Assessment of tear osmolarity and other dry eye parameters in post-LASIK eyes

An experimental model for primary neuropathic corneal pain induced by long ciliary nerve ligation in rats

ABSTRACT

Neuropathic corneal pain (NCP) is a new and ill-defined disease characterized by pain, discomfort, aching, burning sensation, irritation, dryness, and grittiness. However, the mechanism underlying NCP remain unclear. Here, we reported a novel rat model of primary NCP induced by long ciliary nerve (LCN) ligation. After sustained LCN ligation, the rats developed increased corneal mechanical and chemical sensitivity, spontaneous blinking, and photophobia, which were ameliorated by intraperitoneal injection of morphine or gabapentin. However, neither tear reduction nor corneal injury was observed in LCN-ligated rats. Furthermore, after LCN ligation, the rats displayed a significant reduction in corneal nerve density, as well as increased tortuosity and beading nerve ending. Long ciliary nerve ligation also notably elevated corneal responsiveness under resting or menthol-stimulated conditions. At a cellular level, we observed that LCN ligation increased calcitonin gene-related peptide (neuropeptide)-positive cells in the trigeminal ganglion (TG). At a molecular level, upregulated mRNA levels of ion channels Piezo2, TRPM8, and TRPV1, as well as inflammatory factors TNF-α, IL-1β, and IL-6, were also detected in the TG after LCN ligation. Meanwhile, consecutive oral gabapentin attenuated LCN ligation-induced corneal hyperalgesia and increased levels of ion channels and inflammation factors in TG. This study provides a reliable primary NCP model induced by LCN ligation in rats using a simple, minimally invasive surgery technique, which may help shed light on the underlying cellular and molecular bases of NCP and aid in developing a new treatment for the disease.

Patient-Reported Dry Eye Outcomes After Myopic Femtosecond-LASIK: A 6-Month Prospective Analysis

Purpose

To evaluate patient-reported outcomes in relation to dry eye symptoms following femtosecond LASIK (FS-LASIK).

Methods

This study was conducted as a prospective, observational case series of patients undergoing bilateral myopic FS-LASIK at a single private practice institution. Enrolled patients were prospectively administered a standardized Dry Eye Symptom Index survey (analog score of 1 to 5 with 5 being the worst) prior to treatment and at 6-months after FS-LASIK. The following objective measurements were also recorded: objective scatter index (OSI), tear film osmolarity (TFO), and automated tear break-up times (TBUT).

Results

There were 40 enrolled patients who underwent bilateral myopic FS-LASIK and completed the 6-month study period. The Dry Eye Symptom Index score improved from 2.3 (2.0-2.6, 95% Confidence Intervals) prior to treatment to 1.3 (1.0-1.5) at 6 months (p < 0.0001). Subset analysis of the subjective dry eye symptoms showed improvement in "grittiness" (p = 0.001) but not in "light sensitivity" or "soreness" (p = 0.13 and p = 0.24, respectively). There were no significant changes in the OSI, TFO, or TBUT measurements at 6 months (p > 0.05 for all), and there were no adverse events or complications during the study period.

Conclusion

Patient-reported dry eye symptoms improve after 6 months following myopic FS-LASIK. This did not correlate with the objective dry eye measurement changes at 6 months.

The Effect of Meibomian Gland Dysfunction on Laser-Assisted In Situ Keratomileusis in Asymptomatic Patients

INTRODUCTION

To evaluate the impact of asymptomatic meibomian gland dysfunction (MGD) on laser-assisted in situ keratomileusis (LASIK) outcomes and dry eye signs and symptoms.

METHODS

A retrospective analysis of patients who underwent LASIK surgery between July 2017 and February 2018 at Care Vision Refractive Clinic, Tel Aviv, Israel, was done. Patients were divided into those who had preoperative asymptomatic significant MGD (MGD group) and those who did not have preoperative significant MGD (control group). Outcomes were the postoperative presence of punctate epithelial erosions, dry eye symptoms, the number of postoperative visits as a measure of adverse events, visual acuity, spherical equivalent, safety index, efficacy index, and the type of refractive error (myopia or hyperopia).

