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

Structural and functional alterations in corneal nerves following single-step transepithelial photorefractive keratectomy

PURPOSE

To evaluate the relationship between structural and functional changes of corneal subbasal nerves after single-step transepithelial photorefractive keratectomy (TransPRK).

SETTING

Tianjin Medical University Eye Hospital.

DESIGN

Prospective observational study.

METHODS

Fifty-one eligible candidates who underwent TransPRK for moderate myopia were recruited. The regeneration of corneal subbasal nerves were evaluated by In Vivo Confocal Microscopy (IVCM) prior to surgery at 1 week, 1, 3, 6, and 12 months postoperatively. Meanwhile, the corneal sensitivity was measured by Cochet-Bonnet esthesiometer. The number of complete and incomplete blinks were recorded by LipiView interferometer. A correlation analysis was performed between these variables.

RESULTS

IVCM revealed the density and length of corneal nerve decrease immediately, and do not return to preoperative levels by 12 months post-TransPRK (P<0.01). Mean corneal sensitivity was slightly lower compared with preoperative levels at 1 week after surgery(P=0.001), then increases to baseline preoperatively within 1 month after surgery. Mean total blink frequency and the partial blink rates had no significant change postoperatively(P=0.087). There was no direct correlation between postoperative recovery of corneal sensitivity, changes of blink and regeneration of sub-basal corneal nerve.

CONCLUSIONS

The significant and prolonged decrease in corneal subbasal nerve morphology was accompanied by only a slight and transient reduction in corneal sensitivity to mechanical stimuli within 1 month after TransPRK. The results demonstrated that the structural changes of subbasal nerves were not parallel to their function after TransPRK.

Effects of long-term soft contact lens wear on corneal epithelial thickness after small incision lenticule extraction

The present study investigated changes in corneal epithelial thickness after small incision lenticule extraction (SMILE) in patients with long-term preoperative soft contact lens (SCL) wear, the impact of SCL wear on the efficacy of surgical outcomes and the effects of long-term SCL wear on postoperative corneal aberrations. Patients were assigned to three groups according to the duration of SCL wear: Group A, the non-SCL-wearing group; group B, those with SCL wear ≤1 year; and group C, those with SCL wear >1 year. Epithelial thickness was recorded in nine zones by anterior segment optical coherence tomography across a 5-mm diameter before surgery and at 1 week, and 1, 3 and 6 months post-surgery. Corneal epithelial thickness and corneal aberrations among the three groups were compared, as well as the effects of changes in corneal epithelial thickness on postoperative visual acuity and manifest refraction. No significant differences were noted with regard to age or preoperative spherical equivalent among groups A (22 eyes), B (17 eyes) and C (18 eyes). Preoperative corneal epithelial thickness in the inferonasal, inferior and inferotemporal zones was thinner in group B compared with that in group A, and corneal epithelial thickness was thinner in all nine zones in group C compared with that in group A (P<0.05). At all follow-up time points, in the central, nasal, inferonasal, inferior, inferotemporal and temporal areas, the epithelial thickness was thinner in group C compared with that in group A (P<0.05). At 3 months postoperatively, the epithelial thickness was thinner in the inferonasal and inferior sectors in group C compared with that in group B (P<0.05), and at 6 months postoperatively, the epithelial thickness in the inferior region was thinner in group C compared with that in group B (P<0.05). There were no significant differences in visual acuity or manifest refraction among the three groups at all postoperative time points. The total higher-order aberrations were greater in group C compared with those in group A for all time points (P<0.05) and were greater in group C at 1 and 3 months postoperatively compared with those in group B (P<0.05). The spherical aberrations at 3 and 6 months postoperatively were greater in group C compared with those in group A (P<0.05). The coma aberrations were greater in group C compared with those in groups A and B for all time points (P<0.05). In conclusion, long-term SCL wear will result in corneal epithelial thinning, which does not impact visual acuity or manifest refraction after SMILE.

Assessment of the correlation of the tear breakup time with quality of vision and dry eye symptoms after SMILE surgery

Purpose

It is well reported that dry eye symptoms can increase after many refractive surgery procedures. This study aims to provide a clinical understanding of the correlation of fluorescein tear film breakup time (FTBUT) with quality of vision (QoV) and dry eye symptoms following small incision lenticule extraction surgery (SMILE).

Methods

Patients electing to have SMILE surgery were subdivided into 2 groups: Group 1 included short preoperative FTBUTs of 3 to 6 seconds (s); Group 2 included long FTBUTs of ≥ 8 s. Uncorrected distance visual acuity, corrected distance visual acuity, manifest refraction, FTBUT, QoV and Ocular Surface Disease Index (OSDI) questionnaires were recorded 1 and 6 months postoperatively.

Results

Thirty-nine subjects were included in each group. There was no significant difference in visual outcomes between the 2 groups at both the 1- and 6-month postoperative assessments. FTBUT remained significantly lower in group 1. Oxford staining was initially higher for group 1 at 1 month (P = 0.007), but there was no significant difference at 6 months (P = 0.180). There was no significant difference in QoV or OSDI scores between the 2 groups at both postoperative visits.

Conclusions

Low preoperative FTBUT (3–6 s) does not appear to negatively affect postoperative visual outcomes or results in a greater likelihood of dry eye symptoms and poor ocular surface compared to eyes with a longer preoperative FTBUT. These results suggest that a low preoperative FTBUT does not necessarily increase the likelihood of poor visual acuity, dry eyes symptoms, or poor ocular surface outcomes following SMILE surgery.

The pattern of the inferocentral whorl region of the corneal subbasal nerve plexus is altered with age

PURPOSE

To describe the pattern of the nerves in the inferocentral whorl region of the human corneal subbasal nerve plexus (SBNP) in health and diseases known to affect the subbasal nerves.

METHODS

Laser-scanning in vivo confocal microscopy (IVCM) was used to image the SBNP bilaterally in 91 healthy subjects, 39 subjects with type 2 diabetes mellitus (T2DM), and 43 subjects with Parkinson's disease (PD). Whorl regions were classified according to nerve orientation relative to age and health/disease status.

RESULTS

Of 346 examined eyes, 300 (86.7%) had an identifiable whorl pattern. In healthy subjects, a clockwise nerve orientation of the whorl was most common (67.9%), followed by non-rotatory or 'seam' morphology (21.4%), and counterclockwise (10.7%). The clockwise orientation was more prevalent in healthy subjects than in T2DM or PD (P < 0.001). Healthy individuals below 50 years of age had a predominantly clockwise orientation (93.8%) which was reduced to 51.9% in those over 50 years (P < 0.001). Age but not disease status explained whorl orientation in T2DM and PD groups. Moreover, whorl orientation is bilaterally clockwise in the young, but adopts other orientations and becomes asymmetric across eyes with age. Finally, we report reflective 'dot-like' features confined to the whorl region of the subbasal plexus, sometimes appearing in close association with subbasal nerves and present in 84-93% of examined eyes regardless of disease status, eye or sex.

CONCLUSION

Subbasal nerves in the inferocentral whorl region are predominantly clockwise in young, healthy corneas. With aging and conditions of T2DM and PD, counterclockwise and non-rotatory configurations increase in prevalence, and bilateral symmetry is lost. Mechanisms regulating these changes warrant further investigation.

Prevalence of Tear Film Hyperosmolarity in 1150 patients presenting for refractive surgery assessment

PURPOSE

To present an analysis of tear film hyperosmolarity in a large, consecutive population and evaluate the correlation of ocular and systemic conditions with tear film osmolarity.

SETTING

Private practice Sydney, Australia.

DESIGN

Single-centre, retrospective, consecutive cohort.

METHOD

1404 patients (n=1357 standard, n=47 post-refractive) undergoing screening for laser refractive surgery from October 2017 to October 2020 were reviewed. Routine examination included tear film osmolarity (TFO) and Ocular Surface Disease Index questionnaire). TFO was conducted prior to further tests and patients refrained from topical eye drops minimum two hours before the appointment.

