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James Thomas Brodie, Luke Membrey; Structural vs. Functional Changes in Diabetic Macular Oedema Treated with Ranibizumab. Invest. Ophthalmol. Vis. Sci. 2014;55(13):1773.
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Anti-VEGF therapies have emerged as a novel treatment for diabetic macular oedema (DMO). Clinical trials investigating the efficacy of treatment modalities for DMO typically use measurements of macular thickness on ocular coherence tomography (OCT) to assess therapeutic effect. Colour discrimination testing has been shown to be highly sensitive and specific in identifying the presence of clinically significant macular oedema. The purpose of this study was to compare the structural changes seen on OCT imaging with the functional changes on testing colour vision using the Cambridge Colour Test ™ (CCT) in patients with DMO undergoing treatment with Ranibizumab (Lucentis).
14 patients (mean age = 61) initiating treatment with Lucentis for DMO were recruited. Colour vision was assessed by quantitatively measuring colour discrimination thresholds along the protan, deutan, and tritan chromatic axes using the CCT at baseline and 4 weeks post-injection. Visual acuity was measured using the LogMAR chart and central macular thickness (CMT) using the Topcon 3D OCT-2000.
Tritan vector impairment was the most sensitive colour discrimination measure to the presence of DMO with impairment found in all treated eyes (n=19). Tritan discrimination was also the most significantly impaired vector compared with protan and deutan vectors. At baseline, there was a significant correlation between impairment in tritan discrimination and reduction in BCVA (r=-0.46, p=0.05). However, there was no significant correlation between CMT, BCVA, and impairments in the other colour discrimination vectors. The majority of treated eyes (15/19) had both reduced CMT and improved BCVA. Colour discrimination along the protan and tritan vectors was improved in more than half of treated eyes. Deutan discrimination was the least improved vector. Although there was a positive trend of improvements in CMT, BCVA, and protan and tritan colour discrimination after treatment, the correlation between these changes was not statistically significant.
Impairment in tritan colour discrimination thresholds provides a sensitive indication of the presence of retinal thickening and correlates strongly with reductions in visual acuity. These preliminary findings also suggest that colour discrimination, as measured by the CCT, may be a novel way to monitor the efficacy of treatment in DMO in conjunction with BCVA and CMT measurements.
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