Bilateral severe keratoconus after laser in situ keratomileusis in a patient with forme fruste keratoconus

Tomographic Predictors of Ectasia Development After Keratorefractive Surgery

PURPOSE

The aim of this study was to identify the risk factors for postkeratorefractive surgery ectasia in unsuspicious tomographies and to report a new index coined diameter of peak locations (DPLs).

METHODS

All patients who underwent keratorefractive surgery between 2011 and 2018 at Care-Vision Laser Centers, Israel, and later developed ectasia were included. For each ectasia case, 3 matched controls were selected. Demographic and preoperative, intraoperative, and postoperative data were collected. Multivariate analysis was performed to evaluate the interdependence of the variables.

RESULTS

The retrospective study included 19 ectasia and 58 control eyes. There were no significant differences between the groups in ablation depth ( P = 0.73), preoperative spherical equivalent ( P = 0.12), percent tissue altered ( P = 0.71), residual stromal bed ( P = 0.73), and Ectasia Risk Score System ( P = 0.60). The anterior and the posterior symmetry index were significantly higher ( P < 0.001), and DPL was significantly tighter in the ectasia group ( P = 0.01). Binary multiple logistic regression found the symmetry index of the posterior cornea and DPL to be better predictors than age, percent tissue altered, Ectasia Risk Score System, residual stromal bed, and ablation depth.

CONCLUSIONS

A higher posterior symmetry index and a tighter DPL are predictors of ectasia in patients with otherwise normal tomographies. A tight DPL implies a weak area in the cornea, which is thin and slightly bulging, increasing the risk of this area becoming ectatic.

Assessment of Keratoconus Risk in Very Asymmetric Ectasia Using Corneal Tomographic and Biomechanical Parameters

Purpose

To investigate the relationship between corneal tomographic or biomechanical parameters and risk of keratoconus in very asymmetric ectasia (VAE).

Methods

This retrospective case-control single-centre study included patients with VAE and normal controls. The VAE group had clinical ectasia in one eye and normal topography (VAE-NT) in the fellow eye; VAE-NT eyes were selected for analysis. The control group was selected from corneal refractive surgery candidates; the right eye was enrolled. Scheimpflug-based corneal tomography (Pentacam) and corneal biomechanical assessment (Corvis ST) were performed. Univariate and multivariable logistic regression were performed using Cox proportional hazards models to evaluate keratoconus-associated risk factors. A two-piecewise linear regression model was applied to examine the threshold effect of selected vital paragmeters on the risk of keratoconus according to a smoothing plot.

Results

Threshold effect between tomographic integration and risk of keratoconus was observed. Discrepancy between the central corneal thickness and thinnest corneal thickness (discrepancy CCT vs TCT) greater than 5 μm, discrepancy between the apex corneal thickness and thinnest corneal thickness (discrepancy ACT vs TCT) greater than 3 μm, vector distance between CCT and TCT (distance CCT vs TCT) greater than 0.65 mm indicated a significant increased risk of keratoconus. Risk of keratoconus decreased when distance CCT vs TCT was less than 0.65 mm.

Conclusion

Discrepancy CCT vs TCT, discrepancy ACT vs TCT, and distance CCT vs TCT can be used as indicators for risk assessment of early keratoconus.

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

Background

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

Methods

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

Results

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

Conclusion

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

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.

Tomographically normal partner eye in very asymmetrical corneal ectasia: biomechanical analysis

PURPOSE

To point out the biomechanical changes of the topographically and tomographically normal partner eye (NPE) in patients with very asymmetrical corneal ectasia.

SETTING

Department of Ophthalmology, Saarland University Medical Center in Homburg/Saar, Germany.

DESIGN

Retrospective study.

METHODS

The topographical and tomographical results of the NPE were assessed using the Pentacam HR and the biomechanical corneal properties using the Ocular Response Analyzer (keratoconus match index [KMI], corneal hysteresis [CH], and corneal resistance factor [CRF]) and the Corvis ST (topographic biomechanical index [TBI] and Corvis biomechanical index) and compared those results with a normal control group (CG).

