Developmental eye movement test: What is it really measuring?

Purpose. The Developmental Eye Movement (DEM) test is commonly used as a clinical visual-verbal ocular motor assessment tool. However, while the DEM test ratio has been reported to correlate with horizontal saccadic eye movements, there have been no published comparative studies of the DEM test and objective eye movement measures. The aim of this study was to compare DEM test performance with explicit quantification of saccadic eye movements, reading performance, symptomatology and visual processing speed, to assess the validity of the DEM test in clinical practice. Methods. One hundred fifty-eight children aged 8 to 11 years completed the DEM test and a battery of eye movement tasks, recorded by a Microguide 1000 infrared eye tracker. All subjects completed a symptomatology survey. Reading performance and visual processing data was collected for 77 and 75 children, respectively. Results. One hundred twenty-nine of the 158 subjects (81.65%) passed the DEM test. There was no significant correlation between any component of DEM test performance and quantitative eye movement parameters (gain, latency, asymptotic peak velocity, and number of corrective saccades) or symptomatology. There were significant correlations between DEM test outcome and reading performance, and with visual processing speed. Conclusions. DEM test performance does not correlate with saccadic eye movement skills or symptomatology. However, it is related to reading performance and visual processing speed. This study suggests that although DEM test times may not correlate directly with eye movement parameters, they do correlate with aspects of reading performance and thus may serve a diagnostic role in clinical practice. © 2009 American Academy of Optometry

An update on retinal prostheses

Retinal prostheses are designed to restore a basic sense of sight to people with profound vision loss. They require a relatively intact posterior visual pathway (optic nerve, lateral geniculate nucleus and visual cortex). Retinal implants are options for people with severe stages of retinal degenerative disease such as retinitis pigmentosa and age-related macular degeneration. There have now been three regulatory-approved retinal prostheses. Over five hundred patients have been implanted globally over the past 15 years. Devices generally provide an improved ability to localize high-contrast objects, navigate, and perform basic orientation tasks. Adverse events have included conjunctival erosion, retinal detachment, loss of light perception, and the need for revision surgery, but are rare. There are also specific device risks, including overstimulation (which could cause damage to the retina) or delamination of implanted components, but these are very unlikely. Current challenges include how to improve visual acuity, enlarge the field-of-view, and reduce a complex visual scene to its most salient components through image processing. This review encompasses the work of over 40 individual research groups who have built devices, developed stimulation strategies, or investigated the basic physiology underpinning retinal prostheses. Current technologies are summarized, along with future challenges that face the field

Improving population-level refractive error monitoring via mixture distributions

Introduction: Sampling and describing the distribution of refractive error in populations is critical to understanding eye care needs, refractive differences between groups and factors affecting refractive development. We investigated the ability of mixture models to describe refractive error distributions. Methods: We used key informants to identify raw refractive error datasets and a systematic search strategy to identify published binned datasets of community-representative refractive error. Mixture models combine various component distributions via weighting to describe an observed distribution. We modelled raw refractive error data with a single-Gaussian (normal) distribution, mixtures of two to six Gaussian distributions and an additive model of an exponential and Gaussian (ex-Gaussian) distribution. We tested the relative fitting accuracy of each method via Bayesian Information Criterion (BIC) and then compared the ability of selected models to predict the observed prevalence of refractive error across a range of cut-points for both the raw and binned refractive data. Results: We obtained large raw refractive error datasets from the United States and Korea. The ability of our models to fit the data improved significantly from a single-Gaussian to a two-Gaussian-component additive model and then remained stable with ≥3-Gaussian-component mixture models. Means and standard deviations for BIC relative to 1 for the single-Gaussian model, where lower is better, were 0.89 ± 0.05, 0.88 ± 0.06, 0.89 ± 0.06, 0.89 ± 0.06 and 0.90 ± 0.06 for two-, three-, four-, five- and six-Gaussian-component models, respectively, tested across US and Korean raw data grouped by age decade. Means and standard deviations for the difference between observed and model-based estimates of refractive error prevalence across a range of cut-points for the raw data were −3.0% ± 6.3, 0.5% ± 1.9, 0.6% ± 1.5 and −1.8% ± 4.0 for one-, two- and three-Gaussian-component and ex-Gaussian models, respectively. Conclusions: Mixture models appear able to describe the population distribution of refractive error accurately, offering significant advantages over commonly quoted simple summary statistics such as mean, standard deviation and prevalence

