Excimer laser photorefractive keratectomy. 18-month follow-up

Glaucoma and refractive surgery: A comprehensive review

The global surge in refractive surgeries, particularly among myopic individuals, has elicited concerns regarding potential inaccuracies in the measurement of intraocular pressure (IOP) post surgery, primarily associated with central corneal thinning. The incidence of elevated IOP after intraocular refractive surgeries is higher than expected and is multifactorial. Myopic eyes have a higher susceptibility to both primary and secondary glaucoma. Consequently, meticulous preoperative screening for glaucoma is imperative, coupled with systematic postoperative follow-up and evaluation. This comprehensive review analyses the etiology, mechanisms, and therapeutic strategies for managing elevated IOP following refractive surgery. We propose an algorithm to summarize the causative factors of elevated IOP and formulate effective interventions in these instances.

Management of Corneal Haze After Photorefractive Keratectomy

Photorefractive keratectomy (PRK) is a safe and popular corneal surgery performed worldwide. Nevertheless, there is potential risk of corneal haze development after surgery. Proper management of post PRK haze is important for good visual outcome. We performed a comprehensive review of the literature on the various risk factors and treatments for PRK haze, searching the PubMed, Google Scholar, SCOPUS, ScienceDirect, and Embase databases using relevant search terms. All articles in English from August 1989 through April 2023 were reviewed for this study, among which 102 articles were chosen to be included in the study. Depending on the characteristics of and examination findings on post PRK haze, different management options may be preferred. In the proposed framework, management of PRK haze should include a full workup that includes patient's subjective complaints and loss of vision as well as visual acuity, biomicroscopy, anterior segment optical coherence tomography, epithelial mapping, and Scheimpflug densitometry. Topical steroid treatment for haze should be stratified based on early- or late-onset haze. Mechanical debridement or superficial phototherapeutic keratectomy (PTK) may be used to treat superficial corneal haze. Deep PTK and/or PRK can be used to treat deep corneal haze. Mitomycin-C and topical steroids are prophylactic post-surgery agents to prevent recurrence of haze.

Ocular Pain Symptoms in Individuals With and Without a History of Refractive Surgery: Results From a Cross-Sectional Survey

PURPOSE

This study characterized ocular pain symptoms in individuals with and without a history of refractive surgery (RS) using a cross-sectional survey of individuals with ocular pain.

METHODS

A link to an anonymous survey was posted on a corneal neuralgia Facebook group that included individuals with ocular pain from any etiology and sent to individuals seen in our clinic with ocular pain. The survey asked about medical history, ocular pain symptoms (using standardized questionnaires), and treatment responses. Respondents were split into 2 groups based on a history of RS.

RESULTS

One hundred one individuals responded to the survey. The mean age for all respondents was 41.6 ± 15.6 years, and 50% reported a history of RS. A total of 46% of individuals with a history of RS reported that their ocular pain started within 1 month of surgery, with median pain duration of 36 (interquartile range 22-84) months. The median Dry Eye Questionnaire-5 (range 0-22) scores were 16 and 15 for the RS and no-RS groups, respectively. Most individuals in both groups characterized their pain as burning (score ≥1: RS, 86%; no-RS, 80%) and reported evoked pain to wind, light, or temperature (score ≥1: RS, 97%; no-RS, 85%). Fifty-nine of 101 individuals responded to treatment questions. Individuals in both groups reported >30% improvement in pain symptoms with some topical and systemic approaches.

CONCLUSIONS

Individuals with a history of RS developed ocular pain soon after surgery, which persisted for years. Symptom profiles were similar between those with and without RS. Topical and systemic approaches can treat pain in both groups.

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.

[Excimer laser in keratoconus management]

Visual rehabilitation in keratoconus is a challenge, notably because of the significant irregular astigmatism and optical aberrations that it induces. Many surgical techniques have been developed in addition to, or in the case of failure of, spectacles and rigid gas permeable contact lenses: intracorneal ring segments, intraocular lenses, excimer laser and, as a last resort, keratoplasty. Excimer laser photoablates the cornea, allowing remodeling of its surface. There are various treatment modes (wavefront-optimized, wavefront-guided and topography-guided), allowing performance of a customized treatment if needed. Its use in keratoconus has been described since the 2000s, alone or in combination with other procedures. For example, the combination of photoablation and corneal cross linking, a technique that increases corneal rigidity and in so doing can slow or even stop the progression of keratoconus, proved its efficacy and safety in many studies, and various protocols have been described. A triple procedure, including intracorneal ring segments, excimer laser and cross linking, has also given some very promising results in progressive keratoconus, providing a significative improvement in visual acuity and topographic data. The combination of excimer laser and intraocular lenses remains a poorly explored lead that might provide some satisfactory results. The objective of this review is to summarize the recent data on excimer laser in keratoconus management.

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.

Assessment of Factors Associated With Postoperative Pain After Photorefractive Keratectomy

PURPOSE

To define the factors that affect patient's self-assessed postoperative pain after photorefractive keratectomy (PRK).

METHODS

Patients who underwent PRK in 2016 were evaluated. Anonymized data collected included patient gender, age, and season at the time of surgery, ablation depth, surgeon status (attending vs. resident), topical tetracaine use, and subjective pain scores at postoperative days (PODs) 1 and 7. Average pain scores and amount of pain medication taken were analyzed for each of the previously mentioned variables.

RESULTS

Overall, 231 patients who underwent PRK were analyzed. The mean pain score and SD were 0.78 ± 1.87 on POD 1 and 0.03 ± 0.37 by POD 7. Patients who used topical tetracaine reported significantly higher pain on POD 1 and 7 compared with patients who did not use tetracaine (P < 0.001 and P = 0.038, respectively). No significant differences in pain scores were seen based on surgeon status, ablation depth, gender, and season. Patients who used topical tetracaine took a higher amount of oral pain medication (9.44 ± 6.01) compared with those who did not (7.02 ± 4.71) (P = 0.022).

CONCLUSIONS

Postoperative pain was significantly elevated in patients who used tetracaine on POD 1 and POD 7. These patients were also more likely to take oral pain medication than those who did not use topical tetracaine. Surgeon status, season, gender, and ablation depth showed no significant differences in subjective pain scores. Oral pain medication should be evaluated to assess efficacy and safety in inhibiting ocular pain after PRK.

