Background: In a previous study, scanning electron microscopy (SEM) showed age-related changes in the rat retina. We carried out a study to evaluate age-related changes in the human retina.
Methods: Samples of fresh retinal tissue obtained from younger (age 22 years or less) and older (age 66 years or more) donors were studied by means of traditional histologic methods and by SEM. Eight retinas were obtained from four donors whose corneas had been used for transplantation, and four retinas were obtained from four subjects whose eyes had been enucleated owing to injury. All morphologic results were subjected to quantitative analysis of images. The concentration of cytoplasmic (free) and structural (tissue-associated) protein in retinal tissue homogenates was determined by means of biochemical methods.
Results: There was a decrease in all features studied with the exception of structural protein concentration. The mean retinal thickness (and standard error of the mean) was 426 (34.2) microm in the younger subjects and 261 (18.9) microm in the older subjects. The mean numbers of ganglion cells (and standard error of the mean) were 413.5/mm2 (32.3/mm2) and 256.2/mm2 (26.8/mm2) respectively, of capillaries 3.6/mm2 (1.4/mm2) and 1.8/mm2 (1.2/mm2) respectively, of synaptic bodies 122.4 (4.9) conventional units (CU)/area observed and 38.5 (1.6) CU/area observed respectively, of cellular processes 82.3 (3.1) CU/area observed and 13.1 (1.5) CU/ area observed respectively, and of intercellular connections 36.4 (2.5) CU/area observed and 14.3 (1.4) CU/area observed respectively. The mean concentration of total protein per milligram of fresh tissue (and standard error of the mean) was 92.1 (1.8) microg in the younger subjects and 78.7 (1.3) microg in the older subjects; the corresponding values for cytoplasmic protein were 27.6 (1.3) microg and 11.8 (0.8) microg, and for structural protein, 64.4 (1.6) microg and 86.9 (1.4) microg. All differences between the younger and older subjects were significant (p < 0.001) with the exception of mean concentration of cytoplasmic and of structural protein.
Interpretation: The human retina undergoes specific changes with aging. SEM provides new morphometric information regarding age-related changes in photoreceptor cells, bipolar cells and ganglion cells that increases our understanding of this topic. Our results may be adopted as a model or as normal values when studying other changes that may occur in the human retina in pathological conditions.