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Laser-assisted subepithelial keratectomy versus photorefractive keratectomy for the correction of myopia
articles Laser-assisted subepithelial keratectomy versus photorefractive keratectomy for the correction of myopia A prospective comparative study Sergio Litwak, MD, David Zadok, MD, Valente Garcia-de Quevedo, MD, Nora Robledo, OD, Arturo S. Chayet, MD
Purpose: To compare the early postoperative visual rehabilitation after laser-assisted subepithelial keratectomy (LASEK) and photorefractive keratectomy (PRK) for the correction of myopia. Setting: CODET Aris Vision Institute, Tijuana, Mexico. Methods: This prospective study included 50 eyes of 25 patients with myopia who received LASEK in 1 eye and PRK in the contralateral eye. Excimer laser corneal ablation was done using the Nidek EC-5000 excimer laser. Patients were seen at 1 and 3 days, 1 week, and 1 month. Discomfort, subjective uncorrected visual acuity (UCVA), objective UCVA, best corrected visual acuity (BCVA), corneal clarity (haze), and time for corneal reepithelialization were analyzed. Results: Seventy-two percent and 80% of the LASEK eyes had more discomfort at 1 day and 3 days, respectively. Eighty percent and 96% of the PRK eyes had better subjective UCVA at 1 day and 3 days, respectively. Corneas were fully reepithelialized at a mean of 3.3 days ⫾ 0.5 (SD) and 3.6 ⫾ 0.5 days in the PRK and LASEK groups, respectively. At 1 month, the UCVA was similar in both groups; no eye had lost lines of BCVA or developed haze. Conclusions: Both LASEK and PRK were effective and safe procedures in the surgical correction of myopia at the 1-month postoperative visit. Patients reported less discomfort and better visual acuity in their PRK eye during the early postoperative period. Patients should be informed that LASEK, whose acronym is similar to that of laser in situ keratomileusis, has a recovery speed that is similar to that of surface laser refractive procedures such as PRK. J Cataract Refract Surg 2002; 28:1330 –1333 © 2002 ASCRS and ESCRS
A
lthough laser in situ keratomileusis (LASIK) is used worldwide for the correction of most refractive errors, it has some disadvantages, such as dry eye, night
Accepted for publication March 15, 2002. Reprint requests to Arturo S. Chayet, CODET Aris Vision Institute, Padre Kino 10159, Tijuana, BC 22320, Mexico. E-mail: arturo. [email protected]. © 2002 ASCRS and ESCRS Published by Elsevier Science Inc.
halos, and keratectasia.1–5 Potential mechanisms for keratectasia are a reduction in biomechanical corneal strength resulting from the creation of the lamellar flap, preoperative asymmetric astigmatism as an early sign of keratoconus, and leaving a corneal bed of less than 250 m after creating the flap and ablating the cornea. To our knowledge, keratectasia has not been reported following photorefractive keratectomy (PRK). A 0886-3350/02/$–see front matter PII S0886-3350(02)01376-7
LASEK VERSUS PRK
possible explanation is that as no lamellar cut is made during PRK, the biomechanical strength of the cornea is not affected. Since its introduction in the late 1980s, PRK has had good safety and efficacy results.6 Nevertheless, LASIK rapidly became the preferred method of patients and surgeons because it provided more rapid visual rehabilitation and less discomfort than PRK.7 Recently, Massimo Camellin, MD, introduced a procedure that he named LASEK, laser-assisted subepithelial keratectomy (M. Cimberle, “LASEK May Offer the Advantages of Both LASIK and PRK,” Ocular Surgery News, March 1999, page 28). The procedure consists of creating an epithelial flap, ablating the stroma to correct the refractive error, and then repositioning the epithelial flap. The suggested advantages of LASEK over PRK are the potential for less postoperative discomfort along with faster visual rehabilitation and less haze. In addition, since no lamellar flap is created, LASEK may retain the biomechanical stability shown with PRK and therefore be an alternative to LASIK in cases in which the corneal thickness might be reduced. In this study, we looked prospectively at the early postoperative results of LASEK and PRK and analyzed the potential advantage of LASEK as an alternative procedure for the correction of refractive errors.