Main Complications of Photorefractive Keratectomy and their Management

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

A Comparative Study of the Duration and Efficacy of Tetracaine 1% and Bupivacaine 0.75% in Controlling Pain following Photorefractive Keratectomy (PRK)

Objective

To evaluate if topical bupivacaine 0.75% provides better pain control after excimer laser over topical tetracaine 1% without affecting corneal wound healing, refractive outcome of visual function.

Design

A prospective, double-masked trial was conducted in which 38 patients were randomized to receive either tetracaine or bupivacaine every 30 minutes for 24 hours post-operatively. Pain was recorded over a four day period using a Visual Analogue Pain Scale. The rate of epithelial healing was assessed during digitized retro-illumination photography. Visual performance was recorded using best corrected Snellen acuity, objective measurements of haze, halo and glare over a six month period.

Results

Tetracaine afforded better pain control (p=0.05). Full epithelial closure occurred in all patients within 72 hours and no statistically significant difference was recorded in any of the parameters measured.

Conclusions

Contrary to our expectation, the longer acting anaesthetic, bupivacaine, was inferior to tetracaine. Limited and supervised use of topical anaesthetics is recommended in controlling pain following photorefractive keratectomy.

The Early Results of Excimer Laser Photorefractive Keratectomy for Compound Myopic Astigmatism

An excimer laser (VISX Twenty/Twenty Excimer Refractive System) was used to treat 51 eyes for myopia and astigmatism. Uncorrected pretreatment visual acuity was between 6/18 and 6/60 (log unit +0.45 to +1.0) in 59% and worse than 6/60 in 29%. The mean pretreatment spherical refractive error was -4.05 dioptre (range 1.25 to 13.25), and the mean pretreatment cylindrical error was -0.97 dioptre (range 0.25 to 4.00).

RESULTS

Uncorrected visual acuity measured 6/6 or better (log unit 0.0 or less) in 80% at three months, and averaged 6/6 for all eyes at six months post-treatment, with 75% eyes obtaining 6/6 or better. The mean post-treatment spherical error decayed according to pre-treatment values, with a mean sphere of -0.20 dioptre for eyes initially less than -2.00 dioptre, -0.40 dioptre (for those between -2.25 and -3.00), -0.71 dioptre (for those between -4.25 and -5.00), and -1.15 dioptre for eyes initially above -6.25 dioptre. Vectored cylindrical correction exhibited response proportional to initial refraction, with a mean post-treatment cylinder of -1.83 dioptre for eyes formerly averaging -3.08 dioptre, -0.55 dioptre (eyes initially averaging -1.63 dioptre), and -0.51 dioptre (eyes initially averaging -0.67 dioptre). Vector analysis of post-treatment astigmatism showed 58% eyes exhibiting 51 or more degrees of axis shift, although 34% eyes remained within 20 degrees of their pretreatment axis.

CONCLUSIONS

An effective reduction in spherocylindrical error was achieved with all eyes, although axis misalignment was a common event.

Bowman's layer transplantation: evidence to date

Surgical management of keratoconus (KC) has undergone a paradigm shift in the last two decades and component corneal transplantation technique of deep anterior lamellar keratoplasty has established itself as a modality of choice for management of advanced cases of KC. Every now and then, new minimalist modalities are being innovated for the management of KC. On the same lines, a new technique, Bowman's layer transplantation, for surgical management of moderate to advanced KC has been reported in recent years. The procedure has shown to be beneficial in reducing ectasia in advanced KC with minimal intraoperative and postoperative complications. In this review, we intend to describe available information and literature with reference to this new surgical technique - Bowman's layer transplantation.

Effect of Single-Session, Cryogen-Cooled Monopolar Radiofrequency Therapy on Sexual Function in Women with Vaginal Laxity: The VIVEVE I Trial

Objective: This subanalysis of the VIVEVE I trial aimed to evaluate the impact of cryogen-cooled monopolar radiofrequency (CMRF) therapy, for the treatment of vaginal laxity, on the domains of sexual function included in the Female Sexual Function Index (FSFI).

Materials and Methods: The VIVEVE I clinical trial was prospective, randomized, single-blind, and Sham-controlled. Nine clinical study centers in Canada, Italy, Spain, and Japan were included. This subanalysis included premenopausal women with self-reported vaginal laxity who had ≥1 term vaginal delivery and a baseline FSFI total score ≤26.5, indicating sexual dysfunction. Enrolled subjects were randomized (2:1) to receive CMRF therapy [Active (90 J/cm²) vs. Sham (≤1 J/cm²)] delivered to the vaginal tissue. Independent analyses were conducted for each FSFI domain to evaluate both the mean change, as well as the clinically important change for Active- versus Sham-treated subjects at 6 months post-intervention.

Results: Subjects randomized to Active treatment (n = 73) had greater improvement than Sham subjects (n = 35) on all FSFI domains of sexual function at 6 months postintervention. The analysis of covariance change from baseline analyses showed statistically significant improvements, in favor of Active treatment, for sexual arousal (p = 0.004), lubrication (p = 0.04), and orgasm (p = 0.007). In addition, Active treatment was associated with clinically important and statistically significant improvements in sexual desire [Odds ratio (OR) = 3.01 (1.11–8.17)], arousal [OR = 2.73 (1.06–7.04)], and orgasm [OR = 2.58 (1.08–6.18)].

Conclusions: This subanalysis showed CMRF therapy is associated with statistically significant and clinically important improvements in sexual function in women with vaginal laxity. These findings provide the first randomized, placebo-controlled energy-based device evidence for functional improvements associated with a nonsurgical modality for a highly prevalent and undertreated condition.

Long-term Visual and Refractive Outcomes After LASIK for High Myopia and Astigmatism From -8.00 to -14.25 D

PURPOSE

To evaluate outcomes of high myopic LASIK using the MEL 80 excimer laser (Carl Zeiss Meditec, Jena, Germany).

