Corneal sensitivity after photorefractive keratectomy and laser in situ keratomileusis for low myopia

Age-Related Changes in Corneal Sensitivity

PURPOSE

The aim of this prospective cross-sectional cohort study was to clinically test whether corneal sensation decreases with age, based on subject feedback (psychophysical method), and whether it correlates with general pain perception.

METHODS

Subjects were recruited from 2 equally large age groups: group A (18-30 years) and group B (50-70 years; n = 45 per group). The inclusion criteria were healthy eyes, Ocular Surface Disease Index ≤13, and no contact lens wear. Corneal sensitivity threshold (CST) measurements were performed twice during each of the 2 visits, with the aid of the new Swiss liquid jet esthesiometer for corneal sensitivity (SLACS) and Cochet-Bonnet (CB) esthesiometer. A general pain sensitivity score was obtained from all participants.

RESULTS

Ninety subjects completed the study (n = 45 per age group, average age in group A: 24.2 ± 2.94 years, group B: 58.5 ± 5.71 years). Statistically higher CSTs for age group B were only observed for SLACS (mean difference: 1.58 dB, P < 0.001). No correlation was observed between the pain score and the CSTs obtained with either esthesiometry method (r = 0.11, P = 0.25 for liquid jet and r=-0.076, P = 0.61 CB).

CONCLUSIONS

A statistically significant decrease in corneal sensitivity was observed for the older age group with SLACS in this study, with CB however only a trend in the same direction was noted. General pain perception was not found to correlate with ocular surface sensation.

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.

Solving STODS-Surgical Temporary Ocular Discomfort Syndrome

The term STODS (Surgical Temporary Ocular Discomfort Syndrome) has been coined to describe the ocular surface perturbations induced by surgery. As one of the most important refractive elements of the eye, Guided Ocular Surface and Lid Disease (GOLD) optimization is fundamental to success in achieving refractive outcomes and mitigating STODS. Effective GOLD optimization and the prevention/treatment of STODS requires an understanding of the molecular, cellular, and anatomic factors that influence ocular surface microenvironment and the associated perturbations induced by surgical intervention. By reviewing the current understanding of STODS etiologies, we will attempt to outline a rationale for a tailored GOLD optimization depending on the ocular surgical insult. With a bench-to-bedside approach, we will highlight clinical examples of effective GOLD perioperative optimization that can mitigate STODS' deleterious effect on preoperative imaging and postoperative healing.

Corneal neuromediator profiles following laser refractive surgery

Laser refractive surgery is one of the most commonly performed procedures worldwide. In laser refractive surgery, Femtosecond Laser in Situ Keratomileusis and Refractive Lenticule Extraction have emerged as promising alternatives to microkeratome Laser in Situ Keratomileusis and Photorefractive Keratectomy. Following laser refractive surgery, the corneal nerves, epithelial and stromal cells release neuromediators, including neurotrophins, neuropeptides and neurotransmitters. Notably, nerve growth factor, substance P, calcitonin gene-related peptide and various cytokines are important mediators of neurogenic inflammation and corneal nerve regeneration. Alterations in neuromediator profiles and ocular surface parameters following laser refractive surgery are attributed to the surgical techniques and the severity of tissue insult induced. In this review, we will discuss the (1) Functions of neuromediators and their physiological and clinical significance; (2) Changes in the neuromediators following various laser refractive surgeries; (3) Correlation between neuromediators, ocular surface health and corneal nerve status; and (4) Future directions, including the use of neuromediators as potential biomarkers for ocular surface health following laser refractive surgery, and as adjuncts to aid in corneal regeneration after laser refractive surgery.

The structural and functional corneal reinnervation mechanism at different regions after LASIK-an in vivo confocal microscopy study

PURPOSE

To determine the recovery of structural and functional corneal sensory nerves within the LASIK flap in order to provide insight to more proximal corneal reinnervation and symptoms post-LASIK.

METHODS

Twenty participants underwent femtosecond LASIK with a superior flap hinge. Ocular Comfort Index in Chinese (OCI-C), Cochet-Bonnet esthesiometry, and in vivo confocal microscopy were conducted before surgery and 1 week, 1-, 3-, and 6-months post-LASIK to measure symptoms, corneal sensitivity, nerve fiber density, width, and the number of interconnections within the flap (central and mid-temporal regions), and next to the superior flap hinge. Linear mixed models were used to compare differences between corneal regions at each time point post-LASIK and changes over time post-LASIK. Spearman's correlation tests were used to examine the associations between variables post-LASIK.

RESULTS

The least reduction in sensitivity (P < 0.03) and in nerve fiber density (P < 0.02) was found near the flap hinge compared to other regions, but no regional differences were found in nerve fiber width and interconnections. Nerve fiber density and the number of interconnections at all regions within the flap recovered over time (P < 0.02). The recovery of corneal sensitivity and nerve fiber width was only seen at the central and temporal regions (P < 0.04). No association was found between sensitivity and nerve parameters, but a higher OCI-C score was associated with a lower nerve fiber density near the hinge (r =  - 0.43, P = 0.003) over time post-LASIK.

CONCLUSION

Corneal sensitivity and density are preserved in the hinge, but this preservation of the corneal nerve damage does not affect the nerve morphology.

Changes in Tear Osmolarity after Cataract Surgery

BACKGROUND

The purpose of this study was to examine changes in the ocular surface before and after phacoemulsification with small incisions and to examine the changes in tear osmolarity.

