Effect of pupil dilation on biometric measurements and intraocular lens power calculations in schoolchildren

Abstract

Purpose: To investigate the effect of pupil dilation on ocular biometric parameters and intraocular lens (IOL) power calculation in schoolchildren using the Lenstar LS 900.

Methods: One hundred forty eyes of 140 healthy schoolchildren were included in the analysis. Axial length (AL), central corneal thickness (CCT), aqueous depth (AD), anterior chamber depth (ACD), lens thickness (LT), flat keratometry (K), steep K, astigmatism, white-to-white (WTW), and iris/pupil barycenter distance were measured, before and after pupil dilation. Anterior segment length (ASL) was defined as the sum of ACD and LT, and lens position (LP) was defined as ACD plus half of the LT. The relative lens position (RLP) was defined as LP divided by AL. IOL power was calculated using the eight formulas (Hill-RBF, Barrett, Haigis, Hoffer Q, Holladay, Olsen, SRK II, and SRK/T) integrated in the Lenstar LS 900. Parameters before and after pupil dilation were compared.

Results: AL, AD, ACD, LT, ASL, LP, RLP, flat K, iris barycenter distance, pupil barycenter distance, and PD differed significantly after pupil dilation (P < 0.001 in all cases), as compared to before dilation. The Olsen formula demonstrated significant differences in the magnitude of astigmatism (P = 0.010) and IOL power (P = 0.003) after pupil dilation. Using the different formulas, 23.6-40.7% of participants had IOL power changes of more than 0.50 diopters, while 0.7-1.4% had IOL changes of more than 1.0 diopter after pupil dilation.

Conclusions: Dilated and undilated pupil size affected the Lenstar LS 900 measurement of some ocular biometric parameters, and pupil dilation led to IOL power changes exceeding 0.50 diopters with a high percentage (from 23.6% to 40.7%) in schoolchildren, which should be noticed in clinical practice.

Fig 1. Three cases in which the pupil margins were inaccurately drawn despite valid measurements.

In these three cases, the pupil margins were not appropriately defined for measuring pupil diameter (PD). In case 1, no PD or pupil barycenter data were obtained. After correction, the PD was 2.77 mm and the pupil barycentric coordinates were (-0.05, -0.02). In case 2, the default PD and pupil barycentric coordinates were 2.74 mm and (0.18, -0.12), respectively. After correction, the corresponding data were 2.39 mm and (0.32, -0.11). In case 3, the default PD and pupil barycentric coordinates were 7.79 mm and (-0.03, -0.59), respectively. After correction, the corresponding data were 8.54 mm and (0.09, -0.15).

Fig 2. Percentage of participants whose intraocular lens power changed by more than 0.50 diopters and by more than 1.0 diopter after pupil dilation, as calculated using various formulas.