Long-term results of laser in situ keratomileusis for high myopia: Risk for ectasia

Comparative study of small incision refractive lenticule extraction with 5 mm versus 6.5 mm optic zone for myopia

Purpose

To compare residual stromal thickness (RST) in eyes undergoing small incision refractive lenticule extraction (SMILE) using a lenticular diameter of 6.5 mm versus those with a diameter of 5 mm.

Methods: In this retrospective

comparative case series.

, consecutive

patients who underwent SMILE between 2016 and 2021 with at least 6 months of follow-up were included. Preoperative best-corrected distance visual acuity (BCDVA), refractive error, contrast sensitivity, central corneal thickness, keratometry, higher order aberrations, and scotopic pupil size were recorded using a Placido disk topography with Sheimpflug tomography-based system. Patients underwent SMILE with a lenticular diameter of 6.5 mm until 2018 (n = 372 eyes). Thereafter, the lenticular diameter was reduced to 5 mm (n = 318). The RST, postoperative refraction, aberrations, subjective glare, and halos were compared across groups at 1 and 6 months.

Results

The mean age of participants was 26.8 ± 5.8 years with a mean preoperative spherical equivalent of -4.48 D ± 2.16 D (range: -0.75 to -12.25 D) and mean scotopic pupil of 3.7 ± 0.75 mm. Eyes in the 5 mm group had 30.6 m (95% confidence interval [CI] = 28 to 33 m, P < 0.001) greater RST compared to the 6.5 mm group after adjusting for spherical equivalent and preoperative pachymetry. There were no differences in vision, contrast sensitivity, aberrations (wavefront error of 0.19 ± 0.2 vs. 0.25 ± 0.2, P = 0.19) or glare between the two groups.

Conclusion

SMILE performed with a lenticular diameter of 5 mm leads to greater RST across the myopic range, but without inducing significant higher-order aberrations.

A prospective randomized self-controlled study of LASIK combined with accelerated cross-linking for high myopia in Chinese: 24-month follow-up

Background

To assess the visual and refractive outcomes of femtosecond laser-assisted in situ keratomileusis (FS-LASIK) concurrent with accelerated cross-linking (LASIK Xtra) compared with conventional FS-LASIK (convLASIK) for high myopia in Chinese individuals.

Methods

In this prospective, randomized, fellow-eye comparison study, 25 patients with high myopia were treated randomly with LASIK Xtra in one eye and convLASIK in the other. A 24-month follow-up was conducted, and the main outcome measures included uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), manifest refraction spherical equivalent (MRSE) and corneal tomography.

Results

The UDVA was 0.09 ± 0.15 logMAR in the LASIK Xtra group, which was significantly worse than that in the convLASIK group 1 day postoperatively (P = .001), but the difference became nonsignificant from 1 week after surgery. The efficacy index was 0.88 ± 0.18 in the LASIK Xtra eyes and 0.99 ± 0.13 in the convLASIK eyes at 24 months (P = .028). Throughout the follow-up period, a slight myopic shift in the MRSE and keratometry values were observed in both groups without significant intergroup differences. The coefficient of determination was 0.9982 in the LASIK Xtra eyes and 0.9987 in the convLASIK eyes. The corneal density was significantly higher, and demarcation lines were visible in the first 6 months in LASIK Xtra eyes, but both signs of cross-linking gradually disappeared during follow-up. No severe complications were detected in either group.

Conclusions

LASIK Xtra showed comparable safety and predictability with convLASIK for high myopia in Chinese, but lower efficacy and no greater stability was observed up to 24-month follow-up.

Ectasia After Corneal Refractive Surgery: A Systematic Review

INTRODUCTION

The incidence of ectasia following refractive surgery is unclear. This review sought to determine the worldwide rates of ectasia after photorefractive keratectomy (PRK), laser-assisted in situ keratomileusis (LASIK), and small incision lenticule extraction (SMILE) based on reports in the literature.

METHODS

A systematic review was conducted according to modified Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Publications were identified by a search of eight electronic databases for relevant terms between 1984 and 2021. Patient characteristics and preoperative values including manifest refractive spherical refractive equivalent (MRSE), central corneal thickness (CCT), anterior keratometry, postoperative residual stromal bed (RSB), and percent tissue altered (PTA) were summarized. In addition, annual rates of each refractive surgery were determined, and incidence of post-refractive ectasia for each type was calculated using the number of ectatic eyes identified in the literature.

RESULTS

In total, 57 eyes (70 eyes including those with preoperative risk factors for ectasia) were identified to have post-PRK ectasia, while 1453 eyes (1681 eyes including risk factors) had post-LASIK ectasia, and 11 eyes (19 eyes including risk factors) had post-SMILE ectasia. Cases of refractive surgery performed annually were estimated as 283,920 for PRK, 1,608,880 for LASIK, and 96,750 for SMILE. Reported post-refractive ectasia in eyes without preoperative identifiable risk factors occurred with the following incidences: 20 per 100,000 eyes in PRK, 90 per 100,000 eyes in LASIK, and 11 per 100,000 eyes in SMILE. The rate of ectasia in LASIK was found to be 4.5 times higher than that of PRK.

CONCLUSION

Post-refractive ectasia occurs at lower rates in eyes undergoing PRK than LASIK. Although SMILE appears to have the lowest rate of ectasia, the number of cases already reported since its recent approval suggests that post-SMILE ectasia may become a concern. Considering that keratoconus is a spectrum of disease, pre-existing keratoconus may play a larger role in postoperative ectasia than previously accounted for in the literature.

Keratorefractive Surgery Outcomes in Keratoconus Suspect Patients

Purpose. To examine the outcomes of keratorefractive surgeries in keratoconus suspect patients. Methods. This study included 192 keratoconus suspects (351 eyes), treated with photorefractive keratectomy (PRK) (211 eyes), Lasik (96 eyes), and Femto-Lasik (44 eyes) surgeries in an eye clinic. The best spectacle-corrected visual acuity (BSCVA) and subjective refraction were evaluated preoperatively and postoperatively (three months and five years after the procedure). The Orbscan II topography system was also used preoperatively and five years after the procedure. Results. The patients’ mean age was 31.6 ± 5.49 years (range: 21–47 years) in the last follow-up. There was no significant difference between the preoperative and postoperative mean values of BSCVA in any of the surgical methods ( $P$  = 0.49). The mean spherical equivalent, cylindrical power, corneal curvature, the thinnest corneal thickness, and the central corneal thickness decreased significantly in the last follow-up ( $P$  < 0.001). Four patients (3.50%) in the PRK group and one patient (1.85%) in the Lasik group needed glasses in the last follow-up. Eleven cases of corneal ectasia were detected in the last follow-up (six eyes of four patients [2.84%] and five eyes of four patients [5.20%] in the PRK and Lasik groups, respectively). Conclusion. In the present study, the high risk of postoperative ectasia was detected in keratoconus suspects following PRK and Lasik surgeries. According to the results, it can be concluded that Femto-Lasik surgery provides better outcomes than Lasik and PRK. Overall, the surgical criteria are suggested to be evaluated case by case, and the patients must be followed up over time to assess the corneal topography and refraction stability.

Visual outcomes after three different surgical procedures for correction of refractive error in patients with thin corneas

AIM

To investigate and compare the visual and refractive outcomes of small incision lenticule extraction (SMILE), laser assisted sub-epithelial keratomileusis (LASEK), and LASEK combined with corneal collagen cross-linking (LASEK-CXL) surgery in patients with less than 500 µm of central corneal thickness (CCT).

