Glaucoma in southern india: author reply
Authors: A ROBIN
Journal: Ophthalmology (2004)

We appreciate the interest and thoughtful comments made here, which are similar to the authors' prior letter to the editor.1Thomas R. Muliyil J.P. George R. Glaucoma in southern India.Ophthalmology. 2001; 108 ([letter]): 1173-1175Abstract Full Text Full Text PDF PubMed Scopus (17) Google Scholar There is no evidence, to our knowledge, that the distribution of intraocular pressure (IOP) is Gaussian. In fact, in every population-based study that we know of, the distribution of IOP is skewed to higher values. We cannot explain why the IOPs in our populations are lower than the Vellore, Andhra Pradesh, or Baltimore eye studies, or even why there was a racial difference in IOPs found in the Baltimore Eye Survey. We agree that universally acceptable definitions are imperative to compare the burden of illness and health care utilization, analyze statistical associates of potential risk factors, and test new approaches to disease management. Our prevalence study's data collection began in 1995, 7 years before the classification schemes suggested by Foster et al,2Foster P.J. Buhrmann R. Quigley H.A. Johnson G.J. The definition and classification of glaucoma in prevalence surveys.Br J Ophthalmol. 2002; 86: 238-242Crossref PubMed Scopus (1621) Google Scholar and as such we used the same definitions as the Baltimore Eye Survey,3Sommer A. Tielsch J.M. Katz J. et al.Racial differences in the cause-specific prevalence of blindness in east Baltimore.N Engl J Med. 1991; 125: 1412-1417Crossref Scopus (635) Google Scholar which are quite similar to those suggested by Foster. We agree with Foster et al that elevated IOP as a distinguishing feature of glaucoma has been universally discarded, and that the highest level of evidence for glaucoma requires a cup–disc ratio of greater than the 97.5th percentile and visual field damage compatible with glaucoma. We therefore did perimetry on all subjects able to have it, unlike patients in both the Vellore and the Andhra Pradesh eye studies, where perimetry was limited to those with elevated IOPs or suspicious optic nerves. We believe that this study design issue might be responsible for differences in the prevalence of various forms of glaucoma. We feel that perimetry of all enrolled subjects is crucial in detecting glaucoma in eyes with lower pressures. We assure the authors that we continuously monitored all experienced examining ophthalmologists to insure consistent quality of examinations and gonioscopy. However, we must caution Thomas et al that the definition of appositional closure and primary angle-closure in which at least 270° of the posterior trabecular meshwork is not visible is arbitrary, and it has yet to be evaluated in a longitudinal study. Additionally, use of the van Herick technique utilized in Andhra Pradesh has been found by Thomas et al4Thomas R. George T. Braganza A. Muliyil J.P. The flashlight test and van Herick's test are poor predictors for occludable angles.Aust N Z J Ophthalmol. 1996; 24: 251-256Crossref PubMed Scopus (76) Google Scholar to be a poor predictor of occludable angles in Indian populations. Finally, cost-effective methods of screening for glaucoma in a sensitive and specific manner is a daunting problem in all regions of the globe. We in no way suggest labeling subjects. However, we agree with Foster et al2Foster P.J. Buhrmann R. Quigley H.A. Johnson G.J. The definition and classification of glaucoma in prevalence surveys.Br J Ophthalmol. 2002; 86: 238-242Crossref PubMed Scopus (1621) Google Scholar that a vertical cup–disc ratio more than 2 standard deviations above the population mean should certainly raise suspicion and warrant perimetry if at all possible. We warmly welcome Thomas et al's comments and hope that the ongoing dialogue will lead to better approaches in our attempts to eliminate needless blindness.