Association Between Glaucoma, Glaucoma Therapies, and ED
Association Between Glaucoma, Glaucoma Therapies, and ED
The British Columbia Linked Database (BCLHD) is a large repository of administrative data that captures health-related information for approximately 4.5 million residents of British Columbia. The database contains linkable information on hospital admissions, physician visits, and PharmaNet, which is a comprehensive prescription drug database. PharmaNet captures information on all prescription drugs dispensed in British Columbia including drug strength, quantity, and number of days of dispensed medication. The BCLHD has been used in numerous epidemiological and pharmacoepidemiological studies. Institutional review board approval at the University of British Columbia was prospectively obtained.
Cases were identified as those with the first diagnosis of ED defined as the first physician billing code for ED deemed as the index date. Only newly diagnosed cases of ED were included by ensuring that no previous physician visit for ED was registered in the database. Each case was matched to 10 controls with no previous history of ED, so that each control had to have been followed up at least as long as the time of the case (index date) and thus was at risk of developing ED; controls were also matched to the cases within 1 year of birth date (±1 y) and follow-up time (±30 d). Physician visits for glaucoma were defined based on diagnostic codes of the International Statistical Classification of Diseases, Ninth Revision (ICD-9) code 365.
The sample size for this study was calculated based on 1000 incidence cases of ED. Given a 10% prevalence of glaucoma or users of topical BB in the population and a 1:10 case:control ratio, we estimate that the study will have >80% power to detect a rate ratio of 1.5 and an α value of 0.05 (2-sided test).
Descriptive statistics were used to explore data demographics. We used a conditional logistic regression model to estimate rate ratios for 2 main exposures: (1) diagnosis of glaucoma defined as at least 2 physician visits for glaucoma in the year before the index date, and (2) use of a prescription of a topical BB in the 30 days before the index date. As a quality measure, we assessed the risk of ED among users of ED drugs as a "positive control group," as we expect the risk of ED among this group to be high. The conditional logistic regression model was adjusted for the following covariates: sex, coronary artery disease, chronic obstructive pulmonary disease (COPD), and rheumatoid arthritis. We also adjusted for the following prescription drugs: oral BBs, angiotensin converting enzyme inhibitors, angiotensin receptor blockers , calcium channel blockers, diuretics, statins, and drugs used for ED (sildenafil, tadalafil, vardenafil). All rate ratios were compared with (1) those with one or more previous diagnosis of glaucoma or (2) users of topical BBs in the year before the index date.
Methods
Data Sources
The British Columbia Linked Database (BCLHD) is a large repository of administrative data that captures health-related information for approximately 4.5 million residents of British Columbia. The database contains linkable information on hospital admissions, physician visits, and PharmaNet, which is a comprehensive prescription drug database. PharmaNet captures information on all prescription drugs dispensed in British Columbia including drug strength, quantity, and number of days of dispensed medication. The BCLHD has been used in numerous epidemiological and pharmacoepidemiological studies. Institutional review board approval at the University of British Columbia was prospectively obtained.
Case and Control Selection
Cases were identified as those with the first diagnosis of ED defined as the first physician billing code for ED deemed as the index date. Only newly diagnosed cases of ED were included by ensuring that no previous physician visit for ED was registered in the database. Each case was matched to 10 controls with no previous history of ED, so that each control had to have been followed up at least as long as the time of the case (index date) and thus was at risk of developing ED; controls were also matched to the cases within 1 year of birth date (±1 y) and follow-up time (±30 d). Physician visits for glaucoma were defined based on diagnostic codes of the International Statistical Classification of Diseases, Ninth Revision (ICD-9) code 365.
Sample Size Calculation
The sample size for this study was calculated based on 1000 incidence cases of ED. Given a 10% prevalence of glaucoma or users of topical BB in the population and a 1:10 case:control ratio, we estimate that the study will have >80% power to detect a rate ratio of 1.5 and an α value of 0.05 (2-sided test).
Statistical Analysis
Descriptive statistics were used to explore data demographics. We used a conditional logistic regression model to estimate rate ratios for 2 main exposures: (1) diagnosis of glaucoma defined as at least 2 physician visits for glaucoma in the year before the index date, and (2) use of a prescription of a topical BB in the 30 days before the index date. As a quality measure, we assessed the risk of ED among users of ED drugs as a "positive control group," as we expect the risk of ED among this group to be high. The conditional logistic regression model was adjusted for the following covariates: sex, coronary artery disease, chronic obstructive pulmonary disease (COPD), and rheumatoid arthritis. We also adjusted for the following prescription drugs: oral BBs, angiotensin converting enzyme inhibitors, angiotensin receptor blockers , calcium channel blockers, diuretics, statins, and drugs used for ED (sildenafil, tadalafil, vardenafil). All rate ratios were compared with (1) those with one or more previous diagnosis of glaucoma or (2) users of topical BBs in the year before the index date.
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