Clinical results of excimer laser photorefractive keratectomy: a multicenter study of 265 eyes

Comparison of the efficacy and safety of removing bandage contact lenses on the fourth and seventh postoperative day after transepithelial photorefractive keratectomy

Purpose

To compare the differences in the removal of bandage contact lenses (BCLs) at 4 and 7 days after transepithelial photorefractive keratectomy (TransPRK) in term of visual rehabilitation, eye discomfort, and postoperative complications.

Methods

This retrospective cohort study included patients with myopia undergoing TransPRK; in Group 1, the BCLs were removed on the 4th postoperative day, while in Group 2, the BCLs were removed on the 7th postoperative day. All patients underwent a 6-month follow-up, including slit-lamp examination and visual acuity assessment. Subjective evaluations of pain and eye discomfort were recorded after the BCLs removal.

Results

In total, 376 eyes of 191 patients in Group 1 and 346 eyes of 177 patients in Group 2 were enrolled. The two groups were matched for sex, age, preoperative corrected distance visual acuity, and tear film break-up time. Patients in Group 1 exhibited slightly lower levels of myopia, resulting in a shallower ablation depth and shorter ablation time than those in Group 2. No statistically significant differences in visual acuity recovery, haze severity, and incidence of infectious keratitis were observed within 6 months after surgery between the two groups. However, patients in Group 2 experienced significantly fewer discomfort symptoms (discharge, foreign body sensation, and blurred vision) after BCLs removal than patients in Group 1 and had fewer postoperative complications (recurrent corneal epithelial erosion).

Conclusion

Delayed removal of the BCLs one week after TransPRK effectively alleviated early discomfort symptoms and reduced the risk of recurrent corneal epithelial erosion without increasing the likelihood of infectious keratitis.

Single-Step Transepithelial Photorefractive Keratectomy in Low to Moderate Myopia: A One-Year Follow-Up Study

Aim

To evaluate predictability, safety, efficacy, and visual outcome of StreamLight. ™ (SL.), the newly released single-step transepithelial photorefractive keratectomy platform by Alcon WaveLight™ (WL).

Methods

In this prospective cohort study, photorefractive keratectomy (PRK) was conducted on 500 eyes of 250 patients seeking myopic refractive vision correction. The new single-step transepithelial PRK method was applied, using the SL. platform installed in the WL. Ex 500 excimer laser machine. Patients were followed up to monitor intensity and duration of postoperative pain, as well as speed of epithelial healing in the early post-operative period and visual acuity, postoperative refraction and development of postoperative haze for one year post-operatively.

Results

Average pain duration was 1.5 days, and the mean pain intensity score on a scale of 0–10 was 3.74 + 1.51. Mean postoperative spherical equivalence was 0.01 ± 0.38 D, and the final postoperative uncorrected distance visual acuity (UCDVA) was 20/20 in 98% of eyes included in this study. None of the eyes lost more than one Snellen chart line or developed visually significant postoperative haze during the follow-up period.

Conclusion

The new SL. platform for transepithelial PRK is a safe, accurate platform, offering an easier early post-operative recovery, with no compromise in final visual outcome.

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Transepithelial photorefractive keratectomy on the same day of the initial consultation for the correction of myopia

PURPOSE

To examine the clinical outcomes, efficacy, safety, and predictability of transepithelial photorefractive keratectomy (Trans-PRK) operations performed on the day of the first screening visit in comparison with operations scheduled at a following appointment.

METHODS

Data of consecutive patients with myopia of various degrees, who underwent Trans-PRK, were retrospectively analyzed. Findings were compared between patients who underwent Trans-PRK on the same day of first consultation to patients that underwent surgery at subsequent visits, following initial consultation on a different day.

RESULTS

The study included 599 eyes treated on the initial visit day and 1936 eyes treated on a subsequent visit. Mean final spherical equivalent was close to emmetropia in both groups (p = 0.183). Efficacy indices were 0.928 ± 0.192 in the initial-visit group and 0.945 ± 0.163 in the second-visit group (p = 0.152). Safety indices were 0.954 ± 0.156 and 0.955 ± 0.151 (p = 0.707), respectively. No differences between the groups were seen in uncorrected visual acuity (UDVA) of ⩾20/20, ⩾20/25, and ⩾20/32. Only the sub-analysis of patients reaching UDVA of 20/40 or better was slightly lower in the first-visit (95.5%) compared with the second-visit group (97.9%, p = 0.001). Results of attempted correction within ±0.50 D were: 63.3% and 69.0%, respectively (p = 0.009). Complications profiles in the two groups were comparable.

CONCLUSIONS

Trans-PRK completed on the day of the first screening appointment demonstrated a similar safety outcome compared with subsequent-visits procedures, and slightly lower, yet comparable, results regarding efficacy and predictability.

Efficacy and safety of transepithelial photorefractive keratectomy

Transepithelial photorefractive keratectomy (PRK) was introduced to prevent complications from conventional PRK and femtosecond laser-assisted laser in situ keratomileusis (LASIK). In the 2-step platform, phototherapeutic keratectomy is followed by PRK. It did not show notable safety or efficacy superiorities over conventional PRK. In the conventional single-step transepithelial PRK, ablation of epithelium and stroma occurs in a single continuous session by an Amaris laser. It showed better comparative safety results. Reverse single-step transepithelial PRK and the platform using smart-pulse technology were recent improvements in the single-step Amaris laser. They provide a smoother postablative stromal bed counter. In the refined single-step platform, a modified nomogram is used for determination of ablation parameters, along with modifications in postablative measures. It yielded better comparative results in hyperopia. Controlled trials comparing reverse, smart-pulse technology-equipped, or refined platforms of single-step transepithelial PRK with other modern laser-assisted methods could provide more robust evidence on the topic. Some key elements with significant roles in post-transepithelial PRK outcomes are discussed.

Evaluation of the Long-Term Effects of Photorefractive Keratectomy Correction for Myopia in China

Purpose

To evaluate the long-term effects of photorefractive keratectomy (PRK) correction for myopia in China.

Methods

A comprehensive literature research was conducted in 2 Chinese databases and PubMed. Statistical analysis was performed using the RevMan 4.2 software.