METHODS

The retrospective medical records review was conducted on the patients with CCT less than 500 µm treated with SMILE, LASEK, and LASEK-CXL. There was a total of 172 eyes, 76 eyes were in the SMILE group, 53 eyes in the LASEK group, and 43 eyes in the LASEK-CXL group. Uncorrected distance visual acuity (UDVA), spherical equivalent refraction (SE), and corneal haze were followed up in the three groups for 12mo.

RESULTS

At 12mo postoperatively, there were no statistically significant differences in UDVA and in the absolute value of SE between the three groups. The predictability within ±0.50 D in the SMILE group (85.5%) was significantly higher than in both the LASEK group (64.2%, P<0.01) and the LASEK-CXL group (69.8%, P=0.04). The efficacy index and safety index were not significantly different among the three groups. Corneal haze at 12mo postoperatively was higher in the LASEK-CXL group (27.9%) than in the SMILE group (2.6%, P<0.01) and in the LASEK group (7.5%, P<0.01).

CONCLUSION

In patients with CCT less than 500 µm, SMILE, LASEK, and LASEK-CXL appear to be effective for myopic correction. Among them, SMILE surgery shows the highest predictability.

Features of Femtosecond Correction of High Myopia through Small Access

Aim. To modify the calculated parameters of the lenticle extraction refractive surgery through a small access (SMILE), evaluate its safety and clinical efficacy in correcting high myopia.

Materials and methods. 34 patients (68 eyes) underwent surgery by a modified SMILE technology under local anesthesia. In all cases, the patients had a high degree of myopia, in 37 % in combination with astigmatism.

Uncorrected visual acuity before surgery averaged 0.05 ± 0.11, best corrected visual acuity of 0.94 ± 0.1, the pre-operative spherical refraction component was –7.23 ± 0.75, the cylindrical component was –0.48 ± 0.59.

During the operation, to obtain the maximum possible refraction result using the proposed method, the standard operation parameters were changed: the corneal flap thickness was reduced to 100 μm, the neural optical layer by 5 μm, the diameter of the optical zone depended on the residual cornea thickness, which should exceed 280–290 μm. Corneal access was increased by 15–20 degrees.

Results. The next day after surgery, monocular uncorrected visual acuity in distance in 73 % of patients was 0.8 or higher, and in 41 % of cases it was equal to or exceeded 1.0. The spherical equivalent on the first day after surgery had a slight hypermetropic shift, which was completely leveled by the year of follow-up. During the surgical intervention and in the postoperative period, no complications were noted.

Conclusion. Using the proposed algorithm for calculating the refractive effect of the operation SMILE with a high degree of myopia allows obtaining a high refractive effect and avoiding possible complications.

Corneal tomographic features of postrefractive surgery ectasia

The purpose of this study was to evaluate the tomographic features of postrefractive surgery eyes. This was a retrospective evaluation of clinical data. Three patients with post-LASIK (laser-assisted in situ keratomileusis) and two patients with post-SMILE (small incision lenticule extraction) ectasia were imaged with Scheimpflug imaging (SI, Pentacam) and optical coherence tomography (OCT, RTVue). Curvature and wavefront aberrations of the air-epithelium interface (A-E) and epithelium-Bowman's layer interface (E-B) were derived. OCT of normal and keratoconic eyes from an earlier study were compared with the data of the ectasia eyes. Curvature and aberrometry of the A-E interfaces were statistically similar between SI and OCT. However, OCT revealed a steeper and more aberrated E-B interface than A-E though correlation between them was inferior to the correlation for keratoconic eyes. Furthermore, the magnitude of differences between the A-E and E-B interfaces was greater in the ectasia eyes than the keratoconic eyes. OCT could possibly assist better in selecting appropriate treatment plan for postrefractive surgery ectasia eyes than conventional tomographers.

Central corneal thickness measurement using ultrasonic pachymeter, optical coherence tomography, and TMS-5 topographer

AIM:

This study aimed to compare the central corneal thickness (CCT) measurements using Optical Coherence Tomography (OCT) and TMS-5 topographer with that taken with the gold standard digital Ultrasonic pachymeter (USP).

MATERIALS AND METHODS:

A total of 61 subjects (122 eyes) were prospectively and consecutively studied in a period from June 2016 to June 2017 at Sudan Eye Centre (SEC), Khartoum, Sudan. Besides the visual and refractive data, measurements of CCT were taken using OCT, TMS-5 and USP. Data analyzed using SPSS software for windows (IBM SPSS 20, IBM Corp., Armonk, NY).

RESULTS:

A statistically significant differences in mean CCT was detected between the three instruments (P < 0.001). USP was found to measure the CCT 29μm thicker than OCT and 22μm thicker than TMS-5 topographer. A significant difference was also found between OCT and TMS-5. OCT found to give the lower values of CCT compared to both USP and TMS-5 topographer. Further analysis showed that the three procedures were significantly and strongly correlated to each other (USP vs OCT, r = 0.77), (USP vs TMS-5, r = 0.78) and (OCT vs TMS-5, r = 0.80).

CONCLUSION:

Mean central corneal thicknesses (CCT) were comparable among OCT, TMS-5 topographer and the gold standard USP. However, there is a reproducible systematic difference between CCT measurements taken with the three devices. It is important to note in clinical practice, that measurements acquired by these three modalities are not directly interchangeable.

Incidence and Clinical Characteristics of Post LASIK Ectasia: A Review of over 30,000 LASIK Cases

PURPOSE

To report the incidence of postoperative ectasia after laser in situ keratomileusis (LASIK).

METHODS

A retrospective case review of 30,167 eyes (16,732 patients) was conducted following LASIK between August 2007 and August 2015. The follow-up was between 2 and 8 years. Tomography was performed after 2 years postop. After identifying cases of ectasia, the charts of these patients were examined to identify any common factors that may have predisposed them to develop ectasia.

RESULTS

Ten eyes of seven patients developed post-LASIK ectasia. Eight eyes had been treated for myopia and myopic astigmatism, two eyes for mixed astigmatism. There were no cases of ectasia after LASIK for hyperopia. All 10 cases of ectasia had a flap that was created using the Moria M2 mechanical microkeratome (average flap thickness 118.15 ± 12.88 µm) and refractive error corrected using the Wavelight Allegretto excimer laser. Retrospectively, most prevalent risk factors were thin cornea (≤ 500 µm, 50% of cases), anterior topographic map irregularities (e.g., asymmetric bow tie, 40% of cases), Ectasia Risk Score > 3 (40% of cases), percent tissue thickness alteration ≥ 40% (20% of cases) and low residual stromal bed (≤ 300 µm, 30% of cases). One eye had no identifiable risk factors. In the retrospective chart review 14.97% (4,506) of all the eyes had similar risk factors to the cases that went on to develop ectasia.

CONCLUSION

The incidence of ectasia was 0.033% over 8 years. The incidence could be higher as some cases may destabilize beyond this period and some patients were lost to follow-up asymptomatic of any clinical signs. Other intrinsic factors may trigger the development of post LASIK ectasia. The current widely accepted risk factors are not sufficiently rigorous for screening out potential ectasia from developing after LASIK. There is a need to augment accuracy with higher sensitivity and specificity.

Keratectasia after laser-assisted subepithelial keratectomy for myopia: A case report

RATIONALE

Recently, some ophthalmologists performed PRK or LASEK surgeries in FFKC suspicious patients, which is supposed to prevent FFKC evolvement via fibrotic scar formation. Our report indicates that keratectasia can occur after LASEK in FFKC suspicious patients, highlighting the importance of stricter regulation of patient recruitment before the procedure and postoperative follow-up.

