Corneal Ectasia After Laser In Situ Keratomileusis in Patients Without Apparent Preoperative Risk Factors

Redo surgery using IntraLase femtosecond laser for treating a decentered laser in situ keratomileusis flap

Objective

Decentered flaps are rarely reported after femtosecond laser-assisted in situ keratomileusis flap procedures. We present a patient with a decentered flap after preparation of a corneal flap using the Femto LDV technique.

Methods

The 22-year-old man required a redo operation because of a decentered corneal flap. It was performed the same day at the patient's insistence and with his consent. The new corneal flap for the redo surgery was prepared using the femtosecond laser technique and IntraLase.

Results

Uncorrected visual acuity for each eye was 1.2 during the 12-month follow-up. The results of the Femtosecond laser technique showed good predictability and repeatability regarding the preparation of corneal flaps, but it still may cause some intraoperative complications.

Conclusion

Once redo surgery is needed, the size and depth of the initially prepared flap should be determined using anterior segment optical coherence tomography to pre-set the parameters for preparation of the redo flap.

U.S. Multicenter Clinical Trial of Corneal Collagen Crosslinking for Treatment of Corneal Ectasia after Refractive Surgery

PURPOSE

To evaluate the safety and efficacy of corneal collagen crosslinking (CXL) for the treatment of corneal ectasia after laser refractive surgery.

DESIGN

Prospective, randomized, multicenter, controlled clinical trial.

PARTICIPANTS

One hundred seventy-nine subjects with corneal ectasia after previous refractive surgery.

METHODS

The treatment group underwent standard CXL, and the sham control group received riboflavin alone without removal of the epithelium.

MAIN OUTCOME MEASURES

The primary efficacy criterion was the change over 1 year of topography-derived maximum keratometry (K), comparing treatment with control groups. Secondary outcomes evaluated were corrected distance visual acuity (CDVA), uncorrected distance visual acuity (UDVA), manifest refraction spherical equivalent, endothelial cell count, and adverse events.

RESULTS

In the crosslinking treatment group, the maximum K value decreased by 0.7 diopters (D) from baseline to 1 year, whereas there was continued progression in the control group (1.3 D difference between treatment and control, P < 0.0001). In the treatment group, the maximum K value decreased by 2.0 D or more in 14 eyes (18%) and increased by 2.0 D or more in 3 eyes (4%). The CDVA improved by an average of 5.0 logarithm of the minimum angle of resolution (logMAR) letters. Twenty-three eyes (32%) gained and 3 eyes (4%) lost 10 or more logMAR letters. The UDVA improved 4.5 logMAR letters. Corneal haze was the most frequently reported crosslinking-related adverse finding.

CONCLUSIONS

Corneal collagen crosslinking was effective in improving the maximum K value, CDVA, and UDVA in eyes with corneal ectasia 1 year after treatment, with an excellent safety profile. CXL is the first approved procedure to diminish progression of this ectatic corneal process.

In vivo confocal microscopy and tear cytokine analysis in post-LASIK ectasia

AIM

Corneal keratectasia is one of the complications associated with laser in situ keratomileusis (LASIK) that results in vision impairment. The pathogenesis of post-LASIK ectasia (PLE) remains underexplored. We report the tear cytokine profile and in vivo confocal microscopy (IVCM) findings in eyes with PLE.

METHODS

This retrospective study included age-matched 7 (14 eyes) post-LASIK controls (PLCs) and 6 (12 eyes) PLE subjects. Corneal topography was used to categorise the subjects into PLC and PLE groups. Ocular Surface Disease Index (OSDI) scores obtained were based on standard questionnaire and IVCM images were used to determine corneal dendritic cells density (DCD) and sub-basal nerve plexus morphology. Inflammatory cytokines/chemokines in the tears were quantified using flow cytometry based cytometric bead array.

RESULTS

Pentacam-based scores, OSDI scores and corneal DCD were significantly (p<0.05) higher in patients with PLE compared with PLC. Discomfort-related subscale of OSDI score exhibited a positive correlation with total corneal DCD in the PLE cohort. The fold difference of chemokine (C-C motif) ligand/monocyte chemotactic protein-1 (CCL2/MCP1) (3.4±0.6) was found to be significantly (p<0.05) higher in the PLE cohorts and a positive correlation between CCL2/MCP1 levels and total corneal DCD was also observed in the PLE cohort.

CONCLUSION

The current study found a significant difference in the tear film cytokine profile between normal and PLE eyes. Presence of increased corneal dendritic cells and altered tear cytokines suggests an ongoing inflammatory response in PLE.

Pupillary Offset in Keratoconus and its Relationship with Clinical and Topographical Features

PURPOSE

To evaluate the change in the location of pupillary center with corneal tomography in keratoconic patients, and determine the correlation of pupillary offset with clinical and topographical features of keratoconus.

METHODS

Ninety-one eyes of the 54 patients with keratoconus in different stages and 39 eyes of 39 refractive surgery candidates with normal corneas were included in our study. Ocular aberrations and the pupillary offset parameters (x-offset and y-offset) over a 5 mm (undilated) pupil were measured with a Sirius corneal tomographer. A correlation analysis among the pupillary offset parameters and the possible determinative variables (topographical and tomographical parameters, corneal aberrations and best corrected visual acuity) was performed.