Results

Seven prospective studies involving 2,796 eyes were included. The follow-up period was 5 to 11 years. Meta-analysis showed efficacies in low to moderate myopia that surpassed those in high myopia, and pooled odds ratios were 9.14 (95% confidence interval [CI] 4.37–19.11) in the proportion of eyes with uncorrected visual acuity (UCVA) ≥20/20 and 5.61 (95% CI 3.97–7.93) in the proportion of eyes with UCVA ≥20/40. More than 10 years post operation, 82.0% had 20/20 or better UCVA and 96.1% had 20/40 or better in the ≤-6.00 D myopia group. Among patients with >-6.00 D myopia, 31.7% had 20/20 or better UCVA and 80.4% had 20/40 or better. Moreover, 82.1% and 46.4% of the treated eyes were within ±1.0 D of target refraction in the low to moderate myopia and high myopia group, respectively. About 1.4%-3.5% of eyes lost ≥2 lines of best spectacle-corrected visual acuity, and 0.6%-4.1% of eyes had grade 1 corneal haze.

Conclusions

Photorefractive keratectomy for myopia is an effective and safe procedure for the long term in China. The efficacy and predictability of PRK in low to moderate myopia are better than in high myopia.

Haze development after photorefractive keratectomy: mechanical vs ethanol epithelial removal in rabbits

PURPOSE

To compare mechanical and ethanol epithelial removal with respect to myofibroblast development and haze formation after photorefractive keratectomy (PRK).

METHODS

Seventeen rabbits underwent mechanical or ethanol debridement, and the opposite eye of each rabbit served as an unwounded control. In both groups, the epithelium was removed with a spatula and discarded. A -9.00-diopter PRK was performed in each eye. The level of haze in each cornea at 4 weeks was graded at the slit-lamp microscope according to the Fantes scale. Myofibroblast generation was detected with immunocytochemistry for alpha-smooth muscle actin (alpha-SMA) and cells were quantitatively analyzed.

RESULTS

No difference was noted between the two groups in alpha-SMA + myofibroblasts 4 weeks after surgery (43.6+/-2.0/400x field and 45.7+/-4.8/400x field in ethanol and mechanical groups, respectively) (P=.10). A slight difference was noted but did not reach statistical significance with regard to stromal haze between ethanol and mechanical groups (2.0+/-0.5 and 2.3+/-0.4, respectively, P=.063). The ethanol and mechanical groups were statistically different when compared to controls regarding stromal haze and alpha-SMA+ cells (P<.0001for all comparisons).

CONCLUSIONS

No difference was noted in clinical haze or myofibroblast generation between corneas that had PRK with mechanical or ethanol epithelial debridement.

Ethanol Treatment Induces Significant Cell Death in Porcine Corneal Fibroblasts

PURPOSE

To explore the effect of ethanol treatment on corneal stromal cells.

METHODS

Primary porcine corneal fibroblasts from passages 3 to 5 were treated with ethanol at concentrations of 10%, 15%, 20%, and 50% for 30 seconds. A control group was treated with phosphate-buffered saline (PBS) for 30 seconds. Morphologic changes were documented with phase-contrast microscopy, and the growth curves were examined with a PicoGreen assay. Cellular viability was examined with an ethidium homodimer and calcein-AM stain, whereas cellular apoptosis and/or necrosis were analyzed by a YO-PRO-1 dye/propidium iodide apoptosis assay coupled with flow cytometry and further confirmed with a genomic DNA pattern assay. Cellular toxicity was examined with a lactate dehydrogenase (LDH) assay.

RESULTS

Significant cell rounding and detachment from the culture dish were noticed after 20% ethanol treatment of 30 seconds, despite that the cell morphology remained unchanged in the PBS and 10% and 15% ethanol groups. Twenty percent ethanol induced significant cellular toxicity, causing cell death as shown by ethidium homodimer and calcein-AM stain, YO-PRO-1 dye/propidium iodide apoptosis assay, and LDH assay, although 10% and 15% ethanol caused minimal changes to corneal fibroblasts. Cellular death was most significant 6 hours after the 20% ethanol treatment. The genomic DNA pattern revealed intact DNA in the control, 10% ethanol, and 15% ethanol groups at all times, whereas DNA smearing was noticed at 48 hours after the 20% ethanol treatment. However, none of the DNA examined revealed significant DNA laddering patterns of apoptosis. Fifty percent ethanol treatment of 30 seconds resulted in cell fixation and cell death.

CONCLUSION

Treatment with 20% ethanol for 30 seconds induced significant porcine corneal fibroblast cell death, whereas 10% and 15% ethanol treatment of 30 seconds caused minimal changes. We propose that, when applied for 30 seconds, 20% ethanol is the threshold level that causes cell death in cultured porcine corneal fibroblasts.

Phakic posterior chamber intraocular lens for high myopia

PURPOSE

To evaluate the efficacy, predictability, stability, and safety of the surgical correction of high myopia using a phakic posterior chamber intraocular lens (PPC IOL).

SETTING

Centro Oftalmológico de Valencia-CEOVAL, Valencia, Venezuela.

METHODS

A retrospective study was performed to analyze 18 eyes of 12 patients who had implantation of a modified PPC IOL, the implantable contact lens (ICL), for the treatment of high myopia. The target postoperative spherical equivalent (SE) refraction was emmetropia.

RESULTS

The mean follow-up was 26.6 months +/- 11.3 (SD) (range 12 to 36 months). The mean preoperative SE was -15.27 +/- 3.47 diopters (D) (range -10.0 to -21.25 D) and the mean postoperative SE, -0.62 +/- 0.81 D (range -2.75 to +0.75 D). Eleven eyes (61.1%) had an SE within +/-1.00 D of emmetropia. The best spectacle-corrected visual acuity was maintained or improved in all except 1 eye, which lost more than 2 lines of Snellen visual acuity. Two eyes (11.1%) developed pupillary block the first day after surgery. Four eyes (22.2%) had moderate pigmentary dispersion. Two eyes (11.1%) had lens opacification, 1 with mild peripheral anterior capsule opacification and the other eye with central anterior subcapsular opacification. One eye (5.5%) had a significant decrease in anterior chamber depth after surgery.

CONCLUSIONS

Implantation of an ICL was effective for the correction of high myopia. Predictability must be improved and the long-term safety of the ICL determined. The main concerns over potential cataract formation, pigmentary dispersion, and angle-closure glaucoma remain.

Laser in situ keratomileusis for the correction of residual ametropia after penetrating keratoplasty

PURPOSE

To evaluate the safety, efficacy, and predictability of excimer laser in situ keratomileusis (LASIK) to correct residual myopia and astigmatism after penetrating keratoplasty (PKP).

