Vernier acuity and aging

Vision through Healthy Aging Eyes

As life expectancy grows, so too will the number of people adversely affected by age. Although it is acknowledged that many conditions and diseases are associated with age, this mini-review will present a current update of the various visual changes that generally occur in healthy individuals disregarding the possible effects of illness. These alterations influence how the world is perceived and in turn can affect efficiency or the ability to perform ordinary daily tasks such as driving or reading. The most common physical developments include a decreased pupil size and retinal luminance as well as changes both in intercellular and intracellular connections within the retina along the pathway to the visual cortex and within the visual cortex. The quantity and the physical location of retinal cells including photoreceptors, ganglion and bipolar retinal cells are modified. The clarity of intraocular organs, such as the intraocular lens, decreases. These all result in common visual manifestations that include reduced visual acuity, dry eyes, motility changes, a contraction of the visual field, presbyopia, reduced contrast sensitivity, slow dark adaptation, recovery from glare, variation in color vision and a decreased visual processing speed. Highlighting these prevalent issues as well as current and possible future innovations will assist providers to formulate treatments and thereby conserve maximum independence and mobility in the modern mature population.

A Novel Method for Detection and Progress Assessment of Visual Distortion Caused by Macular Disorder: A Central Serous Chorioretinopathy (CSR) Case Study

This paper presents a new mathematical model along with a measurement platform for accurate detection and monitoring of various visual distortions (VD) caused by macular disorders such as central serous chorioretinopathy (CSR) and age-related macular degeneration (AMD). This platform projects a series of graphical patterns on the patient’s retina and calculates the severity of VDs accordingly. The accuracy of this technique relies on the accurate detection of distorted lines by the patient. We also propose a simple mathematical model to evaluate the VD created by CSR. The model is used as a control for the test results achieved from the proposed platform. The proposed platform consists of the required hardware and software for the generation and projection of patterns along with the collection and processing of patients against their standard optical coherence tomography (OCT) images. Based on these results, the OCT images agree with the VD test results, and the proposed platform can be used as an alternative home monitoring method for various macular disorders.

NGRID: A novel platform for detection and progress assessment of visual distortion caused by macular disorders

This paper presents a new graphical macular interface system (GMIS) for accurate, rapid, and quantitative measurement of visual distortion (VD) in the central vision of patients suffering from macular disorders. In this system, a series of predefined graphical patterns or multiple grids (NGRID) are randomly selected from a library of patterns and visualized on the screen, then the VDs identified by the patient are recorded as binary codes using various control methods including speech recognition. Scalable Vector Graphics (SVG) is used to generate the patterns and save them into a central library. Based on the projected patterns and the patients' responses, a VD graph or so-called heatmap is generated for eye-care purposes. We demonstrate and discuss the functionality of the proposed system for the detection and progress assessment of a macular condition in patients suffering from Central Serous Chorioretinopathy (CSR). Also, we characterize the proposed technique to evaluate the systematic error and response time on healthy human subjects with normal vision. Based on these results, the voice recognition input method exhibits a lower error but a higher response time compared to other input devices. We run the proposed NGRID VD technique to evaluate the effect of CSR on the visual field of a CSR patient. The generated heatmaps are in agreement with standard Optical Coherence Tomography (OCT) images obtained at different times from both the left and right eyes. These results reveal the applicability of the proposed technique for the detection and assessment of macular disorders. Based on these results, the proposed NGRID platform shows great promise for use as an alternative solution for in-home monitoring of various macular disorders and as a means of forwarding responses to secured cloud facilities for future data analysis.

Recent Advances of Computerized Graphical Methods for the Detection and Progress Assessment of Visual Distortion Caused by Macular Disorders

Recent advances of computerized graphical methods have received significant attention for detection and home monitoring of various visual distortions caused by macular disorders such as macular edema, central serous chorioretinopathy, and age-related macular degeneration. After a brief review of macular disorders and their conventional diagnostic methods, this paper reviews such graphical interface methods including computerized Amsler Grid, Preferential Hyperacuity Perimeter, and Three-dimensional Computer-automated Threshold Amsler Grid. Thereafter, the challenges of these computerized methods for accurate and rapid detection of macular disorders are discussed. The early detection and progress assessment of macular disorders can significantly enhance the required clinical procedure for the diagnosis and treatment of macular disorders.

