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Keys to success with surface ablation
Surface ablation is becoming an effective refractive surgery option. Papers presented at the 2006 annual meeting of the American Academy of Ophthalmology (AAO) and the 2006 annual meeting of the European Society of Cataract and Refractive Surgeons showed that the number of surface ablations performed is gradually increasing (Figure). Now that surface ablation is gaining popularity, questions are being raised about the best way to perform the procedure.
Performing surface ablations
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I have been performing surface laser treatments since 1990. The main challenge that remains is how to improve the speed of visual recovery. In our practice, we have found that creating an epithelial defect with a 7.5-mm diameter trephine and using 20% alcohol to help remove the epithelium provides the fastest visual recovery. The 7.5-mm defect results in faster visual recovery than the 9-mm defect because it is 44% smaller. We have decreased the healing time to close the epithelial defect by more than 24 hours. Decreasing the epithelial defect size also “cuts off” the sub-ablation threshold treatment at the edge of the ablation, which leads to less post- operative recurrent erosion. The 7.5-mm trephine also allows for smooth edges for removing the epithelium. Although epikeratomes can be used to achieve smooth edges and flap removal, the size of the defect can be controlled more effectively with a manual trephine. Many ophthalmologists think they are forced to use a large epithelial defect because the laser ablations are 9 mm in diameter. In fact, minimal ablation occurs outside the optical zone, which is usually 6.5 mm. We have achieved excellent visual results using this technique.
Postoperative healing techniques
Cooling the surface of the eye has been shown to decrease pain and haze with surface ablation. Chilled balanced salt solution (BSS, Alcon Laboratories, Inc.) and ice have been used since the 1980s in Japan. In 2000, Paulo Vinciguerra, MD, studied ice’s efficacy in decreasing pain (live conversation, July 2000). Following his advice, my colleagues and I devised a way to create a sterile BSS popsicle, which we apply to the surface for 10 seconds prior to epithelial removal and just after ablation. This has dramatically improved patients’ comfort for the first 24 hours. After surface ablation is performed, a contact lens (Acuvue Oasys, Johnson & Johnson, New Brunswick, NJ) is applied, followed by moxifloxacin ophthalmic solution 0.5% and prednisolone acetate suspension 1% for 1 week and nepafenac ophthalmic suspension 0.1% every 4 hours for the first 48 hours. Epithelialization usually occurs in 3 to 5 days, but maximum vision does not return until 30 to 45 days. Mitomycin can be administered with ablations to treat patients who have myopia greater than 6 D or who are younger than 30 years old, but it should not be used routinely. Patients may also place a bag of frozen vegetables over the eye for 20 minutes each hour the first night to maintain temperature control. In our clinical experience, epi-LASIK techniques do not yield visual acuity results as fast as removing the epithelium, but we study each new technique as it is introduced.
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PRK vs. LASIK
Stephen G. Slade, MD, and I presented a study at the 2006 annual meeting of the AAO showing that LASIK results in significantly faster visual recovery than PRK. The speeds of visual recovery were compared after PRK and LASIK performed with a 60 Hz femtosecond laser (IntraLase Corp, Irvine, Calif.). The study included 50 patients who were an average age of 32 years. As expected, at 1 day postoperative, the eyes that underwent LASIK had better vision than the eyes that underwent PRK. However, vision in the PRK eyes worsened at 3 days as the epithelial defect became smaller. At 1 week, the vision in the PRK eyes had not improved since day 1. Although the PRK eyes were improving at 1 week, only 50% had 20/20 vision. The uncorrected vision in the PRK eye did not equal the LASIK eye until 3 months postoperative. In comparison, 100% of the patients who had LASIK could drive at 1 day, with 20/40 vision or better as the driving limit, whereas potentially 50% of patients who underwent PRK may not be able to drive at week 1. This discrepancy was not due to a difference in refractive error because the residual sphere and cylinder between the two groups were the same. Again, as expected, pain was worse in the PRK eye dur ing the first week. But we were surprised that, when patients were asked which eye experienced more pain at 1 month, more than twice as many patients continued to experience discomfort in the PRK eye. The quality of vision was significantly better in the LASIK eye up to 1 month, an outcome reflected in patient satisfaction. The only dissatisfaction that patients had at 1 month was in the PRK eye. Follow-up is needed to determine if the long-term results of PRK outweigh the short-term results.
Use of NSAIDs in PRK
William B. Trattler, MD, and Marguerite B. McDonald, MD, conducted a study comparing nepafenac ophthalmic suspension 0.1% and ketorolac tromethamine ophthalmic solution 0.4% in patients who underwent PRK.1 Dr. Trattler administered the NSAIDs underneath the contact lens in the operating department and continued the medications postoperatively for at least 5 days. Dr. Trattler used punctal plugs in his patients, which would increase NSAID surface time. He then noted delayed epithelialization in eyes that received nepafenac. Because of his concern, I conducted a study showing that the same epithelialization rates resulted from nepafenac and moxifloxacin when compared to ketorolac and gatifloxacin ophthalmic solution 0.3%.2 The NSAID was not placed underneath the contact lens. I administered NSAIDs postoperatively up to four times a day for 2 days. I believe this is the difference between the two studies and is important. When using nepafenac in PRK patients, I strongly suggest that it be used only post- operatively. I have used nepafenac in more than 500 patients without any complications.
A study conducted in the United States Air Force compared nepafenac with BSS for use in PRK.3 Nepafenac was shown to reduce pain at days 1 and 2 post- operatively. No difference in epithelial healing rates occurred in patients with nepafenac as compared to BSS. Thus, nepafenac achieved pain control without adverse effects. One hundred thirty-two eyes were included, and patients were dosed three times a day for 2 days.
Progress in surface ablation
Surface ablation is emerging as an important surgical option for refractive surgery. New techniques help ophthalmologists meet the challenge of recovering vision quickly to meet patients’ needs. Such techniques include the creation of smaller epithelial defects, maintenance of a cool, smooth area and the use of NSAIDs. Positive results are crucial because patients expect to have vision restored as soon as possible.
References
- McDonald MB, Trattler W. Double-masked comparison of ketorolac tromethamine 0.4% versus nepafenac suspension 0.1% for postoperative healing rates and pain control in eyes undergoing surface ablation. Poster presented at: Annual meeting of the Association for Research in Vision and Ophthalmology; May 2006; Fort Lauderdale, Fla.
- Donnenfeld ED, Durrie DS, Holland EJ, Raizman MB. A double-masked study of nepafenac 0.1% and ketorolac 0.4% for pain and epithelial healing following PRK. Poster presented at: Annual meeting of the American Academy of Ophthalmology; November 13, 2006; Las Vegas, Nevada.
- Reilly CD, Caldwell RC. Double-masked study of nepafenac 0.1% and placebo on pain relief and epithelial healing following PRK. Poster presented at the Annual Meeting of the American Academy of Ophthalmology; November 12-13, 2006; Las Vegas, Nevada.