METHODS

This was a prospective, observational study involving 55 eyes of 39 patients (19 male, 20 female patients; average age 72.0±7.3 years) who had cataract surgery at a Nippon Medical School Hospital between December 2013 and June 2018. Compromised tear dynamics were determined by the Schirmer test or the tear break-up time (BUT). An abnormal ocular surface was identified by positive vital staining with fluorescein or lissamine green. Moreover, tear osmolarity (Tosm) and corneal sensitivity were measured. All assessments were done preoperatively and 1 and 4 weeks (P1W and P4W) after the surgery.

RESULTS

None of the operations had any complications. Operating time was 17.8±9.3 minutes. BUT was significantly decreased at P1W, and it recovered at P4W. The Schirmer test did not change significantly. The fluorescein staining score (FSS) increased significantly at P1W and recovered at P4W. The Lissamine green score (LSS) did not change significantly. Tear osmolarity increased significantly at P1W and did not recover at P4W. Corneal sensitivity decreased significantly at P1W and recovered at P4W.

CONCLUSION

In the present study, there were temporary changes in dry eye-related examinations including tear osmolarity after cataract surgery. In particular, tear osmolarity increased significantly 4 weeks after surgery compared to before surgery, and it showed long-term changes, unlike other factors. After cataract surgery, tear osmolarity, BUT, and FSS increase, resulting in dry eye symptoms. Therefore, it is necessary to pay attention to discomfortable eye symptoms of patients after cataract surgery.

Post laser-assisted in-situ keratomileusis dry eye disease and temporary punctal plugs

PURPOSE

The aim of this study was to compare the incidence of post laser in situ keratomileusis (LASIK) dry eye with and without intraoperative extended duration temporary punctal plug placement.

METHODS

This retrospective study included myopicastigmatic eyes without a preoperative diagnosis of dry eye disease that underwent LASIK surgery between January 2017, and March 2018. Patients who received punctal plugs during surgery in addition to usual postoperative care were compared to a control group who received usual postoperative care alone. Visual acuity, safety and efficacy indices, as well as predictability and presence of dry eye disease were assessed 3-6 months after surgery.

RESULTS

A total of 345 eyes of 345 patients were included, 172 eyes received punctal plugs and 173 did not. The mean age was 30.4 ± 10 years (range: 17-60 years) and 46.1% (N = 159) were female. Both groups were similar in terms of preoperative parameters, including age, gender, spherical equivalent, pachymetry or contact lens use. Patients treated with punctal plugs had significantly less postoperative dry eye complaints (N = 37 vs. 58, 21.5% vs. 34.1% respectively, P = 0.001). Patients treated with plugs that did develop dry eye disease did so later (51.2 ± 77.64 days' vs. 20.78 ± 26.9 days, P = 0.009). Postoperative visual acuities were similar between groups (P > 0.05) at all postoperative follow-up visits as were safety (0.95 ± 0.16 vs. 0.99 ± 0.09, P = 0.30) and efficacy (1.01 ± 0.13 vs. 1.00 ± 0.11, P = 0.52) indices.

CONCLUSION

Preventative temporary punctal plug placement during LASIK appears to reduce dry eye disease in the short term, without affecting visual acuity outcomes.

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.

Alteration of the pattern of regenerative corneal subbasal nerves after laser in-situ keratomileusis surgery

PURPOSE

Corneal nerves exhibit high plasticity, which allows successful reinnervation after nerve damage caused by laser in-situ keratomileusis (LASIK) surgery. This study aimed to examine corneal subbasal nerve orientation during regeneration after LASIK.

METHODS

This study involved 20 healthy, myopic subjects who had undergone bilateral Femto-LASIK 12-16 months prior with a superior hinge position. The corneal subbasal nerve plexus at the central, mid-temporal and mid-superior cornea on the right eye were imaged using in vivo confocal microscopy. Global nerve fibre orientation (indicating the overall pattern) and variation of nerve fibre orientation (indicating the consistency of the orientation) was determined using customised MATLAB™ software (www.mathworks.com/products/matlab.html). Differences in nerve orientation variables between groups were examined using the Mann-Whitney U test. Linear mixed models with Bonferroni adjustment were conducted to examine differences between corneal regions, and over time, after LASIK.

RESULTS

There were no differences between post-LASIK and control groups in global nerve orientation at any of the examined corneal regions. The post-LASIK subjects had a greater variation of nerve orientation at the central (p = 0.007) and temporal (p = 0.049) cornea than the controls. There was a difference in global nerve fibre orientation between corneal regions (p < 0.001) in the controls but not in the post-LASIK group. The variation of nerve fibre orientation was higher at the central, compared to the temporal and superior cornea after LASIK (p < 0.001), although there were no differences between corneal regions in controls.

CONCLUSIONS

Our results demonstrate that there was an increased variability in the corneal subbasal innervation patterns following LASIK when compared to controls.