RESULTS

Mean highest TFO in the standard population was 299.12±11.94mOsm/L with 82.3% of eyes <308mOsm/L indicating normal tear film homeostasis. The mean inter-eye TFO difference was 8.17±8.60mOsm/L with 65.2% of eyes <=8mOsm/L. Mean highest TFO in the post-refractive subgroup was 299.72±11.00mOsm/L with a mean inter-eye difference of 9.02±6.92mOsm/L. Post-refractive surgery patients indicated higher mean OSDI values of 15.28±14.46 compared to the remainder of the population 9.69±10.56 (p=0.012). Significant correlation was demonstrated between TFO scores and OSDI normal classification in the standard population only (p=0.005, r=0.077). The use of contact lens correlated inversely with TFO and OSDI scores (p=0.000, r=-0.136 and p=0.000, r=-0.152 respectively).

CONCLUSION

Our study represents the largest available cohort of TFO scores in a standard population presenting for refractive surgery. We found that although the majority of patients can be expected to fall within normal ranges, a reasonable percentage will be diagnosed with tear hyperosmolarity and therefore at risk of dry eye disease.

Comparison of the optical quality after SMILE and FS-LASIK for high myopia by OQAS and iTrace analyzer: a one-year retrospective study

BACKGROUND

To compare the correction effect and optical quality after small-incision lenticule extraction (SMILE) and femtosecond laser assisted laser in situ keratomileusis (FS-LASIK) for high myopia.

METHODS

51 high myopia eyes after SMILE and 49 high myopia eyes after FS-LASIK were enrolled and divided into two groups retrospectively. The OQAS and iTrace analyzer were used for optical quality inspection. Between the two groups the spherical equivalent (SE), astigmatism, uncorrected distant visual acuity (UDVA), strehl ratio (SR), modulation transfer function cutoff frequency (MTF cutoff), objective scatter index (OSI) and wavefront aberrations were analyzed and compared before surgery and at 1, 6 and 12 months after surgery.

RESULTS

After the operation: (1) SE and astigmatism declined and UDVA increased significantly in both groups, and UDVA was better after SMILE than FS-LASIK. (2) SR and MTF cutoff reduced and OSI increased significantly after SMILE and FS-LASIK. SR and MTF cutoff were significantly higher after SMILE than FS-LASIK. OSI was significantly lower after SMILE than FS-LASIK. (3) The total wavefront aberration, total low-order wavefront aberration, defocus and astigmatism aberration as well as trefoil aberration reduced significantly in both groups. The total high-order wavefront aberration increased significantly after FS-LASIK. The spherical and coma aberration increased significantly in both groups. The total high-order wavefront aberration and coma aberration at 1 month were higher after FS-LASIK than SMILE.

CONCLUSION

The optical quality descended after SMILE and FS-LASIK. SMILE was superior to FS-LASIK at the correction effect and optical quality for high myopia. The combination of OQAS and iTrace analyzer is a valuable complementary measurement in evaluating the optical quality after the refractive surgery.

TRIAL REGISTRATION

This is a retrospective study. This research was approved by the ethics committee of Xiangya Hospital and the IRB approval number is 201612074.

Small Incision Lenticule Extraction for Correction of Pediatric Unilateral Anisometropic Myopia

PURPOSE

To evaluate the effects of femtosecond laser small incision lenticule extraction (SMILE) on treating unilateral myopic anisometropia in children with spectacles or contact lens intolerance.

METHODS

This was a retrospective study that included children with unilateral myopic anisometropic amblyopia who underwent a SMILE procedure at Alpha Vision Center, Zagazig, Egypt, from January 2014 to December 2016.

RESULTS

One hundred twenty-four eyes of 124 patients were included in this study. The postoperative corrected distance visual acuity (CDVA) at the 3-month and 1-, 2-, 3-, and 4-year follow-up visits improved significantly (P < .05) compared to the preoperative CDVA, indicating the safety of the procedure. At the 3-month postoperative visit, 23% of cases showed improvement of one or more lines of CDVA, whereas only 2% of cases showed a decline of only one line. Moreover, the postoperative uncorrected distance visual acuity compared favorably to the preoperative CDVA, denoting the efficacy of the refractive correction. The spherical equivalent was within ±0.50 diopters of the intended correction in 75% of the cases and within ±1.00 diopters in 89% of the cases. The intraoperative complications were scarce and relatively innocuous.

CONCLUSIONS

SMILE is a safe and effective alternative method for correcting myopic anisometropic amblyopia in children with spectacles or contact lens intolerance with good refractive results. A larger study with longer follow-up periods is necessary to determine the long-term effects of SMILE. [J Refract Surg. 2021;37(8):510-515.].

Clinical Applications of In Vivo Confocal Microscopy in Keratorefractive Surgery

PURPOSE

To review the contribution of in vivo confocal microscopy (IVCM) to the understanding of corneal wound healing following refractive surgery, and its role in the diagnosis and management of complications arising from keratorefractive procedures.

METHODS

Review of the basic science and clinical literature relating to the study of keratorefractive surgical procedures using IVCM.

RESULTS

Extensive research using IVCM has generated a comprehensive understanding of tissue responses after corneal refractive surgery. Epithelial thickness and stromal keratocyte density can be quantified postoperatively and studied longitudinally. Corneal nerve loss and subsequent reinnervation has been characterized and differs significantly between laser refractive techniques. IVCM has also been used to study complications arising from postoperative inflammation (diffuse lamellar keratitis, central toxic keratopathy, ring keratitis, and ectasia), infection (microbial keratitis), and neuropathy (dry eye and neuralgia). This imaging technique can have a critical role in the diagnosis of these complications and subsequent monitoring of treatment response. Manual processing of IVCM images is time-consuming and there may be significant interobserver and intraobserver variability with poor repeatability. However, increasing automation and the use of artificial intelligence is improving the speed and accuracy of image analysis.

CONCLUSIONS

IVCM has historically been confined to a research setting because image capture and subsequent processing was extremely labor intensive. However, advances in both hardware and software capabilities promise to allow the use of IVCM in routine clinical practice. Real-time evaluation of the cornea at a cellular level will be particularly useful in patients with inflammatory, infectious, or neuropathic complications of keratorefractive surgery. [J Refract Surg. 2021;37(7):493-503.].

Short-Term Impact of FS-LASIK and SMILE on Dry Eye Metrics and Corneal Nerve Morphology

PURPOSE

To analyze the short-term (up to 1 month) clinical outcomes in patients undergoing corneal laser refractive surgery and the impact on dry eye disease (DED) metrics and corneal nerves using in vivo confocal microscopy (IVCM).

METHODS

The unaided distance visual acuity, corrected distance visual acuity, and spherical equivalent refraction (SEQ) were determined in 16 and 13 patients undergoing FS-LASIK and SMILE, respectively. DED metrics assessed were Ocular Surface Disease Index, Dry Eye Questionnaire 5-items (DEQ-5), tear film osmolarity, tear meniscus height, noninvasive keratograph breakup time (NIKBUT), ocular staining, and meibomian gland atrophy. An automated analysis of corneal nerve fiber density, corneal nerve branch density, corneal nerve fiber length (CNFL), and corneal nerve fiber fractal dimension were obtained from the IVCM scans using ACCMetrics software (University of Manchester).

RESULTS

Both surgical techniques provided good refractive and visual outcomes. DED symptoms were found to be higher after FS-LASIK compared with SMILE (P < 0.05). A decrease in tear meniscus height (∼31%) and NIKBUT (∼40%) was reported after FS-LASIK (P = 0.005 and P = 0.001, respectively) but not after SMILE. Both procedures affected corneal nerve fiber density, corneal nerve branch density, CNFL, and corneal nerve fiber fractal dimension, but the impact was significantly greater with FS-LASIK (P = 0.001). Only CNFL correlated with the reported symptoms (DEQ-5) after FS-LASIK (r = -0.545, P = 0.029).

