A comparative study of post-operative pain in laser epithelial keratomileusis versus photorefractive keratectomy

T.A. Saleh M.A. Almasri
Optimax Laser Clinic, London

Correspondence to: T.A. Saleh, Eye Department, Taunton and Somerset Hospital, Musgrove Park, Taunton, TA1 5DA, U.K. 
Email: tareksaleh@doctors.org.uk

Introduction Patients and Methods  LASEK PRK

Results Discussion References

Keywords: LASEK, laser epithelial keratomileusis, PRK, photorefractive keratectomy, post-operative pain
Surg J R Coll Surg Edinb Irel., 1 August 2003, 229-232

Background: To compare the level of post-operative pain associated with two methods of excimer laser corneal refractive surgery: PRK (photorefractive keratectomy) versus LASEK (laser epithelial keratomileusis). Methods: 14 patients undergoing simultaneous bilateral myopic PRK were included in the study. The first eye of each patient was randomly allocated for treatment by either LASEK or PRK with alcohol-assisted epithelial debridement and second eyes were treated with the other technique. Laser corneal ablation was performed with Nidek EC-5000 excimer laser by one surgeon (MAA) using the same algorithm. Post-operatively, all patients had declofenac sodium 0.1% eye drops four times a day, lorazepam 2mg at night and two solpadol (paracetamol 500mg and codeine phosphate 30mg) tablets every six hours orally for two days. Chloramphenicol 0.5% drops four times a day were also administered for seven days. The level of pain in each eye was assessed 2, 12, 24 and 48 hours following laser surgery using a descriptive pain score from 0 to 10. Statistical analysis was performed using paired t test. Results: The mean pain score at two hours post-operatively was 3.5± 2.24(SD) in the LASEK group and 5.7 ±2.02(SD) in the PRK group. This difference is statistically significant. At 12 hours it was 4.33 ±2.53 (SD) and 4.75 ±2.30 (SD), at 24 hours it was 3.71 ±2.84 (SD) and 4.00 ±2.48 (SD), and at 48 hours it was 2.86 ±3.43 (SD) and 2.21 ±2.55 (SD). There was no statistically significant difference in the pain score at these intervals. Conclusions: Post-operative pain was less in eyes treated with LASEK than eyes treated with PRK 2 hours following laser surgery. This was statistically significant and there was no statistically significant difference at 12, 24 and 48 hours

INTRODUCTION
LASEK (laser epithelial keratomileusis), was first introduced by Massimo Camellin, (1999) “LASEK may offer the advantages of both LASIK and PRK,” Ocular Surgery News, International Edition, March 1999).¹ Subsequently, other authors confirmed the benefits of LASEK.^2,3 In this technique the corneal epithelium is loosened by ethanol 20% and a circular flap of the epithelium is folded back during excimer laser corneal ablation and then repositioned on the ablated stromal bed once the ablation is completed.

Some studies showed that there is faster visual recovery and less postoperative haze, regression and pain with the LASEK in comparison with PRK.^2-4

PATIENTS AND METHODS
Fourteen patients undergoing bilateral simultaneous myopic PRK were recruited for the study after obtaining written informed consent.

Inclusion criteria for the study were an age of over 20 years, absence of collagen disease, diabetes, pregnancy, previous ocular surgery or ocular surface disease, and refractive errors of less than -3.00D sphere and less than -1.00D of astigmatism.

The first eye (the non-dominant eye) was allocated for treatment by either LASEK or PRK. The technique used for the first eye was read from a sealed envelope prepared by the laser assistant. The second eye was treated by the alternative technique.

All procedures were performed by one surgeon (MAA) using the same algorithm with the Nidek EC-5000 excimer laser (Nidek Co Ltd, Aichi, Japan). The Excimer laser was applied with 6.5mm ablation zone and 1mm transitional zone.

All patients had two days courses of diclofenac sodium 0.1% drops four times a day, two solpadol (paracetamol 500mg and codeine phosphate 30mg) tablets every six hours and lorazepam 2mg at night. Chloramphenicol 0.5% drops four times a day were also administered for seven days following laser surgery.