RESULTS

A total of 497 eyes were included in this study. Both groups had similar rates of punctate epithelial erosions, 30 (12.9%) patients vs. 39 patients (14.8%) (p = 0.31); postoperative complaints of dryness, 75 patients (32.3%) vs. 90 patients (34.2%) (p = 0.36); and postoperative number of visits, 3.15 ± 0.75 vs. 3.12 ± 0.54 (p = 0.59). Uncorrected visual acuity (logMAR) at 1 month (0.026 ± 0.09 vs. 0.026 ± 0.17, p = 0.99) after surgery was similar in both groups. Mean spherical equivalent was 0.03 ± 0.17 and - 0.03 ± 0.18 (p = 0.99) in both groups. Safety index was 1.024 ± 0.06 in the clinically significant MGD group and 1.029 ± 0.07 in the control group (p = 0.45). Efficacy index was also similar in both groups (0.966 ± 0.155 and 0.979 ± 0.14, respectively, p = 0.31). No differences were found between patients with myopia and hyperopia.

CONCLUSIONS

Patients with preoperative asymptomatic MGD have similar LASIK outcomes to patients without preoperative asymptomatic MGD. Accordingly, no preoperative MGD treatment or special caution is needed in these cases.

Ocular Surface Changes Associated with Ophthalmic Surgery

Dry eye disease causes ocular discomfort and visual disturbances. Older adults are at a higher risk of developing dry eye disease as well as needing for ophthalmic surgery. Anterior segment surgery may induce or worsen existing dry eye symptoms usually for a short-term period. Despite good visual outcomes, ocular surface dysfunction can significantly affect quality of life and, therefore, lower a patient’s satisfaction with ophthalmic surgery. Preoperative dry eye disease, factors during surgery and postoperative treatment may all contribute to ocular surface dysfunction and its severity. We reviewed relevant articles from 2010 through to 2021 using keywords “cataract surgery”, ”phacoemulsification”, ”refractive surgery”, ”trabeculectomy”, ”vitrectomy” in combination with ”ocular surface dysfunction”, “dry eye disease”, and analyzed studies on dry eye disease pathophysiology and the impact of anterior segment surgery on the ocular surface.

Comparison of Femto-LASIK With Combined Accelerated Cross-linking to Femto-LASIK in High Myopic Eyes: A Prospective Randomized Trial

PURPOSE

To evaluate the safety and efficacy of femtosecond (fs) laser-assisted in situ keratomileusis (LASIK) combined with accelerated corneal cross-linking (LASIK Xtra) compared to conventional fs-LASIK (convLASIK) in high myopic patients.

DESIGN

Prospective, randomized, fellow-eye controlled clinical trial.

METHODS

Setting: Department of Ophthalmology, Goethe University, Frankfurt/Germany. StudyPopulation: Twenty-six patients with high myopia and/or myopic astigmatism received randomized treatment with LASIK Xtra (30 mW/cm², 90 seconds with continuous ultraviolet-A) in 1 eye and convLASIK in the other eye. MainOutcomeMeasures: Uncorrected distance visual acuity (UDVA), best spectacle-corrected VA (BSCVA), manifest refractive spherical equivalent (MRSE), endothelial cell count (ECC), and corneal thickness.

RESULTS

The UDVA improved from 1.26 ± 0.13 logMAR preoperative to -0.02 ± 0.15logMAR in LASIK Xtra eyes and from 1.27 ± 0.12 logMAR to 0.01 ± 0.15 logMAR in the convLASIK eyes (P > .05). The MRSE changed from -7.35 ± 1.15 diopters (D) and -7.5 ± 1.12 D to -0.17 ± 0.43 D and -0.25 ± 0.46 D, respectively. There was no significant difference in outcomes between both groups during the 12 months follow-up except for the convLASIK eyes' showing slightly better BSCVA after 1 week (P < .05). ConvLASIK eyes revealed a nonsignificant trend toward myopic regression from 3 to 12 months postoperative with a change in MRSE of -0.15 D compared to -0.1 D in LASIK Xtra eyes. Topography showed stability of corneal curvature with no signs of keratectasia in both groups at 12 months.