Patients and Methods Fifty eyes of 25 patients with myopia received simultaneous bilateral surface laser refractive surgery by the same surgeon (A.C.). One eye of each patient was randomly chosen to have PRK, and the fellow eye had LASEK. Patients were told that each eye would have different surface laser refractive surgery but did not know which eye had LASEK and which had PRK. Written informed consent was obtained from the patients. The preoperative ophthalmic examination included manifest and cycloplegic refractions, corneal keratometry and topography, slitlamp biomicroscopy, fundus examination, and tonometry. Patients with diabetes mellitus, connective tissue disease, corneal disease, glaucoma, and retinal disease were excluded from the study.
Photorefractive Keratectomy Procedure Topical tetracaine hydrochloride 0.5 % drops were used to anesthetize the eye. Deepithelialization was performed using a #64 Beaver blade (Beckton-Dickinson) after the epithelium was marked with a 7.0 mm trephine centered over the pupil. This was followed by stromal ablation using the Nidek EC-5000 excimer laser. The ablated stroma was immediately
irrigated with chilled balanced salt solution (BSS威), and topical gentamicin was instilled over the cornea. A soft contact lens (Focus威, Ciba Vision) was placed on the cornea at the end of the procedure.
Laser-Assisted Subepithelial Keratectomy Procedure Topical tetracaine hydrochloride 0.5 % drops were used to anesthetize the eye. A preincision of the corneal epithelium was made using an 8.0 mm trephine with a 55 m blade (Janek); 80 degrees of uncut margin were left at the 12 o’clock position for the hinge. Two to 3 drops of an 18% alcohol solution (diluted with sterile distilled water) were placed on the cornea within an 8.5 mm solution cone (Janek) and left in place for 40 seconds. The area was irrigated with BSS. The epithelial flap was gently detached, gathered, and folded up at the 12 o’clock position. Following traditional PRK treatment, the ablated stroma was immediately irrigated with chilled BSS. The epithelial flap was then rolled to its original position using an irrigating 27-gauge cannula, and topical gentamicin was instilled over the cornea. A Focus lens was placed on the cornea at the end of the procedure. Postoperatively, patients were instructed to apply the same medications to both eyes: ofloxacin 0.3% (Ocuflox威) 1 drop 4 times daily and diclofenac (Voltaren威) and fluorometholone acetate 0.1% (Flarex威) 1 drop 2 times daily until the epithelium healed. After corneal reepithelialization was complete, Flarex was administered 4 times daily for 1 month. Patients were examined at 1 and 3 days, 1 week, and 1 month by an independent refractive surgeon who was not informed of the procedure in each eye (although he might have been able to recognize it from the epithelium). In cases in which the cornea was not fully reepithelialized on the third day, patients were asked to come back to the clinic daily until reepithelialization was complete. At each examination, uncorrected visual acuity (UCVA), best corrected visual acuity (BCVA), and slitlamp biomicroscopy were checked. Manifest refraction was checked at 1 month. The time required for complete reepithelialization was recorded. At each visit, patients were asked to compare the discomfort and vision in their eyes. They were also checked for corneal clarity (haze). A paired Student t test was used to compare epithelial healing time, BCVA, and UCVA. A P value of ⬍0.05 was considered significant.
Results The mean patient age was 28.7 years ⫾ 5.9 (SD) (range 20 to 41 years); 14 patients (56%) were women and 11 (44%) men. The mean preoperative spherical equivalent refraction was ⫺3.0 ⫾ 1.9 diopters (D) (range ⫺0.87 to ⫺7.13 D) in the PRK eyes and ⫺3.1 ⫾ 2.0 D (range ⫺0.75 to ⫺7.75 D) in the LASEK eyes. There was no statistically significant difference in the
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LASEK VERSUS PRK
baseline refraction between the eyes assigned to PRK or LASEK (P ⫽ .57). The preoperative BCVA in all patients was 20/30 or better. The epithelial defect was completely healed by the fourth day in the PRK and LASEK eyes. The mean epithelial healing time was 3.3 ⫾ 0.5 days and 3.6 ⫾ 0.5 days, respectively (P ⫽ .07). At 1 day, 18 patients (72%) reported more discomfort in the LASEK eye compared to 6 patients (24%) who complained more about the PRK eye. At 3 days, this difference was higher: 80% complained about the LASEK eye and 4% complained about the PRK eye. At 1 day, patients reported better vision in 4 LASEK eyes (16%) and 20 PRK eyes (80%) and the same vision in 1 eye (4%). At day 3, patients reported better vision in 1 LASEK eye (4%) and 24 PRK eyes (96%). At 1 week, the UCVA was 20/25 or better in 12 PRK eyes and 12 LASEK eyes (48%). At 1 month, the UCVA was 20/25 or better in 19 PRK eyes (76%) and 20 LASEK eyes (80%). At 1 week, 12 eyes (48%) in each group had lost 1 to 2 lines of best spectacle-corrected visual acuity. No eye had lost 1 or more lines of BCVA at the 1-month follow-up examination. At 1 month, neither group showed the development of postoperative haze and there was no difference in the appearance of the ablated cornea in the 2 groups. Figure 1 summarizes the discomfort and visual rehabilitation in the 2 groups. There were no intraoperative or early postoperative complications.