PATIENT CONCERNS

This is a report of a 25-year-old man with poor corrected distance visual acuity (CDVA) 6 years after LASEK. Preoperatively, central corneal thickness was 532 μm in right eye and 528 μm in leftt eye; corneal keratometry was 42.0/40.3diopters (D) in the right eye and 42.5/40.6D in the left eye; the CDVA was 2/50 in both eyes with the CDVA being 20/20 with -6.00DS/-2.00DC×30 in the right eye and -8.00DS/-2.00DCx150 in the left eye. Six years after LASEK, the CDVA was 20/50 with -5.75DS/-1.75DC×170 in the right eye and 10/50 with -15.00DS/-5.00DC ×155 in the left eye.

DIAGNOSES

Bilateral keratectasia.

INTERVENTIONS

Slit lamp examination, postoperative and in vivo confocal microscopy (IVCM) were performed in both eyes.

OUTCOMES

Examination under the slit lamp showed thinning and protrusion of the central cornea. Corneal topography showed significant inferior steepening with an irregular astigmatism, the corneal thickness at the thinnest point was 376μm and 350 μm and anterior surface keratometry was 43.1/41.2 D and 50.0/48.4 D in the right eye and left eye, respectively (right eye maximum K, 52.1 D; left eye maximum K, 65.6 D). Thin and irregular bands and hyper-reflective deposits in the Bowman's layer were found in IVCM images.

LESSONS

The case indicates that ectasia can occur after LASEK in pre-existing forme fruste keratoconus (FFKC) suspicious patients, highlighting the importance of a stringent preoperative workup on patients before the procedure and proper postoperative follow-up.

Evaluation of Corneal Biomechanics After Excimer Laser Corneal Refractive Surgery in High Myopic Patients Using Dynamic Scheimpflug Technology

OBJECTIVE

To compare the effect of femtosecond-assisted thin flap laser-assisted in situ keratomileusis (FS-LASIK) and photorefractive keratectomy with mitomycin-C (PRK-MMC) in highly myopic patients (>7.0 D [D]) on corneal biomechanical parameters.

METHODS

In this prospective comparative interventional case series, 60 patients (30 patients in each group) with a manifest refractive spherical equivalent (MRSE) greater than 7.0 D were enrolled. Corvis ST parameters were measured before and at 3 and 6 months postoperatively.

RESULTS

Preoperatively, mean MRSE was -8.65±1.51 D in FS-LASIK and -8.04±1.70 D in PRK-MMC groups (P=0.149), and corneal thickness was 570.67±36.79 μm and 507.12±32.55 μm, respectively (P<0.001). At 6 months, both groups showed significantly higher applanation (A) 2 time and A2-velocity (P<0.05 in both), whereas intraocular pressure (IOP), corrected IOP, A1 time, A1-velocity, and radius at highest concavity were significantly reduced (P<0.05 in all). In the FS-LASIK group, there was a significant increase in deformation amplitude (DA) (P=0.001), and significant decreases in A2-length (P=0.004). Peak distance increased in the PRK-MMC group (P=0.029). At 6 months, after controlling for fellow eye correlations and preoperative corneal thickness between the two groups, decreases in IOP, A1-time, A2-length and radius, and the increase in DA was greater in FS-LASIK.

CONCLUSION

This study demonstrated significant changes in Corvis ST ocular biomechanical metrics after both PRK-MMC and FS-LASIK in high myopic patients, indicating the significant effect of excimer laser refractive surgery on corneal biomechanical properties. However, changes that occur with FS-LASIK are more significant than with PRK-MMC. Further randomized studies are needed to better characterize the pattern of biomechanical changes associated with each type of surgery.

Long-term Follow-up of LASEK With Mitomycin C Performed to Correct Myopia in Thin Corneas

PURPOSE

To evaluate the long-term outcomes of laser-assisted subepithelial keratomileusis (LASEK) with intraoperative use of mitomycin C (MMC) performed on thin corneas for the correction of myopia.

METHODS

This retrospective cohort study included 100 eyes with a preoperative central corneal thickness (CCT) thinner than 500 μm that underwent LASEK + MMC with at least 6 years of follow-up. Stability of visual acuity and refraction and the efficacy, safety, and predictability at the examinations 3 months and the last annual postoperative visit were analyzed.

RESULTS

Preoperative CCT was 482.9 ± 14.7 μm (range: 433 to 499 μm). Mean preoperative spherical equivalent was -4.09 ± 2.3 diopters (D). At the 3-month postoperative visit, mean CCT was 419.79 ± 32.6 μm. The residual spherical equivalent showed a statistically significant regression (P = .001) in the comparison between the 3-month and the last annual postoperative visit. The efficacy index showed a significant decrease (P = .01) and the safety index remained stable around 0.96. Six or more years after the surgery, 85 eyes (85%) were within ±0.50 D and 94 eyes (94%) eyes were within ±1.00 D of emmetropia. The topography did not show signs of secondary corneal ectasia in any eye.

CONCLUSIONS

LASEK with intraoperative use of MMC seems to be safe, effective, and predictable to correct myopia in corneas thinner than 500 μm and with normal preoperative topography, providing good visual and refractive outcomes with no topographic signs of corneal ectasia in a mean 6.5-year follow-up. [J Refract Surg. 2017;33(12):813-819.].

Wound healing in rabbit corneas after flapless refractive lenticule extraction with a 345 nm ultraviolet femtosecond laser

PURPOSE

To characterize corneal wound healing in a rabbit model after flapless refractive lenticule extraction with a 345 nm ultraviolet femtosecond laser.

SETTING

Departments of Ophthalmology and Anatomy II, University of Erlangen-Nürnberg and Wavelight GmbH, Erlangen, Germany.

DESIGN

Experimental study.

METHODS

Flapless refractive lenticule extraction was performed in 1 eye each of 20 New Zealand white rabbits (-5.0 diopters). Groups of 4 animals were euthanized after 48 hours, 1 week, 2 weeks, 4 weeks, and 3 months, respectively. Corneal samples were prepared for histology and fluorescence microscopy. To assess corneal cell death, proliferation, and myofibroblastic transdifferentiation, terminal uridine deoxynucleotidyl nick end-labeling (TUNEL) assay as well as immunostaining for Ki67 and α-smooth muscle actin (αSMA) were performed on sagittal cryosections.

RESULTS

Histology revealed a zone of keratocyte depletion with a thickness of approximately 50 μm around the extraction site. At 48 hours, pronounced TUNEL staining of keratocytes was detected around the interface (159.9 cells/mm ± 18.4 [SD]), which steadily decreased to 74.9 ± 19.8 cells/mm at 1 week and 5.7 ± 4.8 cells/mm at 2 weeks. Ki67 staining of keratocytes was evident at 48 hours (10.0 ± 3.8 cells/mm), which then decreased at 1 week (5.2 ± 1.7 cells/mm) and 2 weeks (0.4 ± 0.5 cells/mm). From 4 weeks onward, no TUNEL or Ki67 staining was detected. The corneal stroma was αSMA-negative at all timepoints.

CONCLUSION

Application of the 345 nm laser showed no signs of problematic repair processes in the cornea, which supports the initiation of the clinical phase.

Refractive lenticule extraction (ReLEx) through a small incision (SMILE) for correction of myopia and myopic astigmatism: current perspectives

Small-incision lenticule extraction (SMILE) is an alternative to laser-assisted in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK) for the correction of myopia and myopic astigmatism. SMILE can be performed for the treatment of myopia ≤−12 D and astigmatism ≤5 D. The technology is currently only available in the VisuMax femtosecond laser platform. It offers several advantages over LASIK and PRK; however, hyperopia treatment, topography-guided treatment, and cyclotorsion control are not available in the current platform. The working principles, potential advantages, and disadvantages are discussed in this review.

Unilateral Post-LASIK Ectasia and Contralateral Spontaneous Ectasia

PURPOSE

To report a case of iatrogenic unilateral post-LASIK corneal ectasia with contralateral spontaneous ectatic evolution.