CONCLUSIONS

FS-LASIK and SMILE provided good refractive and visual outcomes. There was an increased impact on DED symptoms after FS-LASIK compared with SMILE, although there were no significant differences between the procedures for most of the other ocular surface metrics assessed. The IVCM findings showed that SMILE had less impact on corneal nerves compared with FS-LASIK.

Advances in refractive corneal lenticule extraction

Refractive errors are the leading cause of reversible visual impairment worldwide. In addition to the desired spectacle independence, refractive procedures can improve quality of life, working ability, and daily working performance. Refractive corneal lenticule extraction (RCLE) is a relatively new technique, dependent only on a femtosecond laser (FS). This leads to potential benefits over laser-assisted in situ keratomileusis (LASIK) including a quicker recovery of dry eye disease, a larger functional optical zone, and no flap-related complications. SMILE, available with the VisuMax FS (Carl Zeiss Meditec AG, Jena, Germany), is the most established RCLE application, offering visual and refractive outcomes comparable to LASIK. SmartSight (SCHWIND eye-tech-solutions GmbH, Kleinostheim, Germany) and CLEAR (Ziemer Ophthalmic Systems AG, Port, Switzerland) are two new RCLE applications that received Conformité Européenne (CE) approval in 2020. In this article, we review refractive and visual outcomes, advantages, and disadvantages of RCLE and also report on the latest advances in RCLE systems.

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.

Long-Term Refractive Outcome of Small Incision Lenticule Extraction in Very High Myopia

PURPOSE

To assess the stability, safety, predictability, and efficacy of small incision lenticule extraction (SMILE) in high myopia.

METHODS

The study was conducted as a retrospective noncomparative analysis of the records of 495 eyes of 270 patients treated by the ReLEx SMILE technique for a mean spherical myopic error of -12.84 ± 2.47 D (range: -10.0 to -14.0 D) combined with a mean astigmatism of -1.17 ± 1.34 D (up to -4.0 D). The mean LogMAR corrected distance visual acuity (CDVA) was 0.2 ± 0.6. In this study, 225 patients had the bilateral SMILE procedure, whereas 45 patients had a single eye treated with SMILE.

RESULTS

One month after surgery, the mean refractive error was 20.72 ± 0.88 D (range: +1 to 21.5 D), and the mean postoperative astigmatism was -0.83 ± 1.04 D. The mean LogMAR UDVA was 0.2 ± 0.34. In the last follow-up visit, 3 years after surgery, all the before mentioned parameters were the same or within minimal changes with no statistically significant difference from the earlier results. However, the spherical error demonstrated a significant change from -0.72 ± 0.88 D at 1 month to -1.17 ± 1.01 D at the end of the follow-up. However, this change had an insignificant visual impact. At the end of the follow-up period, approximately 94% of patients had unchanged CDVA or gained one or more lines, 6% lost one line of CDVA, and 1% lost 2 lines.

CONCLUSIONS

SMILE may be effective and safe, with a stable and predictable outcome for correction of very high myopia.

Middle East Preferred Practice Patterns for Dry Eye Disease: A Modified Delphi Consensus

Background:

Dry Eye Disease (DED) is a common ophthalmic condition resulting from dysfunction in the ocular surface, main lacrimal gland, meibomian glands, or connecting nerves.

Objective:

A group of local experts met to discuss local challenges and establish consensus in DED management across the Middle East.

Methods:

A modified Delphi method was used to reach consensus, comprising two rounds of the survey and a face-to-face meeting. An expert panel of 8 ophthalmologists voted on 23 statements, with consensus reached if ≥75% responded “strongly agree” or “agree” to a statement.

Results:

The expert panel reached consensus on 23 statements relating to the pathophysiology, diagnosis, treatment, and management of DED. Diagnosis begins with recording a detailed patient history and assessing subjective symptoms such as redness, burning, stinging, foreign body sensation, and/or photophobia. Tear Break-up Time (TBUT; <10 s), corneal spots (>5), and fluorescein staining are essential for diagnosing DED, assessing disease severity and ocular surface condition, and differentiating between types of DED. Ocular surface lubricants are the mainstay of treatment for DED. Treatment approaches should be categorized by etiology (if known). An improvement in symptoms can be observed objectively via an increase in TBUT, reduction in corneal and conjunctival spots, and restoration of normal tear production, or subjectively via less dependence on ocular surface lubricants, improved vision quality, and symptom amelioration.

Conclusion:

This consensus will serve to provide a framework for clinical decisions relating to the management of DED across the region.

Comparison of tear proteomic and neuromediator profiles changes between small incision lenticule extraction (SMILE) and femtosecond laser-assisted in-situ keratomileusis (LASIK)

Introduction

The tear proteomics and neuromediators are associated with clinical dry eye parameters following refractive surgery.

Purpose

To investigate and compare the tear proteomic and neuromediator profiles following small incision lenticule extraction (SMILE) versus laser-assisted in-situ keratomileusis (LASIK).

Methods

In this randomized controlled trial with paired-eye design, 70 patients were randomized to receive SMILE in one eye and LASIK in the other eye. Tear samples were collected preoperatively, and 1 week, 1, 3, 6 and 12 months postoperatively, and were examined for protein concentration changes using sequential window acquisition of all theoretical fragment ion mass spectrometry (SWATH-MS). The data were analyzed with DAVID Bioinformatics Resources for enriched gene ontology terms and over-represented pathways. Tear neuromediators levels were correlated with clinical parameters.

Results

Post-SMILE eyes had significantly better Oxford staining scores and tear break-up time (TBUT) than post-LASIK eyes at 1 and 3 months, respectively. Tear substance P and nerve growth factor levels were significantly higher in the LASIK group for 3 months and 1 year, respectively. SMILE and LASIK shared some similar biological responses postoperatively, but there was significant up-regulation in leukocyte migration and wound healing at 1 week, humoral immune response and apoptosis at 1 month, negative regulation of endopeptidase activity at 3 to 6 months, and extracellular structure organization at 1 year in the post-LASIK eyes. Tear mucin-like protein 1 and substance P levels were significantly correlated with TBUT (r = -0.47, r = -0.49, respectively).

Conclusion

Significant differences in the tear neuromediators and proteomics were observed between SMILE and LASIK, even though clinical dry eye signs have subsided and became comparable between 2 procedures.

Comparison of early visual quality in patients with moderate myopia using different optical zones in small incision lenticule extraction (SMILE)

Background

The early visual qualities of patients with moderate myopia were evaluated after small incision lenticule extraction (SMILE) using different optical zones.

Methods

In this retrospective case study, 27 cases (51 eyes) were selected, including 10 cases in Group A (19 eyes), 6.6–6.8 mm in the optical zone, 10 cases in Group B (19 eyes), 6.4–6.5 mm in the optical zone, and 7 cases in Group C (13 eyes),6.1–6.3 mm in the optical zone. The following items were examined preoperatively and 1 month postoperatively: uncorrected visual acuity (UCVA), best-corrected visual acuity (BCVA), spherical, cylinder, central corneal thickness (CCT), corneal mean curvature (CMC), total ocular aberrations (TA), total low order aberrations (tLOAs), defocus, astigmatism and total high order aberrations (tHOAs), spherical, coma, trefoil, modulation transfer function (MTF), MTF_cutoff, SR, objective scatter index (OSI), point scatter function at 50 and 10% (PSF50%, PSF10%), and contrast visual acuity of 100, 20, and 9% (VA100%, VA20%, and VA9%). We compared the three groups by Kruskal-Wallis test. Wilcoxon signed ranks test was used for each group before and 1 month after surgeries. P< 0.05 was considered statistically significant.

