hz. Chaos theory analysis was used to determine the Lyapunov exponent for the time evolution of the rms wavefront error, accommodation, and each individual Zernike coefficient up to and including the fifth radial order. In all cases ther...

Purpose: To assess intrasessional and intersessional repeatability of two commercial partial coherence interferometry instruments for measuring peripheral eye lengths and to investigate the agreement between the two instruments. Methods: Central and peripheral eye lengths were determined with the IOLMaster (Carl-Zeiss Meditec AG, Jena, Germany)...

Purpose: This study describes the axial and peripheral dimensions of myopic and emmetropic eyes in a wide range of retinal locations using a non-contact optical biometer (Zeiss IOLMaster) based upon the principle of partial coherence interferometry. Understanding the optical properties of the peripheral eye may provide insight into myopia developm...

When fixating on a stationary object, the human eye exhibits microfluctuations in accommodation. Changes in the magnitude of these fluctuations reflect changes in the accommodation control system. We used adaptive optics to determine the effect of monochromatic aberration dynamics on the control of steady-state accommodation of four subjects. The s...

  We provide an account of the relationships between eye shape, retinal shape and peripheral refraction.   We discuss how eye and retinal shapes may be described as conicoids, and we describe an axis and section reference system for determining shapes. Explanations are given of how patterns of retinal expansion during the development of myopia may...

Since the characterization of the eye’s monochromatic aberration fluctuations in 2001, the power spectrum has remained the most widely used method for analyzing their dynamics. However, the power spectrum does not capture the complexities of the fluctuations. We measured the monochromatic aberration dynamics of six subjects using a Shack-Hartmann s...

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...

This study was conducted to investigate whether neural compensation for induced defocus can alter visual resolution in other areas of the human retina beyond the fovea. In certain circumstances, the blur adaptation response may be influenced by refractive status. The effect of blur adaptation on the central 10° of the retina was investigated in 20...

The study of peripheral refractive error is of growing interest as degradation of the retinal image quality in the periphery is known to affect central refractive error development and ocular shape in animal models. The purpose of this study was to measure peripheral refraction across the horizontal, vertical, and two oblique meridians in a group o...

Interest in peripheral refraction measurement has grown in recent years in response to the insight it may provide into myopia development. In light of the likely increase in the clinical use of open-field autorefractors for peripheral refraction measurements, the question of instrument alignment and its impact on the accuracy of refraction measurem...

Purpose There is current interest in using adaptive optics (AO) to determining the effect of higher-order monochromatic aberrations on dynamic accommodation control; see for example [1-3]. So far, such studies have been carried out using monocular systems. In real-life situations, however, accommodation occurs binocularly and with associated conver...

Inspired by biological eyes, silicon retinas with pixel-level processing have been developed to achieve very high-speed and high-quality image processing. Due to the limitation on the fill factor and the dimension of a silicon chip, both spatial and luminance resolutions have to be kept low. For recovering fine images from a silicon retina with a l...

Myopia is known to degrade visual performance with both optical and retinal changes implicated. Whether contact lenses or spectacles provide better visual performance for myopes is still under debate. The purpose of this study was to examine central and peripheral visual function in myopic subjects corrected with contact lenses versus spectacles. S...

Ocular monochromatic aberrations display dynamic behavior even when the eye is fixating on a stationary stimulus. The fluctuations are commonly characterized in the frequency domain using the power spectrum obtained via the Fourier transform. In this paper we used a wavelet-based multifractal analytical approach to provide a more in depth analysis...

Accurate measurements of ocular biometry and objective refraction are of vital importance to research laboratories working in the area of refractive error development and oculomotor function. A number of commercially available instruments can provide these measurements, and are used in both their intended modes, and with modifications to increase t...

Dynamic correction of monochromatic aberrations of the eye is known to affect the accommodation response to a step change in stimulus vergence. We used an adaptive optics system to determine how the temporal location of the correction affects the response. The system consists of a Shack-Hartmann sensor sampling at 20 Hz and a 37-actuator piezoelect...

Purpose: To investigate the possibility of using a keratometer to check the specification of the conicoidal back surface of rigid contact lenses. Methods: A conicoidal surface can be described by quoting two parameters. The most useful for the contact lens practitioner are the apical radius (curvature) and the P-value (asphericity). A keratometer w...

We used an adaptive optics system to correct the aberration dynamics of five subjects while they fixated on a monochromatic stimulus undergoing sinusoidal vergence changes between 1.5 and 2.5 D, at a temporal frequency of 0.2 Hz. The aberrations were measured at 20 Hz using a Shack–Hartmann sensor and corrected using a 37-actuator deformable mirror...

Manipulation of the eye’s aberrations using adaptive optics (AO) has shown that optical imperfections can affect the dynamic accommodation response. A limitation of current system designs used for such studies is an inability to make direct measurements of the eye’s aberrations during the experiment. We present an AO system which has a dual wavefro...

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...

Background: Accommodation control is mediated by a number of cues, including blur,chromatic aberration and target proximity. Data from wavefront measurements have shown clear shifts in ocular aberrations during increasing accommodative demand, most notably a negative shift in spherical aberration. Work in adaptive optics, where aberrations have be...

Adaptation to defocus is known to influence the subjective sensitivity to blur in both emmetropes and myopes. Blur is a major contributing factor in the closed-loop dynamic accommodation response. Previous investigations have examined the magnitude of the accommodation response following blur adaptation. We have investigated whether a period of blu...

Fluctuations in accommodation have been shown to be correlated in the two eyes of the same subject. However, the dynamic correlation of higher-order aberrations in the frequency domain has not been studied previously. A binocular Shack-Hartmann wavefront sensor is used to measure the ocular wavefront aberrations concurrently in both eyes of six sub...