METHODS

Retrospective analysis of 479 consecutive high myopic LASIK procedures (318 patients) using the MEL 80 excimer laser and VisuMax femtosecond laser (Carl Zeiss Meditec) in 77% of cases or zero compression Hansatome microkeratome (Bausch & Lomb, Rochester, NY) in 23% of cases. Inclusion criteria were preoperative spherical equivalent refraction (SEQ) of between -8.00 and -14.25 diopters (D) and corrected distance visual acuity (CDVA) of 20/20 or better. Patients were observed for a minimum of 1 year. Flap thickness was between 80 and 160 µm and optical zone was between 5.75 and 6.50 mm. Standard outcomes analysis was performed.

RESULTS

Mean attempted SEQ was -9.39 ± 1.22 D (range: -8.00 to -14.18 D) and mean cylinder was -1.03 ± 0.84 D (range: 0.00 to -4.50 D). Mean age was 37 ± 9 years (range: 21 to 60 years) with 54% female patients. Postoperative SEQ was ±0.50 D in 55% and ±1.00 D in 83% of eyes after primary treatment. After re-treatment, 69% of eyes were within ±0.50 D and 95% were within ±1.00 D. UDVA was 20/20 or better in 89% of eyes after final treatment. One line of CDVA was lost in 3% of eyes and no eyes lost two or more lines. Statistically significant increases (P < .001) were measured in contrast sensitivity (CSV-1000) at 12 and 18 cycles per degree.

CONCLUSIONS

The MEL 80 excimer laser was found to achieve high efficacy and safety for treatment of high myopia between -8.00 and -14.25 D and up to -4.50 D of cylinder. [J Refract Surg. 2016;32(5):290-297.].

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.

Laser-assisted subepithelial keratectomy (LASEK) versus photorefractive keratectomy (PRK) for correction of myopia

BACKGROUND

Myopia (near-sightedness or short-sightedness) is a condition in which the refractive power of the eye is greater than required. The most frequent complaint of people with myopia is blurred distance vision, which can be eliminated by conventional optical aids such as spectacles or contact lenses, or by refractive surgery procedures such as photorefractive keratectomy (PRK) and laser epithelial keratomileusis (LASEK). PRK uses laser to remove the corneal stroma. Similar to PRK, LASEK first creates an epithelial flap and then replaces it after ablating the corneal stroma. The relative benefits and harms of LASEK and PRK, as shown in different trials, warrant a systematic review.

OBJECTIVES

The objective of this review is to compare LASEK versus PRK for correction of myopia by evaluating their efficacy and safety in terms of postoperative uncorrected visual acuity, residual refractive error, and associated complications.

SEARCH METHODS

We searched CENTRAL (which contains the Cochrane Eyes and Vision group Trials Register) (2015 Issue 12), Ovid MEDLINE, Ovid MEDLINE In-Process and Other Non-Indexed Citations, Ovid MEDLINE Daily, Ovid OLDMEDLINE (January 1946 to December 2015), EMBASE (January 1980 to December 2015), Latin American and Caribbean Health Sciences (LILACS) (January 1982 to December 2015), the ISRCTN registry (www.isrctn.com/editAdvancedSearch), ClinicalTrials.gov (www.clinicaltrials.gov) and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) (www.who.int/ictrp/search/en). We did not use any date or language restrictions in the electronic searches for trials. We last searched the electronic databases on 15 December 2015. We used the Science Citation Index and searched the reference lists of the included trials to identify relevant trials for this review.

SELECTION CRITERIA

We included in this review randomized controlled trials (RCTs) comparing LASEK versus PRK for correction of myopia. Trial participants were 18 years of age or older and had no co-existing ocular or systemic diseases that might affect refractive status or wound healing.

DATA COLLECTION AND ANALYSIS

Two review authors independently screened all reports and assessed the risk of bias of trials included in this review. We extracted data and summarized findings using risk ratios and mean differences. We used a random-effects model when we identified at least three trials, and we used a fixed-effect model when we found fewer than three trials.

MAIN RESULTS

We included 11 RCTs with a total of 428 participants 18 years of age or older with low to moderate myopia. These trials were conducted in the Czech Republic, Brazil, Italy, Iran, China, Korea, Mexico, Turkey, USA, and UK. Investigators of 10 out of 11 trials randomly assigned one eye of each participant to be treated with LASEK and the other with PRK, but did not perform paired-eye (matched) analysis. Because of differences in outcome measures and follow-up times among the included trials, few trials contributed data for many of the outcomes we analyzed for this review. Overall, we judged RCTs to be at unclear risk of bias due to poor reporting; however, because of imprecision, inconsistency, and potential reporting bias, we graded the quality of the evidence from very low to moderate for outcomes assessed in this review.The proportion of eyes with uncorrected visual acuity of 20/20 or better at 12-month follow-up was comparable in LASEK and PRK groups (risk ratio (RR) 0.98, 95% confidence interval (95% CI) 0.92 to 1.05). Although the 95% CI suggests little to no difference in effect between groups, we judged the quality of the evidence to be low because only one trial reported this outcome (102 eyes). At 12 months post treatment, data from two trials suggest no difference or a possibly small effect in favor of PRK over LASEK for the proportion of eyes achieving ± 0.50 D of target refraction (RR 0.93, 95% CI 00.84 to 1.03; 152 eyes; low-quality evidence). At 12 months post treatment, one trial reported that one of 51 eyes in the LASEK group lost one line or more best-spectacle corrected visual acuity compared with none of 51 eyes in the PRK group (RR 3.00, 95% CI 0.13 to 71.96; very low-quality evidence).Three trials reported adverse outcomes at 12 months of follow-up or longer. At 12 months post treatment, three trials reported corneal haze score; however, data were insufficient and were inconsistent among the trials, precluding meta-analysis. One trial reported little or no difference in corneal haze scores between groups; another trial reported that corneal haze scores were lower in the LASEK group than in the PRK group; and one trial did not report analyzable data to estimate a treatment effect. At 24 months post treatment, one trial reported a lower, but clinically unimportant, difference in corneal haze score for LASEK compared with PRK (MD -0.22, 95% CI -0.30 to -0.14; 184 eyes; low-quality evidence).

AUTHORS' CONCLUSIONS

Uncertainty surrounds differences in efficacy, accuracy, safety, and adverse effects between LASEK and PRK for eyes with low to moderate myopia. Future trials comparing LASEK versus PRK should follow reporting standards and follow correct analysis. Trial investigators should expand enrollment criteria to include participants with high myopia and should evaluate visual acuity, refraction, epithelial healing time, pain scores, and adverse events.

