Complications of myopic photorefractive keratectomy with the excimer laser

Bibliometric and visualized analysis of myopic corneal refractive surgery research: from 1979 to 2022

Background

Myopic corneal refractive surgery is one of the most prevalent ophthalmic procedures for correcting ametropia. This study aimed to perform a bibliometric analysis of research in the field of corneal refractive surgery over the past 40 years in order to describe the current international status and to identify most influential factors, while highlighting research hotspots.

Methods

A bibliometric analysis based on the Web of Science Core Collection (WoSCC) was used to analyze the publication trends in research related to myopic corneal refractive surgery. VOSviewer v.1.6.10 was used to construct the knowledge map in order to visualize the publications, distribution of countries, international collaborations, author productivity, source journals, cited references, keywords, and research hotspots in this field.

Results

A total of 4,680 publications on myopic corneal refractive surgery published between 1979 and 2022 were retrieved. The United States has published the most papers, with Emory University contributing to the most citations. The Journal of Cataract and Refractive Surgery published the greatest number of articles, and the top 10 cited references mainly focused on outcomes and wound healing in refractive surgery. Previous research emphasized "radial keratotomy (RK)" and excimer laser-associated operation methods. The keywords containing femtosecond (FS) laser associated with "small incision lenticule extraction (SMILE)" and its "safety" had higher burst strength, indicating a shift of operation methods and coinciding with the global trends in refractive surgery. The document citation network was clustered into five groups: (1) outcomes of refractive surgery: (2) preoperative examinations for refractive surgery were as follows: (3) complications of myopic corneal refractive surgery; (4) corneal wound healing and cytobiology research related to photorefractive laser keratotomy; and (5) biomechanics of myopic corneal refractive surgery.

Conclusion

The bibliometric analysis in this study may provide scholars with valuable to information and help them better understand the global trends in myopic corneal refractive surgery research frontiers. Two stages of rapid development occurred around 1991 and 2013, shortly after the innovation of PRK and SMILE surgical techniques. The most cited articles mainly focused on corneal wound healing, clinical outcomes, ocular aberration, corneal ectasia, and corneal topography, representing the safety of the new techniques.

The Most Cited Articles and Authors in Refractive Surgery

PURPOSE

To provide a comprehensive analysis of the most highly cited articles and authors in refractive surgery.

METHODS

The Scopus database was searched for articles pertaining to refractive surgery using multiple search terms to identify the top 100 most cited articles in refractive surgery. A publicly available database of more than 100,000 scientists that provides standardized information on multiple variables resulting in a composite indicator (C score) was searched to identify refractive surgery authors. A refractive surgery-specific composite score was created using only the authors' publications that were directly related to refractive surgery.

RESULTS

The 100 most cited articles and 40 refractive surgery authors with the highest ranked C score were identified. The article with the most citations by Trokel et al has garnered nearly 800 citations to date. All articles included in the top 100 had 200 or more citations. The peak publication years were 1998 to 2001. Laser in situ keratomileusis (22), photorefractive keratectomy (18), and postoperative corneal ectasia and/or corneal biomechanics (16) were the most represented topics. Emory University generated the most articles (7) and the majority of publications (48%) originated in the United States. Steven E. Wilson, MD, had the highest refractive C score and Jorge L. Alió, MD, PhD, had the most refractive surgery articles and citations. Among all authors listed, the average number of refractive surgery publications was 97, with 35% of the group having more than 100 refractive surgery articles published. All authors on the list had more than 2,000 citations for their refractive surgery articles, whereas 38% had 4,000 or more citations.

CONCLUSIONS

This list provides a comprehensive assessment of the most cited articles and authors in refractive surgery and demonstrates key focuses and trends in the field over time. [J Refract Surg. 2023;39(2):78-88.].

Refractive Effect of Epithelial Remodelling in Myopia after Transepithelial Photorefractive Keratectomy

(1) Introduction: We analysed epithelial changes after the treatment of moderate myopia with transepithelial photorefractive keratectomy. (2) Materials and Methods: We used optical coherence tomography data and analysed changes in the stroma and epithelium after ablation. We aimed to ascertain how much epithelium hyperplasia occurred after TransPRK; for this, we used data from 50 eyes treated with TransPRK with the AMARIS 1050 Hz, with a minimum follow-up of 4 months. (3) Results: The measured epithelial changes corresponded to a less than 0.1 ± 0.2D of spherical effect, less than 0.2 ± 0.2D of astigmatic effect, and less than 0.5 ± 0.2D of comatic effect. (4) Conclusions: The changes in epithelial thickness after aberration-neutral transepithelial photorefractive keratectomy for moderate myopia were very small, indicating a low level of epithelial hyperplasia without resembling a regression-inducing lentoid.

Twelve-Month Outcomes of the Wavefront-Optimized Photorefractive Keratectomy for High Myopic Correction Compared with Low-to-Moderate Myopia

Purpose

To evaluate the 12-months outcomes of photorefractive keratectomy (PRK) in patients with high myopia (≥ 6.0 diopters, D) compared with low-to-moderate myopia (< 6.0 D).

