Femtosecond laser–assisted laser in situ keratomileusis versus photorefractive keratectomy: Effect on ocular surface condition

Dry Eye Disease following LASIK, PRK, and LASEK: An Observational Cross-Sectional Study

Dry eye disease is the most frequent non-refractive postoperative complication following refractive surgery. This prospective study investigated the development of dry eye disease after three common refractive laser surgeries: laser in situ keratomileusis (LASIK), photorefractive keratectomy (PRK), and laser-assisted sub-epithelial keratectomy (LASEK). Patients who underwent uneventful refractive surgery in a single private medical center between May 2017 and September 2020 were included. Ocular surface disease was graded according to the Dry Eye Workshop severity (DEWS) classification. Patients were examined 6 months following refractive surgery. The analysis included 251 eyes of 137 patients: 64 eyes (36 patients) after LASEK, 90 eyes (48 patients) after PRK, and 97 eyes (53 patients) after LASIK. At 6 months post-surgery, the DEWS score was higher for the LASIK than the PRK and LASEK groups (p = 0.01). For the total cohort, severe DEWS score (grades 3 and 4) at 6 months post-surgery was correlated with female gender (p = 0.01) and to the amount of refractive correction (p < 0.001), but not to age (p = 0.87). In conclusion, LASIK surgery and female gender were associated with dry eye. Patients, particularly those with high myopia, should be counseled about the risk of developing dry eye after refractive surgeries.

Traumatic displacement of laser in situ keratomileusis flaps: an integrated clinical case presentation

Background

Traumatic dislocation of laser-assisted in situ keratomileusis (LASIK) corneal flaps is an uncommon postoperative complication that could occur any time after LASIK, and could be visually devastating. We evaluated the visual outcomes, corneal sensation, tear function, and dry eye questionnaire results of patients with traumatic dislocation of LASIK flaps, including one LASIK flap amputation.

Methods

This is a retrospective case series. Seven patients who were diagnosed with traumatic displacement of the LASIK flap and underwent flap replacement surgery between August 2014 and January 2019 were included.Patient’s visual acuity, refraction, corneal sensitivity, non-invasive tear breakup time (NIBUT), tear meniscus height (TMH), and ocular surface disease index (OSDI) results were evaluated.

Results

The patients’ mean age was 35.86 ± 5.84 years, and 42.9 % (3/7) were male. The mean duration from LASIK to trauma was 8.86 ± 2.48 years.The mean preoperative and postoperative six-month corrected distance visual acuity (CDVA) were 0.55 ± 0.34 and 0.02 ± 0.03, respectively. The mean spherical equivalent and astigmatism at six months postoperatively was − 1.0 ± 0.95 D and − 0.5 ± 0.25 D, respectively. The corneal flap was clear and well-positioned at the final follow-up (mean: 28.57 ± 6.9 months). 85.71 % (6/7) of the patients showed worse corneal sensation in the injured eye. Interocular OSDI discrepancy was less in those whose last visit was more than 30 months after the trauma.

Conclusions

Postoperative CDVAat six months was improved, and the refractive data also showed some improvement. The corneal nerve and tear function recovery peaked before 30 months, while the OSDI continued to show a strong trend of improvement beyond 30 months.

Femtosecond laser assisted in situ keratomileusis (FS-LASIK) yields better results than transepithelial photorefractive keratectomy (Trans-PRK) for correction of low to moderate grade myopia

INTRODUCTION

The purpose of this study was to compare the outcomes of transepithelial photorefractive keratectomy (Trans-PRK) with femtosecond laser assisted in situ keratomileusis (FS-LASIK) for the correction of low to moderate myopia.

METHODS

A retrospective cohort study design was used. The study group included patients with myopia less than -6.0 D, with or without concomitant astigmatism under 2.0 D, who were treated with FS-LASIK or Trans-PRK in 2013 through 2014. Background, clinical and outcome data were collected from the patient files. A comparison between eyes treated with FS-LASIK or Trans-PRK was performed.