METHODS

Case report with preoperative and postoperative measurements including uncorrected visual acuity, corrected distance visual acuity, refraction, slit-scanning topographic and pachymetric maps, and differential maps.

RESULTS

Six months after unilateral LASIK, the operated eye progressively developed signs of post-LASIK ectasia with increased inferior corneal steepening and corneal thinning and decrease in corrected distance visual acuity. Five years later, the unoperated eye also developed signs of spontaneous ectatic evolution with increased inferior steepening and corneal thinning.

CONCLUSIONS

LASIK accelerates occurrence of ectasia in ectasia-susceptible and biomechanically fragile eyes.

Higher Order Aberrations and Visual Outcomes in Wavefront-Optimized Sub-Bowman Keratomileusis: Flap Creation Using Femtosecond Laser Versus Mechanical Microkeratome

PURPOSE

The aim of this study was to compare the outcomes of wavefront-optimized sub-Bowman keratomileusis (SBK) performed using the 150 KHz IntraLase femtosecond (IFS) laser (Abbot Medical Optics) with those using the Moria Evo 3 One Use-Plus SBK mechanical microkeratome (Moria SA).

DESIGN

A prospective comparative clinical trial.

METHODS

Fifty patients had bilateral wavefront-optimized SBK performed for myopia or myopic astigmatism. In 25 patients, the flap was created with the 150 KHz IFS laser (group 1) and in the other 25 with the Moria One Use-Plus SBK mechanical microkeratome (group 2). All other treatment parameters were the same. Results were reported for 1 eye per patient in each group (ie, 25 eyes in each group).

RESULTS

Efficacy, refractive stability, predictability, and safety profiles were comparable between the 2 groups. Although higher order aberrations (HOAs) increased significantly in both groups after laser in situ keratomileusis, intergroup comparison revealed that group 1 was associated with a significantly higher induction of both total HOAs [mean root mean square (RMS), 0.63 ± 0.20 in group 1 vs 0.52 ± 0.14 in group 2; P = 0.031] and spherical aberrations (RMS, 0.37 ± 0.17 in group 1 vs 0.22 ± 0.09 in group 2; P < 0.001) as compared with group 2.

CONCLUSIONS

Flaps created using the Moria Evo 3 One Use-Plus SBK mechanical microkeratome were associated with significantly lower induction of total HOAs and spherical aberrations as compared with 150 KHz IFS flaps at the end of 3 months follow-up.

Dependability of posterior-segment spectral domain optical coherence tomography for measuring central corneal thickness

PURPOSE

The aim of this study was to assess the intersession and interobserver reliability of central corneal thickness (CCT) measurements using a posterior-segment spectral domain optical coherence tomography (SD-OCT).

METHODS

Sixty patients were examined with a posterior-segment SD-OCT system (Topcon 3D-OCT). To analyze intersession reproducibility, 1 examiner measured CCT in 60 eyes 2 times 1 week apart, and to study interobserver reproducibility, a second examiner obtained another measurement during the first session. Within-subject reproducibility, coefficient of reproducibility (CR), and intraclass correlation coefficients (ICC) were calculated. Agreement between Topcon 3D OCT and ultrasound pachymetry (USP) was also assessed.

RESULTS

Posterior-segment SD-OCT showed an intersession reproducibility of 12.7 μm (CR = 2.4%) and an excellent ICC (0.96). No systematic difference between sessions was found (average difference, 1.7 μm; P = 0.15). We found no significant bias between observers (mean difference, -1.5 μm; P = 0.29). The interobserver reproducibility was 16.4 μm (CR = 3.1%), and the ICC was 0.94. Topcon 3D OCT CCT values were lower than USP readings (mean difference, 7.6 ± 8.1 μm; 95% confidence interval, 9.9-5.3 μm; P < 0.001).

CONCLUSIONS

With a commercially available retinal SD-OCT system, reliable intersession and interobserver CCT measurements can be feasibly obtained. The criteria for a significant change, which would be the one exceeding the reproducibility, indicate that intersession and interobserver variations in CCT of more than 13 and 16 μm, respectively, may reflect true corneal change with this particular device. These estimates should help investigators and clinicians differentiate actual CCT modification from measurement random error. The slight CCT underestimation with respect to USP is within the range of other OCT devices.

Screening of refractive surgery candidates for LASIK and PRK

PURPOSE

The aim of this study was to evaluate exclusion criteria in screening patients for refractive surgery.

METHODS

Patients screened for initial refractive surgery by a single surgeon at the Cole Eye Institute (Cleveland Clinic) between 2007 and 2012 were reviewed. Exclusion criteria for patients who were not offered refractive surgery based on history and/or examination parameters were analyzed.

RESULTS

A total of 1067 refractive candidates were enrolled in the study. Five hundred nineteen (48.6%) were male and 548 (51.4%) were female with a mean age of 39 ± 12 (range, 17-78) years. Refractive surgery was performed in 657 (61.6%) patients, and photorefractive keratectomy was considered the best option for 106 (9.9%) patients. Four hundred ten (38.4%) of all screened patients did not have refractive surgery, and 134 of these patients (12.6%) were considered to have contraindications for laser in situ keratomileusis and photorefractive keratectomy. Among the excluded patients, 69 (51.5%) were male and 65 (48.5%) were female with a mean age of 40 ± 14 (range, 18-78) years. Abnormal corneal topography (34.3%) and low or insufficient corneal thickness (23.1%) were the most common reasons for exclusion. High myopia (10.5%) and (insipient or definite) cataract (9.7%) were also common reasons for exclusion. Other common factors for exclusion were high hyperopia (3.7%), need to wear reading glasses after surgery (3.7%), and severe dry eye unresponsive to treatment (3.7%).

CONCLUSIONS

Abnormal corneal topography and low, or insufficient, corneal thickness remain the most common exclusion factors for corneal refractive surgery. Factors such as cataract, too high of correction, and severe dry eye are also common reasons for exclusion of patients.

A modified risk assessment scoring system for post laser in situ keratomileusis ectasia in topographically normal patients

Purpose:

To evaluate and modify the Randleman Ectasia Risk Score System for predicting post-laser in situ keratomileusis (LASIK) ectasia in patients with normal preoperative corneal topography.

Methods:

In this retrospective study we reviewed data from 136 eyes which had undergone LASIK including 34 ectatic and 102 normal eyes between 1999 and 2009. After determining the sensitivity and specificity of the Randleman system, a modified model was designed to predict the risk of post-LASIK corneal ectasia more accurately. Next, the sensitivity and specificity of this modified scoring system was determined and compared to that of the original scoring system.

Results:

In our sample, the sensitivity and specificity of the Randleman system was 70.1% and 50.5%, respectively. Our modified model included the following parameters: preoperative central corneal thickness, manifest refraction spherical equivalent, and maximum keratometry, as well as the number of months elapsed from surgery. Sensitivity and specificity rates of the modified system were 74.2% and 76.2%, respectively. The difference in receiver operating characteristic curves between the Randleman and modified scoring systems was statistically significant (P<0.001). The best sensitivity and specificity for our model occurred with a cumulative cutoff score of 4.00; a low risk was considered if the score was ≤4.00, and high risk was defined with a score > 4.00.

Conclusion:

Our modified ectasia risk scoring system for patients with normal corneal topography can predict post LASIK ectasia risk with acceptable sensitivity and specificity. However, there are still unidentified risk factors for which further studies are required.