Novel Cross-Linked Ocular Bandage Gel Improves Reepithelialization After Photorefractive Keratectomy: A Randomized, Masked Prospective Study

Purpose: To compare, in a masked manner, a novel cross-linked hyaluronic acid ocular bandage gel (OBG) versus standard-of-care bandage contact lens (BCL) plus artificial tears with respect to safety and effectiveness in healing epithelial defects created for photorefractive keratectomy (PRK). Methods: This was a randomized, reading center-masked, exploratory study. Forty-five patients (myopic without significant anisometropia) scheduled for bilateral PRK (9-mm epithelial defect) were randomized post-PRK to treatment with OBG 8 times daily for 3 days, followed by 4 times daily for 11 days (Group 1); OBG 4 times daily for 14 days (Group 2); or BCL and artificial tears (Control). A masked reading center used image analysis of digital slit lamp photos of the fluorescein-stained cornea to evaluate defect size during the 14-day postoperative follow-up period. Effectiveness endpoints were (1) time to complete closure of the corneal defect and (2) proportion of patients with complete healing on day 3 postoperatively, whose defect remained closed. Safety assessments included findings for adverse events and vision, Standard Patient Evaluation of Eye Dryness (SPEED^™) Questionnaire, slit lamp, intraocular pressure, and fundus examinations. Results: The proportion of patients with complete healing at 3 days was 73.3%, 86.7%, and 66.7% of patients in Groups 1, 2, and Control, respectively. On day 2, the mean wound size was 6%-26% smaller in Groups 1 and 2 compared with Control. No safety concern arose. SPEED scores were not significantly different across groups. Conclusion: OBG offers a well-tolerated and effective therapy for quickly reepithelializing the cornea following trauma, disease, or surgery.

Main Complications of Photorefractive Keratectomy and their Management

Photorefractive keratectomy (PRK) was the first surface ablation procedure introduced for the treatment of refractive errors and has been proven to be effective and safe. In some cases, however, the patient may not be totally satisfied with the final result and retreatment may be necessary. We performed a literature review to describe the main conditions that may arise following PRK that may require retreatment and new promising techniques to allow customized and effective treatments for patients. There is currently no gold standard for retreatment of residual refractive error after PRK. The surgeon must take into account the patient's history and type of problem when choosing the most appropriate technique. LASIK and PRK are the main options. Haze can be treated with good results with phototherapeutic keratectomy and mytomicin C. High order aberrations and decentration may be addressed with topographically-guided excimer photoablation or with wavefront-guided PRK.

Ability of a new crosslinked polymer ocular bandage gel to accelerate reepithelialization after photorefractive keratectomy

PURPOSE

To evaluate the safety and performance of a crosslinked thiolated carboxymethyl hyaluronic acid liquid-gel (CMHA-S) ocular bandage gel in accelerating reepithelialization of corneal defects created for photorefractive keratectomy (PRK).

SETTING

Three community-based clinical research sites.

DESIGN

Prospective case series.

METHODS

Patients scheduled for bilateral PRK had both eyes randomized immediately after PRK to Group 1 (ocular bandage gel 4 times a day for 14 days and bandage contact lens), Group 2 (ocular bandage gel 4 times a day for 14 days), or Group 3 (control; bandage contact lens and artificial tears 4 times a day for 14 days). Patients received a 9.0 mm epithelial defect for PRK and were followed through 28 days postoperatively. Safety assessments included adverse events, vision, pain, slitlamp, intraocular pressure, and fundus examinations. The primary performance endpoint was time to corneal reepithelialization after PRK.

RESULTS

The study comprised 39 patients. The ocular bandage gel was well tolerated. The time to reepithelialization was 3 days for 54.5%, 80.0%, and 45.5% of patients in Group 1, Group 2, and Group 3, respectively. Compared with measurements in the control group, the mean horizontal and vertical defect lengths in Group 2 (ocular bandage gel alone) were 36.9% and 29.0% smaller, respectively, by 1 day.

CONCLUSION

Crosslinked hyaluronic acid showed the ability to quickly reepithelialize the cornea and may promise a well-tolerated and effective therapy for ocular wound care after trauma, disease, or surgery.

Presbyopia and the aging eye: Existing refractive approaches and their potential impact on dry eye signs and symptoms

Every part of the human body is subject to aging, including the eye. An increased prevalence of dry eye disease with age is widely acknowledged. Aging threatens ocular surface homeostasis, altering the normal functioning of the lacrimal functional unit and potentially leading to signs and symptoms of dry eye. Additional age-related processes take place within the crystalline lens, leading to presbyopia and cataractogenesis. Correction strategies for presbyopia and cataracts may directly or indirectly challenge the ocular surface. Contact lenses disturb the normal structure of the tear film and can interact negatively with the ocular surface, further deteriorating an already unbalanced tear film in presbyopes, however, newer contact lens designs can overcome some of these issues. Moreover, cataract and corneal refractive surgeries sever corneal nerves and disrupt the corneal epithelium and ocular surface, which can influence surgical outcomes and aggravate dryness symptoms in older age groups. This review summarises the current understanding of how the invasive nature of contact lens wear and cataract and refractive surgery influence signs and symptoms of ocular dryness in an aging population.

Application of Vitamin E + Coenzyme Q Therapy During FAKO + IOL Implantation

Introduction

Cataract surgery is a widely used procedure around the world. After cataract surgery, one of the important points is that oxidative stress may cause postoperative corneal edema and vision loss.

Aim

In this study, we aim to reduce the oxidative stress and related conditions that may develop during intraoperative and postoperative FAKO + IOL implantation.

Material and Methods

Total amount of 32 patients with cataract were included to the study. The patients were classified as two groups randomly and the same surgical procedure was applied to the patients in both groups, except using visudrop. Group I was defined as a control group and routine FAKO + IOL implantation surgery was performed. In Group II, after the sideport was opened at the beginning of the operation, 0.5 cc visudrop (coenzyme q + vitamin E + hypermellosis) was given to the anterior camara. After the operation, 0.5 cc visudrop was also given to the anterior camara. Postoperative examination findings were compared statistically.