RESULTS

The Trans-PRK group was comprised of 1793 eyes and the FS-LASIK group of 666 eyes. Mean ± SD spherical equivalent (SE) refraction prior to surgery was -3.43 ± 1.27 D in the Trans-PRK group and -3.18 ± 1.34 D in the FS-LASIK group (p < 0.001). Efficacy index values were 0.95 ± 0.14 in the Trans-PRK group and 0.98 ± 0.12 in the FS-LASIK group (p < 0.001), and corresponding safety index values were 0.96 ± 0.13 and 0.99 ± 0.12 (p < 0.001). Distance from target refraction was 0.45 ± 0.42 D in Trans-PRK group and 0.43 ± 0.38 D in the FS-LASIK group (p = 0.537); 71.6% and 74.2% of eyes were within ±0.5 D of attempted correction, respectively (p = 0.193).

CONCLUSIONS

Both Trans-PRK and FS-LASIK demonstrated excellent results, mostly comparable with the current literature. FS-LASIK achieved better results than Trans-PRK surgery in the efficacy and safety parameters.

Impact of corneal refractive surgery on the precorneal tear film

Corneal refractive surgeries are one of the commonly performed procedures for correction of refractive errors. Tear film abnormality is the most common postoperative complication of corneal refractive surgeries. Consequently, these procedures represent a clinically significant cause of dry eye disease. The mechanisms which lead to dry eye disease include corneal sensory nerve dysfunction, ocular surface desiccation, glandular apoptosis and ocular surface inflammation. Although transient tear film abnormalities occur in almost all patients following surgery, patients with pre-existing dry eye symptoms or dry eye disease are at significant risk of developing more severe or long-term ocular surface disease. As such, careful patient selection and preoperative evaluation is essential to ensuring successful surgical outcomes. This is particularly important with LASIK which has the strongest association with dry eye disease. Appropriate surface lubrication and anti-inflammatory therapy remains the cornerstone treatment. Timely and effective management is important to facilitate visual rehabilitation and reduce the risk of secondary complications. In this review we describe the causes, pathophysiology, risk factors, manifestations, and management of tear film dysfunction and dry eye disease following corneal refractive surgery.

Postoperative Corneal Complications in Small Incision Lenticule Extraction: Long-Term Study

PURPOSE

To investigate the incidence and clinical results of corneal complications after small incision lenticule extraction (SMILE).

METHODS

A retrospective cohort study including 3,223 patients (6,373 eyes) who were treated for myopia or myopic astigmatism was conducted. Postoperative corneal complications were recorded. Postoperative follow-up visits were scheduled on days 1 and 7 and months 1, 3, 6, and 12.

RESULTS

Of the 6,373 cases, 432 eyes (6.8%) developed at least one corneal complication postoperatively. These included punctate epithelial erosions (3.26%), diffuse lamellar keratitis (DLK) (2.17%), corneal infiltrates (0.39%), interface debris/secretion (0.30%), interface haze (0.17%), interface foreign body (0.24%), corneal striae (0.14%), corneal edema (0.09%), and epithelial ingrowth (0.02%). Of cases with corneal complications, 308 (71.3%) had an uncorrected distance visual acuity (UDVA) of better than 20/25 and 49 (11.3%) eyes lost two or more lines of corrected distance visual acuity (CDVA) on the first day after surgery. By 3 months, only 2 eyes (0.9%) had lost two or more lines of CDVA. At 6 months, 1 eye (1.0%) did not achieve a UDVA of 20/25 as a result of stage 3 DLK, but achieved 20/20 by 1 year. The postoperative spherical equivalent in cases without complications was lower than that in cases with complications at 1 day and 1 and 3 months (P = .001, .011, and .001, respectively), but there was no statistical difference at 6 and 12 months.

CONCLUSIONS

In this large cohort study, a variety of corneal complications were noted after SMILE. Although some of these complications may temporarily affect visual recovery, most resolve with appropriate treatment. [J Refract Surg. 2019;35(3):146-152.].

