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Excerpt
I read with interest the article “Intraocular and interocular symmetry in normal retinal capillary perfusion” by Doctors Rawji and Flanagan (J Glaucoma 2001;10:4–12). Using the 10 × 10 pixel-sized measuring frame of the Heidelberg retina flowmeter, the authors found that the parameter “volume” was significantly lower in the fovea than in other retinal areas, whereas “flow” and “velocity” showed no such difference. In the discussion, the authors declare that “Our study is the first to examine retinal capillary flow in healthy patients in different segments of the posterior pole”.
In contrast to this statement, our group investigated this problem 6 years ago, and published the results in 1997. 1,2 Using adjacent 10 × 10 pixel-sized frame positions along both the temporal and the nasal retina, the mean interlocation variation of “flow” was 20.5% in healthy volunteers (18% on the temporal and 23% on the nasal retina), 19% both on the temporal and nasal retina in primary open-angle glaucoma, and 16% in normal tension glaucoma (8% on the temporal and 24% on the nasal retinal areas). Interlocation differences were even higher on the peripapillary retinal areas. 2 In our study, both in the glaucoma group and in the controls, “flow” on the temporal retina was consistently higher in myopic eyes that in nonmyopic ones. 2 It is well known that in myopic eyes the retina is frequently thinner than normal, which may cause values from the chorocapillaries also measured. In the peripapillary retina, inadvertent measurement of the choroidal Doppler shift was clearly certified in one of our studies. 2 On the basis of our findings from several years ago, one may speculate that in the foveolar area of 100-μm to 240-μm thickness, the measurements may be influenced by the choroidal blood flow, which may mask some interlocation differences in the authors' study. The huge interlocation variation of flow parameters measured with the 10 × 10 pixel-sized frame of the Heidelberg retina flowmeter is well known, and this was one of the reasons for the development of new software to the instrument. It would be interesting to repeat the measurements using one of the new software versions to measure the whole foveola and the whole perifoveolar retina as distinct areas.
