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Abstract
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PURPOSE: Research has suggested that patients with glaucoma report more driving difficulty and may be at increased risk for motor vehicle collisions (MVCs) though, with respect to MVCs, well-designed studies have reported that such patients may pose no greater threat than other road users. Yet, there may be some segment of this patient population that do indeed experience an elevated risk of MVCs. The ability to identify such individuals using measures routinely available in clinical practice would provide physicians the ability to inform their patients regarding these risks. The objective of this study is to evaluate the association between specific visual field characteristics and MVC involvement in a cohort of glaucoma patients.
METHODS: The study cohort consisted of individuals aged 55 or more who had been seen at least once between January 1994 and December 1995 in any of three university-affiliated ophthalmology and optometry practices specializing in the diagnosis and treatment of glaucoma. The International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) codes 365.1 and 365.2 were used to identify all potentially eligible patients with glaucoma seen at each of these locations. The medical records of each potentially eligible patient were abstracted to verify the diagnosis of glaucoma and to obtain information on use of glaucoma medication, best corrected visual acuity in both eyes, and visual fields (either a 30-2 or 24-2 test) in both eyes. To obtain additional information on demographic, driving, general health, smoking and alcohol use a telephone survey was conducted. Information regarding all MVCs that occurred between January 1994 and June 2000 wherein the study subject was the driver was obtained from the Alabama Department of Public Safety.
For each patient, the first visual field during the observation period was separated into nine regions and the aver- age threshold (TH), total deviation (TD) and pattern deviation (PD) values were obtained taking into account all available points in each region. These average values in each region were then categorized by separating the worst 25% (i.e., "impaired") from the remaining 75% (i.e., "unimpaired") of patients. Poisson regression was used to calculate rate ratios (RRs) and 95% confidence intervals (CIs) for the association between TH, TD, and PD impairment in each region and the rate of MVC involvement adjusted for age, gender, race and visual acuity in the worse eye.
RESULTS: The final study cohort consisted of 438 glaucoma patients and had a mean age of 72.8 years; slightly over half were female (55.5%) and white (60.5%), the remainder black. Over the entire visual field TH, TD and PD impairment was associated with a non-significant 50%, 44% and 68% increase in the rate of at-fault MVCs, respectively. However, once the visual field was separated into regions, significantly increased rates were observed for certain locations (i.e., inferior region) and were limited to specific measures (i.e., TD and PD).
CONCLUSIONS: The results of this study suggest that characteristics of field impairment defined using familiar clinical measures are associated with an increased risk of at-fault MVC involvement. The practical implication of these results is that they can provide clinicians a marker or set of markers that can be used to potentially identify glaucoma patients at risk of MVC involvement. |