Patients and Methods

Records of 46 patients (69 eyes) who underwent PRK for myopic and astigmatic correction between October 2015 and December 2018 were reviewed. High myopic eyes (29 eyes) were compared with low-to-moderate myopic eyes (40 eyes). All surgeries were adjunct with 0.02% mitomycin C intraoperatively. Measured outcomes included postoperative uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), manifest refraction spherical equivalent, corneal haze rate, and any complications.

Results

At 12 months post-PRK, 26 eyes (89.7%) in the high myopia and 39 eyes (97.5%) in the low-to-moderate myopia group had UDVA ≥ 20/20, (p=0.30). Average postoperative logMAR UDVA at 12 months was −0.04 (20/18) and −0.11 (20/15) for the high myopia and low-to-moderate myopia groups, respectively. No eyes in either group had residual refractive errors >1 D. No eyes in both groups developed significant corneal haze at month 12. No eyes had a loss of greater than two Snellen lines of CDVA at 12 months post-surgery. The efficacy and safety indices at 12 months post-surgery were not significantly different between groups (1.06±0.26 vs.1.14±0.27, p =0.25 and 1.14±0.27 vs 1.17±0.26, p=0.60 for low-to-moderate myopia vs high myopia groups, respectively).

Conclusion

PRK with high myopic correction provides excellent refractive outcomes and is safe, compared to those of low-to-moderate myopic correction.

Comparison of transepithelial and conventional photorefractive keratectomy in myopic and myopic astigmatism patients: a randomized contralateral trial

Background

To assess transepithelial photorefractive keratectomy (tPRK) in terms of corneal epithelial healing rate, postoperative pain, postoperative discomfort, and visual and refraction outcomes compared to mechanical epithelial debridement PRK (mPRK) and alcohol-assisted PRK (aaPRK).

Methods

In this double-masked, randomized clinical trial, thirty-nine patients underwent tPRK in one eye and mPRK in the fellow eye (arm A), and 33 patients underwent tPRK in one eye and aaPRK in the contralateral eye (arm B). All surgical procedures were done using the Schwind Amaris excimer laser. The area of corneal epithelial defect in all eyes was captured and analyzed using ImageJ software.

Results

Mean epithelial healing time was respectively 3.74 ± 0.82 and 3.59 ± 0.79 days in tPRK versus mPRK (P = 0.21) in arm A, and 3.67 ± 0.92 and 3.67 ± 0.74 days in tPRK versus aaPRK (P = 1.00) in arm B. Accounting for the initial corneal epithelial defect area, the epithelial healing rate was faster in conventional PRK groups compared to tPRK (both P<0.001) in both arms. However, there was no significant difference in safety, efficacy, spherical equivalent refractive accuracy, or corneal haze development between tPRK and conventional PRK groups (all P > 0.05).

Conclusions

All three methods are effective in terms of visual and refractive outcomes. However, although time to complete re-epithelialization was similar with the three methods, the epithelial healing rate was faster in conventional PRK considering the initial corneal epithelial defect area, and the patients experienced less pain and discomfort in the first postoperative day.

Trial registration

IRCT, IRCT20200317046804N1. Retrospectively registered 5 May 2020.

Transepithelial photorefractive keratectomy on the same day of the initial consultation for the correction of myopia

PURPOSE

To examine the clinical outcomes, efficacy, safety, and predictability of transepithelial photorefractive keratectomy (Trans-PRK) operations performed on the day of the first screening visit in comparison with operations scheduled at a following appointment.

METHODS

Data of consecutive patients with myopia of various degrees, who underwent Trans-PRK, were retrospectively analyzed. Findings were compared between patients who underwent Trans-PRK on the same day of first consultation to patients that underwent surgery at subsequent visits, following initial consultation on a different day.

RESULTS

The study included 599 eyes treated on the initial visit day and 1936 eyes treated on a subsequent visit. Mean final spherical equivalent was close to emmetropia in both groups (p = 0.183). Efficacy indices were 0.928 ± 0.192 in the initial-visit group and 0.945 ± 0.163 in the second-visit group (p = 0.152). Safety indices were 0.954 ± 0.156 and 0.955 ± 0.151 (p = 0.707), respectively. No differences between the groups were seen in uncorrected visual acuity (UDVA) of ⩾20/20, ⩾20/25, and ⩾20/32. Only the sub-analysis of patients reaching UDVA of 20/40 or better was slightly lower in the first-visit (95.5%) compared with the second-visit group (97.9%, p = 0.001). Results of attempted correction within ±0.50 D were: 63.3% and 69.0%, respectively (p = 0.009). Complications profiles in the two groups were comparable.

CONCLUSIONS

Trans-PRK completed on the day of the first screening appointment demonstrated a similar safety outcome compared with subsequent-visits procedures, and slightly lower, yet comparable, results regarding efficacy and predictability.

Transient effect of suction on the retinal neurovasculature in myopic patients after small-incision lenticule extraction

PURPOSE

To characterize retinal neurovasculature changes after small-incision lenticule extraction (SMILE) in myopic patients.

SETTING

Ophthalmic Center, the Second Affiliated Hospital of Guangzhou Medical University, China.

DESIGN

Prospective interventional study.