Results

In Group II, postoperative 1st day and postoperative 7th day visual acuities were significantly higher than in Group I. In Group II, postoperative 1st day and postoperative 7th day visual acuity increments were significantly higher than in Group I. In Group I, postoperative 1st day and 7th day pachymetry value increments were significantly higher than in Group II.

Conclusion

Using visudrop during the FAKO + IOL implantation may be an effective method for postoperative corneal edema and vision.

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.

Corneal re-innervation following refractive surgery treatments

Laser refractive surgery is one of the most performed surgical procedures in the world. Although regarded safe and efficient, it has side effects. All of the laser based refractive surgical procedures invoke corneal nerve injury to some degree. The impact of this denervation can range from mild discomfort to neurotrophic corneas. Currently, three techniques are widely used for laser vision correction: small incision lenticule extraction, laser-assisted keratomileusis in situ and photorefractive keratotomy. Each of these techniques affects corneal innervation differently and has a different pattern of nerve regeneration. The purpose of this review is to summarize the different underlying mechanisms for corneal nerve injury and compare the different patterns of corneal reinnervation.

Goblet cell response after photorefractive keratectomy and laser in situ keratomileusis

PURPOSE

To determine whether patients without dry eye preoperatively have an altered conjunctival goblet cell density and mucin secretion postoperatively and to explore what factors affect changes in goblet cell density and mucin secretion.

SETTING

The former Walter Reed Army Medical Center, Washington, DC, USA.

DESIGN

Prospective nonrandomized clinical study.

METHODS

Impression cytology was used to determine conjunctival goblet cell density before and 1 week, 1 month, and 3 months after photorefractive keratectomy (PRK) or laser in situ keratomileusis (LASIK). The McMonnies questionnaire, Schirmer test, tear breakup time, corneal sensitivity, rose bengal staining, and computerized videokeratoscopy were also performed to assess tear-film and ocular-surface health.

RESULTS

The ratio of goblet cell to total cells changed postoperatively from baseline in both groups (P < .001). The most significant change was a median 29% decrease 1 month postoperatively. However, there were no significant differences between groups over time (P = .772). The ratio of filled goblet cell to total goblet cell did not change significantly over the same time period (P = .128), and there were no significant differences between the PRK group and the LASIK group over time (P = .282).

CONCLUSIONS

Patients without apparent dry eye had an altered conjunctival goblet cell population after PRK or LASIK. The conjunctival goblet cell population tended to decrease in the early postoperative period after either surgery and was most affected by preoperative goblet cell density. The changes in the tear film and ocular surface did not seem to affect goblet cell mucin secretion after either procedure.

FINANCIAL DISCLOSURE

None of the authors has a financial or proprietary interest in any material or method mentioned.

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.

Chronic dry eye in photorefractive keratectomy and laser in situ keratomileusis: Manifestations, incidence, and predictive factors

PURPOSE

To evaluate dry-eye manifestations after photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) and determine the incidence and predictive factors of chronic dry eye using a set of dry-eye criteria.

SETTING

Walter Reed Army Medical Center, Washington, DC, USA.

DESIGN

Prospective, non-randomized clinical study.

METHODS

Dry-eye evaluation was performed before and after surgery. Main outcome measures included dry-eye manifestations, incidence, and predictive factors of chronic dry eye.

RESULTS

This study comprised 143 active-duty U.S. Army personnel, ages 29.9 ± 5.2 years, with myopia or myopic astigmatism (manifest spherical equivalent -3.83 ± 1.96 diopters) having PRK or LASIK. Schirmer scores, corneal sensitivity, ocular surface staining, surface regularity index, and responses to dry-eye questionnaire significantly changed over time after PRK. After LASIK, significant changes were observed in tear breakup time, corneal sensitivity, ocular surface staining, and responses to questionnaire. Twelve months postoperatively, 5.0% of PRK and 0.8% of LASIK participants developed chronic dry eye. Regression analysis showed that pre-operatively lower Schirmer score will significantly influence development of chronic dry eye after PRK, whereas preoperatively, lower Schirmer score or higher ocular surface staining score will significantly influence the occurrence of chronic dry eye after LASIK.

CONCLUSIONS

Chronic dry eye was uncommon after PRK and LASIK. Ocular surface and tear-film characteristics during pre-operative examination might help to predict chronic dry-eye development in PRK and LASIK.

FINANCIAL DISCLOSURE

The authors have no financial interest in any product, drug, instrument, or equipment discussed in this manuscript.

In Vivo Confocal Microscopy of Corneal Nerves in Health and Disease

In vivo confocal microscopy (IVCM) is becoming an indispensable tool for studying corneal physiology and disease. Enabling the dissection of corneal architecture at a cellular level, this technique offers fast and noninvasive in vivo imaging of the cornea with images comparable to those of ex vivo histochemical techniques. Corneal nerves bear substantial relevance to clinicians and scientists alike, given their pivotal roles in regulation of corneal sensation, maintenance of epithelial integrity, as well as proliferation and promotion of wound healing. Thus, IVCM offers a unique method to study corneal nerve alterations in a myriad of conditions, such as ocular and systemic diseases and following corneal surgery, without altering the tissue microenvironment. Of particular interest has been the correlation of corneal subbasal nerves to their function, which has been studied in normal eyes, contact lens wearers, and patients with keratoconus, infectious keratitis, corneal dystrophies, and neurotrophic keratopathy. Longitudinal studies have applied IVCM to investigate the effects of corneal surgery on nerves, demonstrating their regenerative capacity. IVCM is increasingly important in the diagnosis and management of systemic conditions such as peripheral diabetic neuropathy and, more recently, in ocular diseases. In this review, we outline the principles and applications of IVCM in the study of corneal nerves in various ocular and systemic diseases.