RESULTS

The mean pupillary offset was significantly greater in the keratoconic eyes compared with the controls (p = 0.003), and the difference was mostly due to the y-offset (p = 0.03). There was no significant difference between the groups in the mean horizontal pupillary offset value (p = 0.07). Both the vertical and the total pupillary offset values correlated significantly (p < 0.0001) with the keratoconus stage (r = 0.58 and r = 0.51, respectively). They also correlated with the corneal aberrations, and negatively correlated with the visual acuity.

CONCLUSIONS

The pupillary offset seems to correlate with the clinical and topographic features of keratoconus. It may be important to quantify its magnitude and direction in order to ensure correct centralization of the corneal procedures.

Topographic, Tomographic, and Aberrometric Characteristics of Post-LASIK Ectasia

PURPOSE

To report the refractive, topographic, tomographic, and aberrometric characteristics of post-LASIK ectasia; to compare these characteristics with normal post-LASIK controls; and to propose a comprehensive system to grade the severity of post-LASIK ectasia.

METHODS

The refraction, corrected distance visual acuity (CDVA), magnitude, and location of the steepest and thinnest point on the cornea, the highest anterior and posterior surface elevation, the radius of best fit sphere, corneal asphericity, and corneal aberrations were measured in 50 eyes of 29 patients with post-LASIK ectasia. These were compared with corresponding parameters in 50 eyes that did not develop ectasia for more than 1 year after LASIK. A logistic regression analysis was used to create a scoring system to grade the severity.

RESULTS

Eyes with post-LASIK ectasia had significantly higher myopia with astigmatism and a lower CDVA than control eyes. Mean topographic toricity was 3.4 ± 1.9D, mean keratometry at the steepest point was 55.32 ± 6.63D, mean highest posterior elevation was 69.72 ± 3 μm, and mean coma was -2.06 ± 1.2 μm. All these parameters were significantly higher than corresponding values in the control group (p < 0.001 in all). Spherical aberration was more negative and the change in asphericity indicated significantly greater prolate shape of the cornea in eyes with post-LASIK ectasia compared to controls. Five parameters, namely, CDVA, spherical equivalent, highest posterior corneal elevation, spherical aberration, and corneal asphericity, were identified as significant predictors of post-LASIK ectasia and used to create a scoring system.

CONCLUSION

Post-LASIK ectasia is characterized by significant changes in refraction, topography, tomography, and aberrometry. The proposed scoring system may be useful in diagnosing, grading, and monitoring post-LASIK ectasia.

Subclinical keratoconus detection by pattern analysis of corneal and epithelial thickness maps with optical coherence tomography

PURPOSE

To screen for subclinical keratoconus by analyzing corneal, epithelial, and stromal thickness map patterns with Fourier-domain optical coherence tomography (OCT).

SETTING

Four centers in the United States.

DESIGN

Cross-sectional observational study.

METHODS

Eyes of normal subjects, subclinical keratoconus eyes, and the topographically normal eye of a unilateral keratoconus patient were studied. Corneas were scanned using a 26,000 Hz Fourier-domain OCT system (RTVue). Normal subjects were divided into training and evaluation groups. Corneal, epithelial, and stromal thickness maps and derived diagnostic indices, including pattern standard deviation (PSD) variables and pachymetric map-based keratoconus risk scores, were calculated from the OCT data. Area under the receiver operating characteristic curve (AUC) analysis was used to evaluate the diagnostic accuracy of the indices.

RESULTS

The study comprised 150 eyes of 83 normal subjects, 50 subclinical keratoconus eyes of 32 patients, and 1 topographically normal eye of a unilateral keratoconus patient. Subclinical keratoconus was characterized by inferotemporal thinning of the cornea, epithelium, and stroma. The PSD values for corneal (P < .001), epithelial (P < .001), and stromal (P = .049) thickness maps were all significantly higher in subclinical keratoconic eyes than in the normal group. The diagnostic accuracy was significantly higher for PSD variables (pachymetric PSD, AUC = 0.941; epithelial PSD, AUC = 0.985; stromal PSD, AUC = 0.924) than for the pachymetric map-based keratoconus risk score (AUC = 0.735).

CONCLUSIONS

High-resolution Fourier-domain OCT could map corneal, epithelial, and stromal thicknesses. Corneal and sublayer thickness changes in subclinical keratoconus could be detected with high accuracy using PSD variables. These new diagnostic variables might be useful in the detection of early keratoconus.

FINANCIAL DISCLOSURES

Oregon Health and Science University (OHSU) and Drs. Li, Tan, and Huang have a significant financial interest in Optovue, Inc. These potential conflicts have been reviewed and managed by OHSU. Dr. Brass receives research grants from Optovue, Inc. Drs. Chamberlain and Weiss have no financial or proprietary interest in any material or method mentioned.

Correlation between visual function and refractive, topographic, pachymetric and aberrometric data in eyes with keratoconus

AIM

To analyze the relationship between two visual functions and refractive, topographic, pachymetric and aberrometric indicators in eyes with keratoconus.

