Intraoperative cyclorotation and pupil centroid shift during LASIK and PRK.
OBJECTIVE
To determine the degree of cyclorotation and centroid shift in the x and y axis that occurs intraoperatively during LASIK and photorefractive keratectomy (PRK).


METHODS
Intraoperative cyclorotation and centroid shift were measured in 63 eyes from 34 patients with a mean age of 34 years (range: 20 to 56 years) undergoing either LASIK or PRK. Preoperatively, an iris image of each eye was obtained with the VISX WaveScan Wavefront System (Abbott Medical Optics Inc) with iris registration. A VISX Star S4 (Abbott Medical Optics Inc) laser was later used to measure cyclotorsion and pupil centroid shift at the beginning of the refractive procedure and after flap creation or epithelial removal.


RESULTS
The mean change in intraoperative cyclorotation was 1.48±1.11° in LASIK eyes and 2.02±2.63° in PRK eyes. Cyclorotation direction changed by >2° in 21% of eyes after flap creation in LASIK and in 32% of eyes after epithelial removal in PRK. The respective mean intraoperative shift in the x axis and y axis was 0.13±0.15 mm and 0.17±0.14 mm, respectively, in LASIK eyes, and 0.09±0.07 mm and 0.10±0.13 mm, respectively, in PRK eyes. Intraoperative centroid shifts >100 μm in either the x axis or y axis occurred in 71% of LASIK eyes and 55% of PRK eyes.


CONCLUSIONS
Significant changes in cyclotorsion and centroid shifts were noted prior to surgery as well as intraoperatively with both LASIK and PRK. It may be advantageous to engage iris registration immediately prior to ablation to provide a reference point representative of eye position at the initiation of laser delivery.
Department of Ophthalmology, Loma Linda University, Loma Linda, California 92354, USA. junarvaez@llu.edu
Julio
J
Narváez
Matthew
M
Brucks
Grenith
G
Zimmerman
Peter
P
Bekendam
Gregory
G
Bacon
Kristin
K
Schmid
D057128:Aberrometry; D000328:Adult; D005133:Eye Movements; D005260:Female; D006801:Humans; D007431:Intraoperative Complications; D020731:Keratomileusis, Laser In Situ; D054018:Lasers, Excimer; D008297:Male; D008875:Middle Aged; D018903:Photorefractive Keratectomy; D011680:Pupil / Q000502:physiology; D012029:Refraction, Ocular / Q000502:physiology; D012399:Rotation; D014102:Torsion Abnormality / Q000209:etiology* / Q000503:physiopathology; D014792:Visual Acuity / Q000502:physiology; D055815:Young Adult