Risk Factors in Post-LASIK Corneal Ectasia

Purpose. To evaluate the risk factors for post-laser in situ keratomileusis (LASIK) ectasia. Materials and Methods. Medical records of 42 eyes of 28 (10 women, 18 men) patients who developed corneal ectasia after LASIK were retrospectively reviewed. Topographical features and surgical parameters of those patients were evaluated. Results. The mean age of patients was 34.73 ± 6.50 (23–48) years and the mean interval from LASIK to the diagnosis of post-LASIK ectasia was 36.0 ± 16.92 (12–60) months. The following factors were determined as a risk factors: deep ablation (>75 μm) in 10 eyes, FFK (forme fruste keratoconus) in 6 eyes, steep cornea (>47 D) in 3 eyes, pellucid marginal degeneration (PMD) in 2 eyes, thin cornea (<500 μm) in 2 eyes, thin and steep cornea in 2 eyes, thin cornea and deep ablation in 5 eyes, FFK and steep cornea in 2 eyes, and FFK, steep cornea, and deep ablation in 1 eye. However no risk factor has been determined in 9 eyes (21.4%). Conclusion. The findings of our study showed that most of the patients who developed post-LASIK ectasia have a risk factor for post-LASIK ectasia. However, the most common risk factor was deep ablation.

[Post-lasik corneal ectasia in patients with significant differences in keratometry readings between both eyes]

OBJECTIVES

A study is made on the incidence of corneal ectasia after laser in situ keratomileusis (LASIK) in patients with large differences in mean keratometry (MK) readings between both eyes (OU). Visual outcomes were also evaluated.

METHODS

The medical records of 164,603 patients (315,259 eyes) who underwent LASIK from January 2003 to December 2011 were reviewed in order to identify patients with a difference in MK of ≥ 1.25 D between OU. The main outcome measures were incidence of ectasia after LASIK, and visual outcome.

RESULTS

A total of 35 eyes that met the inclusion criteria were found. Functional and visual results were those expected for myopia studies. After a minimum follow-up of 2 years, no corneal ectasia was found in 3 eyes (2 patients).

CONCLUSIONS

The possibility of finding a patient with an asymmetry in MK and normal topography is low (0.021%), and it does not seem to be a contraindication of LASIK. Although no corneal ectasia was found in this case series, and as it is a potentially sight-threatening complication, patients with very different MK between OU should be studied carefully before undergoing LASIK.

Discriminant value of custom ocular response analyzer waveform derivatives in keratoconus

PURPOSE

To evaluate the performance of corneal hysteresis (CH), corneal resistance factor, and 16 investigator-derived Ocular Response Analyzer (ORA) variables in distinguishing keratoconus (KC) from the nondiseased state.

DESIGN

Retrospective case series.

PARTICIPANTS

Fifty-four eyes of 27 unaffected patients and 49 eyes of 25 KC patients from the Instituto de Olhos, Rio de Janeiro, Brazil.

METHODS

Sixteen candidate variables were derived from exported ORA signals to characterize putative indicators of biomechanical behavior. Area under the receiver operating characteristic curve (AUC) and the Z statistic were used to compare diagnostic performance.

MAIN OUTCOME MEASURES

Discriminant value of standard and derived ORA variables as measured by AUC.

RESULTS

Fifteen of 16 candidate variables performed significantly better than chance (AUC, >0.5) at discriminating KC. Diagnostic performance was greatest for a custom variable related to the depth of deformation as defined by the minimum applanation signal intensity during corneal deformation (concavity(min); mean AUC ± standard error, 0.985 ± 0.002) and a new measure incorporating the pressure-deformation relationship of the entire response cycle (hysteresis loop area, 0.967 ± 0.002). Z statistics assessing the discriminative value of each of the top 5 variables demonstrated superiority to CH (AUC, 0.862 ± 0.002). Concavity(min) had the best overall predictive accuracy (cutoff value, 50.37; 94.9% sensitivity, 91.7% specificity, and 93.2% test accuracy), and the top 4 variables demonstrated the most consistent relationships to KC severity.

CONCLUSIONS

Investigator-derived ORA variables related to the depth of deformation and the pressure-deformation relationship demonstrated very high test accuracy for detecting the presence of KC. Beyond their diagnostic value, the candidate variables described in this report provide mechanistic insight into the nature of the ORA signal and the characteristic changes in corneal dynamics associated with KC.

Rate of ectasia and incidence of irregular topography in patients with unidentified preoperative risk factors undergoing femtosecond laser-assisted LASIK

Purpose

To report the rate of postoperative ectasia after laser-assisted in situ keratomileusis (LASIK) with femtosecond laser-assisted flap creation, in a population of patients with no identified preoperative risk factors.

Methods

A retrospective case review of 1,992 eyes (1,364 patients) treated between March 2007 and January 2009 was conducted, with a follow up of over 4 years. After identifying cases of ectasia, all the patient charts were examined retrospectively for preoperative findings suggestive of forme fruste keratoconus (FFKC).

Results

Five eyes of four patients with post-LASIK ectasia were identified. All eyes passed preoperative screening and received bilateral LASIK. One of the five patients developed ectasia in both eyes. Three patients retrospectively revealed preoperative topography suggestive of FFKC, while one patient had no identifiable preoperative risk factors. Upon review of all the charts, a total 69 eyes, including four of the five eyes with ectasia, were retrospectively found to have topographies suggestive of FFKC.

Conclusion

We identified four cases of post-LASIK ectasia that had risk factors for FFKC on reexamination of the chart and one case of post-LASIK ectasia with no identifiable preoperative risk factors. The most conservative screening recommendations would not have precluded this patient from LASIK. The rate of purely iatrogenic post-LASIK ectasia at our center was 0.05% (1/1,992), and the total rate of post-LASIK ectasia for our entire study was 0.25% (1/398). The rate of eyes with unrecognized preoperative FFKC that developed post-LASIK ectasia was 5.8% (1/17).

Corneal collagen cross-linking in the stabilization of PRK, LASIK, thermal keratoplasty, and orthokeratology

PURPOSE OF REVIEW

To describe the use of corneal collagen cross-linking (CXL) and its efficacy in the stabilization of keratorefractive procedures, including PRK, laser in-situ keratomileusis (LASIK), thermal keratoplasty, and orthokeratology.

RECENT FINDINGS

Since its introduction, CXL has quickly gained interest in the treatment of ectactic disorders due to its ability to increase the biomechanical stability of the cornea. In its earliest use, it has shown to be effective in the treatment of both keratoconus and post-LASIK ectasia. More recent studies of CXL in combination with keratorefractive procedures have shown varying degrees of success.

SUMMARY

CXL with PRK has shown to be effective in slowing or halting the progression of keratoconus, pellucid marginal degeneration, and post-LASIK ectasia, in addition to potentially decreasing or delaying the need for penetrating keratoplasty. Several small case series have also demonstrated improved stability and efficacy of PRK and LASIK when combined with CXL, as well as a potentially decreased risk of postprocedure ectasia. In conjunction with thermokeratoplasty and orthokeratology, CXL has shown improved but only temporary results in the treatment of keratoconus. Future studies are needed to determine the efficacy and long-term stability of CXL in combination with keratorefractive procedures, as well as to address possible complications.

Effects of silicone hydrogel contact lenses on ocular surface after Sub-Bowman's Keratomileusis

PURPOSE

To evaluate the efficacy of silicone hydrogel contact lenses on ocular surface after Sub-Bowman Keratomileusis (SBK).

MATERIALS AND METHODS

Forty-six patients suffered from myopia underwent a bilateral SBK. Post-operatively, one eye of each patient wore a PureVision contact lens for 24 h as a treated eye and the contralateral eye was as a blank control. Afterwards, corneal fluorescein (FL) staining, tear break-up time (TBUT), schirmer I test (SIT), central corneal thickness (CCT), ocular surface disease index (OSDI), corneal hysteresis (CH), corneal resistance factor (CRF) and corneal flap complications were assessed 1 d (except for CH and CRF), 1 week, 1 month and 3 months postoperatively.