METHODS

The corrected distance visual acuity/uncorrected distance visual acuity, corrected intraocular pressure (CIOP), and corneal tomography were evaluated at baseline (PRE), postoperative day (POD) 1, and POD 7. Ganglion cell-inner plexiform layer (GCIPL) and peripapillary retinal nerve fiber layer (pRNFL) thicknesses were measured. The vessel area densities (VADs, %), vessel skeleton densities (VSDs, %), vessel diameter index (VDI), and fractal dimensions (Dbox) of the superficial vascular plexus (SVP) and deep vascular plexus (DVP) were measured in a circular area (ϕ 2.5 mm) centered on the fovea.

RESULTS

A total of 38 myopic patients were recruited. The GCIPL thickness was increased after SMILE at POD 1 and POD 7 (P < .01) but no significant changes in the pRNFL thickness. The VAD, VSD, and Dbox of the SVP were decreased at POD 1 (P < .01), but not at POD 7. The VDI in small vessels of the SVP and DVP was decreased at POD 1 (P < .05) and increased at POD 7 (P < .05). Changes in CIOP were positively correlated with changes in the GCIPL thickness. Changes in CIOP were negatively correlated with changes in the VAD of small vessels and the Dbox of total vessels in the DVP. Changes in CIOP were negatively correlated with the VSD and VDI of small vessels in the DVP and changes in the VDI of big vessels in the SVP.

CONCLUSIONS

The transient fluctuations in the retinal neurovasculature after SMILE may represent a characteristic homeostasis pattern in patients after refractive surgery.

Visual outcomes of sterile corneal infiltrates after photorefractive keratectomy

Purpose:

Sterile infiltrates following laser refractive surgery is an uncommon complication. This study was undertaken to analyze the visual outcomes of sterile infiltrates following photorefractive keratectomy (PRK).

Methods:

This retrospective study included 14 eyes that developed sterile infiltrates following PRK out of a total of 6280 eyes that underwent PRK between 2014 and 2017. Medical records of these patients, including patient demographics, characteristics of the infiltrate, presenting visual acuity, and treatment outcomes were recorded and analyzed.

Results:

The incidence of sterile corneal infiltrates post-PRK in our study was 0.22% (14/6280). The mean age of the patients was 27.42 ± 4.87 years. The uncorrected visual acuity (UCVA) at presentation was 0.49 ± 0.13 log MAR units. The mean size of the infiltrate was 3.22 ± 2.85 mm². All cases were successfully managed medically with topical steroids. The mean UCVA and best-corrected visual acuity (BCVA) at the last follow-up visit were 0.08 ± 0.08 and 0.05 ± 0.07 log MAR units, respectively. The mean time taken for resolution of the infiltrate was 8.91 ± 4.57 days.

Conclusion:

Sterile infiltrates following PRK can be effectively treated with aggressive topical steroids. The outcome is generally favorable and does not require surgical intervention if treatment is instituted early.

[Methods of surgical treatment of keratectasia and analysis of postsurgical quality of vision]

Keratectasias are non-inflammatory dystrophic diseases of the cornea characterized by progressive bilateral thinning of the cornea that lead to deterioration in the quantitative and qualitative characteristics of vision reducing patient's quality of life. The changes can be asymmetrical and destructive. A number of surgeries have been proposed to reduce the negative effects of keratectasia including penetrating keratoplasty and its modifications, implantation of corneal ring segments, corneal cross-linking - alone and in combination with other methods, intrastromal keratoplasty. These methods can improve visual acuity to a certain degree and help slow the progression of keratectasia. This article studies various surgical methods used for treating keratectasia and analyses possible assessment of the quality of vision before and after the treatment.

Comparison of refractive outcomes after photorefractive keratectomy with different optical zones using Mel 90 excimer laser

Background

A larger optical zone for photorefractive keratectomy may improve optical quality and stability. However, there is need for limiting ablation diameter in that a larger ablation diameter requires greater ablation depth, and minimizing ablation depth may reduce adverse effects on postoperative wound healing, haze and keratoectasia. In this study, we compared the changes in clinical outcomes and the degree of regression between a 6.0 mm optical zone and 6.5 mm optical zone following PRK.

Methods

The records of 95 eyes that had undergone PRK with a 6.0 OZ (n = 40) and a 6.5 OZ (n = 55) were retrospectively reviewed. We compared data including the spherical equivalent of manifest refraction (SE of MR), simulated K (Sim K), thinnest corneal thickness, change in thinnest corneal thickness (the initial value divided by corrected diopter [ΔTCT/CD]), Q value, corneal higher order aberrations (HOAs) and spherical aberration (SA) pre-operation, at 3 and 6 months postoperative and at the last follow-up visit (Mean; 20.71 ± 10.52, 17.47 ± 6.57 months in the 6.0 and 6.5 OZ group, respectively).

Results

There were no significant differences in the SE of MR, Sim K and UDVA between the 6.0 OZ group and the 6.5 OZ group over 1 year of follow-up after PRK, and the 6.0 OZ group required less ΔTCT/CD than the 6.5 OZ group. The 6.5 OZ group showed better results in terms of post-operative HOAs of RMS, SA and Q value. When comparing that pattern of change in Sim K, there was no significant difference between the 6.0 OZ group and the 6.5 OZ group.

Conclusions

The clinical refractive outcomes and regression after PRK using Mel 90 excimer laser with a 6.0 OZ were comparable to those with a 6.5 OZ.

