The Auckland Cataract Study: demographic, corneal topographic and ocular biometric parameters

Purpose : To determine patient demographics and the ocular biometric parameters in patients presenting for cataract surgery within the public hospital system, in a defined New Zealand population. Method : Prospective study of 502 eyes of 488 consecutive patients undergoing cataract surgery. A clinical assessment, including refraction, keratometry (K), A‐scan ultrasound and Orbscan II computerized topography was performed on each eye. Results : The mean age of the group was 74.9 ± 9.8 years (mean ± SD) with a female predominance (62%). Ethnic origin included 72% European, 8% Maori, 10% Pacific Islander, 4% Asian, 3% Indian and 3% other ethnic origins. The mean Log MAR visual acuity of eyes prior to cataract surgery was 0.88 ± 0.57 (approximately 6/48^–1). Corneal topographic (keratometric) maps were classified into five groups: 34% round, 10% oval, 31% symmetrical bow tie, 12% asymmetrical bow tie and 13% irregular. The mean steepest K measurement was 44.1 ± 1.7 D, the median keratometric astigmatism 0.89 D (range 0.0–6.5 D) and the steepest corneal meridian was horizontal in 50% and vertical in 43%. Seven per cent of corneas were spherical. Refraction revealed a mean sphere of 0.0 ± 3.1 D and a mean cylinder of –1.2 (range 0.0–7.5 D). Refractive astigmatism was with‐the‐rule in 15%, against‐the‐rule in 50% and oblique in 15%, with 20% spherical. Axial length was a mean of 23.14 ± 1.03 mm. Conclusion : Patients presenting for cataract surgery in this study were predominantly elderly, female, of European Caucasian ethnicity and exhibited relatively poor corrected visual acuity in the affected eye. Interestingly, 41% of eyes demonstrated bow‐tie topographic patterns, largely exhibiting with‐the‐rule astigmatism. However, assessment by keratometry or refraction highlighted against‐the‐rule more frequently; this may have implications for combined cataract and astigmatic surgery. The mean axial length was slightly shorter than expected for a group of predominantly European ethnic origin, although the mean refractive error was emmetropic.