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.

Past and present of corneal refractive surgery: a retrospective study of long-term results after photorefractive keratectomy and a prospective study of refractive lenticule extraction

Surgical correction of refractive errors is becoming increasingly popular. In the 1990s, the excimer laser revolutionized the field of corneal refractive surgery with PRK and LASIK, and lately refractive lenticule extraction (ReLEx) of intracorneal tissue, using only a femtosecond laser, has become possible. Two new procedures were developed, ReLEx flex (FLEX) and ReLEx smile (SMILE). Until this thesis, only a few long-term studies of PRK with a relatively limited number of patients had been published; therefore, this thesis intended to retrospectively evaluate long-term outcomes after PRK for all degrees of myopia for a large number of patients. Furthermore, a prospective contralateral eye study comparing FLEX and SMILE, when treating high to moderate degrees of myopia, had not been performed prior to this study. This was the second aim of this thesis. In the first study, results from 160 PRK patients (289 eyes) were presented. Preoperative spherical equivalent ranged from -1.25 to -20.25 D, with 78% having low myopia (<-6 D). Average follow-up time was 16 years (range 13-19 years), making this the longest published follow-up study on PRK patients. Outcomes from eyes with low myopia were generally superior to outcomes from eyes with high myopia, at final follow-up. Seventy-two percent were within ± 1.00 D of target refraction, as compared to 47% of eyes with high myopia. However, results from a subgroup of unilateral treated PRK patients indicated that refraction at final follow-up was affected by myopic progression. Fifty percent of eyes with low myopia had uncorrected 20/20 distance visual acuity or better, as compared to 22% of eyes with high myopia. Haze did not occur if attempted corrections were <-4 D, and only eyes with high myopia lost two lines or more of CDVA (corrected distance visual acuity). Eighty-one per cent were satisfied or very satisfied with their surgery.

CONCLUSION

The results support the continued use of the excimer laser for corneal surface ablation as a treatment option for correction of low degrees of myopia, and as the treatment of choice for subgroups of refractive patients (thin corneas, etc.). The results also highlight that treatment of higher degrees of myopia with standard PRK should only be done today under special circumstances, due to low refractive predictability, and high risk of corneal haze. Technological advances since then should be taken into account when comparing these results with contemporary techniques. In the second study, 35 patients were randomized to receive FLEX in one eye and SMILE in the other. Preoperative spherical equivalent refraction ranged from -6 to -10 D with low degrees of astigmatism. A total of 34 patients completed the 6 month follow-up period. Refractive and visual outcomes were very similar for the two methods, as well as tear film measurements and changes in corneal biomechanics. Ninety-seven percent were within ± 1.00 D of target refraction, no eyes lost two lines or more of CDVA, and contrast sensitivity was unaffected after both procedures. The changes in higher-order aberrations were also very similar. There were also no differences in tear film parameters 6 months after surgery, although less postoperative foreign body sensation was reported within the first week after surgery in SMILE eyes. Corneal sublayer pachymetry measurements demonstrated equally increased epithelial thickness 6 months after surgery. Contrary to expectations, it was not possible to measure the theoretical biomechanical advantages of a small corneal incision in SMILE as compared to a corneal flap in FLEX. The main differences between FLEX and SMILE were found when the corneal nerves and intraoperative complications were evaluated. Thus, corneal sensitivity was better preserved and corneal nerve morphology was less affected after SMILE, but intraoperative complications occurred more frequently, although without visual sequela. Finally, 97% were satisfied or very satisfied with both their surgeries.

CONCLUSION

The results support the continued use of both FLEX and SMILE for treatment of up to high degrees of myopia. Overall, refractive and visual results for both procedures were good and similar, but from a biological point of view, the less invasive SMILE technique is more attractive, as demonstrated in this study, despite being slightly more surgically demanding than FLEX.

Visual stability of laser vision correction in an astronaut on a Soyuz mission to the International Space Station

This report documents the effects of photorefractive keratectomy (PRK) in an astronaut during a 12-day Russian Soyuz mission to the International Space Station in 2008. Changing environmental conditions of launch, microgravity exposure, and reentry create an extremely dynamic ocular environment. Although many normal eyes have repeatedly been subject to such stresses, the effect on an eye with a relatively thin cornea as a result of PRK has not been reported. This report suggests that PRK is a safe, effective, and well-tolerated procedure in astronauts during space flight.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned.

The history of LASIK

Keratomileusis, brainchild of Jose I. Barraquer Moner, was conceived and developed as the first stromal sculpting method to correct refractive error in 1948. The word "keratomileusis" literally means "sculpting" of the "cornea." Barraquer's first procedures involved freezing a disc of anterior corneal tissue before removing stromal tissue with a lathe. Over the years, the procedure continued to develop, first through the Barraquer-Krumeich-Swinger non-freeze technique where tissue was removed from the underside of the disc by a second pass of the microkeratome. In-situ keratomileusis was later developed by passing the microkeratome a second time directly on the stromal bed. The procedure became known as automated lamellar keratoplasty with the invention of an automated microkeratome and was further refined by replacing the disc without sutures and later by stopping the microkeratome before the end of the pass to create a hinged flap, as first demonstrated in 1989. The history of the excimer laser dates back to 1900 and the quantum theory, eventually leading to the discovery that 193-nm ultraviolet excimer laser pulses could photoablate tissue without thermal damage. Ultrastructural and wound healing studies confirmed that large area ablation could be performed in the central cornea. This was described as photorefractive keratectomy in 1986 and the first sighted eyes were treated in 1988. An excimer laser was first used to sculpt from the stromal bed under a hinged flap created manually using a trephine and scalpel in 1988. The incorporation of a microkeratome in 1990 finally led to laser in situ keratomileusis-LASIK-as we know it today.

Effects of decentration of photorefractive keratectomy on the induction of higher order wavefront aberrations

PURPOSE

To evaluate the effects of ablation decentration on the induction of higher order wavefront aberrations (HOAs) in active eye-tracker-assisted myopic photorefractive keratectomy (PRK) using the VISX STAR S4 laser with ActiveTrak (Abbott Medical Optics [AMO]).

