Clinical Investigation of Off-Flap Epi-LASIK for Moderate to High Myopia

Update on Pain Management After Advanced Surface Ablation

PURPOSE

To provide an update for postoperative pain control strategies to help ophthalmic surgeons establish a more effective management plan for patients who underwent advanced surface ablation surgeries.

METHODS

Google Scholar, Scopus, ScienceDirect, and PubMed were the main resources used to search the medical literature.

RESULTS

The postoperative cornea's healing process is accompanied by intense pain as the chief complaint in the first days after the operation. Several strategies were developed to relieve postoperative pain after surface ablation procedures. These strategies included different preoperative, intraoperative, and postoperative methods. Considering the preoperative demographic and emotional factors, underlying dry eye, alternative epithelial removal techniques, bandage contact lenses, and topical or oral therapeutic agents are some examples of postoperative pain treatments after surface ablation procedures.

CONCLUSIONS

The current review revealed that despite the development of numerous protocols to relieve postoperative pain following surface ablations, the best approach could be a combination of different strategies. In practice, no validated and standardized strategy is available for total elimination of postoperative pain following advanced surface ablation surgeries. [J Refract Surg. 2021;37(11):782-790.].

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.

Development and clinical verification of numerical simulation for laser in situ keratomileusis

To develop and validate numerical models of the laser in situ keratomileusis (LASIK) procedure through considering its effect on corneal biomechanical behavior. 3D finite element models of the human eye were developed to simulate LASIK. The models' predictions of post-operative corneal elevation, corneal refractive power with vector decomposition (M_-c-pos, J_0-c-pos, J_45-c-pos) and refractive error correction (M_-rec, J_0-rec, J_45-rec) were compared against clinical data obtained for 28 eyes of 28 patients. A parallel exercise was conducted to estimate the post-operative corneal shape using a shape subtraction method (SSM) - which does not consider the effects of LASIK on corneal mechanical behavior - and the results are compared with the finite element method (FEM). A significant decrease in elevation differences between FEM predictions and clinical data was found compared with the differences between SSM results and clinical data (p = 0.000). In addition, there were no significant differences in post-operative equivalent sperical corneal refractive power between FEM results and corresponding clinical data (M_-c-pos: p = 0.501), while SSM showed significant differences with clinical data (M_-c-pos: p = 0.000). Further, FEM achieved a predicted value of M_-c-pos within ± 1.00D accuracy in 100% of cases, compared with 57% achieved by the SSM. M_-rec predicted by FEM was not significantly different from clinical results (p = 0.085), while SSM overestimated it (p = 0.000). The match between LASIK numerical model predictions with clinical measurements improved significantly when the procedure's effect on corneal biomechanical behavior was considered. This outcome has important implications on efforts to develop planning tools for refractive 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.

Ocular pain and discomfort after advanced surface ablation: an ignored complaint

Purpose

Laser vision correction is one of the most commonly performed elective surgical procedures in ophthalmology. Generally, discomfort besides pain (photophobia, burning sensation, tearing, and foreign body sensation) after these procedures is not taken into consideration in the clinical practice. The objective is to provide data on these symptoms and their relevance after advanced surface ablation (ASA).

Methods

Single-center survey study based on a structured questionnaire relative to the patients’ perceived symptoms after ASA. Inclusion criteria were: ≥18 years old, no ocular disease, with myopia (0.75 to 9 D) or hyperopia (0.25 to 5 D) with or without astigmatism, receiving ASA on at least one eye. All procedures were performed by the same surgeon. A descriptive analysis was performed.

Results

Seventy-three consecutive patients (34 men and 39 women) were included in the study. The median (range) of age was 33 (19–64) years. Sixty-nine patients had surgery done on both eyes. Postoperative pain was the most frequent comorbidity (97% [95% confidence interval {CI}: 90–100]) with a median (range) of intensity (verbal numerical rating scale) score of 7 (2–10). Photophobia: 85% (95% CI: 75–92); burning sensation: 62% (95% CI: 50–73); tearing: 59% (95% CI: 47–70); and foreign body sensation: 48% (95% CI: 36–60) were also prevalent postoperative symptoms. Pain during ASA was reported for 44% (95% CI: 32–56) of patients.

