Comparative evaluation of ‘flap on’ and ‘flap off’ techniques of Epi-LASIK in low-to-moderate myopia

Sodium Channel Blockers Modulate Abnormal Activity of Regenerating Nociceptive Corneal Nerves After Surgical Lesion

Purpose

To test the effect of different sodium channel blockers on the electrical activity of corneal nociceptors in intact and surgically injured corneas.

Methods

In anesthetized guinea pigs, a 4-mm diameter corneal flap was performed in one eye at a midstromal depth using a custom-made microkeratome. At different times after surgery (3 hours to 15 days), the electrical activity of corneal nociceptor fibers was recorded from ciliary nerve filaments in the superfused eye in vitro. Mechanical threshold was measured using calibrated von Frey hairs; chemical stimulation was performed applying 30-second CO2 gas pulses. The characteristics of the spontaneous and stimulus-evoked activity of corneal nociceptors recorded from intact and lesioned corneas, before and after treatment with the sodium channel blockers lidocaine, carbamazepine, and amitriptyline, were compared.

Results

No spontaneous or stimulus-evoked impulse activity was detected inside the flap at any of the studied time points. However, both were recorded from mechanonociceptor and polymodal nociceptors fibers in the surrounding corneal tissue, being significantly higher (sensitization) 24 to 48 hours after surgery. In these fibers, none of the tested drugs affected mechanical threshold, but they significantly reduced the CO2 response of polymodal nociceptors of intact and injured corneas. Likewise, they diminished significantly the transient increase in spontaneous and stimulus-evoked activity of sensitized polymodal nociceptors.

Conclusions

Na+ channel blockers decrease the excitability of intact and sensitized corneal nociceptor fibers, thus acting as potential tools to attenuate their abnormal activity, which underlies the spontaneous pain, hyperalgesia, and allodynia often accompanying surgical corneal lesions, as occurs after photorefractive surgery.

A control-matched comparison of flap off and flap on laser-assisted subepithelial keratectomy (LASEK) for the treatment of myopia and myopic astigmatism

Purpose

To compare the visual and refractive outcomes of flap off and flap on, Laser Assisted Subepithelial Keratectomy (LASEK) for low to moderate myopia.

Methods

A prospective non-randomized control-matched study was conducted in which 53 patients underwent LASEK for the treatment of low to moderate myopia and myopic astigmatism. Right eye of each patient had the flap removed (flap off) while in the left eye the flap was recapped (flap on). Equal number (N = 53) of flap on was matched with flap off having preoperative manifest refraction spherical equivalent within ±0.75 Diopters (D). Primary outcome variables included uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA) and manifest refraction.

Results

Preoperatively, the mean spherical equivalent (SE) was −3.59 ± 1.46 D for flap off and −3.67 ± 1.51 D for flap on (p = 0.779). The mean preoperative sphere was −3.32 ± 1.58 D for flap off group and −3.36 ± 1.61 D for flap on group (p = 0.338) whereas, the mean preoperative cylinder was −0.55 ± 0.70 D and −0.63 ± 0.68 D for flap removal and flap preservation groups respectively (p = 0.576). Postoperatively, the mean LogMAR UCVA was −0.035 ± 0.079 for flap off and −0.043 ± 0.085 for flap on. The percentages of eyes that had UCVA of 20/40 or better were 98.1% for flap off group and 100% for flap on group (p = 0.317). Mean postoperative SE was 0.00 ± 0.19 D for flap off group and −0.03 ± 0.43 D for flap on group. In flap removal group, 100% eyes were within ±0.50 D of the intended correction while in flap preservation group, 92.5% and 100% eyes were within ±0.50 D and ±1.00 D of the intended correction, respectively. Mean postoperative LogMAR BSCVA was −0.013 ± 0.044 for flap removal group and −0.016 ± 0.049 for flap preservation group (p = 0.727).

Conclusions

The differences in the visual and refractive results between flap preservation and flap removal groups were not clinically significant. Both procedures seemed safe and effective for the treatment of myopia and myopic astigmatism.

