Change in pupil size after implantation of an iris-fixated toric phakic intraocular lens

Purpose

To evaluate the changes in pupil size after implantation of an iris-supported toric phakic intraocular lens (TPIOL) for correction of myopia and hyperopia with astigmatism.

Setting

Department of Ophthalmology, Johannes Gutenberg-University, Mainz, Germany.

Methods

Twenty-two myopic eyes and 9 hyperopic eyes were included in the study. The mean age of the 2 groups was 34 years and 40 years, respectively. The scotopic pupil size was measured with a handheld infrared pupillometer (Colvard, Oasis Medical) before and 6 months after implantation of the TPIOL. All examinations were performed under scotopic conditions after 2 minutes of dark adaptation with the fellow eye covered. Intraindividual comparisons were made between preoperative and postoperative pupil sizes. The relationship between implanted IOL power and postoperative pupil width in each group was studied to determine whether lens magnification could lead to misinterpretation of the results. The difference between horizontal and vertical postoperative pupil diameters was assessed in eyes with horizontally aligned IOLs to determine the potential mechanical effect of the TPIOL on pupil size.

Results

The mean scotopic pupil diameter decreased significantly from 4.7 mm (range 3.0 to 6.0 mm) preoperatively to 3.6 mm (range 2.0 to 5.0 mm) postoperatively in myopic eyes and from 5.0 mm (range 4.0 to 6.0 mm) to 4.0 mm (range 2.0 to 5.0 mm) in hyperopic eyes. No significant correlation between the power of the TPIOL and the postoperative pupil size diameter was found, confirming that the IOL did not distort measurements of pupil size. Comparing horizontal and vertical pupil diameters under medical mydriasis revealed reduced pupil size in the axis of enclavation.

Conclusions

The scotopic pupil diameter decreased by a mean of 1.1 mm in myopic eyes and 1.0 mm in hyperopic eyes after implantation of the iris-supported TPIOL. Postoperative pupil size was not related to IOL power, patients' emotional states, or other factors. The slightly smaller pupil diameter in the axis of enclavation suggests that this fixation method restricts pupil size under scotopic conditions, which could reduce the incidence of postoperative photic phenomena.