[Medicamental correction of pathomorphological changes of the ocular surface in patients with steroid therapy intolerance after photorefractive keratectomy]

INTRODUCTION

The problems of controlling inflammatory and proliferative response of the retina and correcting tear production in the post-operative period after photorefractive keratectomy (PRK) have not been fully solved yet. Patients intolerable to local steroids require an alternative. One drug that covers those needs is Cyclosporine 0.05%.

PURPOSE

To analyze clinical effectiveness of Restasis eye drops in solving inflammatory-degenerative response and tear production insufficiency (dry eye syndrome) for post-PRK patients with steroid eye drops intolerance accompanied with increasing intraocular pressure (IOP).

PATIENTS AND METHODS

Retrospective analysis of 14 myopic patients (28 eyes) was conducted; mean patient age was 25.9±6 years; myopia was (-)5.65±1.5 Diopters of spherical equivalent (SE); corneal-compensated IOP was 16.98±3.68 mm Hg before the surgery. All patients underwent excimer laser correction (PRK or Trans-PRK) with Schwind Amaris (SCHWIND eye-tech-solutions). After epithelization, all patients were prescribed 0.1% Dexamethasone solution 4 times a day (with decreasing dosing frequency) for 2 months, as well as local lubricants. The article also describes a separate clinical case of subepithelial fibroplasia that occurred post-PRK and was successfully stopped.

RESULTS

All patients had transitory IOP increase caused by local steroid therapy. Mean IOP at 1-month post-op was 20.5±7 mm Hg. At that point local steroids were replaced with 'Restasis' 0.05% (Cyclosporine) eye drops prescribed 2 times per day for 2 months. As the result, IOP values decreased to 16.2±3.21 mm Hg (without any additional therapy); at 6 months mean uncorrected visual acuity reached 0.98±0.05, best corrected visual acuity achieved 1.03±0.06 and SE was 0.04±0.12 Diopters.

CONCLUSION

Local Cyclosporine ('Restasis') is the method of choice for regulation of inflammatory and degenerative response and tear production insufficiency (dry eye syndrome) for post-PRK patients with intolerance to steroid eye drops.

A Critical Overview of the Biological Effects of Mitomycin C Application on the Cornea Following Refractive Surgery

During the last 2 decades, modifying the shape of the cornea by means of laser photoablation has emerged as a successful and popular treatment option for refractive errors. Corneal surface ablation techniques such as photorefractive keratectomy (PRK) and laser-assisted subepithelial keratomileusis (LASEK) offer good refractive results while having a minimal impact on corneal biomechanical stability. Past limitations of these techniques included the long-term regression of refractive outcome and a vigorous healing response that reduced corneal clarity in some patients (giving rise to what is clinically described as “haze”). Mitomycin C (MMC) was introduced as a healing modulator and applied on the corneal surface after refractive surgery to address these drawbacks. This article critically reviews the available evidence on the biological effects, safety, and clinical benefits of the off-label use of MMC in corneal refractive surgery.

Induced De Novo Astigmatism After Hyperopic LASIK Versus Myopic LASIK Surgery in Nonastigmatic Eyes

PURPOSE

To compare the astigmatism induced surgically (SIA) by spherical hyperopic laser in situ keratomileusis (H-LASIK) versus myopic laser in situ keratomileusis (M-LASIK) in nonastigmatic eyes.

METHODS

A retrospective study of patients who underwent LASIK surgery between 2005 and 2014 at the Care-Vision Laser Center, Israel. We calculated the mean absolute SIA and performed risk factor analysis for induced astigmatism. Differences between H-LASIK and M-LASIK were analyzed.

RESULTS

Eyes of 3877 patients who underwent M-LASIK and of 549 patients who underwent H-LASIK were nonastigmatic preoperatively and received a nonastigmatic treatment. Three months after surgery, hyperopic treatment induced more SIA (0.49 ± 0.48 D) than did myopic treatment (0.36 ± 0.4 D) (P < 0.001). In the H-LASIK group, the risk factors for induced astigmatism of >0.5 D were a higher preoperative refractive error (P = 0.003) and larger optical zone (7 vs. 6 mm). In the M-LASIK group, eyes with SIA >0.5 D tended to have steeper corneas preoperatively (43.8 ± 1.5 vs. 43.6 ± 1.4 D; P = 0.001), a higher spherical equivalent (-3.43 ± 1.53 Vs. -3.07 ± 1.45 P < 0.001), and smaller treatment zones (6 vs. 7 mm). In H-LASIK, the mean induced astigmatic axis was at 74.6 degrees.

CONCLUSIONS

There was a consistent trend toward more SIA in H-LASIK and in higher refractive error correction. In H-LASIK larger optical zones induce more SIA and in M-LASIK smaller ones caused it.

Very Late-Onset Corneal Scarring After Photorefractive Keratectomy Induced by Cataract Surgery

PURPOSE

To report two cases with very late-onset scarring of the cornea after photorefractive keratectomy (PRK) induced by cataract surgery.

METHODS

Case report and literature review.

RESULTS

Two patients presented with a subepithelial corneal scar more than 20 years after PRK. Scarring occurred within the first few months after cataract surgery. Scar tissue was successfully removed by laser-assisted anterior lamellar keratoplasty.