METHODS

Corrected distance visual acuity (CDVA), and letter contrast sensitivity (CS) were correlated with refraction, corneal topography, pachymetry, and total corneal wavefront data prospectively in 71 eyes with keratoconus. The topographic indices assessed were simulated keratometry for the flattest and steepest meridians (SimK1 and SimK2), posterior steeper K (Ks), elevation value in best-fit sphere (BFS) maps, squared eccentricity (Є(2)), aspheric asymmetric index (AAI), pachymetry, thickness progression index (TPI), the amount of pachymetric decentralization (APD), and GalileiTM-keratoconus indices.

RESULTS

The mean CDVA (expressed as logMAR) were 0.25±0.21. The mean CS was 1.25±0.46. The spherical refraction correlated well with CDVA (r=-0.526, P<0.001). From topographic indices, SRI correlated with CS (r=-0.695), and IAI with CS (r=-0.672) (P<0.001 for all). Root mean square (RMS) was 4.3±1.81 µm, spherical aberration (SA) was -0.4±0.67 µm, vertical and horizontal coma were -2.1±1.47 and -0.4±0.72 µm. All wavefront data (except horizontal coma), AAI, Є(2) and maximum BFS correlated significantly with the visual function (P≤0.001 for all).

CONCLUSION

In this study, CS is more affected than CDVA as a visual function. The quantity and quality of vision is significantly correlated with well-known and new topographic indices. There is not a significant correlation between visual function and pachymetric parameters. The significantly correlated indices can be used in staging keratoconus and to follow the outcome of a treatment.

Detection of Keratoconus in Clinically and Algorithmically Topographically Normal Fellow Eyes Using Epithelial Thickness Analysis

PURPOSE

To assess the effectiveness of a keratoconus-detection algorithm derived from Artemis very high-frequency (VHF) digital ultrasound (ArcScan Inc., Morrison, CO) epithelial thickness maps in the fellow eye from a series of patients with unilateral keratoconus.

METHODS

The study included 10 patients with moderate to advanced keratoconus in one eye but a clinically and algorithmically topographically normal fellow eye. VHF digital ultrasound epithelial thickness data were acquired and a previously developed classification model was applied for identification of keratoconus to the clinically normal fellow eyes. Pentacam (Oculus Optikgeräte, Wetzlar, Germany) Belin-Ambrósio Enhanced Ectasia Display "D" score (BAD-D) data (5 of 10 eyes), and Orbscan (Bausch & Lomb, Rochester, NY) SCORE data (9 of 10 eyes) were also evaluated.

RESULTS

Five of the 10 fellow eyes were classified as keratoconic by the VHF digital ultrasound epithelium model. Five of 9 fellow eyes were classified as keratoconic by the SCORE model. For the 5 fellow eyes with Pentacam and VHF digital ultrasound data, one was classified as keratoconic by the VHF digital ultrasound model, one (different) eye by a combined VHF digital ultrasound and Pentacam model, and none by BAD-D alone.

CONCLUSIONS

Under the assumption that keratoconus is a bilateral but asymmetric disease, half of the 'normal' fellow eyes could be found to have keratoconus using epithelial thickness maps. The Orbscan SCORE or the combination of topographic BAD-D criteria with epithelial maps did not perform better.

Effect of fibrin glue on corneal lamellar healing and how it correlates to biomechanical properties: biomechanical wavefront analysis and confocal study

Background

To evaluate, using a rabbit model, the influence of the wound healing process at the flap edge on corneal biomechanics after sutured, glued, and non-augmented microkeratome flaps.

Methods

Unilateral 160 μm thick laser in situ keratomileusis (LASIK) flaps using a mechanical microkeratome were performed on the corneas of the left eyes of 36 rabbits. Animals were then divided into 3 groups of 12 rabbits each: A: the flaps were glued with human fibrin tissue adhesive (Tisseel); B: the flaps were sutured; and C: the flaps were allowed to heal without the use of sutures or glue (non-augmented). The contralateral eyes served as controls. Reichert ocular response analyzer (ORA) was used to measure corneal hysteresis (CH), corneal resistance factor (CRF), Goldmann-correlated intraocular pressure (IOPg) and cornea-compensated IOP (IOPcc) at 6 weeks and 3 months postoperatively. In vivo confocal microscopy (IVCM) was also used to study the corneal wound healing process in all groups.

Results

Both mean CH and mean CRF were significantly higher in sutured and glued groups compared with the non-augmented group at 6 weeks and 3 months postoperatively (P  < 0.0001). No statistically significant difference in corneal biomechanics was found between controls and groups A and B at any time points. Activated keratocytes were detected at the wound edge and peripheral flap interface in sutured and glued groups.

Conclusion

The healing process at the wound edge is critical for optimal corneal integrity. Fibrin glue may serve as a safe and effective substitute to sutures in enhancing the corneal flap edge healing response and in increasing its mechanical strength.

Long-term evaluation of eyes with central corneal thickness <400 μm following laser in situ keratomileusis

Purpose

To study long-term refractive and visual outcomes of laser in situ keratomileusis (LASIK) in eyes with a postoperative thin central cornea.

Methods

In this retrospective observational case series, we studied 282 myopic eyes with a normal preoperative topographic pattern and postoperative thin corneas (<400 μm) that had at least 3 years of follow-up after LASIK in three private clinics. The main outcome measures were safety, efficacy, predictability, percent tissue altered, and complications.