RESULTS

Following SBK, in contrast to the control, corneal fluorescein staining of treated eyes were significantly reduced and tear break-up time of treated eyes were significantly improved at 1 d and 1 week after SBK. However, Schirmer I test of treated and control eyes were not different after SBK. Central corneal thickness of treated eyes were significantly thinner than that of control at 1 d after SBK, however, there were no differences at other time points. Ocular surface disease index of treated eyes were obviously alleviated more than that of control at 1 d after SBK, but no differences were found at other visits. Moreover, Corneal hysteresis and corneal resistance factor of treated and un-treated eyes were not different after surgery. And also the rate of corneal flap complications were not different between treated and control eyes after SBK.

CONCLUSIONS

Silicone hydrogel contact lenses played a positive role in accelerating corneal epithelial healing, enhancing tear film stability and reducing discomfort of patients in the early stage after SBK.

Nonlinear optical collagen cross-linking and mechanical stiffening: a possible photodynamic therapeutic approach to treating corneal ectasia

In this study we test the hypothesis that nonlinear optical (NLO) multiphoton photoactivation of riboflavin using a focused femtosecond (FS) laser light can be used to induce cross-linking (CXL) and mechanically stiffen collagen as a potential clinical therapy for the treatment of keratoconus and corneal ectasia. Riboflavin-soaked, compressed collagen hydrogels are cross-linked using a FS laser tuned to 760 nm and set to either 100 mW (NLO CXL I) or 150 mW (NLO CXL II) of laser power. FS pulses are focused into the hydrogel using a 0.75 NA objective lens, and the hydrogel is three-dimensionally scanned. Measurement of hydrogel stiffness by indentation testing show that the calculated elastic modulus (E) values are significantly increased over twofold following NLO CXL I and II compared with baseline values (P<0.05). Additionally, no significant differences are detected between NLO CXL and single photon, UVA CXL (P>0.05). This data suggests that NLO CXL has a comparable effect to conventional UVA CXL in mechanically stiffening collagen and may provide a safe and effective approach to localize CXL at different regions and depths within the cornea.

Corneal ectasia after myopic laser in situ keratomileusis: a long-term study

Background

The purpose of this study was to evaluate the long-term postoperative incidence of and key factors in the genesis of corneal ectasia after myopic laser-assisted in situ keratomileusis (LASIK) in a large number of cases.

Methods

A retrospective review of one surgeon’s myopic LASIK database was performed. Patients were stratified into two groups based on date of surgery, ie, group 1 (1313 eyes) from 1999 to 2001 and group 2 (2714 eyes) from 2001 to 2003. Visual acuity, refraction, pachymetry, and corneal topography data were available for each patient from examinations performed both before and after the refractive procedures.

Results

Of the 4027 surgically treated eyes, 23 (0.57%) developed keratectasia during the follow-up period, which was a minimum seven years; nine eyes (0.69%) were from group 1 and 14 eyes (0.51%) were from group 2. The onset of corneal ectasia was at 2.57 ± 1.04 (range 1–4) years and 2.64 ± 1.29 (range 0.5–5) years, respectively, for groups 1 and 2. The most important preoperative risk factors using the Randleman Ectasia Risk Score System were manifest refractive spherical error in group 1 and a thin residual stromal bed in group 2. Each of the cases that developed corneal ectasia had risk factors that were identified.

Conclusion

Ectasia was an uncommon outcome after an otherwise uncomplicated laser in situ keratomileusis procedure. The variables present in eyes developing postoperative LASIK ectasia can be better understood using the Randleman Ectasia Risk Score System.

Validation of a New Scoring System for the Detection of Early Forme of Keratoconus

Purpose

To evaluate the accuracy of a new objective method for the detection of ectasia susceptible eyes.

Methods

One hundred and eighty-three elevation and placido topographies were retrospectively evaluated by one experimented refractive surgeon and classified as ‘normal’ or ‘at risk for LASIK’. An objective automated system built on the combination of topography and tomography data in a discriminant function was also used to classify the corneas. The concordance between the objective and the subjective classification was evaluated and the usefulness of the objective scoring system was assessed by receiver operating characteristic (ROC) curve analysis.

Results

The mean age of the studied group was 37 ± 8 years old. One hundred and fifty-nine eyes were subjectively classified as ‘normal’ and 24 as ‘At risk for LASIK’. The scoring system correctly classified 153 eyes as ‘normal’ and 22 eyes as ‘at risk for LASIK’. Six eyes were wrongly detected as ‘at risk’ by the automated system (false-positive) and two eyes were wrongly classified as ‘normal’ (false-negative). The sensitivity and specificity of the automated system were 92 and 96% respectively.

Conclusion

An automated system built on the combination of topography and tomography parameters can help in creating a sensitive and specific artificial intelligence for the detection of corneas at risk for refractive surgery.

How to cite this article

Saad A, Gatinel D. Validation of a New Scoring System for the Detection of Early Forme of Keratoconus. Int J Kerat Ect Cor Dis 2012;1(2):100-108.

Late onset corneal ectasia after LASIK surgery

PURPOSE

To report late onset corneal ectasia following myopic LASIK.

METHODS

A retrospective cohort case series. Nineteen patients with late onset corneal ectasia following LASIK procedure were examined at The Eye Center, Riyadh, Saudi Arabia. Patients underwent LASIK for myopia with spherical equivalent ranging from -1.4 to -13.75 diopters. Age and gender, history of systemic or local diseases, and time of onset of corneal ectasia were recorded. Eye examination and corneal topographical analyses were done before and after LASIK surgery.

RESULTS

Nineteen patients (29 eyes) with late onset corneal ectasia were identified from 1998 to 2008 in 13 male and six female patients. The mean follow-up period was 108 ± 23 months (range 72-144 months). No patient had pre-operative identifiable risk factors for corneal ectasia and the mean time of onset was 57 ± 24 months (range 24-120 months after LASIK). The pre-operative values included mean central pachymetry 553 ± 25 μm, mean keratometry reading of 42.9 ± 1.5 diopters, average oblique cylinder of 1.4 ± 1.2 diopters, posterior surface elevation of 26 ± 2.1 diopters, corneal flap thickness of 160 μm, mean spherical equivalent of -5.6 ± 3.6 diopters, and calculated residual corneal stromal bed thickness was 288 ± 35 μm. Three (5 eyes) patients developed ectasia after pregnancy. Three (4 eyes) patients developed corneal ectasia following severe adenoviral keratoconjunctivitis and had positive PCR for adenovirus type 8.

CONCLUSIONS

Corneal ectasia may develop many years after LASIK surgery and symptoms could go undetected for some time. Pregnancy and adenoviral keratoconjunctivitis occurred post-operatively in six patients.

Corneal elevation topography: best fit sphere, elevation distance, asphericity, toricity, and clinical implications

PURPOSE

To describe the effect of the corneal asphericity and toricity on the map patterns and best fit sphere (BFS) characteristics in elevation topography.

METHODS

The corneal surface was modeled as a biconic surface of principal radii and asphericity values of r1 and r2 and Q1 and Q2, respectively. The apex of the biconic surface corresponded to the origin of a polar coordinates system. Minimization of the squared residuals was used to calculate the values of the radii of the BFSs and apex distance (A-values: z distance between the corneal apex and the BFS) of the modeled corneal surface for various configurations relating to commonly clinically measured values of apical radius, asphericity, and toricity.