Laser-assisted subepithelial keratectomy versus epipolis laser in situ keratomileusis for myopia: a meta-analysis of clinical outcomes

BACKGROUND

To identify possible differences between laser-assisted subepithelial keratectomy and epipolis laser in situ keratomileusis for myopia.

DESIGN

Meta-analysis.

PARTICIPANTS

Patients from previously reported comparative studies treated by laser-assisted subepithelial keratectomy versus epipolis laser in situ keratomileusis.

METHODS

A systematic literature retrieval was conducted in the MEDLINE, EMBASE and Cochrane Library, up to January 2013. The included studies were subject to a meta-analysis using a RevMan 5.1 version software.

MAIN OUTCOME MEASURES

The differences in efficacy, predictability, safety, epithelial healing time, pain perception and corneal haze formation.

RESULTS

A total of six studies involving 517 eyes were included. There were no statistically significant differences in the final proportion of eyes with uncorrected visual acuity of 6/6 or better (P = 0.43), mean postoperative uncorrected visual acuity (P = 0.53), final proportion of eyes with refraction within ± 0.50 D (P = 0.62) and ± 1.00 D (P = 0.16) of target, final proportion of eyes losing two or more lines of best spectacle-corrected visual acuity (P = 1.00), healing time of corneal epithelium (P = 0.58), final proportion of eyes with corneal haze grade 0.5 or higher (P = 0.26), and corneal haze levels (P = 0.36).

CONCLUSIONS

There were no significant differences in efficacy, predictability, safety, epithelial healing time and corneal haze formation between laser-assisted subepithelial keratectomy and epipolis laser in situ keratomileusis, but the result was limited. Future more data are required to detect the potential differences between the two procedures.

Comparison of clinical results between flap-on and flap-off techniques of epithelial-laser in situ keratomileusis in correction of low to moderate myopia in eyes with thin corneas

PURPOSE

To prospectively compare flap-on and flap-off techniques of epithelial-laser in situ keratomileusis (epi-LASIK) for the correction of low to moderate myopia in patients with thin corneas.

METHODS

In this randomized, interventional study, the cohort was comprised of 88 eyes (44 patients) with myopia which underwent epi-LASIK. The epithelium was separated as a 9 mm flap with 2-4 mm nasal hinge with epikeratome (Lasatom, Gebauer Medizintechnik GmbH, Neuhausen, Germany) and the ablation was performed with the MEL 80 excimer laser (Carl Zeiss, Meditec, Jena, Germany). Thirty-eight eyes underwent flap-on Epi-LASIK where the flap was repositioned after ablation (flap-on group) and 50 eyes underwent flap-off Epi-LASIK where the epithelial flap was discarded (flap-off group). Pre- and post-operative uncorrected visual acuity (UCVA), best spectacle corrected visual acuity (BSCVA), and spherical equivalent (SE) were collected for each group. Post-operative pain, time to epithelialization, and corneal haze were also collected postoperatively. Variables were compared with the paired t-test, chi-squared test and one-way analysis of variance. Statistically significance was indicated by p < 0.05.

RESULTS

The mean preoperative SE was -3.89 ± 1.9 diopters (D) for the flap-on group and -3.92 ± 2.17 D for the flap-off group (p = 0.96). The mean follow-up was 12 months. The mean pain score was comparable on all postoperative days except the 2nd postoperative day where the flap-on had significantly lower mean pain scores (p = 00). Time for epithelial healing was 4.39 ± 0.49 days in flap-on group and 4.64 ± 0.69 days in flap-off group (p = 0.07). There was no significant difference in the postoperative UCVA between groups (p = 0.77). Corneal haze at the end of postoperative follow-up was not different between groups (p = 0.217).

CONCLUSION

There is no significant difference in the clinical outcomes between flap-on and flap-off techniques of Epi-LASIK for the correction of low to moderate myopia.