CONCLUSION

While apparently safe, LASIK Xtra showed no advantages over conventional LASIK. At 12 months, both groups showed no difference regarding UDVA and refractive stability, and no signs of keratectasia.

Tear meniscus evaluation after microkeratome laser in situ keratomileusis, femtosecond laser and femtosmile laser techniques using anterior segment optical coherence tomography

Purpose

The purpose of this study was to compare the effects of three different corneal refractive surgeries: microkeratome laser in situ keratomileusis (LASIK), femtosecond laser in situ keratomileusis (FS-LASIK) and femtosecond small incision lenticule extraction (FS-SMILE) on 6-month postoperative stability of tear film to provide a basis for selection of operative procedures.

Patients and methods

This is a prospective, randomized, comparative study that included 90 eyes of three equal groups of patients. Each group was subjected to a different laser technique: LASIK, FS-LASIK and FS-SMILE. Using anterior segment spectral domain optical coherence tomography (AS-SD-OCT), the lower tear meniscus parameters were measured preoperatively and 1 week, 1 month, 3 months and 6 months postoperatively. Changes were studied and compared.

Results

There was a statistically significant difference in tear meniscus height (TMH) between FS-SMILE and FS-LASIK in the first week (P = 0.003) and first month (P = 0.002) with no statistically significant difference between both techniques at 3 and 6 months postoperatively. In FS-SMILE, TMH returned to 95% of its preoperative level after 1 month. There was no statistically significant difference in TMH between FS-LASIK and microkeratome LASIK techniques after 1 week and 1 month, but there was a statistically significant difference between both techniques in 3 months (P = 0.019) and 6 months (P = 0.032). Tear meniscus area (TMA) showed no statistically significant difference between FS-SMILE and FS-LASIK at all points of follow-up, but there was a statistically significant difference between both techniques and microkeratome LASIK (all P < 0.05). Microkeratome LASIK parameters failed to reach the preoperative level till 6 months.

Conclusion

Early recovery of the lower TMH can be achieved as early as 1 month post-operatively with the FS-SMILE technique compared to FS-LASIK and microkeratome LASIK techniques.

Variability of Tear Osmolarity Measurements With a Point-of-Care System in Healthy Subjects-Systematic Review

PURPOSE

To assess the variability of osmolarity measured by the point-of-care TearLab system in healthy eyes.

METHODS

A systematic review was performed by searching MEDLINE, Scopus, and the Web of Science Databases until November 2016 and checking reference lists of included articles and reviews. The requirements for inclusion were the availability of TearLab results in healthy subjects and a minimum study sample of 20 eyes. Two reviewers assessed articles against the inclusion criteria, extracted relevant data, and examined the methodological quality. We computed the weighted mean osmolarity using the study size as the weighting factor and calculated the rate of subjects with osmolarity values >308 mOsm/L, the Dry Eye Workshop Report 2017 (DEWS) cut-off value for dry eye disease (DED). We repeated the analysis after excluding reports with a possible conflict of interest or missing description of subject selection.

RESULTS

Searches retrieved 105 nonduplicate articles, and we included 33 studies investigating 1362 eyes of healthy participants who were asymptomatic and showed no clinical signs of DED. Sixty-three percent were female, and mean age was 37.3 years (range: 21.5-69.0 yr). Weighted mean osmolarity was 298 mOsm/L (95% confidence interval, 282-321 mOsm/L). The result of the subgroup analysis was similar. Overall, 386 of 1362 eyes (28.3%) fulfilled the DEWS's definition of DED (>308 mOsm/L).