The role of dinucleoside polyphosphates on the ocular surface and other eye structures

Dinucleoside polyphosphates comprises a group of dinucleotides formed by two nucleosides linked by a variable number of phosphates, abbreviated NpnN (where n represents the number of phosphates). These compounds are naturally occurring substances present in tears, aqueous humour and in the retina. As the consequence of their presence, these dinucleotides contribute to many ocular physiological processes. On the ocular surface, dinucleoside polyphosphates can stimulate tear secretion, mucin release from goblet cells and they help epithelial wound healing by accelerating cell migration rate. These dinucleotides can also stimulate the presence of proteins known to protect the ocular surface against microorganisms, such as lysozyme and lactoferrin. One of the latest discoveries is the ability of some dinucleotides to facilitate the paracellular way on the cornea, therefore allowing the delivery of compounds, such as antiglaucomatous ones, more easily within the eye. The compound Ap₄A has been described being abnormally elevated in patient's tears suffering of dry eye, Sjogren syndrome, congenital aniridia, or after refractive surgery, suggesting this molecule as biomarker for dry eye condition. At the intraocular level, some diadenosine polyphosphates are abnormally elevated in glaucoma patients, and this can be related to the stimulation of a P2Y₂ receptor that increases the chloride efflux and water movement in the ciliary epithelium. In the retina, the dinucleotide dCp₄U, has been proven to be useful to help in the recovery of retinal detachments. Altogether, dinucleoside polyphosphates are a group of compounds which present relevant physiological actions but which also can perform promising therapeutic benefits.

Corneal sensitivity after small-incision lenticule extraction and laser in situ keratomileusis

PURPOSE

To longitudinally evaluate corneal sensitivity after small-incision lenticule extraction and compare the results with those in previous studies.

SETTING

London Vision Clinic, London, United Kingdom.

DESIGN

Retrospective case series.

METHODS

Consecutive myopic eyes treated with small-incision lenticule extraction using the Visumax femtosecond laser were studied. Corneal sensitivity was measured centrally and at 4 paracentral locations using a Cochet-Bonnet esthesiometer preoperatively and 1 day, 1 week, and 1, 3, 6, and 12 months postoperatively. Results were compared with averaged results from previous laser in situ keratomileusis (LASIK) and small-incision lenticule extraction studies.

RESULTS

The mean spherical equivalent was -6.85 diopters (D) ± 2.57 (SD). The mean age was 36 ± 11 years. After small-incision lenticule extraction, the preoperative mean central corneal sensitivity dropped from 54 mm preoperatively to 33 mm 1 day postoperatively, rising to 40 mm, 45 mm, 48 mm, 54 mm, and 55 mm over 12 months; it reached baseline at 6 months (P > .05). For 21 LASIK studies, the mean central corneal sensitivity dropped from 56 mm preoperatively to 6 mm at 1 day, rising to 14 mm, 23 mm, 34 mm, 45 mm, and 51 mm over 12 months. For 8 small-incision lenticule extraction studies, central corneal sensitivity dropped from 57 mm preoperatively to 39 mm at 1 week, then rose to 39 mm, 42 mm, 49 mm, 52 mm, and 54 mm over 12 months; it was higher than after LASIK at 1 week and 1, 3, and 6 months (P < .05).

CONCLUSION

Recovery of central corneal sensitivity to baseline was reached by 6 months after small-incision lenticule extraction and was higher than after LASIK for the first 6 months after surgery.

FINANCIAL DISCLOSURE

Dr. Reinstein is a consultant to Carl Zeiss Meditec AG, has a proprietary interest in the Artemis technology (Arcscan, Inc.), and is an author of patents related to very high-frequency digital ultrasound administered by the Center for Technology Licensing at Cornell University, Ithaca, New York, USA. No other author has a financial or proprietary interest in any material or method mentioned.

Effect of diquafosol tetrasodium eye drop for persistent dry eye after laser in situ keratomileusis

PURPOSE

To evaluate the effect of diquafosol tetrasodium (DQS) for the treatment of persistent dry eye after laser in situ keratomileusis (LASIK).

SETTING

Miyata Eye Hospital, Miyazaki, Japan.

DESIGN

Noncomparative case series.

METHODS

This prospective study included 30 eyes of 15 patients in whom dry eye had persisted for over 12 months after LASIK, and the symptoms had not improved with artificial tears and sodium hyaluronate treatment. In addition, treatment with DQS 3% eye drops, 6 times a day, was performed for 12 weeks. Best-corrected visual acuity, tear secretion with the Schirmer test, tear break-up time, and fluorescein and lissamine green staining scores on the cornea and conjunctiva were examined before and at 1, 4, and 12 weeks after the addition. A subjective questionnaire of 14 symptoms was also assessed before and 12 weeks after treatment.

RESULTS

The fluorescein and lissamine green staining scores significantly improved over 12 weeks; however, the best-corrected visual acuity and tear secretion did not change. The symptoms of fatigue, dryness, grittiness, discomfort, difficulty in reading, and discomfort within the area of dryness improved after the additional DQS treatment.