Flap-off epi-LASIK versus automated epithelial brush in PRK: a prospective comparison study of pain and reepithelialization times

PURPOSE

To compare the effect of flap-off epi-LASIK versus automated brush epithelial removal on pain and wound healing in low myopic photorefractive keratectomy (PRK).

METHODS

In this prospective intraindividual study 60 patients received surface ablation in each eye. Epithelial removal was performed by an automated brush technique in one eye (brush group) and epi-LASIK with flap removal (flap-off group) in the fellow eye. The epithelial defect size was measured daily after surgery until both eyes were reepithelialized. Postoperative pain on a scale from 0 to 6 and topical and oral analgesic medication use was recorded until the bandage contact lens was removed.

RESULTS

The flap-off group had significantly less postoperative pain on days 1 (P=.0003), 2 (P=.0001), 3 (P<.0001), and 4 (P<.0001) compared to the brush group. However, the average difference in pain scores between groups was only 0.33 points out of 6. No difference was noted in the normalized overall percentage rate of healing over the first 4 days in the flap-off group (5.41±1.39%/hour) compared to the brush group (5.42±1.94%/hour) (P=.97).

CONCLUSIONS

The flap-off group showed a statistically but not clinically significant advantage over the brush group in pain scores. However, no difference was noted in the percentage rate of epithelial healing time between the two groups.

Subjective pain, visual recovery and visual quality after LASIK, EpiLASIK (flap off) and APRK - a consecutive, non-randomized study

INTRODUCTION

Laser in situ keratomileusis (LASIK) is superior to surface ablation techniques (SAT) such as alcohol photorefractive keratectomy (APRK) or Epi-LASIK (EpiK) in terms of visual recovery and postoperative pain. This study compares subjective symptoms and visual recovery of two different SATs with LASIK.

MATERIALS AND METHODS

One hundred and twenty seven patients were operated using one of the three techniques. Patients filled out a questionnaire describing symptoms assessing subjective visual recovery on a linear scale from 'not functioning' to 'full visual function' and pain on a linear scale from 'no pain' to 'severe daily pain'. Subjective symptoms such as halos, double vision, low night vision, reduced contrast and dry eyes were also evaluated.

RESULTS

Visual recovery was faster and discomfort symptoms less pronounced with the LASIK than with surface ablation procedures. More pain was reported after APRK than after EpiK (flap-off technique) in the early postoperative period, with a maximum of pain on postoperative days 3-4. Subjective visual recovery showed no statistically significant difference between the two surface ablation procedures. Halos, double vision, low night vision, reduced contrast and dry eyes were more extensively reported by the EpiK than the APRK group and were less pronounced in the LASIK than in the SAT group.

DISCUSSION AND CONCLUSIONS

Our study does not uniformly support the previously published favourable results of EpiK compared to APRK with regard to subjective recovery of vision and postoperative pain.

Comparison of Tear cytokines and clinical outcomes between off-flap and on-flap epi-LASIK with mitomycin C

PURPOSE

To compare tear cytokines and clinical outcomes between off-flap and on-flap epi-LASIK eyes and explore the possible mechanism for the clinical differences.

METHODS

This double-masked, randomized study enrolled 18 myopic patients who underwent off-flap epi-LASIK with mitomycin C (MMC) in 1 eye and on-flap epi-LASIK with MMC in the contralateral eye. Tears were collected from each eye preoperatively and 2 hours, 1 day, and 5 days postoperatively. Concentrations of multiple tear cytokines were measured by a multiplex immunobead assay. Uncorrected distance visual acuity (UDVA), refraction, haze scores, pain scores, and percentage of corneal epithelial healing were evaluated.

