Wavefront optimized LASIK is an advanced type of LASIK surgery designed to correct nearsightedness, farsightedness and astigmatism, and also produce sharper vision by inducing less spherical aberration — a specific type of higher-order aberration (HOA) — than conventional LASIK.

The wavefront-optimized procedure sometimes is confused with wavefront-guided LASIK (also called custom LASIK), which is designed to correct nearsightedness, farsightedness, astigmatism and a variety of pre-existing higher-order aberrations of the eye, with the intent of producing sharper vision than that attainable with eyeglasses or conventional LASIK.

Researchers in India conducted a study of 117 eyes of 59 nearsighted patients that underwent the wavefront-optimized procedure. In all cases, the LASIK flap was created with a Hansatome microkeratome (Bausch & Lomb, Rochester, N.Y.) and the wavefront-optimized ablation was performed with an Allegretto Wave excimer laser (Alcon, Fort Worth, Texas).

Higher-order aberrations of the eyes were measured prior to LASIK and at one and six months after the procedure.

The mean age of patients in the study was 25 years (range: 18 to 35 years) and the mean spherical equivalent of myopia prior to surgery was -5.33 diopters (D). A total of 98 eyes also had astigmatism, ranging from -0.25 to -4.00 D.

Outcomes measured following surgery included uncorrected visual acuity (UCVA) and total root mean square (RMS) value of higher-order aberrations.

At one month after wavefront-optimized LASIK:

• 102 eyes (87 percent) achieved UCVA of 20/20 or better.
• 104 eyes (89 percent) were within +/-0.50 D of the attempted refractive correction.
• Mean refractive result was -0.21 D (+/-0.38 D).
• The RMS value for total higher-order aberrations increased 96 percent.

The researchers also found that spherical aberration — a common HOA associated with glare and halos around lights at night — was reduced when larger ablation zones were used.

The authors of the study concluded that wavefront-optimized LASIK, despite producing excellent high-contrast visual acuity as measured by a standard eye chart, induces significant higher-order aberrations during the correction of myopia.

It is possible that increased higher-order aberrations might affect visual quality in low-contrast situations, such as driving at night.

SOURCE: Ocular aberrations after wavefront optimized LASIK for myopia. Indian Journal of Ophthalmology. July/August 2010.

LASIK, PRK and other corneal refractive surgery have been shown to increase higher-order aberrations in the eye that can affect visual clarity. Even customized, wavefront-guided LASIK typically increases these aberrations to some extent.

Researchers in France, however, have found that within 3 months after LASIK surgery, the human eye appears to be able to compensate to some degree for aberrations in the cornea caused by LASIK, thereby reducing the total aberrations of the eye.

The investigators studied 57 eyes of 57 patients who underwent conventional LASIK surgery for the correction of myopia. All eyes were measured before and 3 months after surgery to compare corneal aberrations and total eye aberrations, using an OPD-Scan aberrometer (NIDEK Co Ltd.)

Measurements taken 3 months after LASIK surgery revealed that although total corneal higher-order aberrations (HOA) increased by a factor of 2.47 after LASIK, total eye HOA increased by a factor of 1.77.

For a specific type of HOA called spherical aberration, corneal spherical aberration (SA) increased by a factor of 2.64 after LASIK, while total eye SA increased by a factor of 1.46.

The lower magnitude of total eye aberrations compared with corneal aberrations after LASIK suggest some degree of compensation by the internal optics of the eye to reduce the affect of the corneal aberrations, according to the study authors.

The researchers concluded that the human eye appears to have an adaptive ability that enables it to partially compensate for corneal aberrations caused by LASIK performed for the correction of myopia.

A full report of the study appears in the May 2010 issue of Journal of Refractive Surgery.

Researchers at Mayo Clinic (Rochester, Minn.) studied 21 patients who underwent bilateral LASIK eye surgery for the correction of myopia and/or myopic astigmatism. On one eye, the LASIK flap was created with a bladed microkeratome; on the other eye, the flap was created with a femtosecond laser.

Corneal topography and visual acuity were measured prior to surgery and at 1, 3, 6, 12 and 36 months after the procedure. Analysis of the topography data was performed both for conditions of a 4-mm and 6-mm pupil diameter.