Results

There was no significant difference in UCVA, BCVA, CCT, cylinder, and CMC in three groups preoperatively and 1 month postoperatively (P> 0.05). Comparison of the aberrations of the three groups showed statistically significant difference only in TA, tLOA, defocus, astigmatism and SA preoperatively, and trefoil 1 month postoperatively(P< 0.05). The postoperative TA, tLOAs, defocus, astigmatism and trefoil of the three groups were lower than those before surgeries (P< 0.05). The postoperative tHOAs of Group B and C was lower than those before surgeries (P< 0.05). The MTF results showed that before surgeries, there were significant differences in three groups (P< 0.05) in spatial frequencies 5~15 cycles per degree (cpd), and no differences in 20~30 cpd(P> 0.05), while no difference were observed in all spatial frequencies postoperatively (P> 0.05). Comparing the preoperative and postoperative MTF values for each group, the results showed that there was a significant difference in Group C at 5~20 cpd after surgeries(P< 0.05). There was no significant difference in MTF_cutoff, SR, OSI, PSF50%, PSF10%, VA100%, VA20%, and VA9% in the three groups preoperatively (P> 0.05). One month after surgeries, higher VA9% values were measured for Group C compared to Group A and B (P < 0.05). There was no significant difference in each group before and after surgeries (P> 0.05).

Conclusion

SMILE could improve the visual qualities of patients with moderate myopia. Reducing the surgical optical zone will only affect night vision slightly.

The effect of nerve growth factor on corneal nerve regeneration and dry eye after LASIK

Dry eye is the most common complication after refractive surgery, especially after laser in situ keratomileusis (LASIK), in which nerves may be cut when making the corneal flap. Nerve growth factor (NGF) has been demonstrated to stimulate corneal sensitivity and nerve regeneration and NGF has been suggested as a potential treatment for dry eye disease (DED). Hence, this study aimed to investigate the effect of NGF on corneal nerve regeneration, sensitivity and dry eye symptoms after LASIK, compared to hycosan and normal saline (NS) treatments. Thirty-eight New Zealand white rabbits that underwent LASIK procedures were randomly assigned to three groups. Each group underwent NGF, hycosan, and NS treatment. The nerve densities and the number of corneal sub-basal and superficial stromal nerves were measured with confocal microscopy, and the results were compared before surgery and at one month and three months postoperatively. Corneal sensitivity was assessed with an esthesiometer. The tear breakup time (TBUT) was recorded to check for signs of dry eye. The whole corneas of the experimental animals were excised at three months after the surgery for immunohistochemically analysis. After LASIK, treatment with NGF significantly accelerated the recovery of sub-basal and superficial stromal nerve densities and the numbers, compared to hycosan and NS treatments at one month and three months postoperatively (NGF vs. hycosan, P < 0.01 each; NGF vs. NS, P < 0.01 each). The recovery of corneal sensitivity was significantly enhanced in the NGF group compared to the hycosan or NS treatment groups after surgery (P < 0.05). Also, the TBUT data showed a statistically significant longer time in the NGF group at one month, and three months postoperatively (P < 0.05). Immunofluorescence analysis showed the nerve fiber quantity of the NGF group was larger than in the hycosan and NS groups. Taken together, the experimental results suggested that mNGF had an obvious effect on promoting corneal nerve repairing and the potential to improve dry eye in different periods following LASIK.

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.

Decade - long journey with small incision lenticule extraction: The learnings

Over the past decade, small incision lenticule extraction (SMILE) has revolutionized the field of keratorefractive surgery. With the promise of superior corneal biomechanics and reduced postoperative dry eye, SMILE afforded a distinct advantage over flap-based procedures. Our evolving understanding of the surgical technique and management of its unique complications has further enhanced the outcomes. This review will highlight specific pearls on various preoperative and intraoperative principles allowing optimization of outcomes with SMILE.

SMILE – Small Incision Lenticule Extraction

Die SMILE (small incision lenticule extraction) zählt zu den Verfahren der refraktiven Lentikel-Extraktion und hat sich im letzten Jahrzehnt zu einem etablierten Bestandteil des modernen refraktivchirurgischen Spektrums entwickelt. Dieser Beitrag gibt einen Überblick über Patientenselektion, Operationsmethode, mögliche Komplikationen und klinische Ergebnisse dieser Methode.

Meibomian Gland Dysfunction: What Have Animal Models Taught Us?

Studies have estimated that currently 344 million people worldwide and 16.4 million adults in the US have some form of dry eye disease (DED). It is believed that approximately 70% of DED cases are due to some form of evaporative dry eye, for which Meibomian gland dysfunction (MGD) is the major cause. Unfortunately, currently there is no effective treatment for MGD, and solely palliative care is available. Given the importance of MGD in DED, there has been a growing interest in studying Meibomian gland development, homeostasis and pathology, and, also, in developing therapies for treating and/or preventing MGD. For such, animal models have shown to be a vital tool. Much of what is known today about the Meibomian gland and MGD was learnt from these important animal models. In particular, canine and rabbit models have been essential for studying the physiopathology and progression of DED, and the mouse model, which includes different knockout strains, has enabled the identification of specific pathways potentially involved in MGD. Herein, we provide a bibliographic review on the various animal models that have been used to study Meibomian gland development, Meibomian gland homeostasis and MGD, primarily focusing on publications between 2000 and 2020.

[SMILE - Small Incision Lenticule Extraction]

Refractive lenticule extraction is a corneal surgical technique that uses a femtosecond laser exclusively to create an intrastromal refractive lenticule for the correction of myopia and myopic astigmatism. In small incision lenticule extraction (SMILE) the generated refractive lenticule is subsequently extracted through a small incision. The reported efficacy, predictability and safety of the flap-less SMILE procedure is similar to those of femtosecond laser in situ keratomileusis (LASIK). Advantages of SMILE over LASIK include less iatrogenic dry eye, fewer induced higher-order aberrations, and potentially less biomechanical weakening of the cornea. However, there is a steeper surgeon learning curve for SMILE as the procedure is technically more challenging than LASIK. Furthermore, the current SMILE laser platform cannot use cyclotorsion control or eye-tracking technology and retreatment options are more complex compared to LASIK. This review looks at patient selection, surgical method, possible complications, retreatment options, and postoperative outcome of the SMILE technique.

Genetically Encoded Calcium Indicators for In Situ Functional Studies of Corneal Nerves

Purpose

Millions of people suffer from diseases that involve corneal nerve dysfunction, caused by various conditions, including dry eye syndrome, neurotrophic keratopathy, diabetes, herpes simplex, glaucoma, and Alzheimer's disease. The morphology of corneal nerves has been studied extensively. However, corneal nerve function has only been studied in a limited fashion owing to a lack of tools. Here, we present a new system for studying corneal nerve function.

Methods

Optical imaging was performed on the cornea of excised murine globes taken from a model animal expressing a genetically encoded calcium indicator, GCaMP6f, to record calcium transients. A custom perfusion and imaging chamber for ex vivo murine globes was designed to maintain and stabilize the cornea, while allowing the introduction of chemical stimulation during imaging.

Results

Imaging of calcium signals in the ex vivo murine cornea was demonstrated. Strong calcium signals with minimal photobleaching were observed in experiments lasting up to 10 minutes. Concentrated potassium and lidocaine solutions both modulated corneal nerve activity. Similar responses were observed in the same neurons across multiple chemical stimulations, suggesting the feasibility of using chemical stimulations to test the response of the corneal nerves.

Conclusions

Our studies suggest that this tool will be of great use for studying functional changes to corneal nerves in response to disease and ocular procedures. This process will enable preclinical testing of new ocular procedures to minimize damage to corneal innervation and therapies for diminished neural function.

A Prospective Comparison of Wavefront-Guided LASIK versus Wavefront-Guided PRK After Previous Keratorefractive Surgery

Purpose

To compare the results of retreatment with wavefront-guided LASIK versus wavefront-guided PRK for residual refractive error following previous myopic keratorefractive surgery.

Methods

In this prospective study, 32 eyes of 28 patients after prior myopic keratorefractive surgery underwent retreatment with flap-lift wavefront-guided LASIK (n = 12) or wavefront-guided PRK (n = 20) for residual refractive error. Safety, efficacy, predictability, and wavefront outcomes were evaluated.

