• Refractive Mgmt/Intervention

    Introduction

    Advances in laser vision correction techniques have improved the refractive surgeon's ability to treat the complicated cornea. Nevertheless, treating the radial keratotomy (RK) patient for residual refractive errors is still fraught with a higher rate of complications. As with laser refractive surgery in general, there are 2 main approaches to treating the post-RK cornea: laser in situ keratomileusis (LASIK) and surface ablation.

    Further confounding the treatment plan are the often-encountered fluctuations in vision, making it difficult to define an accurate refraction. Though many surgeons performing these procedures have developed their treatment of choice based on their personal experience or that of a colleague's, a consensus approach is still lacking. A comprehensive literature review of published peer-reviewed data does not help in making this decision. Furthermore, a review is limited by the paucity of large prospective trials.

    Review of Post-RK LASIK Results

    There are fewer than 20 studies evaluating the results of post-RK LASIK in the mainstream peer-reviewed journals. Initially, interest in LASIK peaked because of the higher rates of haze induced by photorefractive keratectomy (PRK) in the early days of that technique. Problems associated with flap cutting, however, limited the appeal of performing LASIK in the post-RK eye. Flap cutting and lifting often led to dismemberment along the old RK incisions, especially in cases where many incisions were present.

    In the largest published series of patients, 80 eyes underwent LASIK for residual myopia, astigmatism, and hyperopia after RK.1 Preoperative uncorrected visual acuity (UCVA) was better than 20/40 in only 4 eyes (5%), improving to a postoperative UCVA better than 20/40 in 60 eyes (75%). Though 4 eyes (5%) showed 1 or 2 lines of improvement in best spectacle corrected visual acuity (BSCVA), 7 eyes (9%) lost 1 or 2 lines of BSCVA and 1 (1%) lost more than 2 lines of BSCVA (Table 1). Complications included epithelial ingrowth and stromal opacity.

    Rahul T. Pandit, MD
    Table 1. Summary of studies cited.

    In another retrospective study evaluating 69 eyes, 75% of eyes had a preoperative UCVA of 20/50 or worse, improving to a postoperative level of 20/40 or better in 65% of eyes (Figure 1).2 Again, complications were prevalent, with 15 eyes (22%) losing 1 Snellen line of BSCVA, and 4 eyes (6%) losing 2 Snellen lines due to diffuse lamellar keratitis and epithelial ingrowth (Figure 2).1,2

    Reproduced, with permission, from T Francesconi CM, Nosé RA, Nosé W "Hyperopic laser-assisted in situ keratomileusis for radial keratotomy induced hyperopia", Ophthalmology, 2002 Mar;109(3):602-5
    Figure 1. Spectacle-corrected visual acuity in 69 eyes after hyperopic laser in situ keratomileusis after radial keratotomy.

     

    Reproduced, with permission, from T Francesconi CM, Nosé RA, Nosé W "Hyperopic laser-assisted in situ keratomileusis for radial keratotomy induced hyperopia", Ophthalmology, 2002 Mar;109(3):602-5
    Figure 2. Epithelial ingrowth in the interface of an eye treated for hyperopia with laser in situ keratomileusis after radial keratotomy.

    Though no clear association has been demonstrated in the published literature between intraoperative complications such as a flap tear and significant postoperative loss of vision, anecdotally this has been a concern for surgeons. Regardless of visual outcomes, a flap tear does involve greater time and management in repositioning the flap pieces. To that extent, femtosecond laser technology has at least theoretic appeal over a microkeratome, given that it does not require a moving blade to cross the corneal incisions and that it produces a more vertical flap edge, allowing for greater stability with flap repositioning.

    Two prospective studies examined a series of patients (with a total of 24 eyes evaluated) undergoing Intralase-assisted flap creation.3,4 The visual outcomes were better in the eyes treated for myopia than for hyperopia and overall seemed to slightly exceed that of published microkeratome results. Twenty-three eyes (96%) achieved a UCVA of 20/40 or better, but 5 of these eyes (21% overall rate) lost 1 line of BSCVA. High rates of complications, including incision opening (Figure 3),3 diffuse lamellar keratitis, haze, and loss of BSCVA were still present. More dramatic was the significantly greater rate of these complications in those patients with more than 8 RK incisions.3

    Reprinted from the Journal of Cataract and Refractive Surgery., 33(7, Muñoz G, Albarrán-Diego C, Sakla HF, Javaloy J, " Femtosecond laser in situ keratomileusis for consecutive hyperopia after radial keratotomy", pages 1183-9, Copyright 2007, with permission from Elsevier.
    Figure 3. The opening of 2 radial keratotomy incisions next to the hinge in a case of femtosecond hyperopic laser in situ keratomileusis after radial keratotomy.

    Review of Post-RK PRK Results

    When evaluating the peer-reviewed published data on PRK after RK, we find mostly older data from first-generation excimer lasers. There are just over 20 peer-reviewed studies on post-RK PRK, but only 2 have been published in this decade.

