Perimetric severity in hospital-based and population-based glaucoma patients

Background: The aim was to compare the severity of glaucoma among newly diagnosed patients presenting to a hospital-based glaucoma care centre (HBGS: Sankara Nethralaya, Medical Research Foundation) with that of age matched subjects from the population-based Chennai Glaucoma Follow-up Study (CGFS). Methods: Newly diagnosed subjects with primary glaucoma from HBGS and age- and gender-matched subjects from the urban arm of CGFS examined during the same time period were included. All subjects underwent comprehensive ocular examinations including Humphrey visual field (HVF: 24-2 SITA Standard). Glaucoma was defined as: an intraocular pressure (IOP) of 22 or greater mmHg in either eye; vertical cup-to-disc ratio (VCDR) of 0.7 or greater or asymmetry 0.2 or more or the presence of focal thinning, notching or a splinter haemorrhage. All subjects had a minimum of three follow-up visits and reliable visual fields. The IOP, vertical cup-to-disc ratio, mean deviation (MD) and pattern standard deviation (PSD) of the Humphrey field measurements at the third follow-up visit of CGFS were compared for assessing the severity of glaucoma with the HBGS group. Results: Forty-seven age-matched subjects from both the study populations were selected. Significantly higher (p = 0.04) IOP was noted in the HBGS population than the CGFS, with a difference in mean IOP of 2.80 mmHg (95% CI of diff: 0.14 to 5.46). The mean +/- SD of the mean deviation and pattern standard deviation were -6.92 +/- 6.53 dB and 6.05 +/- 4.20 dB among the HBGS and -4.47 +/- 4.19 dB and 3.26 +/- 2.69 dB among the CGFS population, respectively, the difference in the mean deviation (p = 0.036) and pattern standard deviation (p = 0.0001) were statistically significant. The mean vertical cup-to-disc ratio did not vary between populations (p = 0.14). Conclusion: Patients from the HBGS group had higher IOP and more severe visual field defects than the CGFS group. Hence, results from hospital-based studies on severity and the rates of progression should be interpreted with caution.