Results

At last follow-up, both LASIK and PRK retreatment resulted in similar improvement in visual acuity with respective mean ± standard deviation (SD) uncorrected distance visual acuity of −0.07 ± 0.11 logMAR and −0.06 ± 0.13 logMAR (p = 0.87). In the study, 16.7% of LASIK and 33.3% of PRK eyes gained one or more lines of best-corrected distance visual acuity (CDVA), while 16.7% and 9.5% of eyes lost one or more lines of CDVA with LASIK and PRK, respectively. One hundred % of LASIK eyes and 89.5% of PRK eyes were within ± 0.50 diopters of emmetropia. Wavefront analysis demonstrated similar reductions in total RMS error higher-order aberrations (p = 0.84) with no difference in coma, trefoil, or spherical aberration between eyes undergoing LASIK or PRK retreatment.

Conclusion

Wavefront-guided LASIK and wavefront-guided PRK following previous keratorefractive surgery demonstrate similar safety, efficacy, and predictability with comparable wavefront outcomes.

Lacrimal gland excision in male and female mice causes ocular pain and anxiety-like behaviors

Lacrimal gland excision (LGE) induced dry eye produces more severe corneal damage in female mice, yet signs of LGE-induced ocular pain and anxiety in male and female mice have not been characterized. Excision of either the extraorbital gland (single LGE), or both the extraorbital and intraorbital glands (double LGE) was performed in male and female C57BL/6J mice to induce moderate and severe dry eye. Ongoing pain was assessed by quantifying palpebral opening and evoked nociceptive responses after corneal application of capsaicin and menthol. The open-field and plus maze were used to assess anxiety. Single LGE caused a reduction in palpebral opening and an increase in capsaicin and menthol-evoked responses only in female mice. Furthermore, single LGE produced signs of increased anxiety in female but not male mice. Overall, female mice appear more susceptible to signs of ocular pain, irritation, and anxiety in response to aqueous tear deficiency.

Corneal Nerve Abnormalities in Ocular and Systemic Diseases

The trigeminal nerve gives rise to the corneal subbasal nerve system, which plays a crucial role in sensations of touch, pain, and temperature and in ocular healing processes. Technological advancements in instruments, in particular in vivo confocal microscopy and aethesiometry, have allowed for the structural and functional evaluation of corneal nerves in health and disease. Through application of these technologies in humans and animal models, structural and functional abnormalities have been detected in several ocular and systemic disorders, including dry eye disease (DED), glaucoma, migraine, and fibromyalgia. However, studies across a number of conditions have found that structural abnormalities do not always relate to functional abnormalities. This review will discuss instruments used to evaluate corneal nerves and summarize data on nerve abnormalities in a number of ocular and systemic conditions. Furthermore, it will discuss potential treatments that can alleviate the main manifestations of nerve dysfunction, namely ocular surface pain and persistent epithelial defects.

Comparison Between the Effect of Femtosecond Laser in situ Keratomileusis (FS-LASIK) and Femtosecond Small Incision Lenticule Extraction (FS-SMILE) on the Corneal Endothelium

Purpose

To compare the effect of FS-LASIK and FS-SMILE on the corneal endothelial cell density (ECD) and morphology.

Patients and Methods

This is a prospective, cohort observational study that included 80 eyes of two equal groups of patients. Forty eyes were subjected to the FS-LASIK, and 40 eyes were subjected to the FS-SMILE. In both groups, patients, age ranged between 19 and 37 years with myopia ranges from −0.75 to −9.00 diopters (D) and astigmatism up to −3.00D. The ECD, coefficient of variation (CV), and hexagonality (HEX) in both groups were compared over six months. Specular microscopy was used to evaluate the corneal endothelium throughout the study.

Results

In both groups, ECD showed a statistically significant decrease while CV showed a statistically significant increase in the first month postoperatively. The FS-SMILE had more impact on both ECD and CV until the third and six months, respectively. Hexagonality showed a significant decrease in both groups throughout the whole study. In both groups, no vision-threatening complications occurred, and no eyes developed any corneal complications over a six-month follow-up period.

Conclusion

Although the ECD, CV, HEX are statistically affected in both FS-LASIK and FS-SMILE groups, both procedures have no significant adverse effects on the ECD and morphology. The impact of the FS-SMILE group may be due to the deeper penetration of the femto laser in the corneal tissue compared to the FS-LASIK. The closer the femto laser to the endothelium, the more exposure to the shock waves and heat energy, although minimal but it can cause collateral damage to this layer. The effects of FS-SMILE surgery on corneal endothelial cells and morphology need further investigations.

Corneal nerves anatomy, function, injury and regeneration

The cornea is a highly innervated tissue, exhibiting a complex nerve architecture, distribution, and structural organization. Significant contributions over the years have allowed us to come to the current understanding about the corneal nerves. Mechanical or chemical trauma, infections, surgical wounds, ocular or systemic comorbidities, can induce corneal neuroplastic changes. Consequently, a cascade of events involving the corneal wound healing, trophic functions, neural circuits, and the lacrimal products may interfere in the corneal homeostasis. Nerve physiology drew the attention of investigators due to the popularization of modern laser refractive surgery and the perception of the destructive potential of the excimer laser to the corneal nerve population. Nerve fiber loss can lead to symptoms that may impact the patient's quality of life, and impair the best-corrected vision, leading to patient and physician dissatisfaction. Therefore, there is a need to better understand preoperative signs of corneal nerve dysfunction, the postoperative mechanisms of nerve degeneration and recovery, aiming to achieve the most efficient way of treating nerve disorders related to diseases and refractive surgery.

Refractive surgery beyond 2020

Refractive surgery refers to any procedure that corrects or minimizes refractive errors. Today, refractive surgery has evolved beyond the traditional laser refractive surgery, embodied by the popular laser in situ keratomileusis or 'LASIK'. New keratorefractive techniques such as small incision lenticule extraction (SMILE) avoids corneal flap creation and uses a single laser device, while advances in surface ablation techniques have seen a resurgence in its popularity. Presbyopic treatment options have also expanded to include new ablation profiles, intracorneal implants, and phakic intraocular implants. With the improved safety and efficacy of refractive lens exchange, a wider variety of intraocular lens implants with advanced optics provide more options for refractive correction in carefully selected patients. In this review, we also discuss possible developments in refractive surgery beyond 2020, such as preoperative evaluation of refractive patients using machine learning and artificial intelligence, potential use of stromal lenticules harvested from SMILE for presbyopic treatments, and various advances in intraocular lens implants that may provide a closer to 'physiological correction' of refractive errors.

The best optical zone for small-incision lenticule extraction in high myopic patients

Small-incision lenticule extraction (SMILE) is an effective and safe procedure for the correction of myopia due to minimally invasive and noncorneal flap surgery. However, the SMILE procedure has certain requirements for corneal cap thickness, attempted refractive correction, residual stromal bed thickness, and optical zone diameter, which sometimes make surgeons hesitant to choose SMILE or other refractive surgeries. The requirements limit its use in patients with high myopia. The purpose of this review was to find the optimal parameters of SMILE through discussing the best optical zone for high myopic patients, the visual quality of different optical zones, the choice of corneal cap thickness, and their effects on corneal biomechanical parameters, so surgeons can provide reference recommendations for patients with high myopia in choosing a reasonable and safe procedure.

Vector analysis of small incision lenticule extraction and toric implantable collamer lens implantation for astigmatism correction

OBJECTIVES

To compare the efficacy of small incision lenticule extraction (SMILE) and toric implantable collamer lens (TICL) implantation for myopic astigmatism correction using vector analysis.

METHODS

In this retrospective study, 171 eyes of 171 patients with cylinder ⩾1.0 diopters (D) were recruited, with 97 eyes underwent SMILE and 74 eyes underwent TICL implantation. Preoperative and 3-months postoperative visual and refractive results were examined. The astigmatism correction, graded by the degree of preoperative cylinder was compared between two groups using vector analysis.