SETTING

Buzard Eye Institute, Las Vegas, Nevada, USA.

METHODS

Twenty-six eyes had LASIK at least 1 year after PKP. All eyes were followed for at least 6 months after LASIK; 22 eyes were followed for 12 months. Sutures were removed at a mean of 13 months post PKP. Laser in situ keratomileusis was performed with the Chiron Automated Corneal Shaper microkeratome (Bausch & Lomb) and the Visx Star excimer laser. Before LASIK, the mean spherical equivalent (SE) was -4.94 diopters (D) +/- 2.79 (SD) and the mean astigmatism was 2.71 +/- 2.33 D; all eyes had regular astigmatism or slightly decentered, irregular astigmatism.

RESULTS

At the last follow-up, the mean postoperative uncorrected visual acuity (UCVA) was 20/30, the mean SE was -0.35 +/- 0.65 D, and the mean residual astigmatism was 1.06 +/- 0.67 D. Eighty-six percent of patients had an SE within +/-1.00 D of emmetropia and a UCVA of 20/40 or better. Ten eyes (39%) had 1 or more enhancements, which were performed a mean of 6 months after the primary LASIK. Significant complications such as wound dehiscence, epithelial ingrowth, and corneal decompensation did not occur. At the last follow-up, 18% of patients lost 1 line of best corrected visual acuity and 27% gained 1 line.

CONCLUSION

Laser in situ keratomileusis appeared to be a reliable and safe procedure to correct residual myopia and astigmatism after PKP.

Vitality of epithelial cells after alcohol exposure during laser-assisted subepithelial keratectomy flap preparation

PURPOSE

To evaluate the vitality of epithelial cells after various exposure times to 20% ethanol and epithelial flap preparation in laser-assisted subepithelial keratectomy (LASEK) using the trypan blue dye test.

SETTING

University Eye Clinic Regensburg, Regensburg, Germany, and the Rayne Institute, Department of Ophthalmology, St. Thomas' Hospital, London, United Kingdom.

METHODS

Five human cadaver eyes were exposed to 20% ethanol for 15, 30, 45, 60, and 120 seconds, respectively. After an epithelial flap (as in LASEK) was prepared, the flap was deliberately cut off. The flaps were soaked in a trypan blue 0.1% solution at 37 degrees C. After 3 washes with phosphate-buffered saline (PBS), the specimens were reincubated for 30 minutes in culture medium containing 10% fetal calf serum at 37 degrees C. After an additional wash with PBS, the cells were observed with a standard inverted light microscope.

RESULTS

After 15- and 30-second exposure to 20% ethanol, most epithelial cells were vital. This changed substantially after 45 seconds, when vital and dead cells were approximately equal. Longer exposure times (60 seconds and 120 seconds) showed predominantly dead epithelial cells.

CONCLUSIONS

Exposure to 20% ethanol should be 20 to 30 seconds as the number of vital epithelial cells rapidly decreased after that. Vitality of the epithelial flap is probably a crucial factor in the dampened wound response in LASEK compared to that in photorefractive keratectomy.

Prospective Study of Photorefractive Keratectomy for Myopia Using the VISX StarS2 Excimer Laser System

PURPOSE

To evaluate the safety, efficacy, and predictability of excimer laser photorefractive keratectomy (PRK) for compound myopic astigmatism using the VISX StarS2 excimer laser system with international version 3.1 software.

METHODS

We report a prospective consecutive study of myopic excimer laser PRK, performed in a multi-surgeon environment with 200 eyes of 117 patients, to correct naturally occurring compound myopic astigmatism of between -0.50 to -5.90 D manifest refractive sphere and up to -3.50 D manifest refractive astigmatism. Patients were assessed prior to surgery and at 1, 3, 6, and 12 months after treatment.

RESULTS

One hundred and ninety-eight of 200 treatments (99%) were reviewed 1 year after surgery; 193 of 198 eyes (97%) achieved 20/40 or better uncorrected visual acuity and 163 of 198 eyes (82%) achieved 20/20 or better. One eye lost two lines of Snellen visual acuity assessed at 12 months but recovered acuity when assessed at 18 months. Mean spherical equivalent corneal plane power was reduced from -3.50 to +0.90 D 1 month after treatment and 0 D at 12 months (SD 0.67 D). Three eyes of three patients underwent further treatment, two with LASIK and one with PRK for residual refractive error. Refractive astigmatism of >1.00 D was reduced from a mean -1.70 to -0.70 D at 1 year after treatment. Vector magnitude was 79% of that intended and mean vector axis error (absolute) was 8.5 degrees. No eye had a severe haze response. Pelli-Robson contrast acuity was significantly reduced after treatment from a mean 1.72 D preoperatively to 1.63 D at 12 months (P<.01).

CONCLUSIONS

PRK for myopia using the VISX StarS2 excimer laser system was effective in the treatment of low myopic astigmatism, although there was a significant reduction in Pelli-Robson contrast sensitivity.

Phakic intraocular lenses and refractory lensectomy for myopia

Phakic intraocular lens implantation (IOLs) and clear lens extraction for high to extreme myopia have grown in popularity recently as a consequence of potentially unsatisfactory results with corneal refractive surgery in higher ranges of refractive errors. The refractive outcome of these alternative modalities has been encouraging to date, yet the potential for significant complications exists. Current evidence shows that the risk of retinal detachment after clear lens extraction for myopes is high. Trials with angle-supported phakic IOLs revealed unacceptable rates of pupillary ovalization, IOL rotation, and endothelial cell loss. Iris-fixated and posterior chamber phakic IOLs have proven sufficient safety, but long-term follow-ups of current cohorts are still to be awaited. The implantation of either of the latter two phakic IOLs followed by laser in situ keratomileusis or photorefractive keratectomy (bioptics) provides another option in refractive surgery for high ametropia.

Twenty percent alcohol toxicity on rabbit corneal epithelial cells: electron microscopic study

PURPOSE

To evaluate 20% ethanol toxicity on the rabbit corneal epithelium, ethanol-treated rabbit corneas were examined with electron microscopy.

METHODS

Rabbit corneas (24 eyes) were treated with 20% ethanol for 30 seconds, 1 minute, and 2 minutes by using LASEK (laser-assisted subepithelial keratectomy) instruments and then washed with sterile water. Zero time, 1, 3, 5 days after ethanol treatment, corneas were excised and examined with scanning and transmission electron microscopy (SEM and TEM).