Age-related changes in visually evoked electrical brain activity

Whereas much is known about the degenerative effects of aging on cortical tissue, less is known about how aging affects visually evoked electrical activity, and at what latencies. We compared visual processing in elderly and young controls using a visual masking paradigm, which is particularly sensitive to detect temporal processing deficits, while recording EEG. The results show that, on average, elderly have weaker visual evoked potentials than controls, and that elderly show a distinct scalp potential topography (microstate) at around 150 ms after stimulus onset. This microstate occurred irrespective of the visual stimulus presented. Electrical source imaging showed that the changes in the scalp potential resulted from decreased activity in lateral occipital cortex and increases in fronto-parietal areas. We saw, however, no evidence that increased fronto-parietal activity enhanced performance on the discrimination task, and no evidence that it compensated for decreased posterior activity. Our results show qualitatively different patterns of visual evoked potentials (VEPs) in the elderly, and demonstrate that increased fronto-parietal activity arises during visual processing in the elderly already between 150 and 200 ms after stimulus onset. The microstate associated with these changes is a potential diagnostic tool to detect age-related cortical changes.

Combining vernier acuity and visual backward masking as a sensitive test for visual temporal deficits in aging research

Performance in many everyday situations slows down when age increases. The causes of slowing down may be found on any stage of information processing. Here, we show that the combination of a vernier acuity task and the shine-through backward masking paradigm is a good paradigm to determine temporal processing deficits. The paradigm is relatively robust to optical blur and unlikely affected by motor dysfunctions. Strong masking deficits are found from an age of about 50 years on.

Visual function and dysfunction in early and late age-related maculopathy

Late age-related maculopathy (ARM) is responsible for the majority of blind registrations in the Western world among persons over 50 years of age. It has devastating effects on quality of life and independence and is becoming a major public health concern. Current treatment options are limited and most aim to slow progression rather than restore vision; therefore, early detection to identify those patients most suitable for these interventions is essential. In this work, we review the literature encompassing the investigation of visual function in ARM in order to highlight those visual function parameters which are affected very early in the disease process. We pay particular attention to measures of acuity, contrast sensitivity (CS), cone function, electrophysiology, visual adaptation, central visual field sensitivity and metamorphopsia. We also consider the impact of bilateral late ARM on visual function as well as the relationship between measures of vision function and self-reported visual functioning. Much interest has centred on the identification of functional changes which may predict progression to neovascular disease; therefore, we outline the longitudinal studies, which to date have reported dark-adaptation time, short-wavelength cone sensitivity, colour-match area effect, dark-adapted foveal sensitivity, foveal flicker sensitivity, slow recovery from glare and slower foveal electroretinogram implicit time as functional risk factors for the development of neovascular disease. Despite progress in this area, we emphasise the need for longitudinal studies designed in light of developments in disease classification and retinal imaging, which would ensure the correct classification of cases and controls, and provide increased understanding of the natural course and progression of the disease and further elucidate the structure-function relationships in this devastating disorder.

Visual function assessment and metamorphopsia after macular hole surgery*,+

The purpose of this study was to develop a new resolution acuity measure for patients after macular hole surgery. Fifty eyes of 44 patients who had undergone successful treatment were tested. Visual acuity was measured with the Snellen, Early Treatment of Diabetic Retinopathy Study and Landolt-C charts. A Line Resolution Test was performed as part of their follow-up exam where a vertical line was presented. Participants were categorized by their perception of the line as solid, bent or broken. The line could be distorted into a sine-wave pattern in order to determine the participants' detection threshold for the distortion. Chart acuities did not differ among the three groups, as categorized by their line perception. Only the distortion measure was sensitive enough to differentiate the solid- from the broken-line group. The distortion measure assesses resolution power of the macula in smaller increments than acuity charts. This hyperacuity approach is more appropriate in the assessment of functional outcome after microsurgery.

A comparison of the effects of ageing upon vernier and bisection acuity

While most positional acuity tasks exhibit an age-related decline in performance, the effect of ageing upon vernier acuity continues to be the subject of some debate. In the present study we employed a stimulus design that enabled the simultaneous determination of bisection and vernier acuities in 36 subjects, aged between 22 and 84 years. This approach provided a means for directly testing the hypothesis that ageing affects bisection acuity but not vernier acuity by ensuring that differences in stimulus configuration and in the subject's task were kept to an absolute minimum. Optimum thresholds increased as a function of age for both bisection and vernier tasks. Inter-subject threshold variability also increased with age. Issues surrounding the comparison of absolute vernier thresholds across different studies are discussed and two important methodological factors are identified: the precise statistical method used to estimate thresholds, and the magnitude, in angular terms, of the smallest spatial offset of the elements of the vernier stimulus which can be displayed. Comparison with previously published data indicates that the discrepancy between this study and most previous investigations with respect to the effect of age upon vernier performance can be at least partly accounted for by differences in the minimum displayable vernier offset. Vernier thresholds do increase with age. The increased variability of vernier thresholds in older subjects would appear to limit the diagnostic value of the test as a means of enabling normal ageing to be distinguished from visual loss due to pathology of the eye or visual system.

