The two currently accepted methods for correcting

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1 New Technique Therapeutic Alloplastic Laser in situ Keratomileusis for Myopia Arturo Maldonado-Bas, MD; Ruben Pulido-Garcia, MD ABSTRACT BACKGROUND: A new technique, therapeutic alloplastic laser in situ keratomileusis to correct high myopia, is introduced. METHODS: Therapeutic alloplastic laser in situ keratomileusis consists of neutral homoplastic epikeratoplasty combined with superficial keratectomy performed with an excimer laser and/or a microkeratome. Indications for the technique are: myopia over 20 diopters (D), eyes with corneal scarring after photorefractive keratectomy (PRK), complications following keratomileusis, radial keratotomy complications with undercorrection, and keratoconus suspect myopic eyes. RESULTS: In all five eyes we achieved precise corneal lathing with the microkeratome or the excimer laser, and obtained a clear allograft. In all eyes, we maintained or improved the patient s spectacle-corrected visual acuity related to baseline values. We did not induce astigmatism, and corneal thickness was almost unchanged. CONCLUSIONS: Advantages of therapeutic alloplastic laser in situ keratomileusis are that it provides a Bowman s layer for the cornea following keratectomy, it is possible to lathe ablation diameters larger than 5 mm, it prevents the appearance of corneal haze, and reduces the need for corticosteroid treatment. [J Refract Surg 1998;14:64-69] From the Department of Ophthalmology, National University of Córdoba, Argentina. The authors have no proprietary interest in the research presented herein. Correspondence: Arturo Maldonado-Bas, MD, Achával Rodríguez 544, Cordoba 5000, Argentina. Tel: ; Fax: Received: November 11, 1995 Accepted: October 8, 1997 The two currently accepted methods for correcting myopia of a range greater than radial keratotomy can achieve are photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK). PRK has the advantage of producing accurate corneal lathing, and ablation zones greater than 5 mm in diameter can be obtained. Its principal disadvantage is that it destroys Bowman s layer. This often produces a transient opacity known as haze, or a permanent opacity referred to as a scar, which reduces vision, and the thickness of which causes a regression in the initial correction. 1,2 The incidence of haze is proportional to the amount of correction attempted. 3-6 The topical use of corticosteroids may be necessary for several months to minimize this alteration. 7 LASIK avoids both haze and the prolonged use of corticosteroids since it preserves Bowman s layer. To achieve corneal transparency, a sufficient correction of the refractive defect, and for the results to be stable, the various parameters already described for in situ keratomileusis should be handled precisely 8,9 in LASIK, as well as in therapeutic alloplastic LASIK. For keratomileusis in situ, cutting a lamellar disc 8.25 mm in diameter, with a thickness of 160 µm, including the epithelium, Bowman s layer, and a thin layer of superficial stroma, is essential for transparency of the cornea. This corneal disc has parallel faces and has no dioptric power, although its thickness does condition the ablation of the plano lenticule in the residual stroma and, consequently, the result of the surgery. The second step in the surgery is the ablation of a positive plano lenticule at least 4 mm in diameter. The best results with keratomileusis in situ were obtained with diameters greater than 4 mm. Keeping the thickness constant, the diameter is 64 Journal of Refractive Surgery Volume 14 January/February 1998

2 Figure 1: On the donor eye, the disc is 8.25 mm in diameter and 130 µm thick and provides Bowman s layer. Figure 2: The disc is being resected from the donor eye with the automated microkeratome. inversely proportional to the diopters to be corrected. With constant diameter, the thickness is directly proportional to the diopters to be corrected. The corneal thickness remaining after the ablation of the plano lenticule must be greater than 250 µm in order to prevent ectasia of the posterior stroma, with the resultant loss of the initial flattening of the central portion of the anterior surface of the cornea. 