CONCLUSIONS

The DQS treatment improved the subjective and objective symptoms of persistent dry eye after LASIK. Increased mucin production because of the addition of DQS probably improved the tear film stability and reduced the symptoms of dry eye in patients who had persistent dry eye after LASIK.

Corneal nerves in health and disease

Corneal nerves are responsible for the sensations of touch, pain, and temperature and play an important role in the blink reflex, wound healing, and tear production and secretion. Corneal nerve dysfunction is a frequent feature of diseases that cause opacities and result in corneal blindness. Corneal opacities rank as the second most frequent cause of blindness. Technological advances in in vivo corneal nerve imaging, such as optical coherence tomography and confocal scanning, have generated new knowledge regarding the phenomenological events that occur during reinnervation of the cornea following disease, injury, or surgery. The recent availability of transgenic neurofluorescent murine models has stimulated the search for molecular modulators of corneal nerve regeneration. New evidence suggests that neuroregenerative and inflammatory pathways in the cornea are intertwined. Evidence-based treatment of neurotrophic corneal diseases includes using neuroregenerative (blood component-based and neurotrophic factors), neuroprotective, and ensconcing (bandage contact lens and amniotic membrane) strategies and avoiding anti-inflammatory therapies, such as cyclosporine and corticosteroids.

Diadenosine polyphosphates after laser in situ keratomileusis and photorefractive keratectomy refractive techniques

PURPOSE

To study the concentrations of diadenosine polyphosphates in the ocular surface after PRK and LASIK.

METHODS

Sixty-one patients (30 males and 31 females) with ages ranging from 20 to 63 (34.04 ± 9.13 years) were recruited in Balear Institute of Ophthalmology, Palma de Mallorca, Spain. LASIK was performed in 92 eyes of 46 patients and PRK in 25 eyes of 15 patients. Variations in the levels of diadenosine polyphosphate (Ap4 A and Ap5 A), Schirmer I (Jones test), TBUT, corneal staining together with the Dry Eye Questionnaire to evaluate discomfort and dryness were studied. All tests were performed at the preoperative visit and at 1-day, 2-week, 1-month and 3-month postoperative visits.

RESULTS

Ap4 A showed a 5 and 3.5 fold increase at the 1-day visit for LASIK and PRK, respectively. LASIK patients continued having higher statistically significant concentrations (p = 0.01) all over the follow-up. Ap5 A showed no significant differences at any visit. Tear volume decreased during the 3 months in LASIK. The PRK cases had a normal volume at 1 month. TBUT in LASIK increased at the 1-day visit (p = 0,002) and decreased from the 2 weeks onwards and for the PRK, decreased by a 35% at the 1-day visit and kept reduced for a month. Discomfort only increased at the 1-day visit (p = 0.007). Dryness frequency was similar in all visits.

CONCLUSIONS

Ap4 A levels only are increased in refractive surgery patients during the first day after the surgery. This increasing suggests that Ap4 A may help accelerating the healing process.

Post-LASIK dry eye

Laser-assisted in situ keratomileusis (LASIK) is a frequently performed corneal refractive surgery with excellent refractive outcomes. The most common complication of LASIK is dry eyes, with virtually all patients developing some degree of dryness in the immediate postoperative period. Identifying preoperative dry eyes, and conscientious attention and treatment in the perioperative time period, can lead to enhanced patient satisfaction and more accurate visual outcomes. Improved understanding of the development of dry eyes after LASIK will advance our understanding of the complex pathophysiology of dry eye disease.

Assessment of dry eye signs and symptoms and ocular tolerance of a preservative-free lacrimal substitute (Hylabak®) versus a preserved lacrimal substitute (Systane®) used for 3 months in patients after LASIK

Laser-assisted in situ keratomileusis (LASIK) is commonly used to correct refractive defects. The procedure frequently results in dry eye symptoms, usually of short but sometimes longer duration. This study was designed to assess dry eye and ocular tolerability after LASIK in patients treated with a preservative-free lacrimal substitute (Hylabak®) or preserved lacrimal substitute (Systane®). In a single-center, investigator-masked, prospective, noninferiority, clinical study, patients undergoing LASIK surgery were randomized to receive Hylabak or Systane eye drops (one drop in each eye four times daily for 3 months). Fluorescein test scores were the primary efficacy variable and were similar on day 1 (mean 0.26 and 0.28 for Hylabak and Systane, respectively). At the final visit (day 84 ± 3) the fluorescein scores had improved to 0.11 and 0.04, respectively. The difference was not significant and thus noninferiority was established. A trend of more rapid improvement in the Hylabak group was evident. Both treatments were well tolerated and there were no serious adverse events, discontinuations for adverse events or other safety-related reasons, and no systemic adverse events. The results suggest that Hylabak is not less effective than Systane in reducing the symptoms of dry eye after LASIK surgery.

Corneal involvement in uneventful cataract surgery: an in vivo confocal microscopy study

PURPOSE

To evaluate corneal subbasal layer changes after uneventful cataract surgery by means of in vivo confocal microscopy.

METHODS

This prospective study included 30 patients. Before surgery, and 1, 3, 6, 8 and 10 months after cataract surgery, all patients underwent a complete ophthalmological and confocal microscopy examination in the central and temporal corneal areas. Number of fibers, beading, tortuosity and reflectivity were analyzed.

