How does visual performance change as we get older:
In order to diagnose abnormal ocular conditions, it is important for an optometrist to understand the changes in visual performance which occur in older adults as a normal part of ageing
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How does visual performance change as we get older ?
– in order to diagnose abnormal ocular conditions, it is important for an optometrist to understand the changes in visual performance which occur in older adults as a normal part of ageing. The literature review could consider any aspect of visual function, including; visual acuity, contrast sensitivity dark adaptation, motion detection, and will evaluate the evidence regarding the effect of increasing age. The review will also consider physiological reasons for these changes.
Ageing is a process the entire population faces which is what makes research on how visual performance changes as we get older important. There are several reasons why this could be with one being the increasing population of people over the age of 60 across the globe. Benefits that can come from research into vision changes with age is the improvement of ‘quality of life’ as the results can be used to develop interventions that can reduce age related declines in vision. In addition to this the research can be used to identify potential risk factors to eye diseases that affect visual performance. Reduction of visual performance (specifically visual acuity and contrast sensitivity) during adulthood can reveal problems within the visual system that can be pointed out as signs that a disease is developing. To differentiate older adults who have ‘aged well’ to those who have not biological factors that can be either be neural or optical as well as environmental factors (if a person smokes) should also be considered.
Visual function/performance includes many aspects which are visual acuity, contrast sensitivity, dark adaptation, and motion detection. Visual acuity is the eyes’ ability to recognize details of an object at a given distance (Ebri, Marsden and Stevens, 2014) It is a test that is performed routinely as part of an eye examination using a Snellen or LogMAR chart. These charts consist of letters arranged in rows and an optometrist will ask the patient to read the smallest line of letter they can read. This testing essentially allows optometrist to assess how an individual’s vision changes overtime and many studies suggest that there is a strong correlation between ageing and the decline in visual acuity (Daffner et al., 2013)
Similar to visual acuity, contrast sensitivity is the ability of the eyes to distinguish object on a background (Salmon, 2020) rather than at different distances. However unlike visual acuity, contrast sensitivity is not frequently tested during a routine eye examination and was previously used as screening for glaucoma or clinically used for patient management (Moseley and Hill, 1994) An example of a contrast sensitivity test used in clinical practice is the Pelli-Robson letter sensitivity chart (Fig.1) Each line on the chart consists of two groups of three letters which decrease in contrast progressively down the chart (Pelli, Robson and J, 1988) The observer will score a patient based on (Fig.2) where the last group the patient was able to correctly name two or three lettters. (need to write more about contrast sensitivty)
In order to understand how ageing effects vision it is first important to define the ‘normal’ ageing process; how the eye changes structurally, physiologically, and how these changes are arisen from different ocular conditions. Examples of these ocular condition could be age related macular degeneration where drusen begins to form on older retinas as well as cataracts where the density of the crystalline lens’s changes as we get older (Xu, Pokorny, and Smith, 1997). In recent years there have been numerous studies on retinal health trying to define ‘normal’ ageing however there are still many studies that depend solely on clinical judgment and self-report when trying to define normal ageing. Self-report can be an issue as people in the older population are usually unaware that they have early signs of diseases that can affect their visual performance. In America, it has been reported that around fifty percent of older adults do not seek eye care with regards to conditions that can be diagnosed (McGwin et al., 2010)
There are a plethora of studies, and articles that consider how visual performance varies with age and when reading through them you can gain a good overview of recent and past developments into the changes in vision within the ageing population. However the purpose of this review is to recognize areas studied from the past to summarize, compare it current knowledge, and discuss any possible gaps that may arise from this body of work. The main focus of this study is on how visual function specifically contrast sensitivity and visual acuity changes with age as well as physiological changes that can also occur when ageing.