9 In the case of normal corneal thickness, taking out a 160 µm disc, the diameter of the ablation is conditioned by the remaining corneal thickness in high myopia and must be progressively reduced to be able to maintain a thickness of 250 µm in the underlying stroma for stable results. In ablations with diameters less than 4 mm, physiologic mydriasis produces glare and monocular diplopia. The ideal surgical technique is the resection of the disc with the microkeratome to preserve Bowman s layer and the lathing of the optical area in the stroma 11 with the excimer laser. LASIK has good functional results and is sufficiently stable only when the above parameters are considered, thus limiting the treatment to myopia less than diopters (D). 10 PATIENTS AND METHODS Therapeutic alloplastic LASIK was used to correct high myopia in cases of corneal scarring and regression of effect following PRK. It can also be used following phototherapeutic keratectomy (PTK) to supply a Bowman s layer to the central area treated, in complicated cases with previous radial keratotomy or automated lamellar keratoplasty (ALK), and in keratoconus suspect myopic eyes. The transparency of the cornea is assured by the allograft lenticule (160 µm thick), which provides its own Bowman s layer to cover the central host stroma. The ablation of the lenticule in the host stromal bed is done without reducing the total corneal thickness (as is necessary in LASIK), and in this way it is possible to have ablation diameters greater than 5 mm, whatever the thickness of the ablation may be. The remaining corneal stromal bed is always greater than 250 µm thick, which reduces the possibility of ectasia. The allograft lenticule is approximately 160 µm, so that ultimately the cornea has almost normal thickness and the regularity of the anterior surface is very good. The Omnimed excimer laser (Summit Technology, Inc., Waltham, Mass) and the Automated Corneal Shaper (Chiron Vision, Irvine, Calif) were used. Surgical Technique Proparacaine 0.5% and lidocaine 4% drops were given every 5 minutes during 30 minutes before the procedure to provide topical anesthesia. With an automated or manual microkeratome, a disc of 8.25 mm in diameter and 160 µm thick with parallel faces (thus without refractive power) was removed from a pressurized fresh donor eye (Figs 1, 2) or from a corneo-scleral button using an artificial chamber. It was commonly necessary to use a plate 240 µm thick to achieve a final result of approximately 160 µm, taking into account the artificially edematous donor eye. A PRK or a PTK procedure was performed. It was possible to perform ablations with diameters over 5 mm because the surgeon was often dealing with a cornea of full thickness (Fig 3). A circular cut 150 µm thick and 6.5 mm or more in diameter was made with a trephine and a lamellar intrastromal pocket was dissected between the 6.5 and 8.5 mm zone (Fig 4), centering it with the visual axis. The allograft lenticule was placed over the Journal of Refractive Surgery Volume 14 January/February

3 Figure 4: Shown on the myopic eye are the 5-mm diameter PRK, the circular keratotomy at 7.25 mm, and the pocket in the corneal stroma from the keratectomy up to 8.5 mm, to receive the allograft lenticule. Figure 3: The PRK is performed on the myopic eye with the excimer laser. stromal bed with the epithelial face upward, and the disc wings were inserted into the stromal pocket. Finally, the epikeratoplasty was fixed with 8 to 16 interrupted 10-0 nylon sutures (Fig 5). This technique was used to treat four complicated cases following in situ keratomileusis and one complicated case of ALK followed by a PRK procedure (Table). CASE REPORTS Case #1: A 20 year old male was seen in May 1988 because of contact lens intolerance. His right eye spherical equivalent refraction was -20 diopters (D) and spectacle-corrected visual acuity 20/100; keratometric power was x D at 130º; intraocular pressure (IOP) was 16 mmhg, and corneal thickness was 510 µm. The anterior segment was normal. The fundus showed a myopic staphyloma with pigmented equatorial lesions. The patient underwent Figure 5: The allograft lenticule in place with 8 or nylon sutures. an in situ keratomileusis procedure on July 14, Due to technical problems with the microkeratome, the disc was cut irregularly which led to posterior partial necrosis and subsequent removal. The