Journal of Cataract and Refractive Surgery highlights chosen by Professor Thomas Kohnen
DRY EYE AFTER PRK, LASIK
Dry eye symptoms are perhaps the most common complaint from patients undergoing refractive laser surgery. Researchers at Walter Reed Medical Centre in the USA conducted a prospective, non-randomised clinical study looking at the incidence and predictive factors of chronic dry eye using a set of dry-eye criteria in 143 patients undergoing photorefractive keratectomy (PRK) or LASIK. Evaluations included Schirmer scores, corneal sensitivity, ocular surface staining, surface regularity index and responses to dry-eye questionnaires. After LASIK, significant changes were observed in tear break-up time, corneal sensitivity, ocular surface staining, and responses to questionnaire. By one year after surgery, five per cent of PRK patients and 0.8 per cent of LASIK participants developed chronic dry eye. Significant changes were observed in the LASIK group in tear break-up time, corneal sensitivity, ocular surface staining and responses to the questionnaire. A statistical analysis indicated that lower Schirmer score before surgery significantly influenced the development of chronic dry eye after PRK. Among LASIK patients, lower preoperative Schirmer score or higher ocular surface staining score significantly influenced the occurrence of chronic dry eye. KS Bower et al, JCRS, “Chronic dry eye in photorefractive keratectomy and laser in situ keratomileusis: manifestations, incidence, and predictive factors”, Volume 41, Issue 12, 2624-34.
CUSTOM SELECTION OF CUSTOM LENSES
Determining the optimum amount of spherical aberration in intraocular lenses (IOLs) to maximise optical quality in eyes that have undergone previous hyperopic corneal surgery poses a significant challenge for the surgeon. US researchers conducted a simulation study of aspheric IOL implantation in 106 eyes of 80 patients. The range of optimum IOL spherical aberration that produces the best optical image varied widely. With 0.00D, -0.50D, and +0.50D defocus, respectively, the ranges of 25th to 75th percentiles of the optimum IOL spherical aberration were -0.12 to +0.20μm, +0.10 to +0.42μm, and -0.35 to -0.03μm for a 6.0mm pupil, and -0.14 to +0.26μm, +0.41 to +0.86μm, and -0.74 to -0.24μm for a 4.0mm pupil. The amount of optimum IOL spherical aberration could be predicted on the basis of other higher-order aberrations of the cornea with multiple correlation coefficients up to 0.98. The researchers comment that as more options of aspherical IOL selection become available in the market, clinical studies should be conducted to validate the approach of custom selection of optimum IOL spherical aberration, based on total corneal higher-order aberrations. The study results also suggest the need for clinical studies to evaluate quality of vision in these pseudophakic eyes, with the ultimate goal of developing methods to address residual aberrations postoperatively. L Wang et al, JCRS, “Custom selection of aspheric intraocular lens in eyes with previous hyperopic corneal surgery”, Volume 41, Issue 12, 2652-2663.