Results

The mean postoperative central corneal thickness was 392.05 μm (range: 363.00–399.00 μm). After a mean follow-up of 6.89±2.35 years (standard deviation), the safety index was 1.17, the efficacy index was 0.94, and predictability (±1.00 diopter [D]) was 73.49. The mean residual stromal bed thickness was 317.34±13.75 μm (range: 275–356 μm), the mean flap thickness was 74.76±13.57 μm (range: 55–124 μm), and the mean percent tissue altered was 37.12%±3.62% (range: 27.25%–49.26%). No major complications were recorded.

Conclusion

LASIK with a resultant central cornea thickness <400 μm seems to be effective, safe, and predictable provided that preoperative topography is normal and the residual stromal bed thickness is >275 μm.

Contralateral Eye Comparison Between Femtosecond Small Incision Intrastromal Lenticule Extraction at Depths of 100 and 160 μm

PURPOSE

To compare the visual results, higher-order aberrations, and corneal biomechanical properties of femtosecond small incision lenticule extraction (SMILE) at depths of 100 and 160 μm.

METHODS

A prospective comparative interventional clinical trial of a series of patients who underwent SMILE. In the right eye, a refractive lenticule was created at a depth of 100 μm, and in the left eye, a depth of 160 μm was used. Manifest refraction, uncorrected visual acuity, total high-order aberrations (THOA), and corneal biomechanical properties of both eyes were evaluated 1 month postoperatively.

RESULTS

Thirty patients with bilaterally stable refractive errors were included in this study. One month postoperatively, mean corneal hysteresis was 9.71 ± 0.68 in the right eyes and 9.97 ± 0.77 in the left eyes, whereas the mean corneal resistant factor was 9.13 ± 1.04 and 9.31 ± 0.92 in the right and left eyes, respectively. Both corneal hysteresis and corneal resistant factor showed statistically significantly higher values in the left eyes (lenticule at a depth of 160 μm). No statistically significant differences were found between the right and the left eyes regarding manifest refraction, uncorrected visual acuity, and THOA.

CONCLUSIONS

Creating the refractive lenticule at a depth of 160 μm in SMILE had less effect on the corneal biomechanics than did creating a lenticule at a depth of 100 μm with no statistically significant differences in the refractive outcome and THOA between both groups.

In-vivo corneal biomechanical analysis of unilateral keratoconus

AIM

To evaluate and compare corneal biomechanical findings measured by ocular response analyzer, topographic and pachymetric findings in patients with unilateral keratoconus patients and healthy controls.

METHODS

This is an observational, case-control study. Patients with keratoconus in one eye and forme fruste keratoconus in the fellow eye were compared with sex and age matched with controls healthy subjects. All subjects were evaluated with rotating scheimpflug imaging system. The receiver-operating-characteristic curves were analyzed to evaluate the sensitivity and specificity of the parameters.

RESULTS

Twenty-seven patients with keratoconus in one eye and forme fruste keratoconus in the fellow eye were compared with 40 eyes of 40 normal subjects. Corneal hysteresis (CH) was 8.0±1.7 mm Hg in keratoconus group, 8.3±1.6 mm Hg in forme fruste keratoconus group, and 9.8±1.6 mm Hg in control groups (P=0.54 between keratoconus and forme fruste keratoconus groups, P<0.01 between control group and other groups). Corneal resistance factor (CRF) was 7.1±2.2 mm Hg in keratoconus group, 7.8±1.2 mm Hg in forme fruste keratoconus group and 9.9±1.5 mm Hg in control group (P<0.001 between control group and other groups). Using receiver-operating-characteristic analysis, the area under curve values of the parameters to distinguish forme fruste keratoconus from control subjects were: CH (0.768), CRF (0.866). Best cut-off points were 9.3 mm Hg and 8.8 mm Hg for CH and CRF respectively.

CONCLUSION

Ocular response analyzer parameters (CH and CRF) are found to be significantly lower in forme fruste keratoconus patients compared to normal control subjects.

Ocular response analyzer parameters in healthy, keratoconus suspect and manifest keratoconus eyes

Background:

To evaluate and compare corneal biomechanical indices and their specificity among keratoconus (KC), keratoconus suspect (KCS), and normal eyes (NL) before and after controlling potential confounders.

Materials and Methods:

A total of 160 eyes in three groups were included prospectively: NL, KC, and KCS groups based on clinical examination and topography. Corneal hysteresis (CH) and corneal resistance factor (CRF) were measured by the ocular response analyzer. CH and CRF were compared between the three groups by analysis of variances test.

Results:

The three groups consisted of 80 NL, 48 KC, and 32 KCS eyes. The mean CH measured was 10.4 ± 1.25, 7.83 ± 1.28 and 10.17 ± 1.80 mm Hg in NL, KC and KCS eyes, respectively. The mean CRF was 10.23 ± 1.75, 6.5 ± 1.63 and 9.98 ± 2.00 mm Hg in NL, KC and KCS eyes, respectively. Mean CH and CRF were significantly different between the NL and KC (P < 0.05); however after controlling for central corneal thickness and sex; there was no significant difference between NL and KCS (P > 0.05).

Conclusion:

CH and CRF can be helpful in differentiating KC from NL eyes; however, they are not valuable for detecting KCS that is the main concern for refractive surgery. Future studies focusing on more accurate tests for identifying KCS, using a consistent grading scale for defining KC and KCS are still warranted.

