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Editors Selection IGR 12-4

Epidemiology

Comment by Rohit Varma on:

18123 Lifetime visual disability in open-angle glaucoma and ocular hypertension, Forsman E; Kivelä T; Vesti E, Journal of Glaucoma, 2007; 16: 313-319

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Forsman et al. (400) present retrospective data on glaucoma-related visual impairment and blindness in 66 glaucoma patients and 40 ocular hypertensive patients from a private 'non-referral' office in southern Finland, who died between 1991 and 2002.
The clinical records were reviewed and data on intraocular pressure, visual fields, visual acuity, were extracted to stage the severity of glaucoma and change in the severity of glaucoma over the follow-up period. The five stages of glaucoma were: ocular hypertension (normal visual field and optic disc), early, moderate and advanced glaucoma and blindness. The cause of death and visual impairment/blindness were also extracted. Over an average of 9.8 years (range 1-23 years) of follow-up, glaucoma related blindness (bilateral) occurred in 6% of patients. The incidence of unilateral severe visual impairment (visual acuity of 20/200 or worse or visual field of <10° from fixation at the greatest extent using the Goldmann kinetic perimeter isopter IIIe) was 6% at five years, 9% at ten years and 15% at fifteen years. Over the 9.8 years of follow-up, 48% of study eyes were stable, 29% had a one-stage increase, 14% had a two-stage increase and 8% had a three-stage increase. Of the study eyes with ocular hypertension, 50% developed glaucomatous damage, and the mean time for conversion from ocular hypertension to glaucoma was 8.6 years. The factors associated with eyes developing unilateral severe visual impairment (the authors call this as unilateral blindness) older age, more severe stage at the time of diagnosis, higher pre-treatment IOP, greater IOP fluctuation (as measured by inter-visit standard deviation of IOP) and poor compliance with medication use/follow-up visits/acceptance of medications or surgery. The presence of exfoliation was associated with a trend towards being more likely to develop blindness, however, a small sample size did not allow for a robust assessment of this risk factor. Factors not found to be significant in this analysis were family history of glaucoma, level of IOP on treatment, percent reduction of IOP, or vascular cause of death. Overall, in this study, the life-time risk of becoming blind from glaucoma appears to be small (6%) and when patients are being treated, almost half remain stable and three out of 4 patients remain stable or get worse by one stage. There are some issues that deserve cautious interpretation when generalizing the data from this paper. First, this is a retrospective study and all the caveats of a retrospective analysis apply to this paper - lack of standardized data collection methods, lack of standardized follow-up, biases associated with inclusion into the study and who gets treatment and when treatment is 'stepped-up'. Secondly, these data apply to a presumably European derived population one practice in Finland. The generalizibility of these data to the general Finnish population, to other European derived populations, and to other racial/ethnic groups deserves further study. Thirdly, the assignment of causes of blindness/visual impairment in eyes with multiple ocular diseases is difficult at best and deserves careful assessment. Finally, the terminology used in this study should be clearly understood. The authors refer to 'life-time visual disability' as having reduced visual acuity or constriction of visual fields in either one or both eyes. It does not refer to an inability to perform daily tasks or visually dependant tasks. Also, the term blindness is referred to either one or both eyes.The World Health Organization and the United States Social Security Administration refer to blindness as a reduction of visual acuity or visual fields to a specified level in the worse eye. In summary, with careful caveats, this paper provides some important information on what patients can be told regarding their lifetime risk of going blind. Such studies deserve to be conducted in other countries and in other racial/ethnic groups so that the accurate information can be provided to patients who have glaucoma or are at risk of developing it.

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