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Barbara Boughton in San Francisco

CENTRING on the corneal light reflex may provide better visual results in hyperopic LASIK than centring on the pupil, reported Brian S. Boxer Wachler MD at the annual meeting of the ASCRS.

He presented his results in a series of 61 eyes he treated in this way. Patients had an average of +2.73 D (range: 0.38 D to +6 D) of hyperopia and cylinder up to -5 D with a minimum of three months follow-up. Some 50% of the patients achieved 20/20 or better, and no patient lost two or more lines of acuity.
"This level of safety is unheard of in hyperopia, especially if you're treating up to +6 D. And only a small percent of patients lost contrast sensitivity," he noted.

Dr Boxer Wachler said he has achieved good results with hyperopic LASIK since he began centring on the visual axis in 1999. At that time, while doing LASIK with a 5.5 mm optical zone on a 58-year-old male moderate to low hyperope, he noticed that the patient's visual axis was markedly nasal in both eyes relative to the pupil centres.
This denoted positive angle kappa. As a result he decentred the ablation a little more nasally in one eye relative to the pupil and centred the ablation on the pupil in the fellow eye. The results: a topographically well-centred ablation in the first eye and a temporally decentred ablation in the fellow eye.

That experience caused Boxer Wachler to do a few more hyperopic LASIK cases in which he centred on the corneal light reflex, which approximates the visual axis. He noted that in corneal topography, the patient looks through the visual axis, not the centre of the pupil, as he focuses on the fixation light.
"After a few surgeries, I began to realise that we should be centring on the corneal light reflex. Hyperopes tend to have a fair amount of nasal decentration of their visual axis relative to the pupil centre."

He said that the reason surgeons tend to centre on the pupil in hyperopic LASIK- and the reason why excimer laser manufacturers recommend this method- stems from the calculations in a 1987 study (Uozato H, et al. Am J Ophth 1987; 103:264-75).
In that study, the authors used mathematical calculations to prove that the best outcomes were achieved by centring the surgical procedure on the line of sight and entrance pupil of the eye, not the visual axis. They found an error rate of 0.5 to 0.8 mm in the method of marking the visual axis, arising from the use of the corneal light reflex as a sighting point, or from inadvertent monocular sighting in techniques requiring binocular sighting.

"Proper centring requires the patient to fixate on a point that is coaxial with the surgeon's sighting eye," the authors wrote at the time.
However, another study published in 1993 (Pande M, Hillman JS. et al. Ophthalmology 1993:100; 1230-37) found that the ideal physiologic centration is the corneal intercept of the visual axis. The authors marked and compared the geometric corneal centre, the entrance pupil centre, the visual axis, and the coaxially sighted corneal reflex as centration points after photographing the cornea in 50 volunteers.
"The decentration from the visual axis was least if the coaxially sighted corneal reflex was used for centration," the authors reported.

"Unfortunately, this 1993 paper has been buried and forgotten. But the authors did as much complex math as in the earlier paper to prove that centring on the pupil is wrong. We should be centring on the corneal light reflex. There are two very strong arguments about centration in the scientific literature, but in my experience centring on the corneal light reflex is a safe and effective procedure," Dr Boxer Wachler stressed.
Dr Boxer Wachler's study appeared in the Journal of Refractive Surgery (2003; 19:464-65).

Brian S. Boxer Wachler MD
Faculty, UCLA Medical Center
bbw@boxerwachler.com

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