RESULTS

Widespread partial or total damage of microvilli, focal breaks of intercellular junction, and cellular edema was observed. The damage was more severe in corneas with longer ethanol treatment. In corneas with ethanol treatment more than 1 minute, slough of superficial corneal epithelium occurred and progressed with time. Two-minute ethanol treatment resulted in complete destruction of microvilli and significant separation of intercellular junction. These pathologic changes persisted 5 days after ethanol treatment.

CONCLUSIONS

From these results, increasing exposure time to ethanol more than 1 minute results in significant damage to superficial corneal epithelium and prolongs its normal recovery time.

Predictability and outcomes of photoastigmatic keratectomy using the Nidek EC-5000 excimer laser

PURPOSE

To evaluate the effect of astigmatic correction on the accuracy of the myopic and astigmatic correction in patients having photorefractive astigmatic keratectomy (PARK) and in those having photorefractive keratectomy (PRK).

SETTING

Specialist excimer laser refractive clinic.

METHODS

This prospective consecutive case series comprised 6097 eyes with a preoperative mean spherical equivalent (MSE) of -4.63 diopters (D) +/- 1.95 (SD) (range -0.75 to -13.00 D) and a mean cylinder of -1.13 +/- 0.73 D (range -0.50 to -6.00 D) having PARK with a Nidek EC-5000 excimer laser. Visual and refractive outcomes were assessed 12 months postoperatively and compared with those in 3004 eyes that had spherical PRK.

RESULTS

At 12 months, the MSE was -0.02 +/- 0.79 D and the mean cylinder was -0.49 +/- 0.47 D in the PARK group; the MSE was -0.07 +/- 0.66 D in the PRK group. An MSE within +/-0.05 D of emmetropia was achieved by 69.8% and within +/-1.00 D, by 87.9%. The uncorrected visual acuity (UCVA) was 20/20 or better in 42.6% and 20/40 or better in 91.2%. Statistical significance (P <.001, analysis of variance) was achieved for MSE, sphere, cylinder, haze, and visual acuity (best corrected [BCVA] and UCVA) based on the preoperative cylinder. The loss of BCVA varied from 1.1% to 5.8% depending on the degree of astigmatism treated. Accuracy varied with the attempted myopic correction and the attempted astigmatic correction.

CONCLUSIONS

Excimer laser PARK was an effective treatment for compound myopic astigmatism, but predictability decreased and complications increased as the attempted astigmatic correction increased.

Effect of Photorefractive Keratectomy for Myopia on Measurement of Retinal Nerve Fiber Layer Thickness Using Optical Coherence Tomography

PURPOSE

To evaluate the effect of excimer laser photorefractive keratectomy (PRK) on nerve fiber layer thickness measurements by optical coherence tomography in myopic eyes.

METHODS

Twenty-two patients who had PRK for myopia underwent nerve fiber layer measurement by optical coherence tomography in both eyes before and 6 months after surgery in the first operated eye and before surgery in the fellow (control) eye, 6 months after the first PRK. Optical coherence tomography was performed with a Humphrey Optical Coherence Tomography Scanner. Each eye was scanned at the nerve head program radius of 1.5. For each of the optical coherence tomography parameters (average for each quadrant, superior, inferior, temporal, nasal; average for each clock hour; average over the entire cylindrical section), descriptive statistics were calculated. The difference between the observed change from the first to the second examination was calculated between the treated and the control eye. Individual mean differences were tested with Student's t-test. Hotelling's T-squared generalized means test was used to determine whether the set of mean differences was equal to zero.

RESULTS

The average preoperative refractive error was -3.90+/-1.50 D in treated eyes and -3.89+/-1.50 D in control eyes (P = .81, Student's t-test). Mean achieved refractive correction was 3.70+/-1.70 D, corresponding to 48.1+/-22.1 microm of corneal ablation. No statistically significant difference was found in any measurement in the treated eye compared with the untreated control eye.

CONCLUSIONS

At 6 months postoperatively, photorefractive keratectomy for moderate myopia that resulted in clear corneas did not affect nerve fiber layer thickness measurements, as obtained by optical coherence tomography.

Relationships between vitreoretinal and refractive surgery

OBJECTIVE

To describe retinal complications after posterior chamber phakic intraocular lens (PCPIOL) implantation and refractive surgery complications after scleral buckling surgery.

DESIGN

Retrospective, noncomparative, small case series.

PARTICIPANTS

Four patients in whom retinal detachment developed after PCPIOL implantation and two patients with previously placed encircling scleral buckles in whom corneal steepening developed after laser in situ keratomileusis (LASIK).

INTERVENTION

The four patients with retinal detachment after PCPIOL implantation underwent vitreoretinal surgery. One of the two patients in whom corneal steepening developed after LASIK underwent buckle removal.

MAIN OUTCOME MEASURES

The main parameters evaluated were vitreoretinal findings, corneal topography, and pachymetry.

RESULTS

Retinal attachment was achieved for all patients. Mean postoperative best-corrected visual acuity (BCVA) was 20/30. One patient lost one line of BCVA. One patient with corneal steepening achieved partial corneal flattening after buckle removal.

CONCLUSIONS

Vitreous base stimulation related to PCPIOL implantation and manipulation during LASIK may trigger retinal complications. Laser in situ keratomileusis in patients with previously placed scleral buckles may result in unexpected corneal steepening.

The epithelial flap for photorefractive keratectomy

BACKGROUND/AIMS

Epithelial debridement for photorefractive keratectomy (PRK) is associated with pain, slower visual recovery, and may be aetiological in haze production. The aim of this study was to assess the clinical results of a new technique involving raising and replacing of an epithelial flap in photorefractive keratectomy.

METHODS

A prospective, non-randomised, comparative, paired eye trial was performed in 72 eyes of 36 patients who underwent PRK with a Nidek EC-5000 excimer laser. For epithelial debridement before PRK, the eyes were divided into two groups. The first eye of each patient was treated with 20% ethanol debridement and the second eye with an epithelial flap which was replaced after treatment. PRK was carried out with the same laser and nomogram in both groups by the same surgeon. Visual and refractive outcome of PRK treatment was compared in both groups.