Progress in the clinical development and utilization of vision prostheses: an update

Alice Brandli, Chi D Luu, Robyn H Guymer, Lauren N Ayton Centre for Eye Research Australia, Department of Surgery (Ophthalmology), The University of Melbourne, Royal Victorian Eye and Ear Hospital, Melbourne, VIC, Australia Abstract: Vision prostheses, or “bionic eyes”, are implantable medical bionic devices with the potential to restore rudimentary sight to people with profound vision loss or blindness. In the past two decades, this field has rapidly progressed, and there are now two commercially available retinal prostheses in the US and Europe, and a number of next-generation devices in development. This review provides an update on the development of these devices and a discussion on the future directions for the field. Keywords: vision prostheses, bionic eye, vision restoration, blindness, medical bionics, retinitis pigmentos

Progress in the clinical development and utilization of vision prostheses: an update

Vision prostheses, or "bionic eyes", are implantable medical bionic devices with the potential to restore rudimentary sight to people with profound vision loss or blindness. In the past two decades, this field has rapidly progressed, and there are now two commercially available retinal prostheses in the US and Europe, and a number of next-generation devices in development. This review provides an update on the development of these devices and a discussion on the future directions for the field

Comparison Between Multifocal Electroretinography and Microperimetry in Age-Related Macular Degeneration

PURPOSE. To correlate and compare retinal function measured using multifocal electroretinography (mfERG) with microperimetry in intermediate age-related macular degeneration (AMD). METHODS. Sixty AMD participants underwent multifocal electroretinography (mfERG) and microperimetry testing in one eye, and 44 control participants were included to provide normative values for each test. Thirteen hexagons in the central three rings of a 103-hexagon stimulus grid for mfERG and retinotopically matched points on microperimetry were chosen and converted into standard deviations (SDs) away from that of normal participants (Z-score) to represent the magnitude of measured functional deficit and to allow a comparison of the two measures. RESULTS. For the average of all points on mfERG and microperimetry, mfERG N1 to P1 response amplitude and microperimetric retinal sensitivity was significantly lower (P ¼ 0.013 and P < 0.001, respectively) and mfERG P1 implicit time was significantly increased (P < 0.001) in the AMD participants compared to those in the control participants. Considering retinotopically matched points, there was no significant correlation between the average Zscores of the microperimetric retinal sensitivity and mfERG implicit time (correlation coefficient, R ¼ 0.254, P ¼ 0.051), nor response amplitudes (R ¼ 0.006, P ¼ 0.965), and the measured functional deficit with microperimetry was consistently greater than both mfERG parameters (P < 0.001). CONCLUSIONS. The measured functional deficit with microperimetry was greater than mfERG parameters in eyes with intermediate AMD. The absence of correlations between these two measures suggests that mfERG may be capturing unique aspects of retinal dysfunction. These findings are important when considering the use of these functional measures in intermediate AMD

Advances in implantable bionic devices for blindness: a review

Since the 1950s, vision researchers have been working towards the ambitious goal of restoring a functional level of vision to the blind via electrical stimulation of the visual pathways. Groups based in Australia, USA, Germany, France and Japan report progress in the translation of retinal visual prosthetics from the experimental to clinical domains, with two retinal visual prostheses having recently received regulatory approval for clinical use. Regulatory approval for cortical visual prostheses is yet to be obtained; however, several groups report plans to conduct clinical trials in the near future, building upon the seminal clinical studies of Brindley and Dobelle. In this review, we discuss the general principles of visual prostheses employing electrical stimulation of the visual pathways, focusing on the retina and visual cortex as the two most extensively studied stimulation sites. We also discuss the surgical and functional outcomes reported to date for retinal and cortical prostheses, concluding with a brief discussion of novel developments in this field and an outlook for the future

Developing an instrumental activities of daily living tool as part of the low vision assessment of daily activities protocol

To determine the validity, reliability, and measurement characteristics using factor and Rasch analysis of the Very Low Vision Instrumental Activities of Daily Living (IADL-VLV) in persons with severe vision loss