stroma developed a scar (Fig 6A) and the spherical equivalent refraction increased to x 160 with a spectacle-corrected visual acuity of 20/200. In October 1989, a central surface Table Results of Therapeutic Alloplastic LASIK in Five Eyes Baseline After Surgery Kerato- Ablation Spherical Intra- Spectacle- Spherical Un- Spectacle- Kerato- Intra- Case metric (diameter- Manifest Equivalent ocular corrected Manifest Equivalent corrected corrected metric ocular No. Power mm x Refraction Refraction Pressure Visual Refraction Refraction Visual Visual Power Pressure (D) depth-µm) (D) (D) (mmhg) Acuity (D) (D) Acuity Acuity (D) (mmhg) x x x x x x x x x x x x x x x Journal of Refractive Surgery Volume 14 January/February 1998

4 A B Figure 6: A) Case #1. A myopic eye that underwent in situ keratomileusis in The partially damaged disc was removed. Haze can be seen on the pupillary area of the keratectomy, similar to that produced in PRK. B) Same eye 5 years after an alloplastic lamellar keratoplasty. Figure 7: Case #1. Videokeratograph of the same eye, 5 years after the alloplastic lamellar keratoplasty, shows central corneal flattening and irregular astigmatism. keratectomy was performed with the microkeratome using settings of 4.5 mm in diameter and 120 µm thickness. The corneal bed was then prepared as described and the allograft lenticule was placed (Fig 6B). In September 1995, the spherical equivalent manifest refraction was x 135. Spectacle-corrected visual acuity was 20/100; uncorrected visual acuity was 20/200. Videokeratography revealed irregular astigmatism (Fig 7). Case #2: A 33 year old female was seen in May 1989 after a myopic in situ keratomileusis with a complication in the disc cut, apparently due to failure of the microkeratome. She had a circular corneal scar 5 mm in diameter, interface fibrosis in the visual axis, a spherical equivalent refraction of x 120º with a spectacle-corrected visual acuity of 20/200, and corneal thickness of 540 µm. The fundus showed choroidal Journal of Refractive Surgery Volume 14 January/February

5 atrophy. In July 1989, a central keratectomy (with a microkeratome) of 6.25 mm diameter by 210 µm thick and an alloplastic lamellar keratoplasty were performed. At last examination, keratometric power was D, spherical equivalent refraction was x 120º, uncorrected visual acuity was 20/60, and spectacle-corrected visual acuity was 20/40. Case #3: A 28 year old male who consulted for refractive surgery was seen in April The right eye had a spherical equivalent refraction of x 0º, spectacle-corrected visual acuity was 20/100, and keratometric power was x D at 90º; intraocular pressure was 17 mmhg and corneal thickness was 560 µm. The anterior segment was normal, the retina examination showed a myopic conus with choroidal atrophy. An in situ myopic keratomileusis was performed in April, The corneal stroma of the disc and the resection totaled over 300 µm and resulted in a central ectasia. The spherical equivalent refraction returned to x 170º, with a spectaclecorrected visual acuity of 5/1000. On May, 1992 a central surface keratectomy with a microkeratome was performed measuring 4.5 mm in diameter and 200 µm thick. The allograft lenticule was then secured as described. At the last examination in July of 1995, keratometric power was D, spherical equivalent refraction was x 30º, spectacle-corrected visual acuity was 20/100, and uncorrected visual acuity was 20/200. Case #4: A 24 year old female was seen in June 1992 because of contact lens intolerance. Her spherical equivalent refraction in the right eye was D and her spectacle-corrected visual acuity was 20/50, with keratometric power of x at 0º. Intraocular pressure was 13 mmhg and corneal thickness was 560 µm. An in situ myopic keratomileusis was performed on September 8, The disc obtained had a thickness of 190 µm and the resection 100 µm. A central ectasia developed and keratometric power increased to D. The spherical equivalent refraction was x 18º with a spectacle-corrected visual acuity of 4/400. In October 1993, a central surface keratectomy was performed with the microkeratome and the allograft lenticule was placed. At last examination (July 1995), her keratometric power was D and spherical equivalent manifest refraction was x 120º. Uncorrected visual acuity was 20/200 and spectacle-corrected