Dear Editor,
We thank Dr Hollo for his interest in our study.1 He has opined that the presence of cataract (nuclear opacity and/or posterior subcapsular opacity) could have confounded the results of our study in several ways. First, increasing lens opacity during the follow-up could have caused a reduction of mean deviation (MD) on visual fields (VF), and thereby show a falsely greater rate of change in MD (progression). Second, the presence of lens opacity could have caused a reduction in the signal strength index (SSI) of the OCT scans, and thereby show lower vessel density values. We agree with these points and have earlier reported on both these aspects; the effect of lens opacity on VF indices,2 and the importance of SSI of OCTA scans on the vessel density measurements.3 Moreover, we believe that the published analysis is correct.
To address the issues raised by Dr Hollo, we provide the following data. Of the 46 eyes included in the study, 16 were pseudophakic, 14 eyes had clear lens, 10 eyes had early nuclear sclerosis (NS grade 1), 4 eyes had NS grade 2 and 2 eyes had posterior subcapsular cataract on the day when the OCT scans were acquired. Best corrected visual acuity was 20/20 in 29 eyes, 20/30 in 13 eyes and 20/40 in 4 eyes. In brief, most included eyes were either pseudophakic, had no cataract or had very minimal cataractous changes. As described in the methods section, SSI of 35 and above was considered as the requirement for inclusion. Therefore, it is unlikely that the lens status affected the MD change, SSI or the results of our study. Dr Hollo also has suggested using visual field index (VFI) instead of MD to determine glaucoma progression as VFI is less influenced by cataract compared to MD. However, VFI has a few disadvantages. First, it is less sensitive to changes in early disease.4 Second, VFI is based on total deviation values when MD goes beyond −20 dB, rather than pattern deviation values. This can cause the VFI to show a falsely large reduction and affect the calculation of rate of change.5 Therefore, we feel that MD was a better parameter to be used in our study.
Footnotes
Financial disclosures: Rao HL: Santen (C), Carl-Zeiss Meditec (C, S), Allergan (C); Thanemozhi S: none; Pradhan ZS: none; Sreenivasaiah S: none; Rao DAS: none; Puttaiah NK: none: Devi S: none; Moghimi S: none; Mansouri K: Santen (C), Allergan (S), ImplanData (C); Webers CAB: Alcon (S), Allergan (C), Pfizer (C), Santen (C); Weinreb RN: Optovue (S), Meditec-Zeiss (S), Heidelberg Engineering (S), Allergan (C), Bausch & Lomb (C), NiCox (C), Centervue (S), ImplanData (C). Supported in part by R01 EY029058 (RNW) for the National Eye Institute and an unrestricted grant from Research to Prevent Blindness (NY, New York)
References
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