LASEK (Laser Epithelial Keratomileusis) Technique
A speculum was applied to the patient’s eye and two drops of proxymetacaine hydrochloride 0.5% were instilled. A 9mm ring marker filled with ethanol 18% was applied on the cornea for 40  seconds. The ethanol was absorbed with a merocel sponge and the cornea was washed with diclofenac sodium 0.1% and proxymetacaine hydrochloride 0.5% drops. The epithelial flap was fashioned with a superior hinge using a SM64 blade and was then rolled over to the 12 o’clock position and the excimer laser applied to the corneal bed. Following stromal ablation, the epithelial flap was repositioned with a Rycroft cannula and was left to adhere to the underlying stromal bed for one minute. Chloramphenicol 0.5% drops and diclofenac sodium 0.1% drops were applied and the eye was covered with a clear shield.

Figure 1: Comparison of mean pain score in LASEK versus PRK with error bars showing the standard deviations (SDs) from the mean

PRK (Photorefractive Keratectomy) technique
A speculum was applied to the patient’s eye and two drops of proxymetacaine hydrochloride 0.5% were instilled. A 9mm ring marker filled with ethanol 18% was applied on the cornea for 40 seconds. The ethanol was absorbed with a merocel sponge and the cornea was washed with topical diclofenac sodium 0.1% drops and proxymetacaine hydrochloride 0.5%. The epithelium was peeled off the corneal surface using a dry merocel sponge and the excimer laser applied to the corneal bed. Chloramphenicol 0.5% drops and diclofenac sodium 0.1% drops were applied and a clear shield was used. Patients were asked to cover both eyes for four hours when they reached home, and then to start applying the medication.

Each patient was given a questionnaire to rate the level of pain in each eye. In this questionnaire patients were asked to prospectively record in a printed table their rating of the pain level for each eye at 2, 12, 24, and 48 hours following laser surgery on a scale of 0 (minimal) to 10 (maximal). Written instructions for patients were to record 0 if there was no pain or discomfort and 10 for the most severe pain. Patients sent their filled in questionnaire by mail. Data were analysed in a masked fashion and paired t test was used for statistical analysis.

RESULTS
Fourteen subjects (28 eyes) were included in the study with a mean age of 32 years and range from 22 to 43. There were six males and eight females and all patients were Caucasians. The mean pre-operative refractive error was -2.15D SE (spherical equivalent) range from -1.125D to -3.375D SE. The mean preoperative spherical equivalent of eyes treated with LASEK was -2.267D and eyes treated with PRK was -2.035D. The pain score results are shown in Table 1.

The mean pain score at two hours post-operatively was 3.5 ±2.24(SD) in the LASEK group and 5.7 ±2.02(SD) in the PRK group and this was statistically significant (P=0.003 paired t test).

The mean pain score at 12 hours was 4.33 ±2.53 (SD) and 4.75 ±2.30 (SD), at 24 hours it was 3.71 ±2.84 (SD) and 4.00 ±2.48 (SD), and at 48 hours it was 2.86 ±3.43 (SD) and 2.21 ±2.55 (SD). There was no statistically significant difference in the pain score at these points. The differences of the mean pain score at 2, 12, 24 and 48 hours following laser surgery are shown in Figure 1.

DISCUSSION
LASEK is rapidly gaining popularity because it combines the advantages of PRK and LASIK (laser in situ keratomileusis). In contrast to PRK, it is associated with faster visual recovery,^2-4 LASEK can be an alternative to LASIK in some myopic patients who have thin corneas, or in patients with a lifestyle or profession that predisposes them to trauma.⁴

Post-operative pain is one of the important disadvantages of PRK. Previous studies have shown that pain usually peaks within the first 24 hours^5,6 and then declines gradually to none by 72 hours.5 Pain following PRK may be due to the induced corneal epithelial defect, which exposes the sensitive nerve endings in the cornea. It may also be due to the release of chemical mediators such as prostaglandin, histamine and substance P by corneal tissue damaged by the physical effects of excimer laser.⁷ It has been suggested that a viable epithelial flap may act as a biological therapeutic contact lens that protects the stroma from lid action.³