Conclusion

Comorbidities such as pain, photophobia, burning sensation, tearing, and foreign body sensation are prevalent after ASA procedure. Postoperative pain should be taken into consideration due to its prevalence and intensity. A new and more efficient postoperative analgesic protocol should be established.

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.

Conventional Epi-LASIK and lamellar epithelial debridement in myopic patients with dermatologic keloids

We report the outcome of conventional epipolis laser in situ keratomileusis (Epi-LASIK, flap-on) and lamellar epithelial debridement (LED; Epi-LASIK, flap-off) in myopic patients with dermatologic keloids. Three patients, who were all noted to be susceptible to keloid scarring, received conventional Epi-LASIK in their right eyes and LED in their left eyes. The patients were followed-up for 6 to 21 months after their surgeries, and the outcomes were then evaluated. In case 1, the preoperative spherical equivalent (SE) was -6.5 diopters (D) in the right eye (OD) and -6.25 D in the left eye (OS). At 21 months postoperatively, the uncorrected visual acuity (UCVA) was 20 / 12.5 in both eyes. In case 2, the preoperative SE was -5.25 (OD) / -6.00 (OS). After six months, the postoperative UCVA was 20 / 12.5 in both eyes. In case 3, the preoperative SE was -4.5 (OD) / -2.0 (OS). The UCVA at the six-month follow-up was 20 / 12.5 in both eyes. No adverse events, including corneal haze, occurred in any of the patients. All three of our patients reported excellent visual outcomes following both conventional Epi-LASIK and LED, despite their histories of keloid formation. The present cases suggest that both Epi-LASIK and LED may be safe and effective techniques for myopic patients with dermatologic keloids.

Surface ablation with iris recognition and dynamic rotational eye tracking-based tissue saving treatment with the Technolas 217z excimer laser

PURPOSE

To evaluate the visual and refractive outcomes and expected benefits of Tissue Saving Treatment algorithm-guided surface ablation with iris recognition and dynamic rotational eye tracking.

METHODS

This prospective, interventional case series comprised 122 eyes (70 patients). Pre- and postoperative assessment included uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), refraction, and higher order aberrations. All patients underwent Tissue Saving Treatment algorithm-guided surface ablation with iris recognition and dynamic rotational eye tracking using the Technolas 217z 100-Hz excimer platform (Technolas Perfect Vision GmbH). Follow-up was performed up to 6 months postoperatively. Theoretical benefit analysis was performed to evaluate the algorithm's outcomes compared to others.

RESULTS

Preoperative spherocylindrical power was sphere -3.62 ± 1.60 diopters (D) (range: 0 to -6.75 D), cylinder -1.15 ± 1.00 D (range: 0 to -3.50 D), and spherical equivalent -4.19 ± 1.60 D (range: -7.75 to -2.00 D). At 6 months, 91% (111/122) of eyes were within ± 0.50 D of attempted correction. Postoperative UDVA was comparable to preoperative CDVA at 1 month (P=.47) and progressively improved at 6 months (P=.004). Two eyes lost one line of CDVA at 6 months. Theoretical benefit analysis revealed that of 101 eyes with astigmatism, 29 would have had cyclotorsion-induced astigmatism of ≥ 10% if iris recognition and dynamic rotational eye tracking were not used. Furthermore, the mean percentage decrease in maximum depth of ablation by using the Tissue Saving Treatment was 11.8 ± 2.9% over Aspheric, 17.8 ± 6.2% over Personalized, and 18.2 ± 2.8% over Planoscan algorithms.

CONCLUSIONS

Tissue saving surface ablation with iris recognition and dynamic rotational eye tracking was safe and effective in this series of eyes.