CONCLUSIONS

There is a high variability of osmolarity measurements with the TearLab system. A substantial number of healthy subjects fulfill the DEWS's definition of DED. We propose interpreting the TearLab osmolarity results cautiously and in the context of other established methods.

Topical Osmoprotectant for the Management of Postrefractive Surgery-Induced Dry Eye Symptoms: A Randomised Controlled Double-Blind Trial

Background

Dry eye disease (DED) is one of the most common complications following refractive surgery.

Purpose

Evaluate the efficacy of an osmoprotective eye drop (Optive®) for the management of induced DED in refractive surgery patients.

Design

Double-masked randomised controlled trial.

Methods

Twenty-two refractive surgery patients oriented to apply FreshTears (FT; n = 13) or Optive (Op; n = 9), topically, QID, for 3 months. Eye exams were performed before surgery (T0) and 1-month (T1) and 3-month (T3) follow-up and consisted of tear film osmolarity, Schirmer 1 test, tear film breakup time (TBUT), fluorescein staining, and ocular surface disease index (OSDI) and patient symptoms questionnaires.

Main Outcome Measures

Pain and osmolarity.

Results

Pain increased significantly for FT at T3 (p < 0.05). A reduction in osmolarity was observed at T1 and T3 for Op group (p < 0.01) and at T3 for FT group (p < 0.05). TBUT showed a decrease between T0 and T1 for FT (p < 0.05). Schirmer 1 values increased significantly for Op in T1.

Conclusions

Op was superior to FT in regard to pain, osmolarity, TBUT, and Schirmer 1. Osmoprotectant solutes, such as L-carnitine, could attenuate inflammation and secondary DED. Osmoprotective lubricants can be effectively applied for the prevention of refractive surgery-related dry eye symptoms and signs.

Dry Eye Post-Laser-Assisted In Situ Keratomileusis: Major Review and Latest Updates

Dry eye is one of the most common complications occurring after laser-assisted in situ keratomileusis (LASIK), with virtually all patients experiencing some degree of postoperative dry eye symptoms. Enhanced understanding of the pathophysiology and mechanism of dry eye development in addition to preoperative screening of patients who are prone to dry eye is essential for better patient satisfaction and for improving short-term visual outcome postoperatively. This article reviews the latest studies published on LASIK-associated dry eye, including epidemiology, pathophysiology, risk factors, preoperative assessment, and management.

Patient-reported Outcomes for Assessment of Quality of Life in Refractive Error: A Systematic Review

SIGNIFICANCE

This review has identified the best existing patient-reported outcome (PRO) instruments in refractive error. The article highlights the limitations of the existing instruments and discusses the way forward.

PURPOSE

A systematic review was conducted to identify the types of PROs used in refractive error, to determine the quality of the existing PRO instruments in terms of their psychometric properties, and to determine the limitations in the content of the existing PRO instruments.

METHODS

Articles describing a PRO instrument measuring 1 or more domains of quality of life in people with refractive error were identified by electronic searches on the MEDLINE, PubMed, Scopus, Web of Science, and Cochrane databases. The information on content development, psychometric properties, validity, reliability, and responsiveness of those PRO instruments was extracted from the selected articles. The analysis was done based on a comprehensive set of assessment criteria.

RESULTS

One hundred forty-eight articles describing 47 PRO instruments in refractive error were included in the review. Most of the articles (99 [66.9%]) used refractive error-specific PRO instruments. The PRO instruments comprised 19 refractive, 12 vision but nonrefractive, and 16 generic PRO instruments. Only 17 PRO instruments were validated in refractive error populations; six of them were developed using Rasch analysis. None of the PRO instruments has items across all domains of quality of life. The Quality of Life Impact of Refractive Correction, the Quality of Vision, and the Contact Lens Impact on Quality of Life have comparatively better quality with some limitations, compared with the other PRO instruments.

