advertisement
Abstract #51290 Published in IGR 14-3
Repeatability of measurements of effectiveness of glaucoma medication
Rotchford AP; King AJBritish Journal of Ophthalmology 2012; 96: 1494-1497
AIMS: To determine short-term repeatability of the effect of intraocular pressure (IOP) reducing medication and the number of repeated measurements necessary to estimate therapeutic effect with a given degree of precision. METHODS: IOP was measured at 8:00, 11:00 and 16:00 h at each of three weekly visits in untreated patients with primary open-angle glaucoma or ocular hypertension. After starting travaprost (0.004%) to both eyes, the measurements were repeated for a further three weekly visits. Repeatability of the change in IOP 1, 2 and 3 weeks after starting treatment was reported as the coefficient of repeatability (CR) and coefficient of variability (CV). RESULTS: Mean reduction in IOP was 7.5 mm Hg (29.9%). CR and CV between visits were 7.8 mm Hg and 37.2%, respectively. Repeated estimates of the effectiveness of treatment in the same subject at the same time of day would, therefore, be expected to lie within a range of 7.8 mm Hg and within ±73.2% of the mean effect with 95% confidence. A reduction in IOP less than 7.8 mm Hg over a single pair of measurements would be indistinguishable from measurement error. Precision improves from ±73.2% for a single pair of readings to ±25.9% for eight pairs. CONCLUSIONS: Day-to-day repeatability in the estimation of medication effectiveness is poor even for time-of-day standardised measurements and the number of IOP measurements required to achieve precision adequate for use in clinical practice is large.
Department of Ophthalmology, Tennent Institute of Ophthalmology, Gartnavel Hospital, Great Western Road, Glasgow G12 0YN, UK; rotchford@doctors.org.uk.
Full articleClassification:
11.4 Prostaglandins (Part of: 11 Medical treatment)
6.1.2 Fluctuation, circadian rhythms (Part of: 6 Clinical examination methods > 6.1 Intraocular pressure measurement; factors affecting IOP)
