29.1 Features
Choroidal thickness depends on race, age, refractive error, and to a lesser extent on gender; the thickness also shows diurnal variation. A very rough rule of thumb is the subfoveal choroidal thickness in a 50-year-old emmetrope is about 250 to 300 µm and decreases by 2 to 4 µm per year. An average 80-year-old may have an expected choroidal thickness of 200 µm. However, some nonmyopic people may have choroidal thicknesses much less than this and develop what is called age-related choroidal atrophy (ARCA).
29.1.1 Common Symptoms
Difficulty in adapting to dim illumination or bright sunlight. Decreased visual acuity if the choroidal thickness is less than 30 µm.
29.1.2 Exam Findings
The easily recognizable fundus appearance includes a rarefaction of choroidal vessels, yellowish-colored choroidal vessels, the central macular granular pigmentary changes, and subretinal drusenoid deposits (SDD; ▶ Fig. 29.1, ▶ Fig. 29.2). With decreasing choroidal thickness, the pigmentary changes become more prominent. The choroid is typically thinner toward the nerve, and in ARCA patients, the choroidal thinning may progress to where peripapillary atrophy develops because the remaining choroid is unable to provide sufficient support for the surrounding tissue. Eyes with SDD show prolonged dark adaptation. Over time SDD can regress with associated loss of the outer retinal architecture, with thinning of the outer nuclear layer and ellipsoid zone attenuation; this is called outer retinal atrophy. SDD preferentially form in areas with high rod concentration. Type 2 and type 3 choroidal neovascularization may develop in the context of SDD. Because ARCA and the often accompanying SDD affect the perifoveal macula, a small focus of neovascularization or geographic atrophy affecting the fovea can be associated with a greater loss of visual function than the size of the offending lesion would suggest.
Fig. 29.1 (a) Color photograph showing age-related choroidal atrophy with scattered pseudodrusen (also known as subretinal drusenoid deposits) and some drusen. (b) The subfoveal choroidal thickness is 58 µm; note the relative avascularity of the choroid. (c) One year later, there was loss of the ellipsoid zone in the central fovea (arrowhead) and early geographic atrophy with subsidence of the retina, loss of the outer nuclear layer and outer retinal architecture, and hypertransmission.
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
