Basal Linear Deposit: Normal Physiological Ageing or a Defining Lesion of Age-Related Macular Degeneration?

Objective

To determine if basal linear deposit (BLinD) is a specific lesion of age-related macular degeneration (AMD).

Methods

The cohort was selected from a clinically and histopathologically validated archive (Sarks Archive) and consisted of 10 normal eyes (age 55-80 years) without any macular basal laminar deposit (BLamD) (Sarks Group I) and 16 normal aged eyes (age 57-88 years) with patchy BLamD (Sarks Group II). Only eyes with in vivo fundus assessment and corresponding high-resolution transmission electron microscopy (TEM) micrographs of the macula were included. Semithin sections and fellow-eye paraffin sections were additionally examined. BLinD was defined as a diffuse layer of electron-lucent vesicles external to the retinal pigment epithelium (RPE) basement membrane by TEM and was graded as follows: (i) Grade 0, absence of a continuous layer; (ii) Grade 1, a continuous layer up to three times the thickness of the RPE basement membrane (0.9 µm); (iii) Grade 2, a continuous layer greater than 0.9 µm. Bruch's membrane (BrM) hyalinisation and RPE abnormalities were determined by light microscopic examination of corresponding semithin and paraffin sections.

Results

BLinD was identified in both normal (30%) and normal aged (62.5%) eyes. BLinD was thicker in normal aged eyes (p = 0.045; 95% CI 0.04-3.4). BLinD thickness positively correlated with both the degree of BrM hyalinisation (p = 0.049; 95% CI 0.05-2.69) and increasing microscopic RPE abnormalities (p = 0.022; 95% CI 0.188-2.422). RPE abnormalities were more likely to be observed in eyes with increased BrM hyalinisation (p = 0.044; 95% CI 0.61-4.319).

Conclusions

BLinD is most likely an age-related deposit rather than a specific lesion of AMD. Its accumulation is associated with increasing BrM hyalinisation and microscopic RPE abnormalities, suggesting a relationship with dysregulated RPE metabolism and/or transport.