CONCLUSIONS

This review describes the PRO instruments and informs the choice of an appropriate measure in refractive error. We identified need of a comprehensive and scientifically robust refractive error-specific PRO instrument. Item banking and computer-adaptive testing system can be the way to provide such an instrument.

Effectiveness of an Eyelid Thermal Pulsation Procedure to Treat Recalcitrant Dry Eye Symptoms After Laser Vision Correction

PURPOSE

To provide an initial retrospective evaluation of the effectiveness of a thermal pulsation system to treat intractable patient-reported dye eye symptoms following laser vision correction.

METHODS

A total of 109 eyes of 57 patients underwent thermal pulsation therapy (LipiFlow; TearScience, Morrisville, NC) for the treatment of dry eye symptoms following laser vision correction. A standardized dry eye questionnaire, the Standard Patient Evaluation of Eye Dryness (SPEED II), was administered to all patients before and after thermal pulsation therapy. The primary outcome was patient-reported dry eye symptoms as measured by this questionnaire.

RESULTS

The mean patient age was 49 years (interquartile range [IQR]: 38 to 60), 70% were female, and the primary refractive procedure was LASIK (n = 91, 83%) or photorefractive keratectomy (PRK) (n = 18, 17%). Patients underwent thermal pulsation therapy at a mean of 40.5 months (IQR: 27.6 to 55.0) after the primary procedure. The mean pre-therapy SPEED II questionnaire score was 17.5 (IQR: 14 to 21), with a reduced mean post-therapy score of 10.2 (IQR: 6 to 14; 95% confidence interval [CI]: 8.8 to 11.5, P < .001). Patients with PRK tended to report more improvement. At the follow-up clinical evaluation, objective improvements were noted in tear break-up time (+1.9 sec; 95% CI: 1.3 to 2.5), reduction in grade of meibomian gland dysfunction (-0.69; 95% CI: -0.54 to -0.84), and corneal staining (-0.74; 95% CI: -0.57 to -0.91).

CONCLUSIONS

In this initial retrospective evaluation, a significant improvement in patient-reported dry eye symptoms was observed following thermal pulsation therapy. This treatment modality may have utility in the management of dry eye symptoms following laser vision correction, but further study is needed to define its role. [J Refract Surg. 2017;33(1):30-36.].

TFOS DEWS II Tear Film Report

The members of the Tear Film Subcommittee reviewed the role of the tear film in dry eye disease (DED). The Subcommittee reviewed biophysical and biochemical aspects of tears and how these change in DED. Clinically, DED is characterized by loss of tear volume, more rapid breakup of the tear film and increased evaporation of tears from the ocular surface. The tear film is composed of many substances including lipids, proteins, mucins and electrolytes. All of these contribute to the integrity of the tear film but exactly how they interact is still an area of active research. Tear film osmolarity increases in DED. Changes to other components such as proteins and mucins can be used as biomarkers for DED. The Subcommittee recommended areas for future research to advance our understanding of the tear film and how this changes with DED. The final report was written after review by all Subcommittee members and the entire TFOS DEWS II membership.

Recent advances in laser in situ keratomileusis-associated dry eye

Dry eye is the most common complication after laser in situ keratomileusis (LASIK). The major cause of LASIK-associated dry eye is corneal nerve damage. Early identification and treatment of post-operative dry eye are essential to prevent further ocular surface damage. This article reviews the recent studies of LASIK-associated dry eye, including clinical features, aetiology, risk factors, evaluations and treatment. The applications of novel technologies in LASIK-associated dry eye evaluation like anterior segment spectral-domain optical coherence tomography (SD-OCT) and corneal confocal microscopy are also introduced in this review.

Contralateral Eye Comparison Between Femtosecond Small Incision Intrastromal Lenticule Extraction at Depths of 100 and 160 μm

PURPOSE

To compare the visual results, higher-order aberrations, and corneal biomechanical properties of femtosecond small incision lenticule extraction (SMILE) at depths of 100 and 160 μm.