Posterior Corneal Surface Stability after Femtosecond Laser-Assisted Keratomileusis

The purpose of this study was to evaluate posterior corneal surface variation after femtosecond laser-assisted keratomileusis in patients with myopia and myopic astigmatism. Patients were evaluated by corneal tomography preoperatively and at 1, 6, and 12 months. We analyzed changes in the posterior corneal curvature, posterior corneal elevation, and anterior chamber depth. Moreover, we explored correlation between corneal ablation depth, residual corneal thickness, percentage of ablated corneal tissue, and preoperative corneal thickness. During follow-up, the posterior corneal surface did not have a significant forward corneal shift: no significant linear relationships emerged between the anterior displacement of the posterior corneal surface and corneal ablation depth, residual corneal thickness, or percentage of ablated corneal tissue.

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.

Effects of laser in situ keratomileusis (LASIK) on corneal biomechanical measurements with the Corvis ST tonometer

Purpose

This study was initiated to evaluate biomechanical changes using the Corvis ST tonometer (CST) on the cornea after laser in situ keratomileusis (LASIK).

Setting

University Medical Center Hamburg-Eppendorf, Germany, and Care Vision Refractive Centers, Germany.

Design

Retrospective cohort study.

Methods

This retrospective study included 37 eyes of 37 refractive patients. All CST measurements were performed 1 day before surgery and at the 1-month follow-up examination. The LASIK procedure included mechanical flap preparation using a Moria SBK microkeratome and an Allegretto excimer laser platform.

Results

Statistically significant differences were observed for mean first applanation length, mean first and second deflection lengths, mean first and second deflection amplitudes, radius of curvature, and peak distance. Significant positive correlations were found between the change (Δ) of radius of curvature and manifest refraction spherical equivalent (MRSE), ablation depth, and Δintraocular pressure as well as between AD and ΔHC-time. Each diopter of myopic correction in MRSE resulted in an increase in Δradius of curvature of 0.2 mm.

Conclusion

Several CST parameters were statistically significantly altered by LASIK, thereby indicating that flap creation, ablation, or both, significantly change the ability of the cornea to absorb or dissipate energy.

Reliability of corneal dynamic scheimpflug analyser measurements in virgin and post-PRK eyes

Purpose

To determine the measurement reliability of CorVis ST, a dynamic Scheimpflug analyser, in virgin and post-photorefractive keratectomy (PRK) eyes and compare the results between these two groups.

Methods

Forty virgin eyes and 42 post-PRK eyes underwent CorVis ST measurements performed by two technicians. Repeatability was evaluated by comparing three consecutive measurements by technician A. Reproducibility was determined by comparing the first measurement by technician A with one performed by technician B. Intraobserver and interobserver intraclass correlation coefficients (ICCs) were calculated. Univariate analysis of covariance (ANCOVA) was used to compare measured parameters between virgin and post-PRK eyes.

Results

The intraocular pressure (IOP), central corneal thickness (CCT) and 1_st applanation time demonstrated good intraobserver repeatability and interobserver reproducibility (ICC≧0.90) in virgin and post-PRK eyes. The deformation amplitude showed a good or close to good repeatability and reproducibility in both groups (ICC≧0.88). The CCT correlated positively with 1_st applanation time (r = 0.437 and 0.483, respectively, p<0.05) and negatively with deformation amplitude (r = −0.384 and −0.375, respectively, p<0.05) in both groups. Compared to post-PRK eyes, virgin eyes showed longer 1_st applanation time (7.29±0.21 vs. 6.96±0.17 ms, p<0.05) and lower deformation amplitude (1.06±0.07 vs. 1.17±0.08 mm, p<0.05).

Conclusions

CorVis ST demonstrated reliable measurements for CCT, IOP, and 1_st applanation time, as well as relatively reliable measurement for deformation amplitude in both virgin and post-PRK eyes. There were differences in 1_st applanation time and deformation amplitude between virgin and post-PRK eyes, which may reflect corneal biomechanical changes occurring after the surgery in the latter.

Pentacam Scheimpflug tomography findings in topographically normal patients and subclinical keratoconus cases

PURPOSE

To evaluate Pentacam ectasia detection indices in topographically normal patients and in subclinical keratoconus cases.

DESIGN

Prospective, observational case series.

METHODS

setting: Institutional. patients: Group 1 comprised 1 eye from 189 patients with unremarkable topography and Groups 2 and 3 included the better and worse eyes, respectively, of 55 keratoconic patients. Group 2 eyes with normal topography (n = 37) were considered subclinical keratoconus cases. observation procedure: Pentacam Scheimpflug tomography. main outcome measures: Eleven Pentacam ectasia detection indices.

RESULTS

All Pentacam ectasia indices significantly differed between Groups 1 and 2 and were correlated with keratoconus grade. Only 99 eyes (52%) in Group 1 had normal values for every index, whereas 7 subclinical keratoconus eyes (19%) showed 2 or fewer abnormal indices. Standardized relational thickness and overall deviation indices had 73% and 89% sensitivity for subclinical keratoconus, respectively. Both average and maximum pachymetric progression indices offered 84% sensitivity while maximum relational thickness index showed 78% sensitivity for subclinical keratoconus. Optimized cutoff values for subclinical keratoconus increased the sensitivity of the standardized and maximum relational thickness indices.