RESULTS

At 3-months postoperatively, the residual cylinder was -0.10 ± 0.21 D in the SMILE group and -0.30 ± 0.32 D in the TCL group (p < 0.05). Furthermore, 98% and 85% of eyes had the cylinder within ±0.5 D in the SMILE and TICL group, respectively. The vector analysis revealed similar target induced astigmatism vector in two groups. However, the difference vector, magnitude of error, angle of error, and index of success were significantly higher (0.30 ± 0.32 D, -0.19 ± 0.25, -2° ± 4.35°, and 0.16 ± 0.17 D, respectively) in the TICL group than the values in the SMILE group (0.10 ± 0.21 D, -0.05 ± 0.20, -0.03° ± 2.13°, and 0.05 ± 0.12, respectively), regardless of the degree of preoperative cylinder (all p < 0.05). For preoperative cylinder < 2.0 D, surgically induced astigmatism vector and correction index in the SMILE group were higher than those in the TICL group (p < 0.05).

CONCLUSION

Both SMILE and TICL implantation are effective techniques for myopic astigmatism correction. However, the accuracy of correction in the magnitude and axis of astigmatism with SMILE was better than that achieved with TICL implantation.

The neuroregenerative effects of topical decorin on the injured mouse cornea

Background

The cornea is innervated with a rich supply of sensory nerves that play important roles in ocular surface health. Any injury or pathology of the corneal nerves increases the risk of dry eye disease and infection. This study aims to evaluate the therapeutic potential of topical decorin to improve corneal nerve regeneration in a mouse model of sterile epithelial abrasion injury.

Methods

Bilateral central corneal epithelial abrasions (2-mm, Alger Brush) were performed on young C57BL/6 J mice to remove the corneal sensory nerves. Decorin, or vehicle, was applied topically, three times per day for 1 week or every 2 h for 6 h. Spectral-domain optical coherence tomography was performed to measure the abrasion area and corneal thickness. Wholemount immunofluorescence staining was used to assess sensory nerve regeneration (β-tubulin III) and immune cell density (CD45, Iba1, CD11c). To investigate the specific role of dendritic cells (DCs), Cx3cr1^gfp/gfp mice, which spontaneously lack resident corneal epithelial DCs, were also investigated. The effect of prophylactic topical administration of recombinant human decorin (applied prior to the abrasion) was also investigated. Nerve tracing (NeuronJ software) was performed to compare recovery of basal nerve axons and superficial nerve terminals in the central and peripheral cornea.

Results

At 6 h after injury, topical decorin application was associated with greater intraepithelial DC recruitment but no change in re-epithelialisation or corneal thickness, compared to the vehicle control. One week after injury, sub-basal nerve plexus and superficial nerve terminal density were significantly higher in the central cornea in the decorin-treated eyes. The density of corneal stromal macrophages in the decorin-treated eyes and their contralateral eyes was significantly lower compared to saline-treated corneas. No significant improvement in corneal nerve regeneration was observed in Cx3cr1^gfp/gfp mice treated with decorin.

Conclusions

Decorin promotes corneal epithelial nerve regeneration after injury. The neuroregenerative effect of topical decorin was associated with a higher corneal DC density during the acute phase, and fewer macrophages at the study endpoint. The corneal neuroregenerative effects of decorin were absent in mice lacking intraepithelial DCs. Together, these findings support a role for decorin in DC-mediated neuroregeneration following corneal abrasion injury.

Quality of life impact of refractive correction (QIRC) results three years after SMILE and FS-LASIK

Background

This study aimed to compare long-term postoperative quality of life and satisfaction differences between SMILE and FS-LASIK for myopia correction.

Methods

This cross-sectional study enrolled patients under the age of 39 years, who chose to undergo SMILE or FS-LASIK surgery to both eyes 3 years previously. Patients completed a common vision test and Quality of Life Impact of Refractive Correction (QIRC) questionnaire, together with the surgical satisfaction, adverse symptoms subjective survey. Patients with preoperative corrected distance visual acuity and postoperative uncorrected distance visual acuity of 20/20 or greater were included. Propensity score matching (PSM) was used to match the preoperative and postoperative spherical equivalent, age, and designed optical zones of the left and right eyes between the two groups.

Results

Forty-nine patients were included in each group after PSM from 188 patients. No significant difference in the total QIRC score was found between the SMILE and FS-LASIK groups (45.89 ± 5.91 vs 45.09 ± 5.65, p = 0.492). There were no differences in surgical satisfaction between the groups (p = 0.178). Compared to the SMILE group, the FS-LASIK group had more glare (2.12 ± 2.25 vs 3.22 ± 2.54, p = 0.026) and severe dryness (1.80 ± 1.98 vs 2.79 ± 2.19, p = 0.021).

Conclusion

Postoperative quality of life is similar after SMILE or FS-LASIK. Dry eye symptoms and glare were milder in the SMILE group than in the FS-LASIK group.

Early Corneal Wound Healing Response After Small Incision Lenticule Extraction

PURPOSE

To evaluate the corneal wound healing response after small incision lenticule extraction surgery.

METHODS

Small incision lenticule extraction was performed in both eyes of 12 New Zealand White rabbits. The refractive spherical correction was set at -6.00 D. Two animals were analyzed at each time point (1 hour, 4 hours, 1 day, 3 days, 7 days, and 28 days). The corneas were evaluated using slit-lamp and in vivo confocal microscopy. After euthanatization, the corneal tissues were subjected to light microscopy, transferase 2'-Deoxyuridine 5'-Triphosphate (dUTP) nick end labeling assay, and immunofluorescence microscopy (CD11b, fibronectin, tenascin, alpha-smooth muscle actin [α-SMA]).

RESULTS

The corneas did not show any opacity at any time point except at the side-cut incision. By contrast, there was obvious scar tissue at the side-cut incision. Scattered, hyperreflective spots were seen by confocal microscopy from 1 hour postoperatively. Transferase dUTP nick end labeling-positive keratocytes were abundant near the femtosecond laser incision area at 1 hour and reached a peak at 4 hours postoperatively and then decreased. Inflammatory cells migrated from the incision into the central cornea, and this process began 1 hour after surgery and peaked at 7 days. Extracellular matrix components were deposited at the beginning of day 1 postoperatively, and the distribution pattern differed between the central cornea and the incision site. α-SMA-positive myofibroblasts were only detected at the side-cut incision.

CONCLUSIONS

The scar tissue response in the peripheral cornea is related to the epithelium debridement. Inflammatory cells begin to be recruited by 1 hour after surgery. Therefore, it is necessary to implement antiinflammation interventions at a very early stage.

Clinical and tear cytokine profiles after advanced surface ablation refractive surgery: A six-month follow-up

Neuropathic dry eye is one of the most frequently seen complications after corneal refractive surgery, however, its incidence decreases in a significant manner along the first six months postoperative, reaching between 10 and 45% incidence. However, little is known on the inflammatory status of the ocular surface during this recovery process. We aim to analyze the clinical and tear molecule concentration changes along six months after advanced surface ablation for myopia correction, in a prospective study including 18 eyes of 18 subjects who bilaterally underwent advanced surface ablation corneal refractive surgery. Clinical variables (uncorrected distance visual acuity, symptoms, conjunctival hyperemia, tear osmolarity, tear stability, corneal fluorescein staining, conjunctival lissamine staining, Schirmer test, and corneal esthesiometry) and a panel of 23 pro and anti-inflammatory cytokines/chemokines concentration in tears preoperatively and at 1, 3 and 6 months postoperatively were evaluated. We found that uncorrected distance visual acuity improved significantly from baseline at 1-month visit, symptoms improved and tear osmolarity decreased significantly from baseline at 3-month visit and there was a decrease in mechanical corneal threshold between 1-month and 3- and 6-month visits. Regarding tear molecules, IL-4, IL-5, IL-6, IL-13, IL-17A, and IFN-γ tear levels were significantly increased at all the three visits, compared to preoperative levels at V0; IL-2 and VEGF were also significantly increased at 1-month and 6-month visits, but not at 3-month visit, whereas IL-9 IL-10 and IL-12 were only significantly increased at 6-month visit. Although we found that there is a recovery in clinical variables at 6 months postoperatively (i.e. neuropathic dry eye was not developed in the sample), ocular surface homeostasis is not completely restored, as it can be seen by the changes in concentration of some pro and anti-inflammatory molecules measured in tears.

