Refractive outcome of toric intraocular lens calculation in cases of oblique anterior corneal astigmatism.

PURPOSE: To establish whether toric intraocular lens (IOL) calculation on the basis of anterior corneal measurements alone, in corneas with oblique anterior astigmatism, will result in a systematic overcorrection or undercorrection of postoperative refractive astigmatism, and to establish whether adjustment of oblique anterior corneal astigmatism to allow for the likely effect of posterior corneal astigmatism is needed in such eyes. SETTING: The Queen Elizabeth Hospital, Department of Ophthalmology, Adelaide, South Australia. DESIGN: Retrospective case series. METHODS: Data were collected from consecutive eyes with oblique anterior corneal astigmatism undergoing cataract surgery or refractive lens exchange. Toric IOL calculations were made using unadjusted anterior corneal astigmatism measurements and an astigmatically neutral technique. By comparison of targeted vs achieved astigmatic correction using vector analysis, the astigmatic power prediction error and angle of error were derived. RESULTS: In 50 eyes, the mean postoperatively measured refractive astigmatism was 0.42 diopters (D) (SD 0.33 D), the mean targeted refractive astigmatism was 0.15 (SD 0.18), and the vector-derived mean absolute prediction error was 0.23 D (SD 0.21). All 50 eyes (100%) fell at or within ±1.00 D of the target and 45 eyes (90%) at or within ±0.50 D. The geometric mean astigmatism correction index was 0.98, and the mean absolute angle of error was 8.63 degrees (SD 8.55). CONCLUSIONS: There is no systematic error attributable to posterior corneal astigmatism in toric IOL calculation and no need for adjustment of anteriorly measured corneal keratometric values for toric IOL calculation in eyes with oblique anterior corneal astigmatism. To do so may introduce an error in astigmatic outcome.

The utility of routine conjunctival swabs in management of conjunctivitis.

AIM: To determine the accuracy of preliminary results of conjunctival swab culture and to evaluate the utility of preliminary and final conjunctival swab culture results in the routine management of conjunctivitis. METHODS: We prospectively identified 164 conjunctival swabs from adults and children over 3 weeks of age and compared preliminary (next day) with final culture results. We modelled the would-be effect on treatment and clinical outcome of three strategies (indiscriminant, delayed and targeted) for management of acute conjunctivitis. RESULTS: In total, 54 of 164 (33%) samples yielded significant bacterial growth. Compared to final culture, preliminary culture had a sensitivity of 86%, positive predictive value of 98% and specificity of 99%. Modelling showed that an indiscriminant approach to management (all patients given topical antibacterial treatment, no swabs taken) was the most effective at reducing symptoms but led to substantial unnecessary use of topical antibacterial treatment. Modelling showed that a delayed treatment strategy (patients start topical antibacterial treatment only if not improving satisfactorily after 2 days, no swabs taken) was the least effective at reducing symptoms and lead to moderate unnecessary use of topical antibacterial treatment. The targeted treatment strategy (topical antibacterial treatment given to those with clinical predictors of bacterial infection on day 0, positive preliminary culture results on day 1 and positive final culture results on day 2) was highly effective at reducing symptoms and potentially the least wasteful of topical antibacterial treatment. CONCLUSION: Preliminary (next day) conjunctival swab culture results are highly predictive of the final result and could be used by practitioners to guide prescription of topical antibacterial treatment.