By Gail F. Schwartz, MD
The authors of this study in the August Archives of Ophthalmology compared peripapillary choroidal thickness (PCT) in healthy controls and in glaucoma patients with focal, diffuse and sclerotic optic disc damage. They found that the peripapillary choroid of those with sclerotic optic disc damage was approximately 25 to 30 percent thinner compared with patients with focal and diffuse optic disc damage and healthy controls.
While these results adds another dimension to the literature and to the evidence that morphological patterns of optic disc damage may help distinguish between clinically meaningful subtypes of glaucoma, further study in a larger, more broad demographic is warranted. The authors say observations of patients over time are needed in order to investigate whether the reduced PCT observed in patients with sclerotic optic disc damage is part of the cause or part of the consequence of the glaucomatous disease process.
The peripapillary region has been discussed for many years as a means of detecting glaucomatous progression. Spectral domain OCT (SD-OCT) can now quantitatively measure this region and enable further evaluation.
The study included data from healthy controls (n = 92) and patients with glaucoma who had focal (n = 34), diffuse (n = 35) and sclerotic (n = 34) optic disc damage. They had undergone SD-OCT imaging (12° circular scan protocol centered on optic nerve head).
The authors found that the anterior scleral border was visible in 76 controls (83 percent) and 89 patients (86 percent). PCT in healthy controls decreased linearly with age (-11 μm/decade; P < 0.001), with a predicted value of 137 μm at age 70 (95% prediction interval, 62 - 212 μm). While this value was similar in patients with focal and diffuse optic disc damage (126 and 130 μm, respectively; P = 0.22 compared with controls), it was approximately 30 percent lower in patients with sclerotic optic disc damage (96 μm; P < 0.001 compared with controls).
One of the difficulties in analyzing differences between the four groups into which the subjects were divided is standardizing the definitions and descriptions for these categories. One observer might label a disc diffuse, while another calls it sclerotic. Also the demographics of the population studied were homogeneous, with the study's extrapolation potential unknown. Additionally, measurement of choroidal atrophy may have a range with overlap between a normal patient, such as a high myope, and one with a glaucomatous disc.
Nevertheless, the authors conclude that given that the age-related rate of choroidal thinning estimated from cross-sectional data is only approximately 10 to 20 μm per decade, the reduction of 25 to 30 percent seen in patients with sclerotic optic disc damage is substantial and adds to the evidence that there may be a connection between choroidal atrophy and glaucomatous optic disc damage of the sclerotic type.