RESULTS

Increased apical radius of curvature and increased prolateness (negative asphericity) led to an increase in BFS radius but had opposite effects on the A-value. Increased prolateness resulted in increased BFS radius and A-value. Increasing toricity did not alter these findings. Color-plot elevation maps of the modeled corneal surface showed complete ridge patterns when toricity was increased and showed incomplete ridge and island patterns when prolateness was increased.

CONCLUSIONS

High A-values in patients with corneal astigmatism may result from steep apical curvature and/or high prolateness (negative asphericity). The BFS radius may help in distinguishing between these 2 causes of increased A-values. Increased prolateness and decreased apical radius of curvature (often seen in keratoconus) have opposite effects on the BFS radius but similar effects on the apex distance.

Relationship of age and refraction to central corneal thickness

PURPOSE

To obtain descriptive statistics of central corneal thickness (CCT) in a large population of normal eyes undergoing refractive surgery and study the relationship of 2 variables, age and refraction, with CCT.

SETTING

Cornea and Laser Eye Institute, Hersh Vision Group, Teaneck, NJ.

METHODS

The CCT of 5158 patients was measured using an ultrasound pachymeter. Age and preoperative spherical equivalent were recorded for all patients. The entire population and subgroups stratified to age and spherical equivalent were analyzed.

RESULTS

Mean CCT was 544 μm with an SD of 34 μm and a range of 415-695 μm. CCT did not correlate with either age (r = 0.00645) or refraction (r = 0.00072).

CONCLUSIONS

This study defines the CCT in a large population of patients undergoing refractive surgery. In this population, age and refraction did not affect CCT.

A prospective, contralateral comparison of photorefractive keratectomy (PRK) versus thin-flap LASIK: assessment of visual function

Purpose:

To compare differences in visual acuity, contrast sensitivity, complications, and higher-order ocular aberrations (HOAs) in eyes with stable myopia undergoing either photo-refractive keratectomy (PRK) or thin-flap laser in situ keratomileusis (LASIK) (intended flap thickness of 90 μm) using the VISX Star S4 CustomVue excimer laser and the IntraLase FS60 femtosecond laser at 1, 3, and 6 months postoperatively.

Methods:

In this prospective, masked, and randomized pilot study, refractive surgery was performed contralaterally on 52 eyes: 26 with PRK and 26 with thin-flap LASIK. Primary outcome measures were uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), contrast sensitivity, and complications.

Results:

At 6 months, mean values for UDVA (logMAR) were −0.043 ± 0.668 and −0.061 ± 0.099 in the PRK and thin-flap LASIK groups, respectively (n = 25, P = 0.466). UDVA of 20/20 or better was achieved in 96% of eyes undergoing PRK and 92% of eyes undergoing thin-flap LASIK, whereas 20/15 vision or better was achieved in 73% of eyes undergoing PRK and 72% of eyes undergoing thin-flap LASIK (P > 0.600). Significant differences were not found between treatment groups in contrast sensitivity (P ≥ 0.156) or CDVA (P = 0.800) at postoperative 6 months. Types of complications differed between groups, notably 35% of eyes in the thin-flap LASIK group experiencing complications, including microstriae and 2 flap tears.

Conclusion:

Under well-controlled surgical conditions, PRK and thin-flap LASIK refractive surgeries achieve similar results in visual acuity, contrast sensitivity, and induction of HOAs, with differences in experienced complications.

Myopic LASIK and LASEK in patients with preoperative mean central keratometry ≥47.50 D

PURPOSE

To evaluate whether patients who undergo myopic LASIK or laser epithelial keratomileusis (LASEK) with preoperative central keratometry ≥47.50 diopters (D) are at higher risk for developing corneal ectasia postoperatively.

METHODS

Records of 32 patients (54 eyes) who underwent myopic LASIK or LASEK between May 2002 and July 2005 with preoperative mean central keratometry ≥47.50 D were retrospectively reviewed. Patients eligible for the study were offered free follow-up. Last follow-up was at least 3 years after surgery. All procedures were performed with the Technolas Keracor 217z excimer laser (Bausch & Lomb).

RESULTS

Twenty-four patients (40 eyes) had LASIK and 8 patients (14 eyes) had LASEK. At last follow-up, no patient had developed ectasia.

CONCLUSIONS

This study suggests that patients with preoperative central keratometry ≥47.50 D as the only parameter evaluated should not be excluded from corneal refractive surgery due to increased risk of postoperative ectasia. However, when this preoperative finding is accompanied by other topographic abnormalities, treatment options should be carefully evaluated.

Reasons for not performing LASIK in refractive surgery candidates in Yemen

PURPOSE

To determine and analyze the reasons that laser in situ keratomileusis (LASIK) was not performed in patients who requested refractive surgical correction of their refractive errors.

METHODS

A retrospective observational study was performed in Yemen Magrabi Hospital between June 2005 and October 2006; the case records of 1596 new consecutive patients who presented for refractive surgery at our refractive surgery unit were reviewed. Data on the ocular status, refractive problems, and investigations performed were analyzed. The reasons for not performing LASIK in the cases that were rejected were recorded and analyzed.

RESULTS

A total of 1191 patients (74.6%) were advised to have LASIK of the 1596 patients examined. LASIK was not advised in 405 patients (25.4%). The most common reasons for rejecting LASIK were suboptimal central corneal thickness (25.9%), high myopia >-11.00 D (17.0%), keratoconus (15.5%), cataract (11.4%), and suspicious corneal topography (forme fruste keratoconus) (9.4%).

CONCLUSIONS

Patients who request refractive surgery have a variety of problems and attention must be given to these patients. Suboptimal corneal thickness, high amount of refractive error, and keratoconus were found to be the leading causes of not performing LASIK in Yemeni patients.

Refractive stability of LASIK with the Visx 20/20 excimer laser vs ZB5m phakic iol implantation in patients with high myopia (>-10.00 d): a 10-year retrospective study

PURPOSE

To compare the long-term outcomes of LASIK and ZB5M phakic intraocular lens implantation (PIOL) (Domilens) for high myopia (>-10.00 diopters [D]).

METHODS

This long-term (10 years) follow-up retrospective interventional case series study included 126 eyes that underwent LASIK and 52 eyes that underwent ZB5M angle-supported PIOL implantation. Both groups of eyes were similar in terms of preoperative spherical equivalent refraction (SE), corrected distance visual acuity (CDVA), and age.

RESULTS

Mean preoperative SE was -14.33 D in the LASIK group and -14.84 D in the PIOL group. At 10-year follow-up, mean postoperative SE was -1.47±2.00 D in the LASIK group and -1.01±1.36 D in the PIOL group (P=.21). In the LASIK group, 67% of eyes were within ±1.00 D of emmetropia at 2 years after surgery, compared to 42% at 10 years. In the PIOL group, 68% of eyes were within ±1.00 D of emmetropia 2 years after implantation compared to 53% at 10 years. In the LASIK group, 43.5% of eyes achieved UDVA of 20/40 or better 10 years after surgery compared to 67.9% in the PIOL group (P=.02).

CONCLUSIONS

The ZB5M angle-supported PIOL was shown to have better predictability and stability compared to LASIK over 10 years. However, reductions in endothelial cell count over time were observed in eyes with PIOLs.

Seven-year follow-up of LASIK for myopia

PURPOSE

To assess the long-term refractive results, subjective parameters, and late sequelae of LASIK.

METHODS

A retrospective follow-up study was conducted on 38 eyes of 21 patients (17 with bilateral treatment and 4 with unilateral treatment) who had LASIK surgery between 1999 and 2000. Laser ablations were done with an excimer laser (VISX STAR and STAR S2). Follow-up was 2 months, 2 years, and > 7 years postoperatively. Uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), manifest refraction, indirect ophthalmoscopy, and wavefront analysis were measured at the last follow-up and a questionnaire was answered.