Discussion Laser-assisted subepithelial keratomileusis is a relatively new technique for treating myopia, astigmatism,
and hyperopia. It has recently gained the attention of refractive surgeons and patients as an alternative to PRK since it may cause less postoperative discomfort and haze and results in a shorter visual recovery time and as an alternative to LASIK because there are no flap and microkeratome complications, no interface problems, and more residual tissue for retreatment.8 –11 To our knowledge, we present the first study comparing the results of PRK and LASEK in the same patients on the first days after the surgery. The results do not favor LASEK. In our study, LASEK did not reduce the immediate postoperative discomfort compared to PRK. We believe this is because the remaining epithelial flap does not smooth out promptly and sometimes sloughs, factors that induce pain and discomfort. One variable could have been that the PRK epithelial defect was between 7.0 and 8.0 mm, slightly smaller than the epithelial flap in LASEK (8.0 mm). Nevertheless, we think that if less discomfort is a potential major advantage of LASEK, this should have been the case despite there being less than 1.0 mm of difference in the epithelial ablated area between the 2 groups. At 1 month, there was no difference in the UCVA between the 2 groups. There was no significant difference in the speed of visual rehabilitation because in both procedures the epithelium has to regenerate and reform the outer part of the cornea. Since LASEK competes with LASIK, we were interested in the patients’ subjective perception of vision. At 1 and 3 days, most patients thought they could see better with the PRK eye. These results demonstrate that the immediate results of LASEK compared to PRK are greater discomfort and
Figure 1. (Litwak) Discomfort and visual acuity at various intervals after PRK and LASEK.
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LASEK VERSUS PRK
lower subjective UCVA. At 1 month, the objective UCVA results were similar in the 2 groups. There was no development of postoperative corneal haze at 1 month in either group. In a study with a follow-up of more than 1 year, Shah et al.10 found statistically significant less haze in LASEK eyes than in PRK eyes. We are currently following our cohort of patients to analyze the difference in haze between the 2 groups after a longer follow-up. In a study similar to ours of 27 patients who had PRK in 1 eye and LASIK in the other, Lee et al.11 found a better postoperative course after LASEK. One of the main differences between the studies was the interval between the procedures. In our study, the procedures were performed simultaneously in both eyes; in Lee at al.’s study, there were 2 weeks between the procedures. Another difference was in the time at which patients were asked about pain: immediately postoperatively and after 1 week, respectively. Our experience with PRK indicates that most complaints of discomfort and poor vision occur during the first 72 hours. Therefore, we believe the best time to fairly compare discomfort and vision after surface laser refractive surgery is in the immediate postoperative period. This is especially important in our search for a procedure that is similar in early postoperative rehabilitation to LASIK but less risky. The prospective, paired, comparative, and randomized nature of our study gives the results more strength. Another important point is that an independent, unbiased observer carried out the postoperative follow-up without being told which eye had LASEK and which had PRK. One limitation of the study is that it was possible for the observer to identify the procedure in each eye by examining the epithelium on the first postoperative days. Some surgeons have advocated that exposing the epithelium to 18% alcohol for only 20 seconds is sufficient to create an epithelial flap in LASEK. We performed over 20 LASEK procedures before starting the study and found that it takes longer to loosen the corneal epithelium in Hispanic patients than in white patients; the minimum exposure time was 40 seconds to create a complete epithelial flap. We do not know whether this extra time made the difference in the LASEK eyes compared to reports in which the exposure to the alcohol solution was less than 30 seconds.
In summary, LASEK did not result in faster visual rehabilitation than PRK in eyes with low to moderate myopia. Nevertheless, we found LASEK to be a safe procedure, effective in rehabilitating the vision of patients with myopia when examined at 1 month. Patients should be informed that LASEK may not result in the same speed of recovery as LASIK and that it may be similar to PRK as it is classified as surface laser refractive surgery.