METHODS

Ninety-four myopic eyes (53 patients) were divided into three groups according to ablation decentration (group 1, ≤0.15 mm, 20 eyes; group 2, >0.15 to ≤0.30 mm, 54 eyes; and group 3, >0.30 mm, 20 eyes). The distances of ablation centers from the centers of the entrance pupils were analyzed using corneal topography. Wavefront errors were measured preoperatively and at 6 months after PRK using a VISX WaveScan aberrometer (AMO). Statistical analysis was performed to assess the influence of ablation decentration on PRK-induced HOAs.

RESULTS

The mean decentration was 0.23±0.10 mm (range: 0.04 to 0.52 7 mm). The magnitude of all HOAs was significantly increased at 6 months postoperatively (P<.05). Increases in PRK-induced HOAs including total HOA, coma, and spherical aberration were significantly different among the three groups (P<.05). Statistically significant differences were noted between pairs of data in group 1 versus group 3 for total HOA (P=.015), coma (P=.038), and spherical aberration (P=.038), and group 2 versus group 3 for coma (P=.049).

CONCLUSIONS

Ablation decentration >0.30 mm from the center of the entrance pupil was associated with greater induction of total HOA, coma, and spherical aberration after PRK, as compared with ablation decentration <0.15 mm. In addition, ablation decentration has a more significant influence on coma-inducing effects.

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.

Comparison between three- and six-month postoperative refractive and visual results after laser epithelial keratomileusis with mitomycin C

PURPOSE

To compare the residual refraction and visual results between the three- and six-month postoperative visits to detect the optimal moment for enhancement after myopic laser epithelial keratomileusis (LASEK) with mitomycin C (MMC).

DESIGN

Nonrandomized, interventional, prospective study.

METHODS

One hundred and forty-one consecutive eyes that underwent LASEK with MMC to correct their myopia using the Esiris excimer laser (Schwind Eye Tech Solutions, Kleinostheim, Germany), and that showed three months postoperatively a residual defect or a suboptimal uncorrected visual acuity (UCVA) or best spectacle-corrected visual acuity (BSCVA) were included in the study. We compared the residual spherical refraction and cylinder, the UCVA, and the BSCVA between the three- and six-month postoperative examinations.

RESULTS

Preoperative spherical refraction was -5.2 +/- 2.90 diopters (D). Preoperative cylinder was -1.66 +/- 1.20 D. The residual sphere was +0.43 +/- 0.90 D three months and +0.21 +/- 0.90 D six months after surgery (P = .0001). The cylinder was -0.71 +/- 0.60 D and -0.67 +/- 0.60 D, respectively (P = .4). The UCVA was 0.75 +/- 0.2 and 0.81 +/- 0.2 (P = .0001) and the BSCVA was 0.94 +/- 0.1 and 1.01 +/- 0.1 (P = .0001), respectively. Those patients with a myopic defect (sphere or cylinder) three months postoperatively did not show any significant change in UCVA or refractive defect six months after surgery, while those with a hyperopic defect (sphere or cylinder) showed an improvement in UCVA and residual refraction six months postoperatively (P < .05).

CONCLUSIONS

Our results suggest that retreatment after myopic LASEK with MMC may be performed three months after surgery when the residual refraction is myopic, but it seems wise to wait at least six months after surgery when the residual refraction is hyperopic.

LASEK and Photorefractive Keratectomy for Myopia: Clinical and Confocal Microscopy Comparison

PURPOSE

To compare postoperative visual acuity and corneal morphology after laser epithelial keratomileusis (LASEK) versus photorefractive keratectomy (PRK) in the correction of low to moderate myopia.

METHODS

In a double-blind, randomized clinical trial, 50 myopic patients (mean: -4.5 +/- 1.35 diopters) were randomized to receive LASEK in one eye and PRK in the fellow eye. No mitomycin C eye drops were used in this study. Patients were observed daily for 4 days, then at 1 month and every 3 months up to 1 year. Uncorrected and best-corrected visual acuity (UCVA and BSCVA), manifest refraction, corneal epithelium healing time, postoperative pain, and corneal haze were evaluated. Corneal wound healing was quantified with corneal confocal microscopy.

RESULTS

Refractive error, UCVA, and BSCVA were not statistically different between eyes treated with LASEK and PRK. Corneal epithelium healing time was 2.52 +/- 0.99 days in the eyes treated with PRK and 2.29 +/- 0.52 days in the eyes treated with LASEK (P=.22). The postoperative pain score was 2.17 +/- 0.87 in the eyes treated with PRK and 2.62 +/- 0.60 (P=.02) in the eyes treated with LASEK. Corneal confocal microscopy showed fewer stromal activated keratocytes and less extracellular matrix deposition in the eyes treated with LASEK than in the eyes treated with PRK at 1 month postoperatively (P=.003).

CONCLUSIONS

LASEK is an effective and safe procedure for low to moderate myopia, but it seems more painful until full corneal reepithelization. In the early postoperative period, the corneal wound healing process is significantly less intense in eyes treated with LASEK than in eyes treated with PRK. The role of LASEK in corneal wound healing modulation remains controversial.

Improvement of Visual Acuity Following Refractive Surgery for Myopia and Myopic Anisometropia

PURPOSE

To test the hypothesis that anisometropic adults without significant amblyopia suffer from mild visual impairment probably due to aniseikonia, which might be improved by corneal refractive surgery.

METHODS

Fifty-seven patients presenting with myopic anisometropia > or = 3.25 diopters (D) and 174 myopic controls appropriate for refractive surgery were included. Photorefractive keratectomy (PRK) or LASIK was performed on 57 anisometropic eyes. As 43 of the 174 myopic control patients had bilateral surgery, PRK or LASIK was performed on 217 myopic control eyes. Best spectacle-corrected visual acuity (BSCVA), refraction, and refractive correction were measured preoperatively and at 1, 3, 5 to 7, 8 to 13, and 25 months following surgery.