RESULTS

The mean (SD) preoperative mean spherical equivalent (MSE) was -3.61 (1.38) dioptres (D) (range -1.00 D to -7.88 D) with no significant difference between the two groups. After a mean follow up period of 62.6 weeks (range 52-70) the final MSE was +0.07 (0.61) D (range -5.50 D to +4.50 D) in the debridement group and -0.24 (0.43) D in the epithelial flap group. There was no statistically significant difference between the two groups in postoperative MSE. The best corrected visual acuity was better in the epithelial flap group at all visits; this difference was statistically significant (p<0.05). The corneal haze was less in the epithelial flap group and this difference was also statistically significant (p<0.05).

CONCLUSIONS

Managing the corneal epithelium as a hinged flap with 20% ethanol is a safe technique with faster visual rehabilitation and reduced haze compared with debridement of the epithelium with alcohol. Further studies need to be performed to compare pain levels postoperatively with the epithelial flap and epithelial debridement.

Pain After Epithelial Removal by Ethanol-assisted Mechanical Versus Transepithelial Excimer Laser Debridement

PURPOSE

To compare subjective pain responses between two techniques of epithelial removal prior to photorefractive keratectomy (PRK) treatment: ethanol-soaked pledget with mechanical debridement of the epithelium versus excimer laser transepithelial ablation.

METHODS

Nine patients underwent bilateral PRK. Each had the epithelium in one eye debrided by placing a pledget soaked in 20% ethanol on the cornea for 2 minutes followed by gentle scraping with a blade. The epithelium in the other eye was removed by transepithelial phototherapeutic keratectomy (PTK) treatment. For each eye, PRK was initiated immediately after removal of the epithelium. On postoperative day one, each patient was asked to rate the level of pain suffered over the last 24 hours on a scale of 0 (minimal) to 10 (maximal). Data were analyzed in a masked fashion.

RESULTS

Postoperative day one average pain level in the ethanol-assisted mechanically debrided eyes was 3.0 +/- 2.5 and in the transepithelial PTK eyes was 6.8 +/- 1.8. The difference was statistically significant by Student's t-test (P < .01). All epithelial defects healed within 3 days with no clinically significant difference in healing time between the two techniques.

CONCLUSION

In preparation for PRK, ethanol-assisted mechanical debridement of the epithelium caused significantly less postoperative pain than epithelial removal using the excimer laser.

Reoperations after myopic laser in situ keratomileusis

PURPOSE

To evaluate the results after enhancement of myopic laser in situ keratomileusis (LASIK) using the VISX Star excimer laser.

SETTING

The Buzard Eye Institute, Las Vegas, Nevada, USA.

METHODS

In this prospective study, 52 eyes of 40 patients had LASIK enhancement. The existing flap was lifted and the excimer laser treatment reapplied for the residual refractive error. The VISX Star excimer laser was used for the primary LASIK and the enhancement procedure. Retreatments for undercorrection, regression, and overcorrection were performed after 6 weeks and up to 40 weeks after the primary LASIK. Follow-up was 96% at 1 month, 67% at 6 months, and 71% at 12 months.

RESULTS

Mean pre-enhancement spherical equivalent was -0.77 diopters (D) +/- 0.94 (SD) and mean uncorrected visual acuity (UCVA), 20/60. One year after the enhancement, mean spherical equivalent was -0.13 +/- 0.33 D, and mean UCVA was 20/25. Refraction remained stable during the 1 year follow-up, with no treatment required. After the enhancement, all patients had a UCVA of 20/40 or better. At 1 year, 3% of patients had lost 1 line of best corrected visual acuity and 32% had gained 1 line. No epithelial ingrowth was noted.

CONCLUSION

Retreatment for LASIK beginning 6 weeks after the initial procedure proved to be effective with minimal complications and good results. The technique to raise and reposition the flap appeared safe, and complications were few.

One year clinical results of photoastigmatic refractive keratectomy for compound myopic astigmatism

PURPOSE

To evaluate the efficacy, predictability, and safety of excimer laser photoastigmatic refractive keratectomy (PARK) to correct compound myopic astigmatism.

SETTING

Departments of Ophthalmology, Robert Debré Hospital and Rothschild Foundation, Paris, France.

METHODS

This retrospective study included 27 eyes with compound myopic astigmatism treated with a Nidek EC 5000 excimer laser. The refractive results were measured at 1 year, and the cylindrical component was analyzed by the Alpins method. Mean preoperative myopia was -4.50 diopters (D) (range -0.75 to -4.00 D) and mean preoperative cylinder, -1.64 D (range -0.75 to -4.00 D).

RESULTS

At 1 year, the spherical equivalent was -0.47 D (range +1.00 to -3.00 D) and residual subjective astigmatism, -0.40 (range -0.25 to -1.50 D). Uncorrected visual acuity of 20/40 or better was obtained in 22 of the 27 eyes; 21 eyes were within +/- 1.0 D of emmetropia. Vector analysis showed a mean coefficient adjustment of 1.50 D +/- 0.53 (SD), a mean axis shift of 2.64 +/- 12.10 degrees, and a mean magnitude of error of 0.45 +/- 0.56 D. Haze was absent in 22 eyes and grade 1+ in 5 eyes. Five eyes gained 1 line of best corrected visual acuity and 3 lost 1 line. No patient lost more than 1 line.

CONCLUSION

Excimer laser PARK successfully corrected low and moderate myopia combined with up to 4.0 D of astigmatism with a low mean angle of error. To increase the accuracy of toric ablation, specific algorithms for the cylinder component are needed.

Corneal topography of small-beam tracking excimer laser photorefractive keratectomy

PURPOSE

To evaluate the topographic characteristic of photorefractive keratectomy (PRK) for low myopia performed with a small-beam (0.9 mm) tracking excimer laser.

SETTING

Department of Ophthalmology, LSU Eye Center, Louisiana State University Medical Center School of Medicine in New Orleans, and the Refractive Surgery Center of the South at the Eye, Ear, Nose, & Throat Hospital, New Orleans, Louisiana, USA.

METHODS

Sixty-seven eyes of 47 patients had PRK with a small-beam tracking laser. Of these, 49 eyes had data permitting evaluation of ablation centration; usable data for topographic analysis were available for 59 eyes preoperatively, 54 eyes at 1 month, 42 eyes at 3 months, and 25 eyes at 6 months, permitting measurement of various topographic parameters, including the cylinder (CYL), average corneal power (ACP), surface regularity index (SRI), surface asymmetry index (SAI), corneal eccentricity index (CEI), and coefficient of variation of corneal power (CVP).