References 1. Ang RT, Dartt DA, Tsubota K. Dry eye after refractive surgery. Curr Opin Ophthalmol 2001; 12:318 –322 2. El Danasoury MA. Prospective bilateral study of night glare after laser in situ keratomileusis with single zone and transition zone ablation. J Refract Surg 1998; 14:512– 516 3. Amoils SP, Deist MB, Gous P, Amoils PM. Iatrogenic keratectasia after laser in situ keratomileusis for less than ⫺4.0 to ⫺7.0 diopters of myopia. J Cataract Refract Surg 2000; 26:967–977 4. Seiler T, Quurke AW. Iatrogenic keratectasia after LASIK in a case of forme fruste keratoconus. J Cataract Refract Surg 1988; 24:1007–1009 5. Tervo TM. Iatrogenic keratectasia after laser in situ keratomileusis. (letter and reply by SP Amoils) J Cataract Refract Surg 2001; 27:490 –491 6. Stephenson CG, Gartry DS, O’Brart DPS, et al. Photorefractive keratectomy; a 6-year follow-up study. Ophthalmology 1998; 105:273–281 7. Montes M, Chayet A, Go´ mez L, et al. Laser in situ keratomileusis for myopia of ⫺1.50 to ⫺6.00 diopters. J Refract Surg 1999; 15:106 –110 8. Kornilovsky IM. Clinical results after subepithelial photorefractive keratectomy (LASEK). J Refract Surg 2001; 17:S222–S223 9. Scerrati E. Laser in situ keratomileusis vs laser epithelial keratomileusis (LASIK vs LASEK). J Refract Surg 2001; 17:S219 –S221 10. Shah S, Sebai Sarhan AR, Doyle SJ, et al. The epithelial flap for photorefractive keratectomy. Br J Ophthalmol 2001; 85:393–396 11. Lee JB, Seong GJ, Lee JH, et al. Comparison of laser epithelial keratomileusis and photorefractive keratectomy for low to moderate myopia. J Cataract Refract Surg 2001; 27:565–570 From CODET Aris Vision Institute, Tijuana, Mexico (Litwak, Garcia-da Quevedo, Robledo, Chayet) and the Department of Ophthalmology, Asaf A. Roffe Hospital, Tel Aviv, Israel (Zadok) None of the authors has a financial interest in any product mentioned.
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Purpose: To compare the early postoperative visual rehabilitation after laser-assisted subepithelial keratectomy (LASEK) and photorefractive keratectomy (PRK) for the correction of myopia. Setting: CODET Aris Vision Institute, Tijuana, Mexico. Methods: This prospective study included 50 eyes of 25 patients with myopia who received LASEK in 1 eye and PRK in the contralateral eye. Excimer laser corneal ablation was done using the Nidek EC-5000 excimer laser. Patients were seen at 1 and 3 days, 1 week, and 1 month. Discomfort, subjective uncorrected visual acuity (UCVA), objective UCVA, best corrected visual acuity (BCVA), corneal clarity (haze), and time for corneal reepithelialization were analyzed. Results: Seventy-two percent and 80% of the LASEK eyes had more discomfort at 1 day and 3 days, respectively. Eighty percent and 96% of the PRK eyes had better subjective UCVA at 1 day and 3 days, respectively. Corneas were fully reepithelialized at a mean of 3.3 days ⫾ 0.5 (SD) and 3.6 ⫾ 0.5 days in the PRK and LASEK groups, respectively. At 1 month, the UCVA was similar in both groups; no eye had lost lines of BCVA or developed haze. Conclusions: Both LASEK and PRK were effective and safe procedures in the surgical correction of myopia at the 1-month postoperative visit. Patients reported less discomfort and better visual acuity in their PRK eye during the early postoperative period. Patients should be informed that LASEK, whose acronym is similar to that of laser in situ keratomileusis, has a recovery speed that is similar to that of surface laser refractive procedures such as PRK. J Cataract Refract Surg 2002; 28:1330 –1333 © 2002 ASCRS and ESCRS
A
lthough laser in situ keratomileusis (LASIK) is used worldwide for the correction of most refractive errors, it has some disadvantages, such as dry eye, night
Accepted for publication March 15, 2002. Reprint requests to Arturo S. Chayet, CODET Aris Vision Institute, Padre Kino 10159, Tijuana, BC 22320, Mexico. E-mail: arturo. [email protected]. © 2002 ASCRS and ESCRS Published by Elsevier Science Inc.