RESULTS

Preoperative mean spherical equivalent was -7.20 +/- 2.40 D for anisometropic patients and -6.40 +/- 1.90 D for myopic patients. At 8 to 13 months postoperatively, when 23 (40%) anisometropic eyes and 94 (43%) myopic eyes were examined, the mean spherical equivalent refractions were -0.80 +/- 1.60 D and -0.30 +/- 0.60 D, respectively. Preoperatively, the mean BSCVA on a logMAR scale was -0.0143 +/- 0.0572 (Snellen 0.98 +/- 0.12) in the anisometropic group and 0.0136 +/- 0.0361 (Snellen 1.04 +/- 0.09) in the control group (P = .001). Eight to 13 months postoperatively, these values were 0.0076 +/- 0.0659 (Snellen 1.03 +/- 0.15) and 0.0495 +/- 0.0692 (Snellen 1.13 +/- 0.18) and this difference remained statistically significant (P = .012). For the myopic patients, the improvement in BSCVA reached almost maximum at 3 months, and this improvement was found to be highly significant 3 months after surgery (P = .001). The improvement in BSCVA was significantly slower for anisometropic patients and became statistically significant only after 8 to 13 months postoperatively (P = .041).

CONCLUSIONS

Anisometropia reduces visual acuity in the more myopic eye and can be at least partially reversed by refractive correction. The slower improvement in BSCVA for anisometropic patients suggests plastic changes in the visual cortex following refractive surgery.

Confocal Microscopy Changes in Epithelial and Stromal Thickness up to 7 Years After LASIK and Photorefractive Keratectomy for Myopia

PURPOSE

To determine the long-term changes in epithelial, stromal, and corneal thickness after LASIK and photorefractive keratectomy (PRK).

METHODS

In two prospective observational case series, 11 patients (16 eyes) received LASIK and 12 patients (18 eyes) received PRK to correct myopia or myopic astigmatism. None of the corneas had retreatment procedures. Corneas were examined using confocal microscopy before and at 1 month, and at 1, 2, 3, 5, and 7 years after surgery. Central thicknesses were measured from reflected light intensity profiles recorded by confocal microscopy. Postoperative epithelial thickness was compared to preoperative, and postoperative stromal and corneal thicknesses were compared to thickness at 1 month after surgery.

RESULTS

In LASIK, epithelial thickness at 1 month (51 +/- 4 microm, n = 11) was greater than before surgery (41 +/- 4 microm, n = 16; P < .001) and remained thicker through 7 years (52 +/- 6 microm, n = 13; P < .001). Stromal and corneal thickness did not change between 1 month and 7 years after LASIK. After PRK, corneal thickness at 1 year (464 +/- 44 microm, n = 17) was greater than at 1 month (442 +/- 39 microm, n = 15; P = .001) and remained thicker at 7 years after PRK (471 +/- 45 microm, n = 17; P > .001).

CONCLUSIONS

The early increase in central epithelial thickness after myopic LASIK persists for at least 7 years and is probably the result of epithelial hyperplasia. Central corneal thickness increases during the first year after PRK and remains stable thereafter up to 7 years.

Uses and complications of mitomycin C in ophthalmology

Mitomycin C is a chemotherapeutic agent that acts by inhibiting DNA synthesis. Its use and application in ophthalmology has been increasing in recent years because of its modulatory effects on wound healing. Current applications include pterygium surgery, glaucoma surgery, corneal refractive surgery, cicatricial eye disease, conjunctival neoplasia and allergic eye disease. Although it has been used successfully in these conditions, it has also been associated with significant complications. This article reviews the current trends and uses of mitomycin C in the eye and its reported complications.

Cellular effects of mitomycin-C on human corneas after photorefractive keratectomy

PURPOSE

To investigate the effects of mitomycin-C (MMC) on epithelial and keratocyte cell kinetics after photorefractive keratectomy (PRK) using an in vitro human cornea model.

SETTING

Department of Academic Ophthalmology, Rayne Institute, St. Thomas' Hospital, London, United Kingdom.

METHODS

Twenty-four human eye-bank corneas were placed in a specially designed acrylic corneal holder and cultured using the air-interface organ culture technique for up to 4 weeks. The corneas were divided into 3 groups. Group 1 consisted of 8 human corneas that had -9.00 diopter (D) myopic PRK without MMC application. Group 2 consisted of 8 corneas that had -9.00 D PRK with MMC (0.2 microg/mL) application for 1 minute on the stromal surface after ablation. Group 3 consisted of 8 corneas that had -9.00 D PRK with 2-minute exposure to MMC (0.2 microg/mL). Temporal events in epithelial and keratocyte cell kinetics were evaluated using digital imaging, confocal microscopy, and light microscopy.

RESULTS

Epithelial latency was significantly delayed with MMC application in Groups 2 and 3 (P<.001). Epithelial migration was delayed in Group 3 (2-minute exposure) compared to migration in Group 2 (P<.04), with a consequent delay in epithelial closure (P<.001). Group 3 corneas had poorly differentiated epithelium that was significantly thinner than in Groups 1 and 2 (P<.0001). A significant delay in keratocyte regeneration occurred after MMC application (P<.0005). At 4 weeks, the anterior stromal cell density was significantly lower in Group 3 than Group 2 (P<.001). There were no significant differences in the mid- and posterior stromal keratocyte density between the groups.

CONCLUSIONS

Results suggest that epithelial healing after MMC is characterized by prolonged latency and decreased migration rate dependent on exposure time. Mitomycin C application did not result in increased loss of keratocytes, but it significantly delayed keratocyte repopulation in the anterior stroma. The use of MMC 0.2 microg/mL for 1 minute resulted in optimum modulation of healing characterized by reduced keratocyte activation with normal epithelial differentiation.

Effects of ablation diameter on long-term refractive stability and corneal transparency after photorefractive keratectomy

OBJECTIVE

To evaluate the effects of ablation diameter on long-term refractive stability and corneal transparency after photorefractive keratectomy (PRK).

DESIGN

Long-term, prospective, follow-up study.

PARTICIPANTS

One hundred twenty-three eyes treated between 1990 and 1993 at one institution as part of a number of ethical committee-approved clinical studies underwent long-term follow-up at 10 to 12 years after PRK.

INTERVENTION

Photorefractive keratectomy was performed using the Summit Technology UV 200 and OmniMed Excimer lasers with either 4.0-mm (n = 36), 5.0-mm (n = 47), or 6.0-mm (n = 40) optical zones and either -3.0-diopters (D) or -6.0-D myopic spherical corrections, based on the original Munnerlyn algorithms.