METHODS

A prospective comparative interventional clinical trial of a series of patients who underwent SMILE. In the right eye, a refractive lenticule was created at a depth of 100 μm, and in the left eye, a depth of 160 μm was used. Manifest refraction, uncorrected visual acuity, total high-order aberrations (THOA), and corneal biomechanical properties of both eyes were evaluated 1 month postoperatively.

RESULTS

Thirty patients with bilaterally stable refractive errors were included in this study. One month postoperatively, mean corneal hysteresis was 9.71 ± 0.68 in the right eyes and 9.97 ± 0.77 in the left eyes, whereas the mean corneal resistant factor was 9.13 ± 1.04 and 9.31 ± 0.92 in the right and left eyes, respectively. Both corneal hysteresis and corneal resistant factor showed statistically significantly higher values in the left eyes (lenticule at a depth of 160 μm). No statistically significant differences were found between the right and the left eyes regarding manifest refraction, uncorrected visual acuity, and THOA.

CONCLUSIONS

Creating the refractive lenticule at a depth of 160 μm in SMILE had less effect on the corneal biomechanics than did creating a lenticule at a depth of 100 μm with no statistically significant differences in the refractive outcome and THOA between both groups.

[Cyanocobalamin-containing lubricant for topical therapy of LASIK-associated dry eye]

AIM

to study the effect of topical treatment with Artelac Balance, a cyanocobalamin-containing lubricant, in patients with post-LASIK corneal neuropathy and LASIK-associated dry eye.

MATERIAL AND METHODS

Patients scheduled for LASIK were enrolled. Inclusion criteria were contact lens wear for 5 years or longer and more than 6 diopters of myopia. The patients were divided into 3 groups. Group 1 was prescribed the cyanocobalamin-containing topical lubricant for 3 months before and 1 month after surgery, group 2 - the same cyanocobalamin-containing lubricant, but only for the first month after surgery, and group 3 received a standard preservative-free lubricant for the first month after surgery. Tear osmolarity and production as well as corneal sensitivity were assessed 90±10 days before and 30±3 days after surgery. The percentage of patients with dry eye symptoms and those who required prolonged use of lubricants were also estimated at day 30±3.

RESULTS

Preoperatively, there were no statistically significant differences in demographic characteristics, tear osmolarity, tear production, or corneal sensitivity between the three study groups. At day 30±3 after surgery, tear production and corneal sensitivity were both significantly higher in group 1 than in group 3 (16.8 mm vs. 13.2 mm, p=0.003 and 37.7±3.1 mm vs. 32.4±2.2 mm, p=0.023, respectively). As to the percentage of patients with dry eye symptoms and those who required prolonged use of lubricants, it was lower in group 1 than in group 3 (51.3% vs. 76.3%, p=0.03 and 38.5% vs. 63.2%, p=0.03, respectively). Between the groups 2 and 3, none of the studied parameters differed significantly.

CONCLUSION

Combined pre- and postoperative use of Artelac Balance, a cyanocobalamin-containing lubricant, has been proved effective in restoring corneal sensitivity and reducing dry eye symptoms in patients at high risk for developing LASIK-associated dry eye.

Advances in Refractive Surgery: May 2013 to June 2014

PURPOSE

The field of refractive surgery is changing quickly in the areas of screening, treatment, and postoperative management. The objective of this study was to review advances in the field of refractive surgery as reported in the peer-reviewed literature during the previous year.

DESIGN

This was a literature review.

METHODS

In this article, we highlight the progression in the field from May 2013 to the end of June 2014. This article is organized as preoperative, intraoperative, and postoperative considerations.

RESULTS

The growing use of newer modalities of treatment, such as small-incision lenticule extraction (SmILE) and phakic intraocular lenses, and their safety and efficacy add to the armamentarium in treating refractive error. This past year has seen many studies, which show these procedures to be safe and effective. Also, structurally, SmILE may result in a more biomechanically stable cornea, so that we may be able to safely treat higher refractive errors.