CONCLUSIONS

A few cases of late-onset corneal scarring after PRK have been described in the literature following trauma or ophthalmic surgery. Due to the need for cataract surgery in an aging population with previous PRK, this might become a more common problem.

Higher incidence of steroid-induced ocular hypertension in keratoconus

BACKGROUND

To compare intraocular pressure (IOP) changes following topical dexamethasone administration for 1 month in keratoconic versus normal eyes.

METHODS

This is a retrospective, single-center, non-randomized case series evaluation of 350 eyes. Two groups were formed: normal/control Group A (nA =73), eyes that underwent excimer laser photorefractive keratectomy; and keratoconic (KCN) Group B (nB =277), eyes that were subjected to partial laser photorefractive keratectomy combined with collagen cross-linking (The Athens Protocol). All eyes received the same post-operative regimen of topical dexamethasone 0.1 % for at least 1 month. Goldmann applanation tonometry IOP readings and central corneal thickness (CCT) measurements were monitored. Cases with induced ocular hypertension (OHT, defined as post-operative IOP higher than 21 mmHg), were identified and correlated to refractive procedure, gender, and corneal thickness.

RESULTS

At 4 weeks postoperatively, OHT was noted on 27.4 % (20 /73 eyes) in Group A, and 43.7 % (121 /277 eyes) in KCN Group B, (p <0.01). Six months post-operatively (following 5-months of discontinuing topical dexamethasone treatment and commencing treatment of IOP-lowering medications), OHT rate was 1.8 % in Group A and 3.9 % in the KCN Group B.

CONCLUSION

This study demonstrates a potentially significant pre-disposition of keratoconic eyes to the development of steroid-induced OHT.

Transepithelial Photorefractive Keratectomy for Low to Moderate Myopia in Comparison with Conventional Photorefractive Keratectomy

Purpose:

To compare the effectiveness, safety and stability of the results of transepithelial photorefractive keratectomy (tPRK) with conventional photorefractive keratectomy (PRK) for low to moderate myopia.

Methods:

In this prospective non-randomized case-control study, patients with low to moderate myopia were assigned to the tPRK group (cases) or the PRK group (controls). In the tPRK group, eyes were treated using the Amaris excimer laser (SCHWIND eye-tech-solutions GmbH and Co. KG, Germany). Outcome measures included postoperative pain using McGill Pain Questionnaire, epithelial healing time, uncorrected visual acuity (UCVA), best corrected visual acuity (BCVA), manifest refraction, and safety and efficacy indexes which were compared between the study groups.

Results:

Three hundred forty eyes of 170 patients were enrolled in this study. Each study group comprised of 170 eyes of 85 patients. There was a significant difference between the two groups regarding the postoperative pain scores in favor of the tPRK group (P = 0.04). The tPRK group had a shorter epithelial healing time than the conventional PRK group postoperatively (P = 0.01). Mean UCVA was significantly better in the case group than in the control group at the postoperative month 2 (P = 0.01). Regarding the safety and efficacy indexes, the tPRK group had better results than the conventional PRK group (P < 0.01 for both comparisons).

Conclusion:

Transepithelial PRK seems to be superior to conventional PRK for treatment of low to moderate myopia in terms of postoperative pain, epithelial healing time, visual recovery and safety and efficacy indexes.

Central islands: rate and effect on visual recovery after phototherapeutic keratectomy

PURPOSE

To retrospectively assess the proportion of patients affected by a central island (CI) and its effect on visual recovery after phototherapeutic keratectomy (PTK).

METHODS

This retrospective study evaluated 30 eyes of 21 consecutive patients (mean age ± standard deviation, 69.6 ± 6.8 years) undergoing PTK for the treatment of band keratopathy or granular corneal dystrophy. We investigated the rate of CI formation, which was defined as a steepening area of 3 D, 1.5 mm in diameter, on each corneal videokeratograph (ATLAS 9000; Carl Zeiss Meditec), and its effect on visual recovery at 3 months and at 1 year postoperatively.

RESULTS

A CI was found in 22 of 30 eyes (73%) 3 months postoperatively and in 14 of 25 eyes (56%) 1 year postoperatively. The degree of CI was significantly correlated with the change in logMAR corrected visual acuity (Spearman correlation coefficient r = 0.445, P = 0.026). The degree of CI in eyes with band keratopathy was significantly larger than that in eyes with granular dystrophy 1 year postoperatively (Mann-Whitney test, P = 0.045). The degree of CI was not significantly correlated with the ablation depth (Spearman correlation coefficient r = 0.116, P = 0.582) or the residual corneal thickness (r = -0.235, P = 0.278).

CONCLUSIONS

CI formation was found in as many as 73 and 56% of patients 3 months and 1 year after PTK, respectively, using the VISX Star S4 excimer laser system, and significantly affected the improvement of visual acuity. The anti-CI program should be applied by the manufacturer, not only for corneal refractive surgery but also for PTK in a clinical setting.

Photorefractive keratectomy results in myopic patients with thin cornea eyes

BACKGROUND

To evaluate the results of visual acuity and quality, and corneal integrity in myopic patients with a thin cornea who received photorefractive keratectomy (PRK).