RESULTS

Preoperatively, all eyes were topographically normal. Postoperatively, no eye exhibited a "central island" by even the least-restrictive definition, and all eyes had best spectacle-corrected visual acuities (BSCVAs) of 20/20 or better at all follow-ups. Mean decentration of the ablations from the pupil centers was 0.42 mm +/- 0.28 (SD) (n = 49). There was no correlation between measured decentration and BSCVA (P = .46). The central cornea was flattened (decreased ACP; P < .001) and made oblate (decreased CEI; P < .001) as expected. There was no increase in SRI or SAI (irregular astigmatism) at 6 months compared with preoperative values (P = .91); however, CYL and CVP (varifocality) increased slightly (P = .04 and .02, respectively).

CONCLUSION

The absence of significant regular or irregular astigmatism 6 months after PRK with the small-beam laser is an improvement over published results achieved with wide-beam lasers and is consistent with the excellent visual acuity results in this cohort.

Comparison of mechanical and transepithelial debridement during photorefractive keratectomy

OBJECTIVE

Comparison of clinical results from mechanical and transepithelial debridement during photorefractive keratectomy.

DESIGN

Randomized, prospective study.

PARTICIPANTS

Two hundred seventy-eight eyes in 173 patients between November 1995 and June 1997.

INTERVENTION

Photorefractive keratectomy treatments with a Summit Omnimed excimer laser (6-mm). Clinical results were measured at 1, 3, and 6 months.

MAIN OUTCOMES MEASURES

Uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BCVA), mean spherical equivalent (MSE), astigmatism, corneal haze, and subjective vision (day, night, glare, and halo).

RESULTS

At all postoperative intervals, no significant difference was present between mean values of MSE, haze, or any subjective parameters. For mean UCVA, BCVA, and astigmatism values, a significant difference (P < 0.05) was present only at 6 months. At all postoperative intervals, mechanical values tended to be superior to transepithelial valves.

CONCLUSION

Clinical results were not statistically different between the two techniques; however, the mechanical technique tended to have superior values for almost all tested parameters.

Predictability of spherical photorefractive keratectomy for myopia

OBJECTIVE

This study aimed to examine the effects of purely spherical excimer laser photorefractive keratectomy (PRK) for myopia.

DESIGN

Consecutive case series.

PARTICIPANTS

A total of 3218 eyes with a mean preoperative mean spherical equivalent (MSE) of -3.75 diopters (D) +/- 1.73 D standard deviation (SD) (range, -1.00 D to -11.88 D) underwent PRK with a Nidek EC-5000 excimer laser. Eyes were divided into groups based on the degree of preoperative myopia in 1 D steps.

INTERVENTION

All eyes underwent PRK with a Nidek EC-5000 excimer laser.

MAIN OUTCOME MEASURE

Visual and refractive outcome of PRK treatment was measured.

RESULTS

After a mean follow-up period of 52.6 weeks (range, 26-150 weeks), the final MSE was -0.07 D (+/-0.68 D) (range, -5.50 D to +4.50 D). Of the 3218 eyes, 2919 (90.7%) were within 1.00 D of emmetropia, and 3038 (94.4%) of eyes had an uncorrected visual acuity of 20/40 or better, with 1886 (58.6%) achieving 20/20 or better visual acuity. Eyes in the lower preoperative myopia groups had a greater chance of attaining 20/40 unaided visual acuity than those in the higher groups (e.g., 98.3% of the -2D group and 53.6% of the -9D group achieved 20/40 unaided visual acuity). Overall, mean postoperative haze was 0.29+/-0.39 SD (scale, 0-3), and 29 eyes (0.9%) lost 0.3 or more logarithm of the minimum angle of resolution (LogMAR) unit of best-corrected visual acuity.

CONCLUSIONS

Excimer laser PRK is an effective treatment for myopia of up to -9.00 D. The outcome parameters are less predictable for eyes with greater than -9.00 D of myopia.

Evaluation of current techniques of corneal epithelial removal in hyperopic photorefractive keratectomy

PURPOSE

To determine the efficacy of 3 current methods used to remove corneal epithelium prior to photorefractive correction of hyperopia and to compare clinical data in patients who had rotary brush or blunt scrape epithelial removal in the treatment of hyperopic photorefractive keratectomy (PRK).

SETTING

University of Ottawa Eye Institute, Ottawa General Hospital, Ottawa, Ontario, Canada.

METHODS

The epithelium from human eye-bank eyes was removed using a Paton spatula, 15% alcohol, and the Amoils rotating plastic brush. The effects were examined by scanning and transmission electron microscopy. Twelve month postoperative data were obtained on 25 eyes with refractions of +1.00 to +4.00 diopters (D) that had been treated for hyperopia with the VISX Star excimer laser, using blunt scrape or the rotary brush to remove the corneal epithelium.

RESULTS

All 3 methods effectively removed corneal epithelium. The Paton spatula, however, left small nicks in Bowman's layer. Both the rotating brush and alcohol debridement left Bowman's layer intact. Alcohol treatment required follow-up epithelial debris removal, while brushing left minimal amounts of debris. There was a strong trend toward rapid epithelial healing in the brushed corneas compared with the scraped ones, but this was not statistically significant. Clinically, at 12 months postoperatively, brushed corneas showed a trend toward more superior outcomes than scraped corneas in actual refractive outcome, uncorrected visual acuity (UCVA), lines of UCVA gained, and predictability of the desired outcomes. However, only the outcome in UCVA of 20/40 or better and the decreased incidence of haze in the brushed corneas over scraped ones were statistically significant.

CONCLUSIONS

Both alcohol and the rotating brush provide a quick, effective means of removing the corneal epithelium with minimal risk of damage to Bowman's layer. In our experience, the brush technique was as effective as and possibly superior to the blunt scrape for epithelial removal in hyperopic PRK.

Posterior Chamber Phakic Intraocular Lens for Myopia of -8 to -19 Diopters

PURPOSE

To examine the efficacy, predictability, stability, and safety of posterior chamber phakic intraocular lens (IOL) implantation in patients with extreme myopia.

METHODS

We analyzed the results of 124 eyes that received a posterior chamber hydrogel collagen plate phakic IOL (Staar Collamer Implantable Contact Lens, ICL) for the correction of their myopia. The target postoperative spherical equivalent refraction was emmetropia. Mean follow-up was 11 months (range 1 to 36 mo).