CONCLUSION

Pentacam Scheimpflug tomography can detect most subclinical keratoconus cases with unremarkable topography, but performance is not as good as reported and varies considerably for each index. The overall deviation, average and maximum pachymetric progression, and maximum relational thickness indices offer the highest sensitivity, which can be improved by using optimized cutoff values. Specificity constitutes an issue for some indices and up to 10% of subclinical keratoconus cases may go undetected by this technology.

Association between the percent tissue altered and post-laser in situ keratomileusis ectasia in eyes with normal preoperative topography

PURPOSE

To investigate the association of a novel metric, percent tissue altered, with the occurrence of ectasia after laser in situ keratomileusis (LASIK) in eyes with normal corneal topography and to compare this metric with other recognized risk factors.

DESIGN

Retrospective case-control study.

METHODS

The study included 30 eyes from 16 patients with bilateral normal preoperative Placido-based corneal topography that developed ectasia after LASIK (ectasia group) and 174 eyes from 88 consecutive patients with uncomplicated LASIK and at least 3 years of postoperative follow-up. The following metrics were evaluated: age, preoperative central corneal thickness, residual stromal bed, Ectasia Risk Score System scores, and percent tissue altered, derived from [PTA = (FT + AD)/CCT], where FT = flap thickness, AD = ablation depth, and CCT = preoperative central corneal thickness.

RESULTS

In the ectasia group, percent tissue altered ≥40 was the most prevalent factor (97%), followed by age <30 years (63%), residual stromal bed ≤300 μm (57%), and ectasia risk score ≥ 3 (43%) (P < .001 for all). Percent tissue altered ≥ 40 had the highest odds ratio (223), followed by residual stromal bed ≤ 300 μm (74) and ectasia risk score ≥ 4 (8). Stepwise logistic regression revealed percent tissue altered ≥ 40 as the single most significant independent variable (P < .0001).

CONCLUSIONS

Percent tissue altered at the time of LASIK was significantly associated with the development of ectasia in eyes with normal preoperative topography and was a more robust indicator of risk than all other variables in this patient population.

Biomechanics of corneal ectasia and biomechanical treatments

Many algorithms exist for the topographic/tomographic detection of corneas at risk for post-refractive surgery ectasia. It is proposed that the reason for the difficulty in finding a universal screening tool based on corneal morphologic features is that curvature, elevation, and pachymetric changes are all secondary signs of keratoconus and post-refractive surgery ectasia and that the primary abnormality is in the biomechanical properties. It is further proposed that the biomechanical modification is focal in nature, rather than a uniform generalized weakening, and that the focal reduction in elastic modulus precipitates a cycle of biomechanical decompensation that is driven by asymmetry in the biomechanical properties. This initiates a repeating cycle of increased strain, stress redistribution, and subsequent focal steepening and thinning. Various interventions are described in terms of how this cycle of biomechanical decompensation is interrupted, such as intrastromal corneal ring segments, which redistribute the corneal stress, and collagen crosslinking, which modifies the basic structural properties.

FINANCIAL DISCLOSURES

Proprietary or commercial disclosures are listed after the references.

Corneal topographic and tomographic analysis of fellow eyes in unilateral keratoconus patients using Pentacam

PURPOSE

To evaluate topographic and tomographic changes in fellow eyes in unilateral keratoconus (KCN) patients by comparing them with normal eyes.

DESIGN

Retrospective comparative case series.

METHODS

Fourteen eyes of 14 patients with unilateral KCN and 34 eyes of 34 refractive surgery candidates were divided into 3 diagnostic groups using a Pentacam rotating Scheimpflug camera: advanced KCN eyes of unilateral KCN (KCN group, 14 eyes), normal fellow eyes of unilateral KCN (fellow eye group, 14 eyes), and refractive surgery candidates (normal group, 34 eyes). Topographic and tomographic parameters, which were obtained from Pentacam using sagittal curvature, elevation, and corneal thickness maps, were compared among the 3 groups. Receiver operating characteristic (ROC) curves were used to identify cutoff points in discriminating between fellow and normal eyes.

RESULTS

Keratometric asymmetry, topometric indices, and elevation differences (maximum - minimum) on both the anterior and posterior surfaces were statistically different (P < .05). On ROC curve analysis, keratometric asymmetry and topometric index were best at discriminating fellow eyes from normal, followed by elevation differences (maximum - minimum) on the posterior and anterior cornea surface.

CONCLUSIONS

Fellow eyes in unilateral KCN showed differences in several parameters that were not detectable with the Pentacam detection program, when compared with normal. However, each single parameter alone is not sufficient to detect early changes; thus, elevation indices as well as indices of anterior curvature should be considered together.

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).

Evaluation of corneal microstructure in keratoconus: a confocal microscopy study

PURPOSE

To compare the corneal microstructure in patients with manifest keratoconus (KCN), subclinical KCN, and topographically normal relatives of patients with KCN and in healthy controls.

DESIGN

Prospective and cross-sectional study.

METHODS

We enrolled 145 subjects in the study. The participants were divided into 4 groups, based on clinical and topographical evaluation: the manifest KCN group (n = 30), the subclinical KCN group (n = 32), the KCN relatives group (n = 53), and the control group (n = 30). Corneal microstructure was assessed by corneal in vivo confocal microscopy in all of the individuals. Mean outcome measures were basal epithelial cell density, endothelial cell density, anterior keratocyte density, posterior keratocyte density, sub-basal nerve density, sub-basal nerve diameter, and stromal nerve diameter.