    The largest study was part of the Summit Therapeutic Refractive Study Group and dates from 1995. Even in those days of broad-beam laser and small ablation zones, the results were comparable to some of the LASIK studies. One hundred seven eyes were evaluated for treatment of residual myopia with PRK (only 97 of these eyes were post-RK treatments), with 74% achieving 20/40 or better UCVA at 1 year.5 Twenty-nine percent, however, lost 2 or more Snellen lines of BSCVA. Durrie and colleagues also evaluated a large series of patients, with nearly 90% of the 91 eyes achieving UCVA of 20/40 or better at 1 year.6

    The PRK After RK Study Group led by Azar published a retrospective analysis of results on 38 eyes from 10 different surgeons.7 As expected, results favored those with less initial myopia, both pre-RK as well as pre-PRK. Overall, 75% of eyes had UCVA of 20/40 or better at 1 year, with 33% losing 1 Snellen line of BCVA and 11% losing 2 or more lines.

    Recent Developments in PRK Add to Its Appeal

    More recent developments in excimer laser technology, as well as advances in PRK techniques, have improved the refractive surgeon's ability to offer surface ablation on post-RK eyes. Recent studies evaluating treatment of both residual myopia and overcorrected hyperopia seem to suggest better results than were previously obtainable.8,9

    The use of mitomycin C also has been widely accepted as an adjunct to PRK in eyes that are more prone to an aggressive fibroblastic response with haze and scarring. In recently published data on PRK for residual myopia, the use of mitomycin C 0.02% for 2 minutes appeared to have a positive effect on the incidence of visual loss, with 77% of 22 eyes achieving UCVA of 20/40 or better and only 1 eye (4.5%) losing 1 Snellen line of BSCVA.8

    Factors to Consider During Preoperative Counseling

    The pendulum appears to be swinging back in favor of surface ablation, with the adjunctive use of mitomycin C, to treat undercorrected as well as overcorrected post-RK eyes. Regardless of the method used, post-RK patients present a unique challenge to the refractive surgeon. Appropriate preoperative counseling is therefore mandatory to ensure a successful outcome. These patients must understand that results of any laser correction in post-RK eyes are more prone to error and complications than in normal eyes.

    Post-RK patients often complain preoperatively of daily fluctuations in their vision. They need to understand that these fluctuations may persist, but the goal of surgery is to maintain their visual acuity closer to plano than in their current range of spherical error. To that extent, there is some advantage in setting a more myopic target in these eyes, such that any future fluctuation will remain in the myopic to plano range, thus ensuring that the eye always has a real focal point. These patients may also continue to experience a hyperopic drift after vision correction, so the results may not be as "permanent" as with normal eyes, even with eyes that have demonstrated refractive stability of less than 0.5 D over the past year.

    Conclusion

    The post-RK eye presents unique challenges to the refractive surgeon. Successful visual rehabilitation may be possible if the surgeon takes a close look at the patient's specific conditions and needs, while appropriately counseling for possible complications.

    References

    1. Clausse MA, Boutros G, Khanjian G, et al. A retrospective study of laser in situ keratomileusis after radial keratotomy. J Refract Surg. 2001;17(suppl 2):200S-201S.

    2. Francesconi CM, Nosé RA, Nosé W. Hyperopic laser-assisted in situ keratomileusis for radial keratotomy induced hyperopia. Ophthalmology. 2002;109(3):602-605.

    3. Muñoz G, Albarrán-Diego C, Sakla HF, Javaloy J. Femtosecond laser in situ keratomileusis for consecutive hyperopia after radial keratotomy. J Cataract Refract Surg. 2007;33(7):1183-1189.

    4. Muñoz G, Albarrán-Diego C, Sakla HF, et al. Femtosecond laser in situ keratomileusis after radial keratotomy. J Cataract Refract Surg. 2006 Aug;32(8):1270-1305.

    5. Maloney RK, Chan WK, Steinert R, et al. A multicenter trial of photorefractive keratectomy for residual myopia after previous ocular surgery. Summit Therapeutic Refractive Study Group. Ophthalmology. 1995;102(7):1042-1052; discussion 1052-1053.

    6. Durrie DS, Schumer DJ, Cavanaugh TB. Photorefractive keratectomy for residual myopia after previous refractive keratotomy. J Refract Corneal Surg. 1994;10(suppl 2):235S-238S.

    7. Azar DT, Tuli S, Benson RA, Hardten DR. Photorefractive keratectomy for residual myopia after radial keratotomy. PRK After RK Study Group. J Cataract Refract Surg. 1998;24(3):303-311.

    8. Nassaralla BA, McLeod SD, Nassaralla JJ Jr. Prophylactic mitomycin C to inhibit corneal haze after photorefractive keratectomy for residual myopia following radial keratotomy. J Refract Surg. 2007;23(3):226-232.

    9. Joyal H, Grégoire J, Faucher A. Photorefractive keratectomy to correct hyperopic shift after radial keratotomy. J Cataract Refract Surg. 2003;29(8):1502-1506.

    Author Disclosure

    Dr. Pandit states that he has no financial relationship with the manufacturer or provider of any product or service discussed in this article or with the manufacturer or provider of any competing product or service.