RESULTS

The mean preoperative spherical equivalent refraction was -13.38 +/- 2.23 D (range, -8.50 to -18.63 D). Mean postoperative spherical equivalent refraction at last examination was -0.78 +/- 0.87 D (range, +1.63 to -3.50 D), with 69% (86 eyes) within +/-1.00 D and 44% (55 eyes) within +/-0.50 D of emmetropia. The refraction remained stable with a statistically insignificant change (p > 0.05 at each interval) during follow-up. A gain of two or more lines of spectacle-corrected visual acuity was seen in 36% (45 eyes) at last examination. One eye (0.8%) lost two or more lines of spectacle-corrected visual acuity from a retinal detachment.

CONCLUSION

Posterior chamber phakic IOL implantation with the Staar Collamer plate lens is an effective and safe method for reducing or correcting myopia between -8 and -19 D. Gains in spectacle-corrected visual acuity were common, and results suggested good refractive stability. Improvements in phakic IOL power calculation formulas are needed to improve the predictability of refractive outcome.

Laser in situ Keratomileusis for Low Myopia and Astigmatism with a Scanning Spot Excimer Laser

PURPOSE

To determine the efficacy, predictability, safety, and short term stability of laser in situ keratomileusis (LASIK) in treating patients with low myopia and astigmatism using the Chiron Technolas Keracor 117 PlanoScan excimer laser.

METHODS

We retrospectively studied the results of our initial 83 eyes with myopia ranging from -1.13 to -7.25 diopters (D) and astigmatism of no more than 4.00 D that underwent LASIK with the Chiron Technolas Keracor 117 PlanoScan. Follow-up was at 1 day, 1 month, and 3 to 6 months.

RESULTS

Mean baseline spherical equivalent refraction was -3.54 +/- 1.41 D and cylinder -1.64 +/- 1.14 D. Mean postoperative spherical equivalent refraction was -0.52 +/- 0.50 D at 1 month and -0.65 +/- 0.62 D at 3 to 6 months; mean postoperative refractive cylinder was -0.45 +/- 0.54 D at 1 month and -0.50 +/- 0.63 D at 3 to 6 months. Fifty-three percent (44 eyes) achieved a spherical equivalent refraction within +/- 0.50 D and 81% (67 eyes) within +/- 1.00 D of emmetropia at the last examination. Fifty-seven percent (47 eyes) achieved a refractive cylinder of < or = 0.50 D, and 27% (22 eyes) had an undercorrection of their refractive cylinder at the last examination. An uncorrected visual acuity of 20/40 or better was achieved in 86% (71 eyes) of patients on postoperative day one, in 81% (67 eyes) at 1 month, and in 76% (63 eyes) at 3 to 6 months. Twenty-eight percent (23 eyes) saw 20/20 or better uncorrected at the last visit (41% [34 eyes] had a baseline spectacle-corrected visual acuity of 20/20). There was no statistically significant difference in the refractions or uncorrected visual acuities between the different postoperative examinations. No eye experienced a loss of spectacle-corrected visual acuity of more than one line at the last examination.

CONCLUSION

LASIK with the Chiron PlanoScan excimer laser appears to be an effective, safe, and reasonably predictable means to reduce low myopia and astigmatism. Adjustment of computer algorithms is needed to decrease the number of under-corrections.

A prospective evaluation of alcohol-assisted versus mechanical epithelial removal before photorefractive keratectomy

OBJECTIVE

The purpose of the study is to compare alcohol-assisted versus mechanical debridement of the corneal epithelium before photorefractive keratectomy (PRK) for low-to-moderate myopia.

DESIGN

A prospective study was performed on a group of consecutive patients operated on at the Massachusetts Eye and Ear Infirmary from February to April 1996 and followed for 6 months.

PARTICIPANTS

Eighty patients (eyes) were divided in 2 groups: 40 alcohol and 40 mechanical.

INTERVENTION

The patients underwent PRK for myopia (-1.5 to -7.5 diopters) with a Summit Apex excimer laser. The corneal epithelium was removed either with 20% ethanol or with a scalpel blade.

MAIN OUTCOME MEASURES

The two groups were compared for epithelial removal time, epithelial defect size at the end of surgery, and rate of re-epithelialization. Uncorrected visual acuity (UCVA), refractive outcome, best-corrected visual acuity (BCVA), and subjective haze were measured at 4 days and at 1, 3, and 6 months. In an additional short-term study, 40 patients (20 alcohol, 20 mechanical) had intraoperative pachymetry performed.

RESULTS

Alcohol-assisted de-epithelialization was faster than mechanical debridement (107 [+/-20.6 standard deviation] versus 141 [+/-30.5] seconds [P < 0.0001]) and led to a more circumscribed and reproducible epithelial defect at the end of surgery (87,739 [+/-11,852] versus 103,518 [+/-33,942] square pixels [t test, P = 0.04; f test, P = 0.001]). At 4 days, 95% of the alcohol-treated patients had healed compared with 78% of the mechanically scraped patients (Fisher's exact test, P = 0.04). The alcohol group had a better UCVA at 4 days (logarithm of the minimum angle of resolution UCVA 0.36 [+/-0.22] versus 0.51 [+/-0.26]) and at 1 month (0.14 [+/-0.17] versus 0.22 [+/-0.16] [Mann-Whitney U test, P = 0.02 and P = 0.03]) but equalized at 3 months (0.10 [+/-0.14] versus 0.13 [+/-0.16]) and at 6 months (0.11 [+/-0.15] versus 0.14 [+/-0.13] [Mann-Whitney U test, P = 0.23 and P = 0.34]). There was a trend toward less subjective haze in the alcohol-treated patients over the course of the study (area under the curve, 71.9 [+/-35.3] versus 87.9 [+/-33.8] [Mann-Whitney U test, P = 0.07]). The difference from target was equivalent in both groups at 6 months (-0.22 [+/-0.58] diopter in the alcohol group and -0.43 [+/-0.52] diopter in the mechanical group [t test, P = 0.14; f test, P = 0.57]). There were no differences in intraoperative pachymetry, corneal uniformity index as calculated from the corneal topography, and loss of BCVA between the two groups.

CONCLUSIONS

Twenty percent ethanol is a simple, safe, and effective alternative to mechanical scraping before PRK and appears to be associated with a quicker visual rehabilitation.

