Abstract
Purpose: :
In normal eyes, three bright lines can be seen in the images of the outer retina obtained by spectral domain optical coherence tomography (SD-OCT). The inner line is believed to be the border between the photoreceptor inner and outer segments (IS/OS), and the outer line is thought to be the retinal pigment epithelium (RPE) and Bruch’s membrane complex. The middle line is probably the OSs. We have hypothesized that the thickness between these lines will change with increasing age and in the fellow eyes of patients with age-related macular degeneration (AMD).
Methods: :
One hundred and fifty-five normal eyes of 108 individuals (88 men and 67 women, 14-89 years) were examined by SD-OCT. The thickness between the "RPE and the middle-line" and the "middle-line and IS/OS" was measured at the fovea. Because the middle line and RPE are not always separated, the thickness was measured at the lower edge of the RPE, the upper edge of the middle line, and the middle of the IS/OS line. In addition, the extent of the separation between the outer two lines was scored into 4 grades; 0=no separation, 1=less than 2 mm separation, 2=2-4 mm separation and 3=more than 4 mm separation, based on 6 mm horizontal scans. The relationship between the thickness and age, and score and age were investigated. In addition, 74 fellow eyes of patients with unilateral AMD and age-matched normal eyes were analyzed by the same methods.
Results: :
Both the thickness between the "PRE and middle-line" and the separation score in normal eyes were significantly negatively correlated with age (both P <0.01, r = -0.42 r = -0.37, respectively). The thickness between the "middle-line and IS/OS" was not significantly correlated with age (P >0.05). The thickness between the "RPE and middle-line" in the fellow eyes of AMD was significantly thinner than that in normal eyes (both P <0.01, 32.2±3.6 µm and 35.4±4.3 µm respectively). The score was significantly smaller in the fellow eyes of AMD than that in normal eyes (both P <0.01, 0.84±1.03, 1.19±1.06, respectively). The thickness between the "middle-line and IS/OS" in the fellow eyes of AMD was not significantly thinner than normal eyes (P >0.05).
Conclusions: :
The tissue between RPE and middle line, which may be the total thickness of the OS+RPE+ Bruch’s membrane, becomes thinner with aging and in the fellow eyes of patients with unilateral AMD. Because the RPE is considered to thicken with aging, this may be consistent with the fact that OS become shorter with age and this may be related with a higher risk of AMD.
Keywords: aging • age-related macular degeneration • photoreceptors