MAIN OUTCOME MEASURES

Refractive stability, refractive predictability, best spectacle-corrected visual acuity, and corneal haze.

RESULTS

Refractive outcome at 1 and 10 to 12 years of follow-up was better with 6.0-mm treatments, especially for -6.0-D corrections (P>0.001). The early hyperopic shift was significantly reduced with 6.0-mm zones, with less regression between 1 and 6 months, compared with 5.0- and 4.00-mm PRK, especially for -6.0-D corrections (P<0.001). The postoperative refraction remained stable between 1 and 10 to 12 years in all groups. Objective measurements of haze were less with 6.0-mm compared with 4.0- and 5.0-mm treatments (P<0.001). Night vision problems were significantly less with 6.0-mm PRK (P<0.01). There was no evidence of progressive hyperopic shift, corneal ectasia, or late onset of corneal haze in any of the eyes during the follow-up period.

CONCLUSIONS

Refractive stability was maintained between 1 year and 10 to 12 years after PRK with 4.0-, 5.0-, and 6.0-mm optical zones. A significant linear trend was observed in terms of refractive predictability, early hyperopic shift, regression, corneal transparency, and night haloes with better outcomes in PRK with a larger ablation zone. None of the eyes had sight-threatening complications such as ectasia or late-onset corneal haze during the follow-up.

Comparison of Laser Epithelial Keratomileusis With and Without the Use of Mitomycin C

PURPOSE

To analyze the results of prophylactic intraoperative use of mitomycin C (MMC) in laser epithelial keratomileusis (LASEK).

METHODS

A retrospective analysis of 30 LASEK cases that received MMC 0.02% intraoperatively (MMC group) was performed and compared to the results obtained in 28 LASEK cases not receiving MMC (no MMC group). Mitomycin C was placed in contact with the ablation zone for 75 seconds with an imbibed microsponge. Both groups received postoperative fluorometholone for 3 months. Preoperative spherical equivalent refraction was -5.72 +/- 2.82 diopters (D) in the MMC group and -5.81 +/- 2.74 D in the no MMC group. Best spectacle-corrected visual acuity was 0.88 +/- 0.12 in the MMC group and 0.88 +/- 0.13 in the no MMC group.

RESULTS

Spherical equivalent refraction at 6 months postoperatively was +0.11 +/- 0.13 D in the MMC group and +0.09 +/- 0.37 D in the no MMC group. Best spectacle-corrected visual acuity was 0.90 +/- 0.13 in the MMC group and 0.88 +/- 0.13 in the no MMC group. Uncorrected visual acuity (UCVA) > or = 20/40 was obtained in 93.3% of cases in the MMC group and in 89.3% of cases in the no MMC group; UCVA > or = 20/25 was achieved in 76.6% of cases in the MMC group and in 71.4% of cases in the no MMC group. Haze incidence for the MMC group was: trace: 0%, Grades I: 0%, II: 0%, III 0%, IV: 0%, and for the no MMC group: trace: 17.9%, Grades I: 3.6%, II: 0%, III: 0%, IV: 0%. A statistically significant difference (P<.001) was noted in haze intensity between the MMC group and no MMC group.

CONCLUSIONS

Prophylactic use of intraoperative MMC in LASEK significantly decreases haze incidence.

Mitomycin: clinical applications in ophthalmic practice

Mitomycin (mitomycin C; MMC) is an antibiotic isolated from Streptomyces caespitosus. The drug is a bioreductive alkylating agent that undergoes metabolic reductive activation, and has various oxygen tension-dependent cytotoxic effects on cells, including the cross-linking of DNA. It is widely used systemically for the treatment of malignancies, and has gained popularity as topical adjunctive therapy in ocular and adnexal surgery over the past 2 decades. In ophthalmic medicine, it is principally used to inhibit the wound healing response and reduce scarring of surgically fashioned ostia. Hence, it has been used as adjunctive therapy in various ocular surgeries, such as glaucoma filtering surgeries, dacryocystorhinostomy, corneal refractive surgery and surgeries for ocular cicatrisation. In addition, it has been used as an adjunct in the surgical management of pterygia, ocular surface squamous neoplasia, primary acquired melanosis with atypia and conjunctival melanoma. In many of these surgeries and ophthalmic pathologies, MMC showed a significant beneficial effect.

Cell delivery in regenerative medicine: the cell sheet engineering approach

Recently, cell-based therapies have developed as a foundation for regenerative medicine. General approaches for cell delivery have thus far involved the use of direct injection of single cell suspensions into the target tissues. Additionally, tissue engineering with the general paradigm of seeding cells into biodegradable scaffolds has also evolved as a method for the reconstruction of various tissues and organs. With success in clinical trials, regenerative therapies using these approaches have therefore garnered significant interest and attention. As a novel alternative, we have developed cell sheet engineering using temperature-responsive culture dishes, which allows for the non-invasive harvest of cultured cells as intact sheets along with their deposited extracellular matrix. Using this approach, cell sheets can be directly transplanted to host tissues without the use of scaffolding or carrier materials, or used to create in vitro tissue constructs via the layering of individual cell sheets. In addition to simple transplantation, cell sheet engineered constructs have also been applied for alternative therapies such as endoscopic transplantation, combinatorial tissue reconstruction, and polysurgery to overcome limitations of regenerative therapies and cell delivery using conventional approaches.

Laser in situ keratomileusis: ablation on the flap and stromal bed in a primary treatment

PURPOSE

To analyze outcomes of laser in situ keratomileusis (LASIK) performed on the flap and on the stromal bed at the same time in a primary treatment.

SETTING

Instituto de la Visión, Buenos Aires, Argentina.