CONCLUSIONS

While laser-assisted in situ keratomileusis is the predominant surgical procedure, photorefractive keratectomy is still an appropriate choice in certain scenarios (higher risk for ectasia postrefractive surgery and patient choice) with safe, predictable results, and patient satisfaction. Many of the new developments in laser-assisted in situ keratomileusis have focused on flap creation with femtosecond lasers. Histopathology and in vivo optical coherence tomography studies have shown that the stromal bed is smoother, the side cuts are vertical, and the flap has predictable thickness. New surgical modalities, such as femtosecond lenticule extraction and SmILE, are increasingly being used.

Dry eye disease after refractive surgery: comparative outcomes of small incision lenticule extraction versus LASIK

PURPOSE

To compare small incision lenticule extraction (SMILE) versus LASIK for post-refractive dry eye disease.

DESIGN

Prospective, comparative, nonrandomized clinical study.

PARTICIPANTS

Thirty patients scheduled for bilateral myopic SMILE and 30 age-, sex-, and refraction-matched patients scheduled for bilateral myopic LASIK were enrolled and followed for 6 months after the surgery.

METHODS

Complete evaluation of dry eye disease was performed at 1 and 6 months postoperatively, which included vision-related quality of life (Ocular Surface Disease Index [OSDI]), clinical examinations (tear film breakup time [TBUT], Schirmer I test, corneal staining), and tear osmolarity measurements, together with an overall severity score. Function and morphology of the corneal innervation were evaluated by corneal esthesiometry and subbasal nerve imaging using in vivo confocal microscopy (IVCM).

MAIN OUTCOME MEASURES

Overall analysis of dry eye disease and corneal innervation.

RESULTS

High incidence of mild to moderate dry eye disease was observed in both groups 1 month postoperatively, which remained significantly higher in the LASIK group than in the SMILE group 6 months after surgery (overall severity score [0-4]: 1.2±1.1 vs. 0.2±0.4, respectively, P < 0.01), leading to more frequent use of tear substitutes over the long term. Corneal sensitivity was better in SMILE than in LASIK eyes 1 month postoperatively (3.5±1.79 vs. 2.45±2.48, respectively, P < 0.01) and then recovered to statistically similar values at 6 months. Corneal nerve density, number of long fibers, and branchings as assessed by IVCM were significantly higher in the SMILE group compared with the LASIK group 1 and 6 months after surgery. Corneal sensitivity was negatively correlated with dry eye-related corneal damage (R² = 0.48, P < 0.01), and the long fiber nerve density was independently correlated with the OSDI score (R² = 0.50, P < 0.01) and the Schirmer test (R² = 0.21, P < 0.01) 6 months postoperatively.

CONCLUSIONS

The SMILE procedure has a less pronounced impact on the ocular surface and corneal innervation compared with LASIK, further reducing the incidence of dry eye disease and subsequent degradation in quality of life after refractive surgery.

The role of corneal innervation in LASIK-induced neuropathic dry eye

Almost half the patients who undergo laser in situ keratomileusis (LASIK) experience dry eye following the procedure. However, the etiology of LASIK-induced dry eye is unclear. The purpose of this review is to examine and summarize the current evidence for the etiology of LASIK-induced dry eye, with a focus on ocular surface sensitivity and corneal innervation. Evidence suggests that the alteration of corneal nerves after LASIK is the most likely cause of the subjective symptoms of LASIK-induced dry eye, even though corneal sensitivity and the clinical indicators of dry eye return to apparently normal values within a year due to the partial recovery of the corneal nerve plexus. The hypothesis is explored that dry eye symptoms following LASIK may result from abnormal sensation due to LASIK-induced corneal neuropathy. Other factors, such as alterations in conjunctival goblet cell density, might also contribute to the symptoms and signs of LASIK-induced dry eye. Inter-relationships between nerve morphology, tear neuropeptide levels and dry eye require further investigation. A better understanding of this phenomenon may result in improved management of post-LASIK dry eye.