RESULTS

Important changes were shown in the central cornea up to 3 months after surgery: a reduction in nerve fiber number (baseline: 4.4 ± 1.7; month 1: 1.2 ± 0.5, p < 0.0001; month 3: 2.5 ± 1.2, p < 0.005) and reflectivity (baseline: 3.6 ± 0.5; month 1: 1.4 ± 0.6, p < 0.0001; month 3: 1.9 ± 0.9, p < 0. 0001), and an increase in beading (baseline: 0.3 ± 0.5 beads/100 µm(2); month 1: 2.7 ± 0.6 beads/100 µm(2), p < 0.0001; month 3: 2.6 ± 0.5 beads/100 µm(2), p < 0. 0001). The confocal parameters completely progressively recovered thereafter (60% at 6 months, 87% at 8 and 10 months). The temporal plexus was absent at 1 month and fully recovered in all patients at month 8.

CONCLUSION

Uneventful cataract surgery induces relevant corneal modifications when inspected by means of confocal microscopy.

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.

Laser-assisted in-situ keratomileusis (LASIK) versus photorefractive keratectomy (PRK) for myopia

BACKGROUND

Myopia (also known as short-sightedness or near-sightedness) is an ocular condition in which the refractive power of the eye is greater than is required, resulting in light from distant objects being focused in front of the retina instead of directly on it. The two most commonly used surgical techniques to permanently correct myopia are photorefractive keratectomy (PRK) and laser-assisted in-situ keratomileusis (LASIK).

OBJECTIVES

To compare the effectiveness and safety of LASIK and PRK for correction of myopia by examining post-treatment uncorrected visual acuity, refractive outcome, loss of best spectacle-corrected visual acuity, pain scores, flap complications in LASIK, subepithelial haze, adverse events, quality of life indices and higher order aberrations.

SEARCH METHODS

We searched CENTRAL (which contains the Cochrane Eyes and Vision Group Trials Register) (The Cochrane Library 2012, Issue 11), Ovid MEDLINE, Ovid MEDLINE In-Process and Other Non-Indexed Citations, Ovid MEDLINE Daily, Ovid OLDMEDLINE (January 1946 to November 2012), EMBASE (January 1980 to November 2012), Latin American and Caribbean Literature on Health Sciences (LILACS) (January 1982 to November 2012), the metaRegister of Controlled Trials (mRCT) (www.controlled-trials.com), ClinicalTrials.gov (www.clinicaltrials.gov) and the WHO International Clinical Trials Registry Platform (ICTRP) (www.who.int/ictrp/search/en). We did not use any date or language restrictions in the electronic searches for trials. We last searched the electronic databases on 15 November 2012. We also searched the reference lists of the studies and the Science Citation Index.

SELECTION CRITERIA

We included randomised controlled trials comparing LASIK and PRK for the correction of any degree of myopia.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed trial quality and extracted data. We summarised data using the odds ratio and mean difference. We combined odds ratios using a random-effects model after testing for heterogeneity.

MAIN RESULTS

We included 13 trials (1135 participants, 1923 eyes) in this review. Nine of these trials randomised eyes to treatment, two trials randomised people to treatment and treated both eyes, and two trials randomised people to treatment and treated one eye. None of the paired trials reported an appropriate paired analysis. We considered the overall quality of evidence to be low for most outcomes because of the risk of bias in the included trials. There was evidence that LASIK gives a faster visual recovery than PRK and is a less painful technique. Results at one year after surgery were comparable: most analyses favoured LASIK but they were not statistically significant.

AUTHORS' CONCLUSIONS

LASIK gives a faster visual recovery and is a less painful technique than PRK. The two techniques appear to give similar outcomes one year after surgery. Further trials using contemporary techniques are required to determine whether LASIK and PRK as currently practised are equally safe. Randomising eyes to treatment is an efficient design, but only if analysed properly. In future trials, more efforts could be made to mask the assessment of outcome.

Effect of corneal collagen cross-linking on corneal innervation, corneal sensitivity, and tear function of patients with keratoconus

PURPOSE

To evaluate the effect of corneal collagen cross-linking (CXL) on corneal innervation, corneal sensitivity, and tear function in patients with keratoconus.

DESIGN

Prospective, interventional case series.

PARTICIPANTS

Twenty-four patients with bilateral keratoconus (30 eyes) who presented to the Institute of Vision and Optics, University of Crete, from May 2008 to October 2008.

METHODS

Patients underwent CXL. Confocal microscopic analysis of corneal sub-basal nerve plexus (total nerve length per image), corneal sensitivity (assessed with the Cochet-Bonnet esthesiometer), basic tear secretion (assessed with Schirmer's I test with anesthesia), and tear film stability (evaluated by means of tear film break-up time [TFBUT]) were assessed preoperatively and at 1, 3, 6, 9, 12, 18, and 24 months postoperatively.

MAIN OUTCOME MEASURES

Comparisons between preoperative and each postoperative value of total nerve length per image, corneal sensitivity, Schirmer's I test results, and TFBUT.

RESULTS

Total nerve length per image and corneal sensitivity were significantly decreased until postoperative month 6 (for both parameters: P<0.05 paired-samples t test at 1, 3, and 6 months postoperatively). Total nerve length per image tended to increase up to 2 years postoperatively, when it reached the preoperative level, but differences with the preoperative values after the sixth post-CXL month were insignificant. The results of Schirmer's I test and TFBUT had no statistically significant difference at any time point.