During steady-state fixation the aberrations of the human eye display dynamic behaviour. It has been suggested that the fluctuations in focus are correlated between both eyes. However, nothing is known about the dynamic correlation between the aberrations other than focus. We have developed an open-view binocular Shack–Hartmann sensor which measure...

Kotulak and Schor have suggested that the accommodative mechanism of the human eye can determine the required response from the changes in retinal image contrast associated with the microfluctuations of accommodation. As other aberrations also display dynamic behaviour, they may too have an input in this self-calibration mechanism. An adaptive opti...

To compare the performance of the Orbscan II topographer with a videokeratoscope for a set of tilted test buttons with known aspheric surface profile characteristics, and for a series of measurements made on normal human corneas. Measurements of apical radius and p-value were obtained from 12 aspheric test surfaces using the Orbscan II, the EyeSys...

To investigate the effects of two levels of blur adaptation on visual resolution and steady-state accommodation responses in emmetropes and myopes. Eleven emmetropes (mean refractive error +0.01 +/- 0.31 DS) and 11 early-onset myopes (EOM, mean refractive error -4.44 +/- 1.64 DS) fixated monocularly at 4 m in three trials of 45 min duration with ei...

Accurate and repeatable assessments of ocular biometric factors are of vital importance to research laboratories conducting studies of ametropia. This is of particular importance to studies assessing the efficacy of myopia control strategies, and when investigating the effect of accommodation and posture on ocular biometry. In this technical note,...

To determine whether blur adaptation influences blur sensitivity and blur discrimination thresholds in young adult myopes and emmetropes. In addition, to determine whether there is a differential effect of blur adaptation on blur sensitivity and discrimination between refractive error groups. Proximal and distal blur sensitivity thresholds and blur...

It is now known that defocus is not the only aberration in the eye that exhibits dynamic behavior during fixation. It is currently unknown what effects, if any, the dynamics of these other aberrations have on steady-state accommodation control. We constructed an adaptive optics system to serve as a tool for future investigations in this area. The s...

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...

No The aims of the research may be outlined as follows: to measure the degree of transient axial elongation during the accommodation response in emmetropic and myopic young adults. To evaluate the effect of refractive error and accommodative demand on transient axial elongation of the eye. Axial length of the right eye was measured in 30 emmetropes...

purpose. To measure the degree of transient axial elongation during the accommodation response in emmetropic and myopic young adults. To evaluate the effect of refractive error and accommodative demand on transient axial elongation of the eye. methods. Axial length of the right eye was measured in 30 emmetropes and 30 myopes, by using the IOLMaster...

Microfluctuations of accommodation are known to increase in magnitude with increasing accommodation stimulus. Reduced sensitivity to blur in myopic subjects could also lead to increases in the magnitude of the microfluctuations. The aim of this study is to examine the effect of variations in accommodation stimulus upon the microfluctuations in diff...

We measured the wavefront aberrations of the eyes of five subjects with a Shack-Hartmann sensor sampling at 21.2 Hz and decomposed the measurements into Zernike aberration terms up to and including the fifth radial order. Coherence function analysis was used to determine the common frequency components between the aberrations within subjects. We fo...

The aim of this study was to establish the prevalence of refractive errors in Jordanian adults of working age, and to study the ocular biometric correlates of refractive error in this population. Refractive error and ocular biometry were measured in 1093 Jordanian adult subjects aged 17-40 years to determine the prevalence of refractive error, and...

Evidence exists for an additional inhibitory accommodative control system mediated by the sympathetic branch of the autonomic nervous system (ANS). This work aims to show the relative prevalence of sympathetic inhibition in young emmetropic and myopic adults, and to evaluate the effect of sympathetic facility on accommodative and oculomotor functio...

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...

Whereas many previous studies have identified the association between sustained near work and myopia, few have assessed the influence of concomitant levels of cognitive effort. This study investigates the effect of cognitive effort on near-work induced transient myopia (NITM). Subjects comprised of six early onset myopes (EOM; mean age 23.7 yrs; me...

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...

Autonomic innervation of ciliary smooth muscle is mediated principally by the parasympathetic nervous system and is supplemented by the sympathetic nervous system. Previous drug and nerve stimulation experiments on humans and animals have demonstrated that sympathetic innervation is inhibitory (via beta-2 adrenoceptors), relatively small, slow and...

A new commercially available device (IOLMaster, Zeiss Instruments) provides high resolution non-contact measurements of axial length (using partial coherent interferometry), anterior chamber depth, and corneal radius (using image analysis). The study evaluates the validity and repeatability of these measurements and compares the findings with those...

Purpose: The Shin-Nippon SRW-5000 is an open view autorefractor that superseded the Canon R-1 autorefractor in the mid-1990s and has been used widely in optometry and vision science laboratories. It has been used to measure refractive error, accommodation responses both statically and dynamically, off-axis refractive error, and adapted to measure...

A newly released commercial autorefractor, the Shin-Nippon SRW-5000 (Japan), has been found to be valid compared to subjective refraction and repeatable over a wide prescription range. Its binocular open field-of-view allows the accommodative state to be monitored while a natural environment is viewed. In conventional static mode, the device can ta...

A clinical evaluation of the Shin-Nippon SRW-5000 (Japan), a newly released commercial autorefractor, was undertaken to assess its repeatability and validity compared to subjective refraction. Measurements of refractive error were performed on 200 eyes of 100 subjects (aged 24.4±8.0 years) subjectively (non-cycloplegic) by one optometrist and objec...

To assess the effect of pupil dilation on vision and driving ability. A series of tests on various parameters of visual function and driving simulator performance were performed on 12 healthy drivers, before and after pupil dilation using guttae tropicamide 1%. A driving simulator (Transport Research Laboratory) was used to measure reaction time (R...