Researchers in San Diego compared changes in simulated night driving performance among patients moderate to high myopia and astigmatism after treatment with either surgical implantation of a toric Visian Implantable Collamer Lens (STAAR Surgical; Monrovia, Calif.) or conventional PRK surgery.

A total of 43 eyes (20 bilateral cases) were treated with the Visian Toric Implantable Collamer Lens (TICL), and 45 eyes were treated with PRK surgery.

Prior to surgery, subjects participating in the study had -6.00 to -20.00 diopters (D) of myopia and 1.00 to 4.00 D of astigmatism.

Before and 6 months following treatment, 27 eyes of 14 TICL patients and 41 eyes of 21 PRK patients underwent a simulated night driving test.  The test required the subjects to detect and identify common road signs and hazards with and without the presence of a glare source.

Examples of a glare source during real-world night driving are the headlights of approaching vehicles.

The results of the night driving simulator testing revealed:

• Without the introduction of a glare source, patients in the TICL group could identify road signs and pedestrian hazards significantly faster than patients in the PRK group.
• With introduction of a glare source, patients in the TICL group could identify pedestrian hazards (but not road signs) significantly faster than patients in the PRK group.
• There was no significant difference in how quickly subjects in the two treatment groups could detect (but not identify) road signs and pedestrian hazards, with and without a glare source.

The researchers concluded that the Visian Toric Implantable Collamer Lens performed better than conventional PRK surgery in the pre- to post-surgical simulated night driving visual performance testing, with and without a glare source present.

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

Researchers in Canada evaluated the bilateral implantation of AcrySof toric refractive IOLs (Alcon; Fort Worth, Texas) in subjects undergoing cataract surgery in both eyes. The study included 234 eyes of 117 subjects.

Prior to surgery, all subjects had cataracts and astigmatism ranging from 1.0 to 2.5 diopters (D).

At 1 day and 1, 3 and 6 months after surgery, the following measurements were taken: uncorrected visual acuity (UCVA) at distance, residual refractive error, and IOL rotational stability.

In addition, all patients completed a questionnaire administered before surgery and at 3 months and 6 months after surgery. Using a 10-point scale, the questionnaire assessed dependence on eyeglasses, visual disturbances and satisfaction with vision (1 = completely unsatisfied; 10 = completely satisfied).

Post-operative findings included:

• Binocular distance UCVA was 20/40 or better in 99 percent of patients and 20/20 or better in 63 percent of patients.
• Mean residual refractive astigmatism was reduced to 0.4 D.
• IOL alignment was within 10 degrees of the intended position in 99 percent of patients and within 5 degrees in 99 percent of patients.
• 69 percent of patients reported never needing glasses for driving and other distance vision tasks.
• Halos and glare present prior to surgery were significantly reduced after surgery.
• 94 percent of patients rated their vision a 7 or higher after surgery.

The researchers concluded that cataract surgery with bilateral implantation of toric IOLs to correct astigmatism produced “excellent and stable visual outcomes that patients rated as highly satisfactory.”

A full report of the study appears in the April 2010 issue of Journal of Cataract and Refractive Surgery.

Optical Express is Europe’s largest provider of laser vision correction and employs over 3,000 optometrists, refractive surgeons and support staff in the United Kingdom, Ireland, the Netherlands, Germany, France, Croatia and the United States, according to the company.

Wavefront-guided LASIK: Study design and methods

Data were gathered from the electronic records of 17,713 patients (32,569 eyes) who underwent wavefront-guided LASIK at Optical Express refractive surgery centers in 2008. The procedures were performed by 30 LASIK surgeons at 40 Optical Express centers.

All procedures were performed using the STAR S4 IR excimer laser system (Abbott Medical Optics) using a wavefront-guided ablation profile (Advanced CustomVue, AMO).

All patients had low to moderate myopia with or without astigmatism prior to surgery. The mean spherical equivalent amount of pre-operative myopia was -2.97 diopters (range: -0.37 to -6.00 D).

The majority of corneal flaps (75.7 percent) were created with an IntraLase FS-60 femtosecond laser (AMO). The remaining flaps were created with a Moria Evo3 One Use-Plus microkeratome (Moria SA).

Patients ranged in age from 18 to 69 years, with an average age of 35.6 years.

Wavefront-guided LASIK: Study results

Data gathered one month after surgery yielded the following results:

• 92 percent of eyes achieved uncorrected visual acuity (UCVA) of 20/20 or better.
• 99 percent of eyes achieved UCVA of 20/40 or better.
• 94 percent of eyes were within 0.50 D of the intended correction.

Intra-operative LASIK complications occurred in 25 eyes (0.06 percent). The most common of these complications (22 eyes; 0.05 percent) were related to flap creation with a microkeratome. (Numbers and percentages based on 42,143 eyes treated in 2008. Not all patients returned for the 1-month follow-up visit of the study, which comprises 32,569 eyes.)

Post-operative LASIK complications occurred in 210 eyes (0.64 percent). The most common complications were dry eyes (58 eyes) and mild diffuse lamellar keratitis (58 eyes).

Conclusions

The researchers concluded that wavefront-guided LASIK can safely and effectively correct low to moderate myopia, with or without astigmatism.

The also said the low overall rate of complications in this large study (intra-operative: 0.06 percent; post-operative: 0.64 percent) reflects the high level of safety that modern LASIK has achieved.

SOURCE: One-month outcomes of wavefront-guided LASIK for low to moderate myopia with the VISX STAR S4 laser in 32,569 eyes. Journal of Refractive Surgery. July 2009. (Supplement: Clinical Outcomes and Quality of Care in Refractive Surgery, sponsored by Optical Express.)

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.)