Bias in self-reported family history and relationship to glaucoma: the Blue Mountains Eye Study.

PURPOSE: To examine bias in the relationship between self-reported family history of glaucoma and its relationship to the prevalence of glaucoma and ocular hypertension.
METHODS: In a cross-sectional population-based study of 3654 Australians aged 49-97, participants were asked whether any first-degree relatives had been diagnosed with glaucoma. Open-angle glaucoma was diagnosed from matching optic disc and typical visual field changes, after gonioscopy. Ocular hypertension (OH) was diagnosed from elevated intraocular pressure (IOP) in subjects without glaucoma.
RESULTS: Glaucoma was present in 3.0% and ocular hypertension in 5.2% of subjects. A parent or sibling was reported to have glaucoma by 8.6%, including 10.5% of women and 5.9% of men. A positive family history was reported more frequently in parents (6.4%) than siblings (2.6%). Glaucoma was reported more frequently to affect mothers (5.0%) and sisters (1.6%) than fathers (1.5%) and brothers (1.2%). A first-degree family history was given by 15.7% of subjects with glaucoma compared to 8.3% of controls, odds ratio (OR) 3.2 (95% CI 1.8-5.6), after adjusting for glaucoma risk factors, including IOP. The association had a similar magnitude for a family history in parents and siblings. Although recall bias was evident from the finding of increased odds (OR 4.2) among previously diagnosed cases, the relationship with family history also persisted in newly-diagnosed cases (OR 2.4). A slightly stronger relationship was found between OH and glaucoma family history, OR 3.9 (95% CI 2.6-5.7), after adjusting for confounders, but was also strongly influenced by recall bias.
CONCLUSIONS: Although a positive family history of glaucoma may help to identify those at risk, it is subject to recall, selection and survival bias as well as community under-diagnosis of glaucoma and will most likely substantially underestimate the genetic influence.