METHODS

Twenty-two cases (13 female, 9 male) were studied retrospectively; the mean age of the patients was 33.15 years +/- 10.44 (SD). Inclusion criteria were low pachymetry or topographic asymmetry. Twenty cases (90.9%) presented with low pachymetry (512.2 +/- 21.40 mum), and 2 cases (9.1%) presented with topographic asymmetry (inferior-superior difference more than 1.5 diopters [D]). Ablation was performed on the flap from the back and on the bed. The flap was made using the Technolas Hansatome microkeratome and the ablation by the Technolas 217z excimer laser (both by Bausch & Lomb). Preoperatively, the spherical equivalent (SE) was -5.61 +/- 1.72 D, the cylinder was -1.78 +/- 1.24 D, and the best spectacle-corrected visual acuity (BSCVA) was 0.77 +/- 0.19. Difficulties and complications of the technique, efficacy and safety index, and aberrations were analyzed.

RESULTS

According to the surgical plan and our nomogram, diopters corrected on the flap were -1.73 +/- 1.08 and on the bed were -4.77 +/- 1.89. The mean follow-up was 8.28 +/- 2.19 months. At 6 months, the SE was -0.21 +/- 0.39, vectorial change was 1.69 +/- 0.74, and the BSCVA was 0.77 +/- 0.20. Postoperatively, no eye had an increase in refractive astigmatism. Uncorrected visual acuity was 20/40 or better in all cases (100%) and 20/25 or better in 13 cases (59.1%). Regarding gained and lost lines of BSCVA, 54.5% conserved the lines, 18.2% lost 1 line, 9.1% gained 1 line, and 18.2% gained 2 lines.

CONCLUSIONS

Simultaneous ablation on the flap and on the bed in cases of low pachymetry or topographical asymmetry was predictable, effective, and safe.

A return to primitive practice? Radial keratotomy revisited

Recently, a refractive surgeon was quoted in the national and professional press as proposing that radial keratotomy (RK) is to be preferred over laser procedures, such as photorefractive keratectomy (PRK) and laser assisted in situ keratomileusis (LASIK). The rationale for this public recommendation was that the RK procedure achieves better visual results and fewer complications than the laser procedures. Peer reviewed literature on these refractive procedures was surveyed to establish the validity of such a statement and it was found that current data do not support the notion that RK results in better visual outcomes than PRK and LASIK The true incidence of complications is difficult to establish. However, when the post procedure chronic effects are compared between RK, PRK and LA SIK, it becomes apparent that the post-RK patient pays the highest price, by a large margin, in visual quality impairment and corneal health. Although the visual acuity outcomes for low to moderate myopes, when corrected by any of the three refractive procedures considered here, are not dramatically different, we concluded that RK is not the preferred methodology because of its associated chronic visual and corneal health complications.

In vitro human corneal model to investigate stromal epithelial interactions following refractive surgery

PURPOSE

To develop an in vitro human corneal model to evaluate stromal epithelial interactions following corneal refractive surgical procedures.

SETTING

Department of Academic Ophthalmology, Rayne Institute, St. Thomas' Hospital, London, United Kingdom.

METHODS

Fifty-six human donor corneas procured from the eye bank were placed in a specially designed acrylic corneal holder and were cultured using the air-interface organ culture technique for up to 4 weeks. Corneal refractive surgical procedures such as a simple epithelial defect, 4 diopter (D) and 9 D photorefractive keratectomy (PRK), 4 D and 9 D laser-assisted subepithelial keratectomy (LASEK), and 9 D laser in situ keratomileusis (LASIK) were performed on the model. Temporal events in epithelial and keratocyte cell kinetics were evaluated using digital imaging, confocal microscopy, and light microscopy. Two-way analysis of variance and Student t tests were used to assess statistical significance.

RESULTS

Epithelial healing following PRK was completed by 92 hours +/- 10 (SD) at a rate of 0.58 +/- 0.45 mm2/hour. In LASEK, the epithelial flap was replaced by regenerating peripheral epithelium that showed significant delay in epithelial closure (120 +/- 5 hours) with prolonged latency (24 +/- 4 hours, P<.0001) in comparison with PRK. The magnitude of keratocyte loss corresponded to ablation depth, and keratocyte regeneration was dependent on epithelial closure. In comparison, LASIK corneas showed a lesser percentage of keratocyte loss with poor recovery of keratocyte density in the stromal flap. Epithelial viability and keratocyte density were well preserved in the in vitro human model as observed in control corneas for up to 4 weeks.

CONCLUSIONS

The temporal events in stromal epithelial interactions in the in vitro human model closely mimicked in vivo observations. The human model further avoided species-specific variations and provided a suitable test bed for evaluating newer algorithms and therapeutic regimens following refractive surgery.

Mitomycin C modulation of corneal wound healing after photorefractive keratectomy in highly myopic eyes

PURPOSE

To evaluate the role of topical mitomycin C in corneal wound healing (CWH) after photorefractive keratectomy (PRK) in highly myopic eyes.

DESIGN

Prospective, double-masked, randomized clinical trial.

PARTICIPANTS

Seventy-two eyes of 36 patients affected by high (>7 diopters) myopia.

METHODS

In each patient, one eye was randomly assigned to PRK with intraoperative topical 0.02% mitomycin C application, and the fellow eye was treated with a placebo. Postoperatively, mitomycin C-treated eyes received artificial tears (3 times daily, tapered in 3 months), whereas the fellow eye was treated with fluorometholone sodium 2% and artificial tears (3 times daily, tapered in 3 months).

MAIN OUTCOME MEASURES

Uncorrected visual acuity (UCVA) and best-corrected visual acuity (BCVA), contrast sensitivity, manifest refraction, and biomicroscopy. Contrast sensitivity was determined using the Pelli-Robson chart. Corneal confocal microscopy documented CWH.

RESULTS

Mean follow-up was 18 months (range, 12-36). No side effects or toxic effects were documented. At 12-month follow-up examination, UCVAs (logarithm of the minimum angle of resolution) were 0.4+/-0.48 and 0.5+/-0.53 (P = .03) in mitomycin C-treated eyes and corticosteroid-treated eyes, respectively. At 1 year, corneal haze developed in 20% of corticosteroid-treated eyes, versus 0% of mitomycin C-treated eyes. At 12, 24, and 36 months, corneal confocal microscopy showed activated keratocytes and extracellular matrix significantly more evident in untreated eyes (Ps = 0.004, 0.024, and 0.046, respectively).

CONCLUSION

Topical intraoperative application of 0.02% mitomycin C can reduce haze formation in highly myopic eyes undergoing PRK.