RESULTS

Postoperatively, BSCVA < or = 0.0 (logMAR) was obtained in 91%, 100%, and 89% of eyes at 2 months, 2 years, and at last follow-up, respectively. Postoperative spherical equivalent refraction within +/- 0.50 diopters (D) was obtained in 75%, 63%, and 42% of eyes at 2 months, 2 years, and 7 to 8 years, respectively. At 2 months and 2 years, 83% of eyes were within +/- 1.00 D, which decreased to 42% at 7 to 8 years. Mean spherical equivalent refraction at 2 months was -0.41 D, at 2 years -0.57 D, and at 7 to 8 years continued to decrease to -1.38 D. Patient satisfaction was high--100% of patients would have LASIK again.

CONCLUSIONS

LASIK outcomes tend to shift toward undercorrection over time. Postoperative ectasia was not noted 7 to 8 years after LASIK. All patients were satisfied with the postoperative results although emmetropia was not reached.

Ten-year follow-up of excimer laser surface ablation for myopia in thin corneas

PURPOSE

To evaluate the long-term outcomes of excimer laser surface ablation performed on thin corneas.

DESIGN

Retrospective study.

METHODS

We included in the study 75 eyes (49 patients) with a preoperative central corneal thickness (CCT) thinner than 500 mum that had undergone surface ablation to correct their myopia and that had at least 10 years of follow-up. We evaluated the stability of visual acuity (VA) and refraction, the predictability, corneal keratometry, safety, efficacy, and postoperative complications at the examinations 3 months and 1, 2, 5, and 10 years after surgery.

RESULTS

Preoperative CCT was 481.54 +/- 15.7 microm (range, 438 to 499 microm). Preoperative spherical equivalent was -6.12 +/- 2.67 diopters (D) (range, -2 to -14 D). The best spectacle-corrected VA significantly improved (P < .01) during the follow-up. The uncorrected VA showed significant improvement in all visits when compared with the 3-month postoperative visit. Both the sphere and cylinder showed a slight but significant regression (P < .01) only in the comparison between 3 months and 10 years after the surgery. Ten years after the surgery, 30 eyes (40%) were within 0.50 D and 43 eyes (57.33%) were within 1.00 D of emmetropia. The safety index improved over the 10 year period and was always higher than 0.9. The efficacy index remained stable around 0.8. The topography did not show signs of corneal ectasia and the keratometry showed no increase in corneal power. Thirty eyes (40%) needed enhancement.

CONCLUSION

Surface ablation seems to be safe and effective to correct myopia in corneas thinner than 500 microm, with stable visual and refractive outcomes in a 10-year follow-up.

High myopia as a risk factor for post-LASIK ectasia: a case report

Purpose

To describe the case of a patient developing corneal ectasia following LASIK for the correction of myopic astigmatism.

Materials and Methods

A 39-year-old man underwent bilateral uneventful LASIK for myopic astigmatism of -10.25 -1.75 ×040 OD and -8.00 -2.50 ×005 OS. Preoperative corneal pachymetry was 542 micrometers OD and 543 micrometers OS. Preoperative corneal topography showed bilateral oblique bow-tie patterns. Central keratometry measurements were 45.12 D @ 124 / 43.87 D @ 34 OD and 44.87 D @ 78 / 43.12 D @ 168 OS. Keratoconus or forme fruste keratoconus were not present preoperatively.

Results

The residual stromal bed was 314 micrometers OD and 295 micrometers OS. Increasing astigmatism was documented progressively after LASIK. Central keratometry and topography were performed with evidence of ectasia OD at 17 months post-operatively and early evidence of ectasia OS at last follow-up of 58 months.

Conclusion

High myopia appears to be a predisposing factor in this patient. High myopia may need to be considered as an ectasia risk factor independent of amount of ablation or residual stromal bed thickness and in the absence of forme fruste keratoconus. The possibility remains that ectasia was due to an unidentified risk factor or an intrinsic corneal problem with this patient's right eye.

Thin-flap (sub-Bowman keratomileusis) versus thick-flap laser in situ keratomileusis for moderate to high myopia: case-control analysis

PURPOSE

To compare the refractive and visual outcomes of sub-Bowman keratomileusis (SBK) and thick-flap laser in situ keratomileusis (LASIK) for moderate to high myopia and evaluate the effect of corneal flap thickness on outcomes.

SETTING

Massachusetts Eye and Ear Infirmary, Boston, Massachusetts, USA.

METHODS

Two studies were performed. In the first study, the refractive and visual outcomes in 33 eyes that had SBK (flap thickness 82 to 120 microm) and 62 eyes that had thick-flap LASIK (flap thickness >or=160) were retrospectively analyzed. Inclusion criteria were spherical equivalent -4.0 to -10.0 diopters (D), astigmatism 3.0 D or less, and follow-up 3 months or more. In the second study, the influence of flap thickness was evaluated. A case-control matched study (21 pairs) that controlled for residual stromal bed (RSB) thickness was performed.

RESULTS

The mean flap thickness was 110.2 microm+/-9.2 (SD) in the SBK group and 179.2+/-19.5 microm in the thick-flap LASIK group. There were no significant differences in visual outcomes. In the second study with equivalent RSB thickness, case-control matched comparisons between SBK (mean 108.6+/-8.0 microm) and thick-flap LASIK (mean 165.7+/-12.6 microm) showed no differences in preoperative and postoperative refractive and visual outcomes. Comparison of the intended versus achieved correction showed no significant differences between the 2 groups.

CONCLUSION

Retrospective analyses showed that the safety, efficacy, and predictability of SBK were similar to those of conventional thick-flap LASIK in corneas with equivalent RSB thickness.

Stability of laser epithelial keratomileusis with and without mitomycin C performed to correct myopia in thin corneas: a 15-month follow-up

PURPOSE

To study the stability of the refraction 15 months after myopic laser epithelial keratomileusis (LASEK) performed in thin corneas with and without adjuvant mitomycin C (MMC).

DESIGN

Retrospective review.

METHODS

One hundred and thirty-six consecutive eyes that had undergone LASEK to correct their myopia and that had a preoperative central corneal thickness (CCT) of <500 microm at Vissum Madrid, Spain, were included. Intraoperative MMC was applied when the ablation depth exceeded 50 microm (49 eyes). We compared the residual refraction between the three- and 15-month examinations to detect a possible myopic change that would suggest secondary corneal ectasia.

RESULTS

Mean preoperative CCT +/- standard deviation (SD) was 484.4 +/- 11.8 microm (range, 440 to 499 microm). Mean CCT +/- SD three months after surgery was 417.9 +/- 32.1 microm (range, 339 to 473 microm). Mean preoperative spherical refraction +/- SD was -3.49 +/- 2.10 diopters (D). Mean preoperative cylinder +/- SD was -0.87 +/- 1.20 D. The mean residual sphere +/- SD was 0.15 +/- 0.40 D three months after surgery and 0.11 +/- 0.60 D 15 months after surgery (P = .45). The mean cylinder +/- SD was -0.13 +/- 0.30 D and -0.25 +/- 0.50 D, respectively (P = .06). Both the uncorrected visual acuity (UCVA) and the best-spectacle corrected visual acuity (BSCVA) showed statistically significant improvement on the 15-month examination (P = .01 and P = .0001, respectively). When analyzed separately, the subgroup treated with intraoperative MMC also showed stability of the refraction and a statistically significant improvement both in UCVA and in BSCVA. Topography showed no signs of ectasia in any case.

CONCLUSIONS

Myopic LASEK performed on thin corneas, regardless of the use of intraoperative MMC, seems to obtain stable refractive results, with no sign of ectasia during a 15-month follow-up.