Potential vision testing--the relationship between visual acuity and Vernier acuity in the presence of simulated cataract

To evaluate the utility of a computer controlled two-bar Vernier acuity measurement as a predictor of visual function in the presence of cataract we measured logMAR visual acuity and Vernier acuity in a group of 40 young normal observers under various levels of dioptric blur (0-3 D in dioptre steps). The Vernier thresholds were resistant to dioptric blur up to 2 D, but performance degraded with blur of 3 D for non-optimised Vernier stimulus parameters. The stimulus parameters, bar length and bar separation, were further investigated in two subjects under conditions of blur. By extending the Vernier bar length and increasing the bar separation the effect of blur could be further reduced even under the most blurred condition. The relationship between visual acuity and Vernier acuity was determined. Vernier acuity was measured in the presence of Vistech cataract simulating lenses and a prediction of visual acuity was made for three observers, two with no ocular abnormality and one with age-related maculopathy. The cataract simulating lenses affected the measured visual acuity in all three subjects, but had less effect on Vernier acuity. Predicted visual acuities were all within six letters (0.12 log units) of the visual acuity without the simulated cataract. As expected, the subject sufferng from age-related maculopathy, whilst showing similar levels of Vernier acuity to the two ocularly healthy subjects at 1.5 degrees of retinal eccentricity, showed much poorer Vernier acuity for stimuli presented at fixation.

Aging effects on vernier hyperacuity: a function of oscillation rate but not target contrast

PURPOSE

Most previous studies have shown static vernier acuity for high-contrast targets to be largely unaffected by aging; those examining adult age differences on oscillatory displacement thresholds have consistently reported marked age deficits. The goals of this study were to (1) measure the age deficit on oscillatory discrimination beyond that attributable to any change in spatial discrimination by using the same target configuration for both task types and (2) determine whether an age-related change in the contrast response of the visual system contributes to age differences on static or oscillatory discrimination.

METHODS

The displacement thresholds of young and old observers for a vernier task configuration were determined at two target contrast levels (0.08 and 0.64) for static and oscillating targets (2 and 6 Hz)

RESULTS

No age differences were seen on static displacement thresholds at either high or low contrast. A marked age deficit that emerged when oscillation was increased was unrelated to target contrast or observer contrast sensitivity.

CONCLUSIONS

Age-related declines in oscillatory discrimination beyond those attributable to spatial discrimination do not appear to be attributable to optical factors nor to a decline in the contrast response of the senescent visual system. These findings are discussed in terms of a functional decline in the magnocellular pathway, or "neural entropy," possibly due to random cell loss.

Variation in vernier acuity with age

Many visual functions deteriorate with increasing age, vernier acuity apparently being an exception. We used an improved experimental protocol to investigate vernier thresholds in subjects in four age groups. Vernier threshold was found to increase with increasing age, and the difference in this, compared with previous findings is probably due to the smaller inter-pixel angle used. Vernier acuities in young subjects in other studies seem to have been underestimated. As vernier acuity did not vary with retinal illuminance and the sensitivity loss does not seem to be a learning effect, neural rather than optical changes are likely to account for the deterioration. Measurement of vernier acuity may have clinical application in the determination of visual function behind cataract, and it will be necessary to consider the effect of age on vernier acuity.

No effect of age on spatial interval discrimination as a function of eccentricity or separation

PURPOSE

Performance on positional acuity tasks exhibits marked resistance to the effects of optical image degradation. This places positional acuity tasks in a unique position for psychophysical examination of the effects of age upon visual performance because any observed age-related changes reflect losses in retinal/neural function. One positional acuity task with important consequences for "real-world" vision is spatial interval discrimination, a task in which the subject is required to detect changes in the size of the gap between two objects. In the present study we examine spatial interval discrimination in young and elderly observers as a function of separation and eccentricity.

METHODS

Stimuli were two Gaussian-modulated luminance patches placed side by side around an imaginary iso-eccentric arc in the upper visual field, allowing eccentricity and separation to be varied independently. Changes in separation were achieved by moving the stimuli around the arc, while eccentricity was varied by changing the radius of the arc. Thresholds were obtained for healthy young and elderly observers using a forced-choice method of constants at two eccentricities (1.25 degrees and 10 degrees) and five separations.

RESULTS

When thresholds, expressed as Weber fractions, are plotted as a function of the geometric ratio of the stimuli (separation/eccentricity) the data from the young and elderly groups collapse to a single function. Performance is independent of age and eccentricity, and depends only on the geometric ratio of the stimuli.

CONCLUSIONS

No effect of age was found for spatial interval discrimination. Our results suggest that spatial interval discrimination belongs to the wider group of positional acuities whose neural substrates are unaffected by ageing.