visual acuity was 20/100. Case #5: A 35 year old woman was seen after previous automated lamellar keratoplasty (ALK) performed on August 10, Prior to ALK, her spherical equivalent refraction had been x 45º, with a spectacle-corrected visual acuity of 20/40 and keratometric power of x at 134º, corneal thickness of 520 µm, and intraocular pressure of 14 mmhg. During the ALK procedure, the microkeratome trapped and disrupted her corneal disc, with subsequent development of severe haze after the disc extraction. PRK was performed but the haze reappeared. At that time the spherical equivalent refraction was x 50º and her spectacle-corrected visual acuity was 20/100. In February 1994, PTK was performed with the Summit Omnimed excimer laser using an optical zone of 6 mm in diameter at a depth of 125 µm. The alloplastic lamellar keratoplasty completed the procedure. After necrosis of the disc due to a complication after keratomileusis that then necessitated PRK, she had dense central haze, and keratometric power of D. At the last examination in July of 1995, her keratometric power was D, manifest spherical equivalent refraction was x 100º, uncorrected visual acuity was 20/200, and spectacle-corrected visual acuity was 20/60. DISCUSSION Keratomileusis has been employed since Thirty years of follow-up has proven its success in maintaining corneal transparency and refractive stability. While PRK with the excimer laser often obtains excellent refractive results, it destroys Bowman s layer, which in some cases causes an atypical healing response that could induce anomalous scarring, often in direct proportion to the number of diopters to be corrected. This scarring increases corneal thickness, resulting in an irregular surface that diminishes both the obtained correction and the postoperative visual acuity. Alloplastic lamellar keratoplasty using excimer laser has the benefits of both PRK (precise lathing) and LASIK (preservation of corneal transparency). In these cases, the main goals were achieved; all eyes maintained or improved corneal transparency and spectacle-corrected visual acuity, while corneal thickness was nearly unchanged. Our present indications for this procedure are: 1) after PRK or PTK, to provide Bowman s layer to the treated area; 2) after ALK or radial keratotomy with complications or undercorrection; 3) for myopia greater than D; and 4) for myopia with topographic keratoconus (keratoconus suspect). REFERENCES 1. Sabetti E, Spadea L, Furcese N, Balestrazzi E. Measurement of corneal thickness by ultrasound after photorefractive keratectomy in high myopia. Refract Corneal Surg 1994;10: S211-S Fantes F, Hanna K, Waring GO III, Pouliquen Y, Thompson K, Savoldelli M. Wound healing after excimer laser keratomileusis keratectomy in monkeys. Arch Ophthalmol 1990;108: Seiler T, Kahle G, Kriegerowski M. Excimer laser myopic keratomileusis in sighted and blind human eyes. Refract Corneal Surg 1990; 6: Seiler T, Holschbach A. Complications of myopic photorefractive keratectomy with excimer laser. 68 Journal of Refractive Surgery Volume 14 January/February 1998

6 Ophthalmology 1994;101: Rogers C, Lawless M, Cohen P. Photorefractive keratectomy for myopia of more than 10 diopters. Refract Corneal Surg 1994;10: Lawless M, Cohen P, Rogers C. Retreatment of undercorrected photorefractive keratectomy for myopia. Refract Corneal Surg 1994;10: Carones F, Brancato R, Venturi E, Scialdone A, Bertuzzi A, Tavola A. Efficacy of corticosteroids in reversing regression after myopic photorefractive keratectomy. Refract Corneal Surg 1993;9(suppl);S52-S Maldonado-Bas A, Nano H. In situ myopic keratomileusis. Results in 30 eyes at 15 months Refract Corneal Surg 1991; 7: Barraquer JI. Cirugía Refractiva de la Cornea, Vol I. Bogotá, Colombia: Instituto Barraquer de América; 1989: Waring GO III. Changing concepts in excimer laser corneal surgery. Refract Corneal Surg 1995;11: Burrato L, Ferrari M, Genisi C: Myopic keratomileusis with excimer laser: one year follow up. Refract Corneal Surg 1993;9: Barraquer C. Epiqueratoplasty. Cornea 1982;1: Kaufman HE., Werblin T. Epikeratophakia for the treatment of keratoconus. Am J Ophthalmol 1982;93: Maldonado-Bas A. Epiqueratoplastia neutra combinada con queratomileusis in situ. Arch de la SAOO. 1990: Journal of Refractive Surgery Volume 14 January/February