RESULTS

Compared with the on-flap group, the off-flap group had outcomes of better UDVA and higher percentages of epithelial healing at 5 days after surgery (P<.001) and lower levels of haze at 1 month after surgery (P=.049). Preoperatively, no significant differences were noted in the release rate of all tear cytokines between groups. At 2 hours postoperatively, the release rate of tear basic fibroblast growth factor (bFGF), platelet-derived growth factor-BB (PDGF-BB), interleukin-8 (IL-8), and tumor necrosis factor alpha (TNF-α) in the off-flap group were significantly lower than those in the on-flap group (P=.011, .017, .048, and .041, respectively).

CONCLUSIONS

Off-flap epi-LASIK with MMC offers faster corneal epithelial healing and visual recovery, and temporary less haze than on-flap epi-LASIK with MMC. The lower tear levels of bFGF, PDGF-BB, IL-8, and TNF-α in the offflap group 2 hours after surgery may suggest a possible mechanism for the clinical differences.

Visual and Refractive Outcome of Epi-LASIK for Myopia in Thin Corneas: a 12-Month Follow-Up

Purpose.

A nonrandomized, retrospective, cohort, single-center study was designed to examine the visual and refractive outcome of epi–laser-assisted in situ keratomileusis (LASIK) for myopia (with and without astigmatism) in patients with thin corneas (less than 500 µm), and to compare these results with those of a group of patients with normal corneal thickness.

Methods.

Uncorrected distance visual acuity (UCVA), spherical and cylindrical residual refractive error, mean keratometry readings (Km), and pupil diameter were measured postoperatively at 24 hours, 1 week, 1 month, 3 months, and 12 months in a group of 28 eyes with thin corneas (group 1) and a second age- and gender-matched group of 28 eyes with normal corneal thickness (group 2). In addition, the efficacy index was calculated at every postoperative examination.

Results.

Postoperative central corneal thickness was 464.14±50.40 µm in group 1 and 421.89±26.63 µm in group 2 (p<0.001). No statistically significant difference was found in UCVA, efficacy index, and spherical and cylindrical residual error between both groups, with an evolution towards stability over time in all cases. Statistically significant between-group differences in Km at all follow-up examinations were explained by between-group differences in ablation depth and attempted spherical correction.

Conclusions.

A 12-month follow-up revealed epi-LASIK for myopia (with and without astigmatism) to be a safe and predictable surface ablation procedure, with good visual and refractive outcome in patients with thin corneas, as compared with a group of patients with normal corneal thickness.

Corneal refractive surgery: past to present

There have been many historical corneal refractive techniques and procedures developed over the years. From early techniques of radial keratotomy to modern excimer laser techniques, the field of refractive surgery is one of the most rapidly developing in ophthalmology. This review details the historical aspects of the many early techniques up to current techniques used on millions of eyes around the world.

Comparison of clinical outcomes between 'on-flap' and 'off-flap' epi-LASIK for myopia: a meta-analysis

OBJECTIVE

To examine possible differences in clinical outcomes between off-flap and on-flap epipolis laser in situ keratomileusis (epi-LASIK) for myopia.

METHODS

Pertinent studies were selected by extensive searches. A total of 9 studies reporting on a total of 958 eyes were included in the present meta-analysis. Statistical analysis was performed using RevMan 5.0 software.

RESULTS

There were no significant differences in the final refractive spherical equivalent (p = 0.38), manifest refractive spherical equivalent within ±0.50 D of the target (p = 0.76), final uncorrected visual acuity (p = 0.90), loss of ≥1 line of best spectacle-corrected visual acuity (p = 0.99), and corneal haze at 3 months postoperatively (p = 0.96) or more than 6 months (p = 0.64). More patients felt severe pain in the on-flap group than in the off-flap group, although this finding was not statistically significant (p = 0.05). However, off-flap epi-LASIK had a better mean uncorrected visual acuity at 3 days (p = 0.04) and 5 days (p = 0.01), and faster re-epithelialization (p < 0.00001) after surgery.

CONCLUSIONS

According to the available data, off-flap and on-flap epi-LASIK had equal visual and refractive outcomes for the treatment of myopia. Off-flap epi-LASIK had more rapid re-epithelialization and visual recovery compared to on-flap epi-LASIK.