|Srinivasan, R., Turpin, A. and McKendrick, A.M. (2021). Contrast Sensitivity on 1/f Noise Is More Greatly Impacted by Older Age for the Fovea Than Parafovea. Optometry and Vision Science, 98(4), pp.394–403.||SIGNIFICANCE: Contrast sensitivity changes across the visual field with age and is often measured clinically with various forms of perimetry on plain backgrounds. In daily life, the visual scene is more complicated, and therefore, the standard clinical measures of contrast sensitivity may not predict a patient’s visual experience in more natural environments. PURPOSE: This study aims to determine whether contrast thresholds in older adults are different from younger adults when measured on a 1/f noise background (a nonuniform background whose spatial frequency content is similar to those present in the natural vision environments). METHODS: Twenty younger (age-range, 20 to 35years) and 20 older adults (age range, 61to 79 years) with normal ocular health were recruited. Contrast thresholds were measured for a Gabor patch of 6 cycles per degree (sinewave grating masked by a Gaussian envelope of standard deviation 0.17°) presented on 1/f noise background (root-mean-square contrast, 0.05 and 0.20) that subtended 15° diameter of the central visual field. The stimulus was presented at four eccentricities (0°, 2°, 4°, and 6°) along the 45° meridian in the noise background, and nine contrast levels were tested at each eccentricity. The proportion of correct responses for detecting the target at each eccentricity was obtained, and psychometric functions were fit to estimate the contrast threshold. RESULTS: Older adults demonstrate increased contrast thresholds compared with younger adults. There was an eccentricity-dependent interaction with age, with the difference between groups being highest in the fovea com-pared with other eccentricities. Performance was similar for the two noise backgrounds tested. CONCLUSIONS: Our results revealed a strong eccentricity dependence in performance between older and younger adults, highlighting age-related differences in the contrast detection mechanisms between fovea and parafovea for stimuli presented on nonuniform backgrounds.|
|Hardy, J.L., Okajima, K., Werner, J.S. and Delahunt, P.B. (2005). Senescence of spatial chromatic contrast sensitivity I Detection under conditions controlling for optical factors. Journal of the Optical Society of America A, 22(1), p.49.||Chromatic contrast thresholds for spatially varying patterns of various spatial frequencies (0.5, 1, 2, and 4 cycles per degree) were measured for ten older (65–77 yr. of age) and ten younger (18–30 yr. of age) observers. The stimuli were Gabor patches modulated along S-varying or (L 2 M)-varying chromatic axes. Thresholds were determined for two sets of stimuli. For one set of stimuli, the mean chromaticity and luminance were equated at the cornea for all observers. The second set of stimuli was corrected for ocular media density differences to equate stimulation of each of the three cone types at the retina for each individual. Chromatic contrast thresholds were higher for older observers for all stimuli tested. The magnitude of this difference showed little dependence on spatial frequency. When stimuli were equated at the cornea, this difference was greater for S-varying stimuli. When stimuli were equated at the retina, the age-related difference in thresholds for S-varying stimuli was reduced. Both optical and neural factors contribute to these age-related losses in spatial chromatic contrast sensitivity.|
|Delahunt, P.B., Okajima, K., Werner, J.S. and Hardy, J.L. (2005). Senescence of spatial chromatic contrast sensitivity II Matching under natural viewing conditions. Journal of the Optical Society of America A, 22(1), p.60.||Age-related changes in the spatial chromatic contrast sensitivity function of detection, measured along S and L 2 M cone axes, were demonstrated in a companion paper [Hardy et al., J. Opt. Soc. Am. A 22, 49 (2005)]. Here senescent changes in chromatic contrast appearance were assessed by contrast-matching functions (CMFs). Luminance and chromatic CMFs (S and L 2 M axes) were compared for younger (age 18–31 yr) and older (age 65–75 yr) trichromatic subjects by using stimuli that were perceptually anchored to the same physical standard contrasts. Subjects matched the contrast of test gratings of various spatial frequencies (0.5–8 cycles per degree) to the standard stimuli under natural viewing conditions. Because of changes in the visual system with age, the standard stimuli were closer to threshold for older subjects; however, in general, the shapes of the CMFs were similar for both groups. The results suggest that the perception of relative contrasts across spatial frequencies is stable with age.|
|Gillespie-Gallery, H., Konstantakopoulou, E., Harlow, J.A. and Barbur, J.L. (2013). Capturing Age-Related Changes in Functional Contrast Sensitivity with Decreasing Light Levels in Monocular and Binocular Vision. Investigative Ophthalmology & Visual Science, [online] 54(9), pp.6093–6103. Available at: https://iovs.arvojournals.org/article.aspx?articleid=2127822 [Accessed 26 Feb. 2021].