RESULTS

The mean basal epithelial cell density, endothelial cell density, and sub-basal nerve diameter were not significantly different among the 4 groups (P = 0.057, P = 0.592, and P = 0.393, respectively). The mean anterior and posterior stromal keratocyte densities were significantly lower in the manifest group, in the subclinical group, and in the relatives group when compared with the control group (for both parameters; P < 0.001, P < 0.001, and P< 0.001, respectively). The mean stromal nerve diameter in the manifest group, subclinical group, and relatives group was significantly higher than in the control group (P = 0.001, P = 0.049, and P = 0.004, respectively).

CONCLUSION

The anterior and posterior stromal keratocyte densities were statistically lower and stromal nerve diameter was statistically higher in patients with manifest KCN, subclinical KCN, and topographically normal KCN relatives compared with controls. Confocal microscopy may be useful for the determination of early corneal microstructural changes before manifestation of typical or subtle topographic signs.

Combining ocular response analyzer metrics for corneal biomechanical diagnosis

PURPOSE

To evaluate corneal biomechanical properties in non-keratoconic myopic eyes and to identify descriptors for improving the specificity of the Ocular Response Analyzer (ORA) (Reichert Ophthalmic Instruments, Depew, NY) testing for subclinical keratoconus detection.

METHODS

Observational case series of 52 non-keratoconic non-myopic eyes and 97 non-keratoconic myopic eyes (spherical equivalent < -5 diopters [D]) in dataset 1 and 87 non-keratoconic eyes and 73 eyes with subclinical keratoconus in dataset 2. Examination included corneal topography, tomography, and biomechanical testing with the ORA. Receiver operating characteristic curves and logistic regression were used to identify optimal combinations of biomechanical indices for keratoconus detection. Main outcome measures were corneal thickness-corrected hysteresis (DifCH) and resistance factor (DifCRF), the difference between these two (CH-CRF), and the diagnostic performance of their combinations.

RESULTS

Compared to non-keratoconic non-myopic eyes, non-keratoconic myopic eyes with flat corneas (average corneal power < 44.0 D) had reduced DifCH (mean ± standard deviation, 0.11 ± 1.27 vs -0.79 ± 1.50, P < .01) and DifCRF (0.24 ± 1.16 vs -0.70 ± 1.59, P < .01) values, whereas non-keratoconic myopic eyes with steep corneas showed no difference. Keratoconic eyes exhibited lower DifCH and DifCRF values than non-keratoconic myopic eyes. Combinations of DifCH, DifCRF, and CH-CRF had increased specificity (> 80%) for subclinical keratoconus compared to the DifCRF index alone (71%).

CONCLUSIONS

In biomechanical keratoconus screening, some non-keratoconic myopic eyes show altered ocular biomechanical properties and are identified as false-positive cases. The low specificity of DifCRF when dealing with these non-keratoconic eyes could be improved by considering additional biomechanical descriptors such as DifCH and CH-CRF, which seem to be indicative of the aforementioned biomechanical profile.

Laser in situ keratomileusis in 2012: a review

Laser in situ keratomileusis (LASIK) is a safe and effective treatment for refractive error. A combination of technological advances and increasing surgeon experience has served to further refine refractive outcomes and reduce complication rates. In this article, we review LASIK as it stands in late 2012: the procedure, indications, technology, complications and refractive outcomes.

Ablation depth and its effects on corneal biomechanical changes in laser in situ keratomileusis and epipolis laser in situ keratomileusis

To assess the corneal biomechanical parameters prior to and following laser in situ keratomileusis (LASIK) and epipolis laser in situ keratomileusis (epi-LASIK) and evaluate the probable correlative factors. Corneal hysteresis (CH), corneal resistance factor (CRF) and other biomechanical metrics were measured and evaluated with an ocular response analyzer preoperatively and 1 month postoperatively. Compared with preoperative values, CH and CRF decreased significantly after surgery in both groups (P = 0.000). The LASIK group exhibited a positive correlation between ablation depth (AD) and ∆CH/∆CRF with a strong r value (r = 0.543, P = 0.000; r = 0.574, P = 0.000). In the epi-LASIK group, however, the correlation was much weaker (r = -0.090, P = 0.682; r = 0.093, P = 0.673), although there were no significant differences between LASIK and epi-LASIK groups in postoperative CH (P = 0.730) and CRF (P = 0.736), and in the changes between CH (P = 0.539) and CRF (P = 0.881). Corneal biomechanical changes correlated with AD in LASIK but not in epi-LASIK, and it appeared that patients with identical demographics and similar attempted corrections are more likely to face a greater danger when undergoing LASIK than epi-LASIK. Therefore, the surface ablation procedure was recommended instead of lamellar ablation especially for correcting high myopia from a biomechanical viewpoint.