In the Camellin series of 249 patients who underwent LASEK, 44.4% had no pain, 41.8% reported discomfort and 13.7% reported pain.⁸ Azar et al (2001) treated 20 patients with LASEK and reported post-operative pain in 53% on day 1 and in 18% on day three.4 In another series of 12 eyes treated with LASEK, Kornilovsky (2001) reported no pain in 50%, discomfort in 33.3% and pain in 16.7%.9 Furthermore, Lee et al (2001) measured post-operative pain using a 4-point scale in a comparative paired eye study of 27 patients. Pain scores were 2.36 ±0.63 in eyes that underwent PRK and 1.63 ±0.81 in eyes that underwent LASEK, and the difference is statistically significant. In the above four series, pain levels were measured at one point in time only and soft contact lenses were used post-operatively. To obtain a more accurate representation of the pain levels we chose to measure them at several time intervals. In our study we also avoided using bandage contact lenses post-operatively as their pain reducing effect could confound the results by decreasing the pain in the LASEK group.¹⁰ Therefore, the only difference between the groups in the study was the epithelial flap in the LASEK eyes.

Our results showed that there was less pain in the LASEK group two hours after surgery (P=0.003). Pain scores also appeared to be less at 12 and 24 hours but the difference did not reach statistical significance. Conversely, pain was slightly more in the LASEK group at 48 hours following laser surgery but this was not statistically significant.

The pain score showed wide inter-subject variations as shown in Figure 1. This is possibly due to the variability of pain threshold among individuals and the potential recall bias that may occur if patients fill in their questionnaire two days after surgery and not at the time points they were instructed to. However, these factors apply equally to the LASEK and PRK groups.

We have, therefore, shown that the pain reducing effect of the epithelial flap is maximal in the early hours following surgery and then this effect disappears gradually.

In conclusion, post-operative pain was less in eyes treated with LASEK than eyes treated with PRK at two could confound the results by decreasing the pain in the following laser surgery. There was no statistically significant difference at 12, 24 and 48 hours.

REFERENCES
1. Camellin M. LASEK may offer the advantages of both LASIK and PRK Ocular Surgery News, International Edition. 1999.
2. Shah S, Sebai Sarhan AR, Doyle SJ, Pillai CT, Dua HS. The epithelial flap for photorefractive keratectomy. Br J Ophthalmol 2001; 85(4):393-396.
3. Lee JB, Seong GJ, Lee JH, Seo KY, Lee YG, Kim EK. Comparison of laser epithelial keratomileusis and photorefractive keratectomy for low to moderate myopia. J Cataract Refract Surg. 2001; 27(4): 565-570.
4. Azar DT, Ang RT, Lee JB, Kato T, Chen CC, Jain S, Gabison E, Abad JC. Laser subepithelial keratomileusis: electron microscopy and visual outcomes of flap photorefractive keratectomy. Curr Opin Ophthalmol. 2001; 12 (4): 323-328. Review
5. Verma S, Corbett MC, Patmore A, Heacock G, Marshall J. A comparative study of the duration and efficacy of tetracaine 1% and bupivacaine 0.75% in controlling pain following photorefractive keratectomy (PRK). Eur J Ophthalmol. 1997; 7(4):327-333.
6. McCarty CA, Garrett SK, Aldred GF, Taylor HR. Assessment of subjective pain following photorefractive keratectomy. Melbourne Excimer Laser Group. J Refract Surg. 1996; 12(3): 365-369.
7. Tutton MK, Cherry PM, Raj PS, Fsadni MG. Efficacy and safety of topical diclofenac in reducing ocular pain after excimer photorefractive keratectomy. J Cataract Refract Surg. 1996; 22(5):536-541.
8. Camellin M. LASEK has more than 1 year of successful experience Ocular Surgery News, International Edition, 2000.
9. Kornilovsky IM. Clinical results after subepithelial photorefractive keratectomy (LASEK). J Refract Surg. 2001; 17(2 Suppl): S222-223.
10. Lim-Bon-Siong R, Valluri S, Gordon MF, Pepose JS. Efficacyand safety of the ProTek (Vifilcon A) therapeutic soft contact lens after photorefractive keratectomy. Am J Ophthalmol. 1998; 126(2): 328-9.

Copyright: 23 June 2003

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