MATERIALS AND METHODS

In this before-after interventional study, 30 myopic eyes with a myopia -3.76 ± 1.72 (-6.50 to -1.25) D and a corneal thickness of 486.03 ± 11.93 (452-499) μm at the thinnest point received PRK. In myopia was more than 4D, mitomycin C was used with PRK. The surgery was performed with an excimer laser (VISX STAR, Abbott Medical Optics, Abbott Park, US).

RESULTS

The safety and the efficacy index of the surgery was 1.01 ± 0.05 and 1.00 ± 0.05 in these patients, respectively. All the patients were within ±0.5D of emmetropia 1 year after the surgery. Mesopic contrast sensitivity (CS) had a significant increase in two spatial frequencies of six (P = 0.003) and 12 (P = 0.003). Total coma (P < 0.001), spherical aberration (P < 0.001), and total higher-order aberrations (HOA) (P < 0.001) also showed a significant increase. Corneal hysteresis (P < 0.001) and corneal resistance factor (P < 0.001) showed a significant decrease after 1 year.

CONCLUSION

PRK is a safe, effective, and predictable procedure with desirable effects on mesopic CS in patients with corneal thickness <500 μm, which increases HOAs and decreases corneal integrity proportionate to its value before the procedure.

Clinical features of subepithelial layer irregularities of cornea

PURPOSE

To illustrate surgical outcomes of subepithelial irregularities that were identified incidentally during laser refractive surgery.

MATERIALS AND METHODS

The study group consisted of 406 patients who underwent 787 surface ablation refractive surgeries. Ophthalmologic evaluations were performed before each procedure and at 1, 3 and 6 months post-operatively. Subepithelial irregularities were evaluated by analyzing still photographs captured from video recordings. Sizes and locations were determined by a calibrated scale located at the major axis of the tracking system's reticle.

RESULTS

Subepithelial irregularities were identified in 27 eyes during 787 surface ablation refractive surgeries. Most of the subepithelial irregularities did not show any abnormalities in the wavefront aberrometer. However, one case with diameter greater than 1.00 mm and one case of clustered multiple subepithelial irregularities with moderate size were corresponded significant coma (Z31) and increased higher order aberration (HOA) in the HOA gradient map.

CONCLUSIONS

Corneal subepithelial irregularities may be related to problems that include significantly increased localized HOA and remaining permanent subepithelial opacity. Subepithelial irregularity should be considered even if the surface of the cornea is intact and there are no specific findings measured by corneal topography.

Astigmatism induced by conventional spherical ablation after PRK and LASIK in myopia with astigmatism < 1.00 D

BACKGROUND

The purpose of this study was to evaluate surgically-induced astigmatism after spherical ablation in photorefractive keratectomy (PRK) and laser-assisted in situ keratomileusis (LASIK) for myopia with astigmatism < 1.00 D.

METHODS

The charts of patients undergoing spherical PRK or LASIK for the correction of myopia with minimal astigmatism of <1.00 D from 2002 to 2012 at the John A Moran Eye Center in Salt Lake City, UT, were retrospectively reviewed. Astigmatism was measured by manifest refraction. The final astigmatic refractive outcome at 6 months postoperatively was compared with the initial refraction by Alpins vector analysis.

RESULTS

For PRK, average cylinder increased from 0.39 ± 0.25 (0.00-0.75) preoperatively to 0.55 ± 0.48 (0.00-1.75) postoperatively (P = 0.014), compared with an increase in LASIK eyes from 0.40 ± 0.27 (0.00-0.75) preoperatively to 0.52 ± 0.45 (0.00-2.00) postoperatively (P = 0.041). PRK eyes experienced an absolute value change in cylinder of 0.41 ± 0.32 (0.00-1.50) and LASIK eyes experienced a change of 0.41 ± 0.31 (0.00-1.50, P = 0.955). Mean surgically-induced astigmatism was 0.59 ± 0.35 (0.00-1.70) in PRK eyes, with an increase in surgically-induced astigmatism of 0.44 D for each additional 1.00 D of preoperative cylinder; in LASIK eyes, mean surgically-induced astigmatism was 0.55 ± 0.32 (0.00-1.80, P = 0.482), with an increase in surgically-induced astigmatism of 0.29 D for each 1.00 D of preoperative cylinder.

CONCLUSION

Spherical ablation can induce substantial astigmatism even in eyes with less than one diopter of preoperative astigmatism in both PRK and LASIK. No significant difference in the magnitude of surgically-induced astigmatism was found between eyes treated with PRK and LASIK, although surgically-induced astigmatism was found to increase with greater levels of preoperative astigmatism in both PRK and LASIK.

Delayed epithelial healing following photorefractive keratectomy with mitomycin C treatment

PURPOSE

To evaluate the epithelial healing following photorefractive keratectomy (PRK) with mitomycin C (MMC) 0.02%.

METHODS

A total of 1520 eyes of 760 patients with myopia with spherical equivalent between -1.5 and -8.0 dioptres underwent PRK during 2004-2008. The epithelium was removed mechanically, and laser ablation was followed by topical application of MMC (0.02%) for 20 seconds. A therapeutic contact lens (TCL), kept in 4°C, was fitted and worn until complete epithelialization. Antibiotic, steroid and diclofenac drops were instilled during the healing phase. Steroid drops were used for 6-8 weeks and gradually reduced. The results were compared with a retrospective analysis of 500 myopic eyes which underwent PRK without MMC therapy during 2002-2004.