halos, and keratectasia.1–5 Potential mechanisms for keratectasia are a reduction in biomechanical corneal strength resulting from the creation of the lamellar flap, preoperative asymmetric astigmatism as an early sign of keratoconus, and leaving a corneal bed of less than 250 m after creating the flap and ablating the cornea. To our knowledge, keratectasia has not been reported following photorefractive keratectomy (PRK). A 0886-3350/02/$–see front matter PII S0886-3350(02)01376-7
LASEK VERSUS PRK
possible explanation is that as no lamellar cut is made during PRK, the biomechanical strength of the cornea is not affected. Since its introduction in the late 1980s, PRK has had good safety and efficacy results.6 Nevertheless, LASIK rapidly became the preferred method of patients and surgeons because it provided more rapid visual rehabilitation and less discomfort than PRK.7 Recently, Massimo Camellin, MD, introduced a procedure that he named LASEK, laser-assisted subepithelial keratectomy (M. Cimberle, “LASEK May Offer the Advantages of Both LASIK and PRK,” Ocular Surgery News, March 1999, page 28). The procedure consists of creating an epithelial flap, ablating the stroma to correct the refractive error, and then repositioning the epithelial flap. The suggested advantages of LASEK over PRK are the potential for less postoperative discomfort along with faster visual rehabilitation and less haze. In addition, since no lamellar flap is created, LASEK may retain the biomechanical stability shown with PRK and therefore be an alternative to LASIK in cases in which the corneal thickness might be reduced. In this study, we looked prospectively at the early postoperative results of LASEK and PRK and analyzed the potential advantage of LASEK as an alternative procedure for the correction of refractive errors.
Patients and Methods Fifty eyes of 25 patients with myopia received simultaneous bilateral surface laser refractive surgery by the same surgeon (A.C.). One eye of each patient was randomly chosen to have PRK, and the fellow eye had LASEK. Patients were told that each eye would have different surface laser refractive surgery but did not know which eye had LASEK and which had PRK. Written informed consent was obtained from the patients. The preoperative ophthalmic examination included manifest and cycloplegic refractions, corneal keratometry and topography, slitlamp biomicroscopy, fundus examination, and tonometry. Patients with diabetes mellitus, connective tissue disease, corneal disease, glaucoma, and retinal disease were excluded from the study.
Photorefractive Keratectomy Procedure Topical tetracaine hydrochloride 0.5 % drops were used to anesthetize the eye. Deepithelialization was performed using a #64 Beaver blade (Beckton-Dickinson) after the epithelium was marked with a 7.0 mm trephine centered over the pupil. This was followed by stromal ablation using the Nidek EC-5000 excimer laser. The ablated stroma was immediately
irrigated with chilled balanced salt solution (BSS威), and topical gentamicin was instilled over the cornea. A soft contact lens (Focus威, Ciba Vision) was placed on the cornea at the end of the procedure.
Laser-Assisted Subepithelial Keratectomy Procedure Topical tetracaine hydrochloride 0.5 % drops were used to anesthetize the eye. A preincision of the corneal epithelium was made using an 8.0 mm trephine with a 55 m blade (Janek); 80 degrees of uncut margin were left at the 12 o’clock position for the hinge. Two to 3 drops of an 18% alcohol solution (diluted with sterile distilled water) were placed on the cornea within an 8.5 mm solution cone (Janek) and left in place for 40 seconds. The area was irrigated with BSS. The epithelial flap was gently detached, gathered, and folded up at the 12 o’clock position. Following traditional PRK treatment, the ablated stroma was immediately irrigated with chilled BSS. The epithelial flap was then rolled to its original position using an irrigating 27-gauge cannula, and topical gentamicin was instilled over the cornea. A Focus lens was placed on the cornea at the end of the procedure. Postoperatively, patients were instructed to apply the same medications to both eyes: ofloxacin 0.3% (Ocuflox威) 1 drop 4 times daily and diclofenac (Voltaren威) and fluorometholone acetate 0.1% (Flarex威) 1 drop 2 times daily until the epithelium healed. After corneal reepithelialization was complete, Flarex was administered 4 times daily for 1 month. Patients were examined at 1 and 3 days, 1 week, and 1 month by an independent refractive surgeon who was not informed of the procedure in each eye (although he might have been able to recognize it from the epithelium). In cases in which the cornea was not fully reepithelialized on the third day, patients were asked to come back to the clinic daily until reepithelialization was complete. At each examination, uncorrected visual acuity (UCVA), best corrected visual acuity (BCVA), and slitlamp biomicroscopy were checked. Manifest refraction was checked at 1 month. The time required for complete reepithelialization was recorded. At each visit, patients were asked to compare the discomfort and vision in their eyes. They were also checked for corneal clarity (haze). A paired Student t test was used to compare epithelial healing time, BCVA, and UCVA. A P value of ⬍0.05 was considered significant.