Results of the study included:

• There were no differences in total corneal higher-order aberrations (HOA) between the two methods of flap creation at any exam for both 4-mm and 6-mm pupil diameters.
• Both flap creation methods increased total HOA for a 6-mm pupil diameter, and this increase persisted throughout the 3-year study period.
• Uncorrected and best-corrected visual acuity of eyes in the two treatment groups were comparable at all post-LASIK exams and remained stable throughout the 3-year study period.

The researchers concluded that femtosecond laser-created corneal flaps in blade-free, all-laser LASIK did not offer an advantage in terms of corneal higher-order aberrations or visual acuity for up to 3 years after LASIK surgery. They also concluded that post-LASIK corneal HOA appear to remain stable for at least 3 years after surgery.

(Ed. note: All-laser LASIK is a premium procedure that increases LASIK cost. Both conventional and wavefront-guided LASIK can be performed with a corneal flap created with either a bladed microkeratome or a femtosecond laser.)

SOURCE:  Corneal aberrations and visual acuity after laser in situ keratomileusis: Femtosecond laser versus mechanical microkeratome. American Journal of Ophthalmology. May 2010.

Typically, fewer higher-order aberrations means better visual outcomes after LASIK surgery. The study suggests wavefront-guided LASIK offers the best results for most patients, with a lower incidence of re-treatments.

What are higher-order aberrations?

Higher-order aberrations (HOAs) are subtle optical defects in the focusing system of the eye that can cause blur, glare, halos and other visual disturbances. Higher order aberrations differ from common refractive errors — nearsightedness, farsightedness and astigmatism — which are easier to identify and can be corrected with eyeglasses and contact lenses.

Higher-order aberrations that are significant enough to affect vision can be present in eyes that have little or no refractive error. Vision problems caused by HOAs typically are most noticeable in low-light conditions, such as night driving.

Spherical aberration is one particular type of higher-order aberration. Uncorrected spherical aberration can cause glare and halos around street lights and headlights at night.

What is wavefront-guided LASIK?

Wavefront-guided LASIK uses pre-operative aberrometry measurements to determine the level of pre-existing higher-order aberrations and to develop a computerized laser treatment (ablation) to reduce these aberrations.

What is wavefront-optimized LASIK?

Wavefront-optimized LASIK, on the other hand, is an enhanced version of conventional LASIK. It does not address pre-operative HOAs, but the laser ablation is adjusted, based on the patient’s eyeglasses prescription, to minimize any increase in spherical aberration induced by the treatment.

So whereas the goal of wavefront-guided LASIK is to identify and treat multiple HOAs (including spherical aberration) and refractive error during the corneal reshaping of the eye, the goal of wavefront-optimized LASIK is only to limit any increase in spherical aberration during the treatment of refractive error by the laser.

Study design

To evaluate the effect of wavefront-guided and wavefront-optimized LASIK on higher-order aberrations, Jack T. Holladay, MD, clinical professor of ophthalmology at Baylor College of Medicine (Houston, Texas) and colleagues reviewed the results of 109 wavefront-guided procedures and 102 wavefront-optimized procedures performed in 2006 and early 2007.

Results and conclusions

Findings of the study revealed:

• Overall, the wavefront-guided LASIK treatments induced significantly less higher-order aberrations (including spherical aberration) than the wavefront-optimized procedures.
• Among eyes treated with wavefront-guided LASIK, approximately 12 percent had less HOAs after surgery than they had prior to surgery, 76 percent had essentially the same amount before and after surgery, and 12 percent had more HOAs after LASIK.
• Among eyes treated with wavefront-optimized treatment, approximately eight percent had less HOAs after surgery, 51 percent had essentially the same amount before and after surgery, and 41 percent had more HOAs after LASIK.
• There was more variation in outcomes among eyes receiving wavefront-optimized procedure.

The researchers concluded that wavefront-guided LASIK reduces or induces fewer higher-order aberrations than wavefront-optimized LASIK and therefore is the better procedure for optimizing post-surgical vision quality.

SOURCE:  Fewer higher-order aberrations yields better visual performance. EyeWorld. May 2009. (Supplement: Premium Clinical Options for Cataract and Refractive Surgery, sponsored by Abbott Medical Optics.)