RESULTS

In 30 MMC treated eyes (2%), epithelial healing was delayed with a stellate defect which healed after 12-14 days. Another fifteen eyes (1%) revealed loose midperipheral epithelium and complete epithelialization took 10-14 days after scraping. Two of these eyes developed recurrent erosion treated by scraping and TCL. Seven eyes (0.5%) revealed delayed healing with paracentral epithelial plaques which were scraped and complete healing took 12-14 days. No final haze was found in the MMC-treated eyes. In comparison, only 0.8% of the eyes which had undergone PRK without MMC revealed epithelial problems. Haze was found in 8% of these eyes. A statistically significant difference was found between the rate of epithelial problems of the two groups (p ≤ 0.002).

CONCLUSIONS

MMC (0.02%) applied for 20 seconds post-PRK was found to delay epithelial wound healing up to 14 days in 3.5% of patients with myopia compared to 0.8% of PRK eyes without MMC application. Final haze was not found despite delayed epithelialization because of MMC treatment.

Comparison of patient outcomes after implantation of Visian toric implantable collamer lens and iris-fixated toric phakic intraocular lens

PURPOSE

We compared visual and refractive outcomes after implantation of Visian toric implantable collamer lenses (toric ICLs) and iris-fixated toric pIOLs (toric Artisans).

PATIENTS AND METHODS

A comparative retrospective analysis was performed. Toric ICLs were implanted into 30 eyes of 18 patients, and toric Artisans into 31 eyes of 22 recipients. We measured the logarithms of the minimum angle of resolution of uncorrected visual acuity (logMAR UCVA), logMAR of best spectacle-corrected corrected VA (logMAR BSCVA), MR, SE, and astigmatism (by the power vector method) before surgery and 1, 3, and 6 months thereafter. Differences between patients receiving each type of lens were compared by using a mixed model of repeated measures.

RESULTS

Visual improvements were evident after operation in both groups. By comparing the attempted to the achieved SE values, we were able to confirm that correction of refractive error was similar in both groups. However, the logMAR UCVA was significantly higher in the toric ICL group at all postoperative time points. Although manifest cylinder power and astigmatism (calculated by using the power vector method) gradually decreased in the toric ICL group, cylinder power 1 month postoperatively increased from -2.62 to -2.75 D; astigmatism was also increased at this time in the toric Artisan group.

CONCLUSION

The two tested toric pIOLs were similar in terms of the ability to correct refractive error, as assessed 3 months postoperatively. However toric ICLs corrected astigmatism more rapidly and safely. Notably, the large difference in astigmatism level between the two groups 1 month postoperatively indicates that toric ICLs are more effective when used to correct astigmatism.

Influence of internal optical astigmatism on the correction of myopic astigmatism by LASIK

PURPOSE

To investigate the influence of the origin of astigmatism on the correction of myopic astigmatism by LASIK.

METHODS

A retrospective study was conducted of the records of 192 patients (192 eyes) undergoing LASIK for correction of myopia and myopic astigmatism from January to September 2010. Ocular residual astigmatism (ORA) and lenticular astigmatism (LA) were determined by vector analysis using objective refraction and Pentacam (Oculus Optikgeräte GmbH) imaging of both corneal surfaces. Patients were divided into two groups according to ORA (high ORA group: ORA/preoperative refractive astigmatism >1; normal ORA group: ORA/preoperative refractive astigmatism ≤ 1) and LA (high LA group: LA/preoperative refractive astigmatism >1; normal LA group: LA/preoperative refractive astigmatism ≤ 1). Procedural efficacy was compared between those eyes with and without a significant amount of internal optical astigmatism using index of success.

RESULTS

Mean preoperative vectors for the astigmatism of the anterior cornea, posterior cornea, and lens were -1.33 × 3.0°, -0.33 × 95.3°, and -0.27 × 103.3°, respectively. Mean indices of success in the high and low ORA groups were 1.75 and 0.59, respectively (t=7.81, P<.001). Mean indices of success in the high and low LA groups were 2.07 and 0.70, respectively (t=12.36, P<.001). The higher indices of success in the high ORA and high LA groups suggest a lower efficacy of LASIK in treating astigmatism primarily located intraocularly.

CONCLUSIONS

Myopic LASIK is less effective in correcting astigmatism when astigmatism is mainly located at the internal optics. Topography and refractive value should be incorporated in the treatment of patients when a significant amount of internal optical astigmatism is detected preoperatively.

Axis alignment and rotational stability after implantation of the toric implantable collamer lens for myopic astigmatism

PURPOSE

To assess axis alignment and stability of the Toric Implantable Collamer Lens (TICL; STAAR Surgical Co) over time.

METHODS

Thirty-five consecutive eyes of 19 patients received the TICL for treatment of myopic astigmatism. Manifest refraction spherical equivalent (MRSE) and manifest refractive cylinder were measured preoperatively and at 3 months postoperatively. The axis alignment of the TICL was measured using the internal OPD map obtained with the OPD-Scan II (NIDEK Co Ltd).