Results The mean patient age was 28.7 years ⫾ 5.9 (SD) (range 20 to 41 years); 14 patients (56%) were women and 11 (44%) men. The mean preoperative spherical equivalent refraction was ⫺3.0 ⫾ 1.9 diopters (D) (range ⫺0.87 to ⫺7.13 D) in the PRK eyes and ⫺3.1 ⫾ 2.0 D (range ⫺0.75 to ⫺7.75 D) in the LASEK eyes. There was no statistically significant difference in the
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LASEK VERSUS PRK
baseline refraction between the eyes assigned to PRK or LASEK (P ⫽ .57). The preoperative BCVA in all patients was 20/30 or better. The epithelial defect was completely healed by the fourth day in the PRK and LASEK eyes. The mean epithelial healing time was 3.3 ⫾ 0.5 days and 3.6 ⫾ 0.5 days, respectively (P ⫽ .07). At 1 day, 18 patients (72%) reported more discomfort in the LASEK eye compared to 6 patients (24%) who complained more about the PRK eye. At 3 days, this difference was higher: 80% complained about the LASEK eye and 4% complained about the PRK eye. At 1 day, patients reported better vision in 4 LASEK eyes (16%) and 20 PRK eyes (80%) and the same vision in 1 eye (4%). At day 3, patients reported better vision in 1 LASEK eye (4%) and 24 PRK eyes (96%). At 1 week, the UCVA was 20/25 or better in 12 PRK eyes and 12 LASEK eyes (48%). At 1 month, the UCVA was 20/25 or better in 19 PRK eyes (76%) and 20 LASEK eyes (80%). At 1 week, 12 eyes (48%) in each group had lost 1 to 2 lines of best spectacle-corrected visual acuity. No eye had lost 1 or more lines of BCVA at the 1-month follow-up examination. At 1 month, neither group showed the development of postoperative haze and there was no difference in the appearance of the ablated cornea in the 2 groups. Figure 1 summarizes the discomfort and visual rehabilitation in the 2 groups. There were no intraoperative or early postoperative complications.
Discussion Laser-assisted subepithelial keratomileusis is a relatively new technique for treating myopia, astigmatism,
and hyperopia. It has recently gained the attention of refractive surgeons and patients as an alternative to PRK since it may cause less postoperative discomfort and haze and results in a shorter visual recovery time and as an alternative to LASIK because there are no flap and microkeratome complications, no interface problems, and more residual tissue for retreatment.8 –11 To our knowledge, we present the first study comparing the results of PRK and LASEK in the same patients on the first days after the surgery. The results do not favor LASEK. In our study, LASEK did not reduce the immediate postoperative discomfort compared to PRK. We believe this is because the remaining epithelial flap does not smooth out promptly and sometimes sloughs, factors that induce pain and discomfort. One variable could have been that the PRK epithelial defect was between 7.0 and 8.0 mm, slightly smaller than the epithelial flap in LASEK (8.0 mm). Nevertheless, we think that if less discomfort is a potential major advantage of LASEK, this should have been the case despite there being less than 1.0 mm of difference in the epithelial ablated area between the 2 groups. At 1 month, there was no difference in the UCVA between the 2 groups. There was no significant difference in the speed of visual rehabilitation because in both procedures the epithelium has to regenerate and reform the outer part of the cornea. Since LASEK competes with LASIK, we were interested in the patients’ subjective perception of vision. At 1 and 3 days, most patients thought they could see better with the PRK eye. These results demonstrate that the immediate results of LASEK compared to PRK are greater discomfort and
Figure 1. (Litwak) Discomfort and visual acuity at various intervals after PRK and LASEK.