||PURPOSE. It is challenging to separate the effects of normal aging of the retina and visual pathways independently from optical factors, decreased retinal illuminance, and early-stage disease. This study determined limits to describe the effect of light level on normal, age-related changes in monocular and binocular functional contrast sensitivity. METHODS. We recruited 95 participants aged 20 to 85 years. Contrast thresholds for correct orientation discrimination of the gap in a Landolt C optotype were measured using a 4-alternative, forced choice (4AFC) procedure at screen luminance’s from 34 to 0.12 cd/m2 at the fovea and parafovea (08 and 648). Pupil size was measured continuously. The health of the Retina index (HRindex) was computed to capture the loss of contrast sensitivity with decreasing light level. Participants were excluded if they exhibited performance outside the normal limits of interocular differences or HRindex values, or signs of ocular disease. RESULTS. Parafoveal contrast thresholds showed a steeper decline and higher correlation with age at the parafovea than the fovea. Of participants with clinical signs of ocular disease, 83% had HRindex values outside the normal limits. Binocular summation of contrast signals declined with age, independent of interocular differences. CONCLUSIONS. The HRindex worsens more rapidly with age at the parafovea, consistent with histologic findings of rod loss and its link to age-related degenerative disease of the retina. The HRindex and interocular differences could be used to screen for and separate the earliest stages of subclinical disease from changes caused by normal aging.|
|Silvestre, D., Arleo, A. and Allard, R. (2019). Healthy Aging Impairs Photon Absorption Efficiency of Cones. Investigative Opthalmology & Visual Science, 60(2), p.544.||PURPOSE. Vision decline with healthy aging is a major public health concern with the unceasing growth of the aged population. In order to prevent or remedy the age-related visual loss, a better understanding of the underlying causes is needed. The current psychophysical study used a novel noise paradigm to investigate the causes of age-related contrast sensitivity loss by estimating the impact of optical factors, absorption rate of photon by photoreceptors, neural noise, and calculation efficiency on contrast sensitivity. METHODS. The impact of these factors on contrast sensitivity was assessed by measuring contrast thresholds with and without external noise over a wide range of spatial frequencies (0.5–16 cycles per degree [cyc/deg]) and different luminance intensities for 20 young (mean ¼ 26.5 years, SD ¼ 3.79) and 20 older (mean ¼ 75.9 years, SD ¼ 4.30) adults, all having a good visual acuity (‡6/7.5). RESULTS. The age-related contrast sensitivity losses were explained by older observers absorbing considerably fewer photons (43), having more neural noise (1.93), and a lower processing efficiency (1.43). The aging effect on optical factors was not significant. CONCLUSIONS. The age-related contrast sensitivity loss was mostly due to less efficient cones absorbing four times fewer photons than young adults. Thus, besides the ocular factors known to be considerably affected with aging, the decline of absorption efficiency of cones is also responsible for a considerable age-related visual decline, especially under dim light.|
|Allard, R., Renaud, J., Molinatti, S. and Faubert, J. (2013). Contrast sensitivity, healthy aging, and noise. Vision Research, 92, pp.47–52.||At least three studies have used external noise paradigms to investigate the cause of contrast sensitivity losses due to healthy aging. These studies have used noise that was spatiotemporally localized on the target. Yet, Allard and Cavanagh (2011) have recently shown that the processing strategy can change with localized noise thereby violating the noise-invariant processing assumption and compromising the application of external noise paradigms. The present study reassessed the cause of age-related contrast sensitivity losses using spatiotemporally extended external noise (i.e., full screen, continuously displayed dynamic noise). Contrast thresholds were measured for young (mean = 24 years) and older adults (mean = 69 years) at 3 spatial frequencies (1, 3 and 9 cpd) and 3 noise conditions (noise-free, local noise and extended noise). At the two highest spatial frequencies, the results were similar with local and extended noise: the sensitivity loss was mainly due to lower calculation efficiency. At the lowest spatial frequency, age-related contrast sensitivity losses were attributed to the internal equivalent noise when using extended noise and like in previous studies, due to calculation efficiency with local noise. These results show that the interpretation of external noise paradigms can drastically differ depending on the noise type suggesting that external nose paradigms should use external noise that is spatiotemporally extended like internal noise to avoid triggering a processing strategy change. Contrary to previous studies, we conclude that healthy aging does not affect the calculation efficiency of the detection process at low spatial frequencies.|
|Pardhan, S. (2004). Contrast sensitivity loss with aging: sampling efficiency and equivalent noise at different spatial frequencies. Journal of the Optical Society of America A, 21(2), p.169.||The relative contributions of optical and neural factors to the decrease in visual function with aging were investigated by measurement of contrast detection at three different spatial frequencies, in the presence of external noise, on young and older subjects. Contrast detection in noise functions allows two parameters to be measured: sampling efficiency, which indicates neural changes, and equivalent noise, which demonstrates optical effects. Contrast thresholds were measured in the presence of four levels (including zero) of externally added visual noise. Measurements were obtained from eight young and eight older visually normal observers. Compared with young subjects, older subjects showed significantly ( p , 0.05) lower sampling efficiencies at spatial frequencies of 1 and 4 cycles per degree (c/deg) and significantly higher equivalent noise levels for gratings of 10 c/deg. Neural and optical factors affect contrast sensitivity loss with aging differently, depending on the spatial frequency tested, implying the existence of different mechanisms.|
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