Impact of topical anti-fibrotics on corneal nerve regeneration in vivo

Recent work in vitro has shown that fibroblasts and myofibroblasts have opposing effects on neurite outgrowth by peripheral sensory neurons. Here, we tested a prediction from this work that dampening the fibrotic response in the early phases of corneal wound healing in vivo could enhance reinnervation after a large, deep corneal injury such as that induced by photorefractive keratectomy (PRK). Since topical steroids and Mitomycin C (MMC) are often used clinically for mitigating corneal inflammation and scarring after PRK, they were ideal to test this prediction. Twenty adult cats underwent bilateral, myopic PRK over a 6 mm optical zone followed by either: (1) intraoperative MMC (n = 12 eyes), (2) intraoperative prednisolone acetate (PA) followed by twice daily topical application for 14 days (n = 12 eyes), or (3) no post-operative treatment (n = 16 eyes). Anti-fibrotic effects of MMC and PA were verified optically and histologically. First, optical coherence tomography (OCT) performed pre-operatively and 2, 4 and 12 weeks post-PRK was used to assess changes in corneal backscatter reflectivity. Post-mortem immunohistochemistry was then performed at 2, 4 and 12 weeks post-PRK, using antibodies against α-smooth muscle actin (α-SMA). Finally, immunohistochemistry with antibodies against βIII-tubulin (Tuj-1) was performed in the same corneas to quantify changes in nerve distribution relative to unoperated, control cat corneas. Two weeks after PRK, untreated corneas exhibited the greatest amount of staining for α-SMA, followed by PA-treated and MMC-treated eyes. This was matched by higher OCT-based stromal reflectivity values in untreated, than PA- and MMC-treated eyes. PA treatment appeared to slow epithelial healing and although normal epithelial thickness was restored by 12 weeks-post-PRK, intra-epithelial nerve length only reached ∼1/6 normal values in PA-treated eyes. Even peripheral cornea (outside the ablation zone) exhibited depressed intra-epithelial nerve densities after PA treatment. Stromal nerves were abundant under the α-SMA zone, but appeared to largely avoid it, creating an area of sub-epithelial stroma devoid of nerve trunks. In turn, this may have led to the lack of sub-basal and intra-epithelial nerves in the ablation zone of PA-treated eyes 4 weeks after PRK, and their continuing paucity 12 weeks after PRK. Intra-operative MMC, which sharply decreased α-SMA staining, was followed by rapid restoration of nerve densities in all corneal layers post-PRK compared to untreated corneas. Curiously, stromal nerves appeared unaffected by the development of large, stromal, acellular zones in MMC-treated corneas. Overall, it appears that post-PRK treatments that were most effective at reducing α-SMA-positive cells in the early post-operative period benefited nerve regeneration the most, resulting in more rapid restoration of nerve densities in all corneal layers of the ablation zone and of the corneal periphery.

Effects of ambient humidity on the Cochet-Bonnet aesthesiometer

PURPOSE

The Cochet-Bonnet (COBO) aesthesiometer is the current standard in corneal sensitivity assessment. This study investigates the influence of ambient room humidity levels on the stimulus force exerted by the instrument.

METHODS

A COBO instrument (Luneau Opthalmologie) with 0.12 mm nominal nylon filament diameter was placed in an environment chamber (Electro-tech systems Inc. PA, USA) at 25 °C and relative humidity (%RH) set to either 20-80%, in 10% steps. After 12 h in the chamber at a chosen %RH level, the instrument was removed and exerted force measured by pressing the nylon filament onto the plate of an analytical microbalance (Mettler-Toledo AB265; precision ±0.0001 g) at a perpendicular angle, by a predetermined amount. Exerted force onto the microbalance was recorded in grams for a specified filament length. Procedure was repeated for filament lengths 10-60 mm, in 5 mm steps. The instrument was returned to the chamber and procedure repeated 5 times, before repeating at the next %RH setting (random order). Measurements at each filament lengths were compared using one-way ANOVA and post-hoc Tukey's range test. A p-value < 0.05 denoted statistical significance.

RESULTS

Significant differences in exerted force were observed with alteration in %RH levels for each filament length (all p < 0.001). Exerted force decreased significantly with an increase in %RH for all filament lengths, with the average force decreasing by 15% with each 10% rise in %RH.

CONCLUSIONS

This study confirms previous suggestions that the rigidity of the COBO nylon filament is affected by ambient room humidity levels, with implications on the stimulus force delivered by the instrument. A conversion table is provided for converting filament lengths to pressure for a range of relative humidity levels.