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LASEK VERSUS PRK
lower subjective UCVA. At 1 month, the objective UCVA results were similar in the 2 groups. There was no development of postoperative corneal haze at 1 month in either group. In a study with a follow-up of more than 1 year, Shah et al.10 found statistically significant less haze in LASEK eyes than in PRK eyes. We are currently following our cohort of patients to analyze the difference in haze between the 2 groups after a longer follow-up. In a study similar to ours of 27 patients who had PRK in 1 eye and LASIK in the other, Lee et al.11 found a better postoperative course after LASEK. One of the main differences between the studies was the interval between the procedures. In our study, the procedures were performed simultaneously in both eyes; in Lee at al.’s study, there were 2 weeks between the procedures. Another difference was in the time at which patients were asked about pain: immediately postoperatively and after 1 week, respectively. Our experience with PRK indicates that most complaints of discomfort and poor vision occur during the first 72 hours. Therefore, we believe the best time to fairly compare discomfort and vision after surface laser refractive surgery is in the immediate postoperative period. This is especially important in our search for a procedure that is similar in early postoperative rehabilitation to LASIK but less risky. The prospective, paired, comparative, and randomized nature of our study gives the results more strength. Another important point is that an independent, unbiased observer carried out the postoperative follow-up without being told which eye had LASEK and which had PRK. One limitation of the study is that it was possible for the observer to identify the procedure in each eye by examining the epithelium on the first postoperative days. Some surgeons have advocated that exposing the epithelium to 18% alcohol for only 20 seconds is sufficient to create an epithelial flap in LASEK. We performed over 20 LASEK procedures before starting the study and found that it takes longer to loosen the corneal epithelium in Hispanic patients than in white patients; the minimum exposure time was 40 seconds to create a complete epithelial flap. We do not know whether this extra time made the difference in the LASEK eyes compared to reports in which the exposure to the alcohol solution was less than 30 seconds.
In summary, LASEK did not result in faster visual rehabilitation than PRK in eyes with low to moderate myopia. Nevertheless, we found LASEK to be a safe procedure, effective in rehabilitating the vision of patients with myopia when examined at 1 month. Patients should be informed that LASEK may not result in the same speed of recovery as LASIK and that it may be similar to PRK as it is classified as surface laser refractive surgery.
References 1. Ang RT, Dartt DA, Tsubota K. Dry eye after refractive surgery. Curr Opin Ophthalmol 2001; 12:318 –322 2. El Danasoury MA. Prospective bilateral study of night glare after laser in situ keratomileusis with single zone and transition zone ablation. J Refract Surg 1998; 14:512– 516 3. Amoils SP, Deist MB, Gous P, Amoils PM. Iatrogenic keratectasia after laser in situ keratomileusis for less than ⫺4.0 to ⫺7.0 diopters of myopia. J Cataract Refract Surg 2000; 26:967–977 4. Seiler T, Quurke AW. Iatrogenic keratectasia after LASIK in a case of forme fruste keratoconus. J Cataract Refract Surg 1988; 24:1007–1009 5. Tervo TM. Iatrogenic keratectasia after laser in situ keratomileusis. (letter and reply by SP Amoils) J Cataract Refract Surg 2001; 27:490 –491 6. Stephenson CG, Gartry DS, O’Brart DPS, et al. Photorefractive keratectomy; a 6-year follow-up study. Ophthalmology 1998; 105:273–281 7. Montes M, Chayet A, Go´ mez L, et al. Laser in situ keratomileusis for myopia of ⫺1.50 to ⫺6.00 diopters. J Refract Surg 1999; 15:106 –110 8. Kornilovsky IM. Clinical results after subepithelial photorefractive keratectomy (LASEK). J Refract Surg 2001; 17:S222–S223 9. Scerrati E. Laser in situ keratomileusis vs laser epithelial keratomileusis (LASIK vs LASEK). J Refract Surg 2001; 17:S219 –S221 10. Shah S, Sebai Sarhan AR, Doyle SJ, et al. The epithelial flap for photorefractive keratectomy. Br J Ophthalmol 2001; 85:393–396 11. Lee JB, Seong GJ, Lee JH, et al. Comparison of laser epithelial keratomileusis and photorefractive keratectomy for low to moderate myopia. J Cataract Refract Surg 2001; 27:565–570 From CODET Aris Vision Institute, Tijuana, Mexico (Litwak, Garcia-da Quevedo, Robledo, Chayet) and the Department of Ophthalmology, Asaf A. Roffe Hospital, Tel Aviv, Israel (Zadok) None of the authors has a financial interest in any product mentioned.
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