City Research Online

Abstract

Purpose: To assess colour vision in Age-related macular degeneration (AMD) while relating chromatic sensitivity to the severity of AMD and AMD morphologies such as drusen and reticular pseudodrusen. To evaluate if chromatic functional loss precedes structural changes in initial stages of AMD, and if it can be a valuable risk stratification tool for advanced AMD. Methods: Chromatic sensitivity was tested using the Colour Assessment and Diagnosis (CAD) test developed by City, University of London and correlated to the structural changes from fundus photography and spectral domain OCT. All patients were asymptomatic with a visual acuity of 6/12 or better. CAD thresholds were compared to clinical classification in all AMD eyes (Ferris et al., 2013); Soft drusen and Reticular drusen (RPD); Central macular thickness (CMT); Fundus autofluorescence (FAF) pattern (Einbock et al., 2005; Wong et al., 2014) and Soft drusen characteristics (Bird et al., 1995). Cases of conversion to ‘Wet’ AMD were identified through a repeat clinical assessment after the first 12 months. Chromatic sensitivity in early onset drusen (EOD) included comparing their colour thresholds to AMD eyes. Student t-test were used for correlation and P<0.05 was considered significant. Results All eyes with AMD had chromatic sensitivity loss in either one of RG / YB or both (p<0.0001) in comparison to the age-matched normative data set. The eyes involved exhibited a range of colour thresholds measured on CAD system (CAD thresholds) affecting both the colour mechanisms but YB losses were at a higher magnitude than RG losses (p<0.001). There was no correlation to the AMD severity grades in clinical classification because of large inter-subject variability within each group. Intermediate AMD was the largest group. Mean chromatic sensitivity increased from normal aging (NA) to soft drusen to reticular drusen, NA< soft drusen< RPD (R2=0.9). Even though EOD (n=10) had the same morphological appearance of drusen as ARM, lower and better CAD thresholds were recorded. Reticular drusen revealed the highest mean CAD thresholds for RG (~ 19 units) and for YB (~14 units), followed by soft drusen group (~ 7 units for both RG/YB). Comparison of CAD thresholds in soft drusen and RPD groups with all other groups (Normative, NA, EOD) was statistically significant (p<0.0001). Forty nine eyes with soft drusen were stratified for drusen morphology, number, size, the area covered and the main location of the drusen on the ETDRS grid. Drusen size was the only characteristic feature found to be significantly associated with both RG / YB chromatic sensitivity loss. Grade 5 eyes were statistically different compared to the rest of the grades (p<0.0003 RG and p<0.02 YB). Autofluorescence was performed in 76 eyes and the results assigned to the 8 FAF patterns from FAM study (Einbock et al., 2005). The patchy pattern of FAF had the highest CAD thresholds and this was in agreement with the FAM group as being the high-risk pattern. CMT was measured in 88 eyes, 3 eyes were noted to have early GA and they showed very severe loss of RG and YB thresholds. The p value correlating the CAD thresholds of eyes with CMT<200 and >200 μm was statistically significant with P<0.01 for RG and <0.002 for YB. Review of baseline CAD thresholds in cases converted to wet AMD at the end of 12 months, revealed six eyes had converted to wet AMD. The baseline CAD thresholds of these eyes were not conclusive of being predictive of the impending change to wet AMD. Conclusions: The visual acuity and hence the integrity of cone photoreceptors remains relatively unaffected in early and intermediate stages of AMD. The processing of cone signals in the retina can however be heavily disrupted with subsequent loss of both YB and RG chromatic sensitivity in the eyes. The greatest losses relate to eyes with reticular pseudodrusen. Chromatic sensitivity change was indicative in early macular thinning but failed to herald the onset of wet AMD in our study sample.

Publication Type:	Thesis (Doctoral)
Subjects:	R Medicine > RE Ophthalmology
Departments:	School of Health & Psychological Sciences > School of Health & Psychological Sciences Doctoral Theses School of Health & Psychological Sciences > Optometry & Visual Sciences

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