Author: Adwaita Nag (India)
Co-authors: Rajiv Raman
Purpose
Idiopathic Macular Telangiectasia type 2 (MacTel) is an idiopathic bilateral symmetric macular disease characterized by a slow decrease in visual acuity due to exudation from telangiectatic vessels in the juxta-foveal zone, mainly temporally. Macular pigment (MP) comprises three carotenoids; lutein, zeaxanthin and meso-zeaxanthin. Helb et al first described the unique topographic pattern of abnormal central depletion of MP in MacTel. This was further categorised by Zeimer et al into three classes, corresponding with the severity of the disease. However quantitative analysis of the MP distribution in MacTel and its correlation with functional parameters and OCT morphologic features have not been studied. Moreover, significant differences in the distribution profile of MP have been reported among different ethnicities. This study assesses the quantitative and spatial distribution of macular pigment optical density (MPOD) in eyes with MacTel in comparison to healthy eyes of the Indian population using dual-wavelength autofluorescence. The quantitative MPOD values were correlated with the best-corrected visual acuity (BCVA), OCT features and clinical staging of MacTel.
Setting/Venue
The study setting was the vitreoretinal department in a tertiary eye care hospital in South India between June 2019 and February 2021.
Methods
The study population included patients with MacTel and healthy controls of South Indian origin. MacTel was classified according to the 5 stages described by Gass-Blodi and Yannuzzi et al. MPOD was measured with dual-wavelength (486, 518nm) autofluorescence on Spectralis HRA+OCT. 30°×30° foveola-centred raster scans were taken after dilation. OCT features noted were foveal pit blunting, inner and outer retinal cavities (IRC and ORC), ILM draping, intraretinal hyperreflective lesions, ELM disruptions, foveal thinning and subretinal neovascularization. Heidelberg Eye Explorer software (HEYEX) was used to create MPOD density maps. The plateau (reference point for the absence of MP) was set at 6° eccentricity. Average MPOD at 1°, 2° radii and macular pigment optical volume (MPOV) corresponding to eccentricities of 1°, 2° and 6° radii were calculated. ImageJ software was used to calculate MPOD in 9 zones of the ETDRS grid and 30° radial sectors (15°, 45°, …, 345°). MPOD in the desired central region and surrounding ring in Mactel patients were also measured with an ImageJ tool. MPOD values were expressed in density units (d.u.) and MPOV (sum of optical density values at all points) in d.u.degrees2. SPSS Statistics 21 software was used for statistical analysis. P<0.05 was considered statistically significant.
Results
60 eyes of 31 controls and 41 eyes of 22 patients were enrolled. The mean age was 39.10 ± 12.74 years in controls and 58.09 ± 10.19 years in patients. There was a significant difference between patients and controls in the mean MPOD and MPOV at all radii eccentricities (1°, 2°, 6°) and mean MPOD in all radial sectors. At 1° eccentricity, mean MPOD was 0.38 ± 0.11 d.u. and -0.10 ± 0.14 d.u. while mean MPOV was 787.95 ± 225.13 d.u.degrees2 and -211.63 ± 223.42 in controls and patients respectively. Highest MPOD was noted in central 1mm ring (0.29) in controls and peripheral 6mm ring (0.01) in patients, with significant differences in all ETDRS zones except 3 peripheral ones. Clinically, no patient was diagnosed with stage 1 MacTel; stages 2-3 were combined in one group and stages 4-5 in another. MPOD was significantly higher in the surrounding ring than the central region in stages 2-3 and 4-5. There was a positive and significant correlation of mean MPOD in the surrounding paracentral ring with BCVA. On correlating with OCT features, there was a significantly lower mean MPOD of the central area in eyes with inner retinal cavities and ELM disruption.
Conlusions
This study shows reduced MP across various spatial profiles in MacTel as compared to healthy subjects among the South Indian population. In all stages of MacTel, there was well-defined central depletion with high MP in the surrounding ring. The high paracentral MP could be due to abnormal binding or centrifugal displacement of central MP. There were no significant differences in the quantitative MPOD between the MacTel stages, implying that central MP loss is not an indicator of early disease. In addition to the measurement and distribution of MP being affected in MacTel, MP levels were associated with structural changes on OCT and functional changes like visual acuity. MP depletion was related to the presence of IRC and ELM disruption on OCT, both of which may be due to Muller cell loss or damage. These findings add to the evidence that Muller cell dysfunction plays an important role in the pathophysiology of MacTel including the redistribution of MP. The positive correlation between paracentral MPOD and BCVA suggests a potential for visual improvement with lutein or zeaxanthin supplementation. These findings may have implications for novel therapeutic strategies targeting Muller cells or involving dietary supplementation.
Financial Disclosure
NIL
Comments
-
