Purpose Colour sensitivity was assessed to establish aging effects both at the fovea and 6 deg away from fixation, in each of the four quadrants. Methods 65 normal healthy subjects (from 20 to 80 years of age) took part in the study. All subjects had Visual Acuity (VA) of 6/6 or better. Fixation accuracy was monitored using infrared imaging of the pupil and the tests were carried out on the P_SCAN system. Target size was adjusted for parafoveal locations to account for retinal and cortical magnification. Yellow‐blue (YB) and red‐green (RG) colour discrimination was assessed using the CAD (colour assessment and diagnosis) test (http://www.caa.co.uk/docs/33/200904.pdf). Results RG and YB colour thresholds were analysed separately for all five locations tested and showed no significant effect with ageing below the age of 60 years. Two age bands were formed based on statistical analysis (20‐59.9 and 60‐79.9). The decline in performance with age was more rapid at the fovea and exhibited a steeper gradient when compared with results in the periphery for both RG and YB discrimination. Foveal YB discrimination showed the largest ageing effect. No significant difference was found between the four parafoveal locations. YB discrimination at the fovea also exhibited the largest inter‐subject variability. Conclusion These findings may have clinical significance in the very early detection of disease processes that remain subclinical in many subjects. Differences between foveal and peripheral locations help to differentiate between the normal effects of ageing and disease. For example, higher foveal and normal peripheral YB thresholds in normal subjects from high peripheral thresholds in early glaucomatous subjects.
Purpose Age Related Macular Degeneration (ARMD) is the leading cause of blindness in the developed world in people over the age of 50. Its prevalence increases with age as does diabetes. Such conditions affect the metabolic stability of the retina, resulting in non‐inflammatory damage to retinal structures, and finally retinopathy. These changes to the visual pathway result in colour vision loss and in general, diminished visual performance. The aim of this study was to quantify accurately using sensitive visual tests the severity of visual loss in subjects with ARMD and diabetes. Methods We investigated a large number of ARMD and Diabetic subjects with varying degrees of retinopathy and assessed their colour vision, achromatic high contrast acuity and flicker sensitivity under photopic and mesopic viewing conditions. Results Results show a loss of chromatic sensitivity in both the red‐green and yellow‐blue channels, more pronounced under mesopic viewing condition. It was observed that chromatic loss was not localised to the site of retinopathy but affected peripheral retina also. Flicker sensitivity and contrast acuity loss were also observed in all subjects diagnosed with the above conditions. Preliminary findings show that significant loss of chromatic and flicker sensitivity precedes structural changes in the retina as revealed in conventional fundus imaging. Conclusion The results so far suggest that loss of chromatic sensitivity is the most sensitive measure for detection of early damage in subjects with eye disease and can be used to detect and to monitor the progress of disease or the outcome of treatment.
Purpose Diabetic retinopathy is a major cause of blindness in the Western World and remains one of the most serious complications of diabetes mellitus. The gold standard to measure functional change in diabetic (DB) patients is LogMAR or Snellen VA. The aim of this study was to measure and characterise the severity of visual function loss in subjects with DB using sensitive psychophysical tests and to quantify accurately how changes in management of the disease correlate with changes in visual function. Methods Three groups of patients (n=50) were included in this study:DB patients with and without retinopathy and patients with no DB. Each patient had a full ophthalmic examination prior to psychophysical assessment. Colour vision assessment was carried out using the CAD test (Colour Assessment & Diagnosis) that provides a measure of both yellow‐blue and red‐green loss of chromatic sensitivity (CS). Rapid flicker (RF) was also measured by assessing sensitivity to a 20Hz flicker stimulus at five locations in the central visual field (fovea and 1.5 degrees from fixation in each quadrant). All tests were carried out at photopic and high mesopic light. Results The results show significant loss of CS (p <.001) and some loss in RF sensitivity (p <.01). The most sensitive measure of visual loss was CS.There was also a positive correlation between CAD thresholds as a measure of CS and improved DB control. Conclusion The results suggest that loss of visual function precedes structural changes in the retina and could be used as a means of detecting early structural changes in the retina that precede clinical diagnosis of retinopathy. Preliminary results also suggest that changes in CAD thresholds provide an objective way of monitoring the progress of DB and/or treatment outcome.
Purpose Clinical tests of visual acuity (VA) that employ multiple, neighbouring optotypes assume that visual 'crowding' at the fovea is negligible. Findings from recent studies suggest that crowding effects can affect high contrast acuity thresholds at the fovea. The absence of data to describe the distribution of crowding effects within 'normal' vision makes it difficult to establish when a measured reduction in VA (with crowding) can no longer be considered to be within the normal range and is therefore indicative of abnormal development or pathology. The aim of this study was to quantify the effects of crowding on VA in the normal population. Methods We measured acuity thresholds, with and without crowding, in central vision (i.e. at the fovea and at +/‐1 degree, +/‐1.5 degrees, and +/‐2 degrees) in 80 normal subjects with the age range of 29.3 +/‐10.7 years. The stimulus optotype was a Landolt ring of 100% luminance contrast presented either in isolation or together with four surrounding rings at a distance equal to 1.5 times the diameter of the stimulus, these parameters were selected on the basis of preliminary studies varying the spacing and the number of distracters. Results The threshold stimulus size for correct discrimination of gap orientation increased almost linearly with eccentricity, the presence of distracter rings caused a significant reduction in VA. Conclusion The statistical distribution of the differences between the two measures of VA provides the data needed to define the effects of crowding in “normal” vision. The template extracted from these data is clinically useful to identify those subjects that show abnormal sensitivity to crowding, i.e. amblyopia or early degenerative conditions/ disease.
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