CONCLUSIONS

A transient decrease in corneal innervation and corneal sensitivity can be observed up to 6 months after CXL. No significant effect of CXL could be detected on basic tear secretion and tear film stability in our group of patients.

FINANCIAL DISCLOSURE(S)

The author(s) have no proprietary or commercial interest in any materials discussed in this article.

The effects of topical coenzyme Q10 and vitamin E D-α-tocopheryl polyethylene glycol 1000 succinate after cataract surgery: a clinical and in vivo confocal study

PURPOSE

To evaluate the postoperative effects of topical coenzyme Q(10) + vitamin E D-α-tocopheryl polyethylene glycol 1000 succinate (CoQ(10)) after cataract surgery.

METHODS

40 consecutive patients were randomized to receive CoQ(10) or saline solution (SS) twice daily for 9 months after uneventful cataract surgery with a temporal port. Before surgery, on day 14 and at months 3, 6 and 9, they underwent non-invasive break-up time (NIBUT) testing, Schirmer test, BUT, aesthesiometry as well as in vivo confocal microscopy of the subbasal nerve plexus of the cornea (SBP). The density of the subbasal nerves was calculated in the central (CFD) and temporal (TFD) cornea (number of fibres per field).

RESULTS

On day 14, surgery reduced CFD and TFD, respectively, by 25-35 and 50%; indices of ocular surface stability were all impaired. The treatment with CoQ(10) was associated with faster nerve regeneration than SS (at month 3, CFD +1.5 ± 1.9 vs. +0.2 ± 1.8, p = 0.04, and TFD +2.5 ± 1.7 vs. +1.0 ± 1.6, p = 0.007; at month 6, TFD +2.7 ± 1.9 vs. +1.4 ± 1.5, p = 0.02) and better stability of ocular surface (NIBUT and BUT) throughout the study. No relevant side effects were found, apart from occasional burning in 10% of CoQ(10) patients.

CONCLUSIONS

Changes of the corneal nerves occurring after cataract surgery may influence the integrity of the ocular surface. Treatment with topical CoQ(10) has a positive effect in restoring SBP anatomy and ocular surface stability.

Epipolis-Laser In Situ Keratomileusis Discarding Epithelium Versus Laser In Situ Keratomileusis for Myopia and Myopic Astigmatism in Asian Eyes

PURPOSE

To compare long-term safety, efficacy, predictability, and visual outcomes of epipolis-laser in situ keratomileusis (epi-LASIK) discarding epithelium versus LASIK in Asian eyes.

DESIGN

This was a prospective, randomized, bilateral case series.

METHODS

This study included 166 eyes of 83 patients with myopia and myopic astigmatism who received epi-LASIK in 1 eye and LASIK in the contralateral eye. Automated separation of the epithelium was performed with epi-K™, and LASIK was performed with M2 microkeratome using 90-μm calibrated heads. Patients were seen post-operatively at 1 and 3 days, 1 week, and on days 1, 3, 7 at 1, 3, 6, and 12 months. Uncorrected visual acuity, best corrected visual acuity, spherical equivalent (SE), contrast sensitivity, total higher-order aberration, corneal sensitivity, and clarity were analyzed.

RESULTS

Mean preoperative SE was -4.26 (SD, 1.64) diopters (D) in epi-LASIK and -4.27 (SD, 1.63) D in the LASIK group. Twelve months after surgery, mean SE was 0.04 (SD, 0.40) and 0.11 (SD, 0.30) D, respectively. There was no significant difference in uncorrected visual acuity (P = 0.451), SE (P = 0.157) and contrast sensitivity between groups at the 1-year follow-up (P > 0.05). During 6 months after operation, corneal sensitivity values were significantly lower in the LASIK group (P < 0.05). No eye lost line of best corrected visual acuity in both groups. In epi-LASIK eyes, there was no haze in 97.5% and haze grade 1 in 2.5% at 3 months postoperatively. From 6 months onward, alls corneas were clear.

CONCLUSIONS

Epi-LASIK was safe, predictable, and effective and may be considered an alternative for LASIK.

MMP-9 and the perioperative management of LASIK surgery

PURPOSE OF REVIEW

Hyperosmolarity is a central mechanism causing ocular surface inflammation and eye irritation in typical patients suffering from tear dysfunction. Tear composition in dry eyes, or dysfunctional tear syndrome, may destabilize the tear film and cause ocular surface epithelial disease. Increased activity of matrix metalloproteinases (MMPs), especially MMP-9, plays a critical role in wound healing and inflammation and is primarily responsible for the pathologic alterations to the ocular surface that leads to a dysfunctional tear state.

RECENT FINDINGS

Altered corneal epithelial barrier function is the cause for ocular irritation and visual morbidity in dry eye disease. The increased MMP-9 activity in dry eyes may contribute to deranged corneal epithelial barrier function, increased corneal epithelial desquamation, and corneal surface irregularity.

SUMMARY

Dry eye is one of the most common complications of photorefractive keratectomy and laser in-situ keratomileusis (LASIK). LASIK has both a neurotrophic effect on the cornea and leads to a physical change in corneal shape that results in a change in tear dynamics, leading to ocular surface desiccation. The reduction in tear function after LASIK may induce an increase in osmolarity and consequently raise the concentration of proinflammatory cytokines and MMP-9 in the tear film, which results in dry eyes and insufficient attachment between the corneal flap and the corneal bed. Appropriate diagnosis and management of dysfunctional tear syndrome may lead to less postoperative LASIK complications.