Excimer Laser in situ Keratomileusis for Myopia

PURPOSE

To evaluate the efficacy, safety, and predictability of excimer laser in situ keratomileusis (LASIK) for the correction of myopia.

METHODS

Forty-six consecutive eyes that had LASIK with the VISX 20/20B laser and Chiron corneal shaper were evaluated. Mean spherical equivalent of the preoperative manifest refraction was -9.40 +/- 3.78 diopters (D) (range, -3.50 to -19.75 D). The refractive effect (postoperative refraction minus baseline refraction), residual refractive error (refractive effect minus planned correction) and uncorrected and spectacle-corrected visual acuity were examined.

RESULTS

Mean follow-up was 6.1 months (range, 3 to 9 mo). Spectacle-corrected visual acuity was unchanged in 39 eyes (84.78%), significantly improved in five eyes (10.86%), and worse in two eyes (4.34%). Uncorrected visual acuity was 20/20 or better in 15 eyes (32.6%) and 20/40 or better in 39 eyes (84.78%). Thirteen eyes (28.26%) had a postoperative spherical equivalent refraction within +/- 0.50 D and 36 eyes (78.26%) within +/- 1.00 D of attempted correction. No intraoperative complication occurred. Postoperative complications were few and not severe: three eyes (6.52%) developed regular astigmatism, two eyes (4.34%) had interface deposits, and three eyes (6.52%) had small epithelial cysts in the interface.

CONCLUSION

LASIK with the VISX 20/20B laser is safe, moderately effective, and relatively predictable for correcting myopia from -3.50 to -19.50 D. Predictability decreases with increasing myopia.

Multizone photorefractive keratectomy for high and very high myopia: long-term results

PURPOSE

To compare 2 year results of multizone excimer laser photorefractive keratectomy (PRK) in eyes with myopia (spherical equivalent [SE]) from 6.00 to 10.00 diopters (D) with those in eyes with myopia from 10.25 to 25.75 D.

SETTING

Wellington Hospital and Laser Vision Harley Street, London, England.

METHODS

Of the 281 PRK cases with an SE of at least -6.00 D, 59 eyes had a minimum follow-up of 2 years. Twenty-six of these had an SE from -6.00 to -10.00 D and 33, from -10.25 to -25.75 D. The single-pass, multizone technique was used to create ablation zones at 5.0, 5.5, and 6.0 mm. Postoperatively, patients received a minimum of 4 weeks of fluorometholone 0.1%; those exhibiting regression after corticosteroids were discontinued were restarted on a tapering regimen.

RESULTS

The refraction stabilized 3 months postoperatively in the -6.00 to -10.00 D group, and the final mean SE refraction was a small undercorrection. Two years postoperatively, 88.5% of eyes had a visual acuity of 20/40 or better, and 77.0% were within +/- 1.00 D of the intended correction. In eyes with myopia greater than 10.00 D, regression continued during the 2 years and refraction did not stabilize. Forty-two percent had an uncorrected acuity of 20/40 or better, and 48.0% were within +/- 1.00 D of the intended correction. The incidence and severity of haze were higher in the group with myopia greater than 10.00 D. The overall incidence of complications was low.

CONCLUSION

Two years after multizone PRK, refractive and visual acuity results in eyes with myopia from 6.00 to 10.00 D were good. Results in eyes with myopia of more than 10.00 D were not satisfactory, and refraction had not stabilized.

Excimer laser photorefractive keratectomy for low hyperopia: safety and efficacy

PURPOSE

To assess the safety and efficacy of photorefractive keratectomy (PRK) to correct low hyperopia.

SETTING

University of Ottawa Eye Institute, Ottawa General Hospital, Ontario, Canada.

METHODS

Twenty-five eyes with refractions of +1.00 to +4.00 diopters (D) and cylinder of 1.00 D or less were treated for hyperopia with the VISX Star excimer laser system using a refined ablation architecture. Thorough visual assessments were performed preoperatively (baseline) and 1, 3, and 6 months postoperatively. Complications were recorded and the level of patient satisfaction was noted.

RESULTS

Mean spherical equivalent at 6 months was +0.27 D +/- 0.55 (SD), which was an 89% reduction over baseline. Eighty-four percent of patients gained two to seven lines of near uncorrected visual acuity (UCVA) and 1 patient (4%) lost more than one line. Eight percent achieved 20/25 or better UCVA. Approximately half realized their preoperative distance best corrected visual acuity (BCVA) by 1 month. By the end of the study, all patients had improved, achieved, or were within one line of their baseline distance BCVA. There were some slight reductions in lower contrast acuity at 6 months, although dim lighting conditions did not further reduce these acuities. Most patients had no clinically meaningful change in cylinder. The most common complications included early, transient corneal surface irregularities and visual symptoms and trace haze (grade < or = 0.5) in 14 of 23 patients at 6 months. All but 1 patient expressed a high degree of satisfaction.

CONCLUSIONS

These results support the hypothesis that PRK shows great promise as a safe and effective treatment for low hyperopia. There were no significant complications and no decentered ablations. The slight regression occurred with or without the presence of trace haze. Overall, refractive stability was encouraging, although longer follow-up is needed.

Dilute ethanol versus mechanical debridement before photorefractive keratectomy

PURPOSE

To compare 18% ethanol versus mechanical epithelial debridement in a group of patients having photorefractive keratectomy (PRK) for low to moderate myopia or astigmatism.

SETTING

Hospital San Jose de Monterrey, Mexico.

METHODS

This prospective, paired study comprised 18 patients who had bilateral PRK between June 1994 and March 1995. One eye had ethanol (alcohol) debridement and the other, mechanical. Time between PRKs was about 6 months. The two groups (alcohol versus mechanical) were compared for rate of re-epithelialization, refractive outcome, improvement in uncorrected visual acuity (UCVA), subjective haze grading, and loss of best corrected visual acuity (BCVA).

RESULTS

There was a nonsignificant trend in the alcohol-treated eyes toward a more rapid visual recovery. One week after PRK, 76% in the alcohol group but only 31% in the mechanical group had a UCVA of 20/40 or better. There were no significant between-group differences in rate of re-epithelialization, refractive outcome, subjective haze grading, and loss of BCVA.

CONCLUSION

Chemical de-epithelialization with dilute ethanol appears to be a simple, safe, and effective alternative to mechanical scraping before PRK and might promote faster visual rehabilitation.