RESULTS

Mean refractive cylinder was reduced from 2.80+/-1.45 diopters (D) preoperatively to 0.63+/-0.75 D at 3 months postoperatively; MRSE was -7.61+/-4.02 D preoperatively and -0.14+/-0.38 D at 3 months. Mean absolute value of the measured axis misalignment from baseline (day 1) to 1 month was 2.90+/-2.11 degrees and from 1 month to 3 months was 4.6+/-11.2 degrees. Mean absolute value of the measured changes in axis misalignment from baseline to 3 months was 2.68+/-2.11 degrees (after excluding one eye that required repositioning due to TICL rotation). At 3 months postoperatively, 96.8% (30/31) eyes had <or=8 degrees and 90.3% (28/31) had <or=5 degrees of axis misalignment.

CONCLUSIONS

The TICL showed minimal axis misalignment after implantation and remained stable 3 months postoperatively.

Postoperative astigmatism and axis stability after implantation of the STAAR Toric Implantable Collamer Lens

PURPOSE

To evaluate the efficacy, safety, and rotational and footplate stability of the STAAR Toric Implantable Collamer Lens (TICL; STAAR Surgical Co) for correction of myopic astigmatism.

METHODS

In this prospective, consecutive, interventional case series, a TICL was implanted uneventfully in 30 consecutive eyes of 20 patients with myopia and astigmatism. The uncorrected visual acuity, best spectacle-corrected visual acuity, refraction, and astigmatism were measured preoperatively and at last follow-up. To evaluate postoperative axis deviation from the intended axis and footplate displacement, a digital anterior segment photograph was taken after full mydriasis and ultrasound biomicroscopy for the four footplates of the TICL in each eye at last follow-up. Possible risk factors for TICL rotation were analyzed through correlation analysis.

RESULTS

After mean follow-up of 7.6 months, the mean refractive astigmatism decreased from 2.43 +/- 1.24 diopters (D) preoperatively to 0.73 +/- 0.47 D postoperatively, and the mean difference between intended and achieved TICL axes was 4.03 +/- 3.39 degrees. The absolute value of TICL rotation had significant correlation with the spherical power of the TICL (P = .037). The footplates of all TICLs were in situ in the ciliary sulcus except for one case in which one of the four footplates was located below the ciliary sulcus.

CONCLUSIONS

Implantation of the STAAR TICL appears to be an effective and safe method for correction of myopic astigmatism. No clinically significant rotation or footplate displacement of the TICLs was detected postoperatively during mean follow-up of 7.6 months.

Comparison of early postoperative clinical outcomes of photorefractive keratectomy and lamellar epithelial debridement

PURPOSE

To compare early postoperative clinical outcomes of photorefractive keratectomy (PRK) and lamellar epithelial debridement (LED).

SETTING

Department of Ophthalmology, Kangbuk Samsung Hospital, Seoul, Korea.

METHODS

This prospective study was of patients randomly assigned to have PRK or LED. In the LED group, an epithelial flap was created using an Amadeus II epikeratome. Postoperative follow-up was at 1, 3, and 7 days and 1, 3, and 6 months. The outcome parameters were uncorrected visual acuity (UCVA), best corrected visual acuity (BCVA), higher-order aberrations (HOAs), epithelial healing time, and corneal haze.

RESULTS

The study comprised 39 patients (76 eyes). The mean preoperative spherical equivalent (SE) was -3.96 diopters (D) +/- 1.24 (SD) in the PRK group and -4.06 +/- 1.39 D in the LED group. Postoperative UCVA was significantly better in the LED group 1 day postoperatively. The UCVA was 20/20 or better in 14.6% in the PRK group and 42.9% in the LED group (P = .006); 20/25 or better in 41.5% and 82.9%, respectively (P = .000); and 20/40 or better in 80.5% and 100%, respectively (P = .006). On subsequent follow-up visits, the UCVA was comparable between groups. No eye lost lines of BCVA at 3 months. There was no difference between groups in postoperative SE refraction, HOAs, or corneal haze.

CONCLUSIONS

Lamellar epithelial debridement and PRK had comparable safety and efficacy in the surgical correction of low to moderate myopia. The UCVA was significantly better after LED than after PRK 1 day postoperatively and equivalent thereafter.

Reversibility of effects of orthokeratology on visual acuity, refractive error, corneal topography, and contrast sensitivity

OBJECTIVES

To investigate the changes in corneal shape and optical performance during and after discontinuation of overnight orthokeratology for correction of myopia.

METHODS

Both eyes of 15 subjects were fitted with overnight reverse-geometry orthokeratology lenses, which were then worn for >4 hr overnight for 52 weeks. Subjects were free of ocular disease and had a corrected visual acuity of > or =1.0. Refractive correction, uncorrected visual acuity, corneal topography, and contrast sensitivity (at 4 spatial frequencies) were measured under photopic conditions.

RESULTS

Refractive error (spherical equivalent) and contrast sensitivity were decreased, whereas uncorrected visual acuity, the surface asymmetry index, and the surface regularity index were increased, 1 week after the onset of overnight orthokeratology and remained so during the 52 weeks of treatment. These parameters had largely returned to baseline values by 8 weeks after treatment discontinuation.

CONCLUSIONS

Overnight orthokeratology improved uncorrected visual acuity and reduced refractive error but increased corneal irregularity and impaired contrast sensitivity. However, these changes in visual function and corneal shape were reversed after discontinuation of orthokeratology lens wear.