Outcomes of Small Incision Lenticule Extraction for Myopic Astigmatic Treatment

BACKGROUND:

Some studies have shown that there is a certain rotation of the eye in the sitting and lying position of the patient. The Visumax system used for the Refractive Lenticule Extraction-Small Incision Lenticule Extraction (ReLEx SMILE) surgery lacks the rotation of eye control function. So, is the ReLEx SMILE surgery for patients with astigmatism safe and effective?

AIM:

To evaluate the outcomes of the ReLEx SMILE surgery in cases with myopic astigmatism.

METHODS:

The case series included 120 eyes with myopic astigmatism undergoing ReLEx SMILE surgery from January 2018 to November 2018. The distribution of patients for two subgroups based on the power of astigmatism, low astigmatic group (≤ 1.50D) and high astigmatic group (> 1.50D). All patients were measured UDVA, CDVA, refractive sphere, astigmatism and sphere equivalent before and after surgery one week, one month and three months carefully. The astigmatic correction was evaluated by the vectorial analysis Alpins.

RESULTS:

The mean efficacy index of the low and high astigmatic group was 1.035 and 1.082 (respectively); the mean safety index was 1.113 and 1.215 (respectively). 93% of eyes in the low astigmatic group had an angle of error (AE) within ± 15 degrees and 100% in high astigmatic group. There was an undercorrection in astigmatic treatment. No complications during and after surgery were recorded.

CONCLUSION:

ReLEx SMILE surgery for the myopic astigmatic treatment was safe and effective.

Remodeling of Substance P Sensory Nerves and Transient Receptor Potential Melastatin 8 (TRPM8) Cold Receptors After Corneal Experimental Surgery

Purpose

To investigate changes in corneal nerves positive to substance P (SP) and transient receptor potential melastatin 8 (TRPM8) and gene expression in the trigeminal ganglia (TG) following corneal surgery to unveil peripheral nerve mechanism of induced dry eye-like pain (DELP).

Methods

Surgery was performed on mice by removing the central epithelial and anterior stromal nerves. Mice were euthanized at different times up to 15 weeks. Immunostaining was performed with TRPM8, SP, or protein gene product 9.5 (PGP9.5) antibodies, and epithelial nerve densities were calculated. The origin of TRPM8- and SP-TG neurons were analyzed by retrograde tracing. Gene expression in TG was studied by real-time PCR analysis.

Results

SP-positive epithelial corneal nerves were more abundant than TRPM8 and were expressed in different TG neurons. After injury, epithelial nerve regeneration occurs in two distinct stages. An early regeneration of the remaining epithelial bundles reached the highest density on day 3 and then rapidly degraded. From day 5, the epithelial nerves originated from the underlying stromal nerves were still lower than normal levels by week 15. The SP- and TRPM8-positive nerve fibers followed the same pattern as the total nerves. TRPM8-positive terminals increased slowly and reached only half of normal values by 3 months. Corneal sensitivity gradually increased and reached normal values on day 12. Corneal injury also induced significant changes in TG gene expression, decreasing trpm8 and tac1 genes.

Conclusions

Abnormal SP expression, low amounts of TRPM8 terminals, and hypersensitive nerve response occur long after the injury and changes in gene expression in the TG suggest a contribution to the pathogenesis of corneal surgery-induced DELP.

Surgical options for retreatment after small-incision lenticule extraction: Advantages and disadvantages

Since the inception of small-incision lenticule extraction (SMILE), many surgeons have speculated the lack of an adequate and standard retreatment procedure will impede its popularity. However, more than 1 million patients worldwide have had this surgery, with visual outcomes nearly equivalent to current laser in situ keratomileusis (LASIK) results. With the procedure's growing popularity, some patients will inevitably have a postoperative residual refractive error from regression, overcorrection, undercorrection, and astigmatic induction and will require retreatment. To our knowledge, literature reviewing major retreatment options is limited. Options include surface ablation, thin-flap LASIK, secondary small-incision lenticule extraction, and a cap-to-flap procedure (CIRCLE) in which a femtosecond laser is use to create cuts that convert the small-incision lenticule extraction cap into a LASIK flap. This review discusses major advantages and disadvantages of these options and compares the visual outcomes based on the existing literature. An algorithmic approach created from this analysis is presented to guide retreatment decision-making.

Unwanted Astigmatism and High-order Aberrations One Year after Excimer and Femtosecond Corneal Surgery

SIGNIFICANCE

Small incision lenticule extraction (SMILE) is advanced as the most minimally invasive and least traumatic corneal procedure for correcting refractive errors using a single laser. Although SMILE obtains similar results to femtosecond laser in situ keratomileusis (LASIK) with spherical myopia, it has deficiencies in astigmatism correction.

PURPOSE

The purpose of this study was to compare refractive outcomes and high-order aberrations (HOAs) between SMILE and femtosecond LASIK corneal procedures at 1 year post-operative.

METHODS

Ninety-two patients (181 eyes) with myopia/myopic astigmatism underwent either SMILE (group 1) or femtosecond LASIK (group 2). The refractive target was to achieve emmetropia in all cases. Data were analyzed to determine significance of change in refraction and HOAs. Furthermore, astigmatism was subjected to vector analysis using the Thibos (calculation of change, Δ, in J0 and J45 values) and Alpins (calculation of difference, ΔC, between target-induced astigmatism [TIA] and surgically induced astigmatism) methods.

RESULTS

Forty-five patients (89 eyes) from group 1 and 47 patients (92 eyes) from group 2 completed the study. The main significant (P ≤ .001) findings were as follows: (a) residual astigmatism was greater in group 1; (b) group 1, ΔJ0 = 1.015J0 + 0.040 (R = 0.861), ΔJ45 = 1.082J45 + 0.019 (R = 0.792), ΔC = 0.401TIA + 0.323 (R = 0.489), and mean spherical aberration increased from -0.003 (SD, ±0.059; 95% confidence interval [CI], -0.015 to 0.009) to 0.028 μm (SD, ±0.041; 95% CI, -0.037 to -0.020); and (c) group 2, ΔJ0 = 0.952J0 - 0.005 (R = 0.921), ΔJ45 = 0.962J45 - 0.002 (R = 0.923), ΔC = 0.187TIA + 0.101 (R = 0.272), mean coma reduced from 0.114 (SD, ±0.087; 95% CI, 0.096 to 0.132) to 0.077 μm (SD, ±0.059; 95% CI, 0.065 to 0.089), and trefoil from 0.089 (SD, ±0.049; 95% CI, 0.079 to 0.0990) to 0.056 μm (SD, ±0.047; 95% CI, 0.046 to 0.066).

CONCLUSIONS

In comparison with SMILE, femtosecond LASIK offered better precision in the overall control of astigmatism and HOAs.

