Abstract
Purpose:
Type 2 idiopathic macular telangiectasia (MacTel) is associated with a focal loss of retinal sensitivity typically starting just temporal of the foveal center. Our aim was to investigate the characteristics of scotomata associated with MacTel.
Methods:
Patients were selected from two clinical sites in the MacTel Study, an international prospective study of MacTel. Retinal sensitivity data were collected using Nidek MP1 microperimeters. The median of measured sensitivity values at 16 test points along a circle 6° in radius centered on the fovea was considered the background sensitivity. The lesion was defined as at least two adjacent test points with at least 6dB of loss relative to background. Lesion area was approximated by the number of affected test points in a Cartesian grid with 2° spacing. Volume loss was calculated as the sum of differences relative to the background sensitivity measured at each test point within the lesion.
Results:
A total of 68 eyes of 45 MacTel patients (23 males and 22 females; ranging in age 43-79 years, mean age 61.2, SD=9.2 years) were examined. Volume loss ranged between 12-144 dB (mean 61.40 dB, SD=37.50 dB), the mean area quantified by the number of test points per lesion was 4.87 (range 2-12, SD=2.80). Within lesions, the proportion of test points with at least 10 dB loss was 0.78 (SD=0.28) and the proportion of 0 dB measured sensitivity was 0.36 (SD=0.28). Correlation between lesion size and volume loss was highly significant (Pearson correlation coefficient r=0.993, p<0.001, n=45). Symmetry of volume loss and of lesion size between eyes were moderate (r=0.520, p=0.011, n=46) and (r=0.530, p=0.009, n=46), respectively.
Conclusions:
Scotomata in MacTel were present with a wide range in area and volume sensitivity loss. However, there was a strong correlation between both parameters, and all scotomata demonstrated similar characteristics. They are typically localized and have - as demonstrated by the proportions of 10 dB loss and of 0 dB measured sensitivity -relatively sharp borders between unaffected areas and those with profound loss in retina sensitivity. The symmetry between fellow eyes in this cohort is moderate, probably because of the very strong definitions for the criteria of sensitivity loss.
Keywords: 696 retinal degenerations: hereditary •
603 Muller cells •
758 visual fields