Aging human RPE: morphometric analysis of macular, equatorial, and peripheral cells

Retinal pigment epithelium (RPE) of 50 human eyes, five from each 10 decades of life, were analyzed using ultrastructural morphometric techniques. Content of three types of pigments, lipofuscin, melanin, and complex granules, (melanolipofuscin, melanolysosomes) were recorded for cells from macular, equatorial, and peripheral retinal specimens. Areas occupied by pigments, nucleus, and cytoplasmic space were calculated. Data were analyzed by a computer for age-related changes and effects of fixation delay time. The largest increase in lipofuscin granules occurred between the first and second decade of life, and further increases occurred with age. The content of "pure" melanin declined with age, whereas the number of complex melanin granules increased. Macular RPE contained more complex granules than nonmacular RPE, particularly in young eyes. The volume of RPE cytoplasm not occupied by pigments ("free space") decreased with age. No significant effects of fixation delays between 2 and 9 hours postmortem were found on the parameters studied here. These findings may serve as a baseline for estimating normalcy of human RPE specimens.