Comparison of Visual, Refractive and Ocular Surface Outcomes Between Small Incision Lenticule Extraction and Laser-Assisted In Situ Keratomileusis for Myopia and Myopic Astigmatism

Laser-assisted in situ keratomileusis (LASIK) is the most commonly performed laser refractive surgical technique worldwide for the treatment of myopia and myopic astigmatism. In recent years, small incision lenticule extraction (SMILE) has emerged as a promising alternative to LASIK, requiring only a single femtosecond laser to create an intrastromal lenticule, which is then removed via a small incision. The technique obviates the need for a corneal flap. A number of published studies have compared the two techniques in terms of visual, refractive and ocular surface outcomes. This review compares the clinical outcomes between LASIK and SMILE in treating myopia and myopic astigmatism based on studies published in the last 5 years. Twenty-two studies were included, all of which were observational in nature. Results suggest that the two techniques have comparable visual outcomes in terms of safety, efficacy and predictability, although recovery in visual acuity may be slower in SMILE-treated than LASIK-treated eyes. SMILE is found to result in less severe postoperative dry eye symptoms and faster recovery of corneal sensitivity than LASIK. It is important to note, however, that the SMILE technique is limited by the lack of a cyclotorsion-compensation system and option for customized treatment profile. The heterogeneity of results in this review may be attributable to the use of different LASIK platforms in different studies. Few studies compared the outcomes regarding severity of myopia. Future prospective randomized controlled trials with a larger sample size and longer follow-up period will be highly beneficial for progress in this field.

Dry Eyes After SMILE

Dry eyes is one of the most common complications after laser vision correction. Small incision lenticule extraction (SMILE) is a flapless procedure with a smaller corneal incision, less corneal nerves are transected during, making it theoretically less prone to dry eyes. Both SMILE and femtosecond-laser-assisted in situ keratomileusis (FS-LASIK) induce a transient worsening in dry eye parameters, but there is evidence showing that SMILE holds promises to have fewer negative impacts on the ocular surface parameters and allow an earlier recovery. SMILE-treated eyes may also have shown less corneal denervation and better corneal sensitivity compared with FS-LASIK eyes. This review summarizes the mechanisms of dry eyes after laser vision correction, the short-term (≤6 months) and long-term (>6 months) results in changes to dry eyes signs and symptoms, and corneal sensitivity of SMILE, as compared with FS-LASIK. Limitation of the studies and reasons accounting for their discrepancies will be discussed. Future randomized controlled trials with standardized postoperative regime are needed for better evaluation of dry eyes after SMILE.

Pregabalin Failed to Prevent Dry Eye Symptoms after Laser-Assisted in Situ Keratomileusis (LASIK) in a Randomized Pilot Study

PURPOSE

Perioperative pregabalin administration has been found to reduce the risk of persistent pain after a variety of surgical procedures. However, this approach has not been tested in relation to eye surgery. As such, the purpose of this study was to evaluate whether perioperative pregabalin can reduce the presence of dry eye (DE) symptoms, including eye pain, six months after laser-assisted in situ keratomileusis (LASIK).

METHODS

Prospective, masked, randomized single-center pilot study. Patients were treated with either pregabalin (oral solution of pregabalin 150 mg twice daily, first dose prior to surgery, continued for a total of 28 doses over 14 days) or placebo solution. The primary outcome was dry eye symptoms as measured by the Dry Eye Questionnaire 5 (DEQ-5). Secondary outcome measures included pain-related eye symptoms.

RESULTS

In total, 43 individuals were enrolled in the study and randomized to pregabalin (n = 21) or placebo (n = 22). Of those, 42 individuals completed the final visit after six months of follow-up. Some differences were noted between the two groups at baseline, including a higher frequency of females in the pregabalin group. At 6-months, there were no significant differences in the percentage of patients with DE symptoms (DEQ5 ≥ 6, 57% vs. 33%, p = 0.14), DE symptom severity (DEQ5, 6.6 ± 5.0 vs. 4.5 ± 4.2, p = 0.14), ocular pain intensity (numerical rating scale, 1.10 ± 1.48 vs. 0.38 ± 0.97, p = 0.08), or neuropathic pain complaints (Neuropathic Pain Symptom Inventory-Eye, 2.81 ± 4.07 vs. 3.14 ± 5.85, p = 0.83) between the pregabalin and control groups. Ocular signs were likewise similar between the groups, and of note, did not correlate with DE symptoms. The strongest predictor of DE symptoms six months post-surgery was the presence of DE symptoms prior to surgery.

CONCLUSIONS

Perioperative pregabalin did not reduce the frequency or severity of DE symptoms at a six month follow-up after LASIK in this small pilot study.

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.

[Secondary dry eye syndrome after keratorefractive surgeries and approaches to its treatment and prevention]

The article reviews the particularities of development and pathogenesis of secondary dry eye syndrome (DES) after refractive surgeries including a complex of problems related to changes in tear film content, damage of eye surface and neurotrophic epitheliopathy. Additionally, modern algorithms of treatment and prevention of secondary DES in patients after refractive surgeries are described. Despite the transient nature of the changes, excimer-laser surgery can lead to lasting deficiencies of eye surface in some patients. Therefore, intensive and early treatment of secondary DES during the early follow-up period after refractive surgery may significantly reduce risks of tear dysfunction and neurotrophic epitheliopathy development in the long term.

Population-based study on the epidemiology of dry eye disease and its association with presbyopia and other risk factors

BACKGROUND

To investigate the incidence and prevalence of dry eye disease (DED) in Taiwan and to explore its potential risk factors.

METHODS

Population-based longitudinal data from 2000 to  2013 based on Taiwan National Health Insurance Research Database were used in this study. To explore potential risks factor of interest, patients who had DED diagnosis before the exposure were excluded. Each patient from the exposure and his/her matched non-exposure controls were followed until either the diagnosis of DED or censorship. Kaplan-Meier method was used to compare the hazard of DED between cohorts. Stratified Cox proportional hazard models were applied to estimate the adjusted effect.

RESULTS

The age-adjusted prevalence for men and women were 6.81% and 16.16%, respectively. The age-gender rate of the same period was 549 per 10⁵ person-years. The propensity-adjusted hazard ratio of DED is 1.816 for the presbyopia versus non-presbyopia (with 95% CI = [1.737, 1.897] with p value < 0.0001).

CONCLUSIONS

The DED incidence for women peaked at age 50-74, while that for men peaked at age ≧ 75. The incidence in young people seems stable both for women and for men. While exploring the factors of DED, there is a significant association between presbyopia and DED even after matching age/gender and comorbidity conditions. Further clinical studies are needed to justify whether the corrective refractive treatment such as presbyopic glasses to treat the frequently hyperopic status of these patients could be beneficial to both dry eye and presbyopic condition.

Efficacy of carbomer sodium hyaluronate trehalose vs hyaluronic acid to improve tear film instability and ocular surface discomfort after cataract surgery

Purpose

To evaluate the effects of carbomer sodium hyaluronate trehalose (CHT) and sodium hyaluronate eye drops on tear film stability and ocular discomfort after cataract surgery.

Setting

Santa Maria della Misericordia Hospital, Rovigo, Italy.

Design

Prospective randomized case-control study.

Patients and methods

This study enrolled sixty patients scheduled for unilateral cataract surgery. After phacoemulsification, subjects received carbomer sodium hyaluronate trehalose (trehalose group) or sodium hyaluronate tears (HG group) substitute and were assessed through objective (break up time, corneal and conjunctival staining) and subjective (OSDI questionnaire) clinical evaluations after a two times a day topical administration. Outcome measures were collected preoperatively (baseline), one week (day 7) and 1 month (day 30) after surgery. Finally, each patient was asked to give his personal treatment satisfaction score.

Results

Trehalose group showed a steeper break up time (BUT) increase compared to patient treated with hyaluronic acid (P<0.001). OSDI questionnaire presented a opposite trend, trehalose patients evidenced a significantly major improvement (P<0.001), and in seven days mean values reduced by more than three times. Fluorescein staining reduction was documented with both treatments, although there was no statistically significant difference between groups. Finally CHT resulted in a significantly greater global satisfaction score (P<0.001).

Conclusions

CHT was effective and well tolerated in reducing dry eye disease symptoms and improving the clinical outcome after cataract surgery. On some parameters (BUT, OSDI), this new formulation was more effective than commonly used sodium hyaluronate in treating ocular irritation and tear film alterations.