In vivo biocompatibility of two PEG/PAA interpenetrating polymer networks as corneal inlays following deep stromal pocket implantation

This study compared the effects of implanting two interpenetrating polymer networks (IPNs) into rabbit corneas. The first (Implant 1) was based on PEG-diacrylate, the second (Implant 2) was based on PEG-diacrylamide. There were inserted into deep stromal pockets created using a manual surgical technique for either 3 or 6 months. The implanted corneas were compared with normal and sham-operated corneas through slit lamp observation, anterior segment optical coherence tomography, in vivo confocal scanning and histological examination. Corneas with Implant 1 (based on PEG-diacrylate) developed diffuse haze, ulcers and opacities within 3 months, while corneas with Implant 2 (based on PEG-diacrylamide) remained clear at 6 months. They also exhibited normal numbers of epithelial cell layers, without any immune cell infiltration, inflammation, oedema or neovascularisation at post-operative 6 month. Morphological studies showed transient epithelial layer thinning over the hydrogel inserted area and elevated keratocyte activity at 3 months; however, the epithelium thickness and keratocyte morphology were improved at 6 months. Implant 2 exhibited superior in vivo biocompatibility and higher optical clarity than Implant 1. PEG-diacrylamide-based IPN hydrogel is therefore a potential candidate for corneal inlays to correct refractive error.

Corneal crosslinking with riboflavin and ultraviolet A. Part II. Clinical indications and results

Changes in the biomechanical properties of the human cornea play an important role in the pathogenesis of corneal ectatic diseases. A variety of conditions in primary acquired (keratoconus and pellucid marginal degeneration) or secondary induced (iatrogenic keratectasia after excimer refractive laser surgery) corneal ectatic disorders lead to reduced biomechanical resistance. Corneal collagen crosslinking (CXL) has emerged as a promising technique to slow or even to stop the progression of these corneal ectatic pathologies. In this procedure, riboflavin (vitamin B2) is administered in conjunction with ultraviolet A light (UVA, 365 nm). This interaction causes the formation of reactive oxygen species, leading to the formation of additional covalent bonds between collagen molecules, with consequent biomechanical stiffening of the cornea. Although this method is not yet accepted as an evidence-based medicine modality for the treatment of corneal primary or secondary ectasias, the results of prospective, randomized studies of CXL used in the treatment of these pathologic entities show significant changes in the properties of corneal tissue. This procedure is currently the only etiopathogenetic approach in ectatic eyes that can delay or stop the process of cornea destabilization, reducing the necessity for keratoplasty. Despite promising results, CXL is associated with issues that include long-term safety and duration of the stabilizing effect. Combination of CXL with vision-improving procedures, such as topography-guided custom ablation and implantation of intracorneal ring segments of phakic intraocular lenses, may expand the indications for this procedure.

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.

Effect of timolol on refractive outcomes in eyes with myopic regression after laser in situ keratomileusis: a prospective randomized clinical trial

PURPOSE

To compare the effects of timolol on refractive outcomes in eyes with myopic regression after laser in situ keratomileusis (LASIK) with a control-matched group.

DESIGN

Prospective, randomized, parallel-controlled, double-masked clinical trial. A computer-generated randomization list based on random block permutation (length 4 to 8) was used for treatment allocation.

METHODS

setting: Basir Eye Center, Tehran, Iran.

PATIENT POPULATION

Of 124 eyes with myopic regression after LASIK using Technolas 217-Z, 45 eyes in each group were analyzed.

INTERVENTION

Patients were randomly assigned into either Group 1, who received timolol 0.5% eye drops, or Group 2, who received artificial tears for 6 months.

MAIN OUTCOME MEASURE

Spherical equivalent (SE) at 6 months posttreatment.

RESULTS

In Group 1, SE improved from -1.48 ± 0.99 diopter (D) before treatment to -0.88 ± 0.91 D and -0.86 ± 0.93 D 6 months after treatment and 6 months after timolol discontinuation, respectively (P < .001). In Group 2, it was -1.57 ± 0.67 D, -1.83 ± 0.76 D, and -1.91 ± 0.70 D, respectively (P < .001). SE was significantly better in Group 1 6 months after treatment and 6 months after discontinuation of treatment (P < .001 for both comparisons). There was a 0.26 D decrease in SE improvement every 4 months after the surgery in the Group 1 (P < .001).

CONCLUSIONS

Timolol application is effective for the treatment of myopic regression after LASIK compared with control group. Its effects last for at least 6 months after its discontinuation.

Post-LASIK keratectasia triggered by eye rubbing and treated with topography-guided ablation and collagen cross-linking--a case report

PURPOSE

To report a case of unilateral post-laser-assisted in situ keratomileusis (LASIK) keratectasia in a 35-year-old woman who had no known predisposing risk factors but who rubbed her affected eye frequently and vigorously in response to allergic conjunctivitis.

METHODS

Case report with relevant literature review.

RESULTS

A 35-year-old woman, with a cumulative risk scale score of 0 (according to the Randleman criteria), who underwent bilateral LASIK developed unilateral post-LASIK keratectasia 32 months later. She presented with a history of vigorous eye rubbing of the affected eye since about a year after allergic conjunctivitis. The fellow eye, which was not rubbed, remained normal. She complained of glare, halos, and ghost images in her affected eye. She underwent transepithelial topography-guided customized ablation with simultaneous UV-A corneal collagen cross-linking, after which she improved symptomatically and topographically.

CONCLUSIONS

Eye rubbing could contribute to the development of keratectasia, even in an eye that has no subclinical features of the disease. When detected early, a simultaneous combined topography-guided customized ablation treatment and collagen cross-linking is effective in improving the irregular corneal contour and restoring biomechanical stability.