Measurement of Pupil Centroid Shift and Cyclotorsional Displacement Using Iris Registration

Abstract

Background/Aims: To estimate the amount and nature of pupil centroid shift and cyclotorsion occurring between preoperative wavefront measurement and refractive surgery. Methods: This retrospective study comprised 183 eyes of 92 patients who had wavefront-guided LASIK using iris registration. We analyzed the pupil centroid shift and cyclotorsional displacement occurring between preoperative wavefront measurements and during the laser procedure. The eyes were measured by the WaveScan® Wavefront® system (VISX, Santa Clara, Calif., USA) and refractive surgery was performed with the VISX STAR S4 excimer laser system. Results: The mean magnitude of shifts in the location of pupil center was 0.26 ± 0.16 mm horizontally, 0.20 ± 0.16 mm vertically and 0.37 ± 0.13 mm vectorally. 162 eyes (88.5%) experienced more than 0.2 mm of shift. The mean amount of torsion was 2.58 ± 1.56° for 83 eyes showing incyclotorsion and 2.94 ± 1.87° for 100 eyes showing excyclotorsion. 117 eyes (63.9%) experienced more than 2° of cyclotorsion and 21 eyes (11.5%) experienced more than 5° of cyclotorsion. Conclusions: Pupil centroid shift and cyclotorsion occur in the majority of eyes undergoing laser treatment. The amount of pupil centroid shift and cyclotorsion shown in this study is considerable. Accurate compensation for cyclotorsion and pupil centroid shift may maximize the potential of visual quality of customized ablations.

Effect of Iris registration on visual outcome in wavefront-guided LASEK for myopic astigmatism

“…Ablation decentration[0.30 mm from the center of the entrance pupil was associated with a greater induction of total HOA, especially in coma, than decentration [0.15 mm [28]. Subclinical decentration of less than 1.0 mm was also found to increase coma-like and spherical-like aberrations after corneal laser surgery [23,29].…”

“…Chernyak [8] reported an average of 0.278 mm nasal shift and 0.030 mm vertical shift. Park et al [23] measured the mean magnitude of centroid shift as being 0.26 mm horizontally and 0.20 mm vertically. The differences among the studies were thought to be due to the different experimental conditions [23].…”

Treatment Strategies and Clinical Outcomes of Aspheric Surgery for Astigmatism Using the SCHWIND Amaris Platform

“…Coupling effects between different HOA terms and between HOAs and manifest refraction have been found, [44][45][46] for example, between defocus and spherical aberration, third-order aberrations and low-order terms, spherical aberration and coma, or secondary and primary astigmatisms. These interactions may provide some relative visual benefits 47 but may also contribute uncertainty in the conversion of wavefront aberration maps to refractive prescriptions.…”

“…Recently, some equipment can facilitate measurement of and potential compensation for static cyclotorsion occurring when the patient moves from upright to the supine position during the procedure 41 , quantifying the cyclorotation occurring between wavefront measurement and laser refractive surgery 42 and compensating for it 43 , 44 , 45 . Further measuring and compensating ocular cyclotorsion during refractive treatments with the patient supine may reduce optical "noise" of the applied versus the intended profiles 46 , 47 , 48 .…”

Optimized Profiles for Astigmatic Refractive Surgery

“…Measuring rotation when the patient is upright 36 to when the refractive treatments are performed with the patient supine may lead to ocular cyclotorsion, resulting in mismatching of the applied versus the intended profiles 37 , 38 . Recently, some equipment can facilitate measurement of and potential compensation for static cyclotorsion occurring when the patient moves from upright to the supine position during the procedure 39 , quantifying the cyclorotation occurring between wavefront measurement and laser refractive surgery 40 and compensating for it 41 , 42 , 43 . Further measuring and compensating ocular cyclotorsion during refractive treatments with the patient supine may reduce optical noise of the applied versus the intended profiles 44 , 45 , 46 .…”