RESULTS

The clinical records of 26 patients recruited from the Homburg Keratoconus Center diagnosed with a very asymmetrical corneal ectasia were reviewed. The NPE (8.5 ± 1.5 mm Hg) showed a significantly more pathological CH (P < .001) compared with the CG. The CRF was also significantly more pathological (P = .04) for the NPE (8.3 ± 1.5 mm Hg) compared with the CG. The NPE (0.62 ± 0.32) showed a nonsignificant (P = .08) more pathological KMI compared with the CG. Nineteen (73.1%) of 26 NPE had a KMI less than 0.72 and were considered pathological. Compared with the CG, the TBI of the NPE (0.19 ± 0.25) did not differ significantly overall (P = .57). However, 5 (19.2%) of 26 eyes had a TBI more than 0.29 and were considered pathological.

CONCLUSIONS

Topographically and tomographically NPEs in very asymmetrical corneal ectasia frequently showed biomechanical changes. This should be considered before planning any type of refractive corneal surgery in such patients.

Corneal Biomechanics in Unilateral Keratoconus and Fellow Eyes with a Scheimpflug-based Tonometer

SIGNIFICANCE

Before the appearance of evident keratoconus, corneal biomechanical changes may be detectable. Here, these properties are analyzed to detect any difference that could help in the early recognition of keratoconus to allow patients to benefit from early treatments and to avoid refractive procedures in these corneas.

PURPOSE

The purpose of this study was to compare corneal biomechanical characteristics as determined by Corvis Scheimpflug Technology tonometry between normal eyes and asymmetric keratoconic eyes.

METHODS

Retrospective data from normal eyes (n = 100), keratoconic eyes (n = 18), and their topographically normal fellow eyes (n = 18) were analyzed. Differences in the variables among the groups were determined. For the parameters that showed significant differences, the receiver operating characteristic curve and the area under the curve (AUC) were used to assess the diagnostic accuracy of each variable. The optimal cutoff points were determined when comparing normal and fellow eyes. Also, a new linear combination of variables was performed to obtain better discriminative values.

RESULTS

The following variables differed significantly between normal and fellow eyes: length of the flattened cornea in the second applanation, peak distance, curvature radius at highest concavity, and central corneal thickness. When each variable was independently considered, AUCs, sensitivity, and specificity were insufficiently high for good discrimination between the two groups. However, using a linear combination of variables, an optimal cutoff point (0.157) was obtained with an AUC of 0.78, sensitivity of 0.84, and specificity of 0.69.

CONCLUSIONS

A best predictive linear combination of corneal biomechanical variables was tested including diameter of the flattened cornea in the second applanation and central corneal thickness. This combination was considered as the best in terms of its prediction capacity, simplicity and clinical application. This formula may be useful in clinical practice to discriminate between normal eyes and incipient keratoconus.

Customised aberration-controlling corrections for keratoconic patients using contact lenses

Technological advancements in the design of soft and scleral contact lenses have led to the development of customised, aberration-controlling corrections for patients with keratoconus. As the number of contact lens manufacturers producing wavefront-guided corrections continues to expand, clinical interest in this customisable technology is also increasing among both patients and practitioners. This review outlines key issues surrounding the measurement of ocular aberrations for patients with keratoconus, with a particular focus on the possible factors affecting the repeatability of Hartmann-Shack aberrometry measurements. This review also discusses and compares the relative successes of studies investigating the design and fitting of soft and scleral customised contact lenses for patients with keratoconus. A series of key limitations that should be considered before designing customised contact lens corrections is also described. Despite the challenges of producing and fitting customised lenses, improvements in visual performance and comfortable wearing times, as provided by these lenses, could help to reduce the rate of keratoplasty in keratoconic patients, thereby significantly reducing clinical issues related to corneal graft surgery. Furthermore, enhancements in optical correction, provided by customised lenses, could lead to increased independence, particularly among young adult keratoconic patients, therefore leading to improvements in quality of life.

Correlation of the KISA% index and Scheimpflug tomography in 'normal', 'subclinical', 'keratoconus-suspect' and 'clinically manifest' keratoconus eyes

PURPOSE

To analyse tomographic changes in eyes classified as 'normal', 'keratoconus-suspect' and 'clinically manifest keratoconus' based on the established KISA% definition of Rabinowitz and Rasheed and to develop the category of 'subclinical keratoconus eyes' to expand the classification into a 'subtopographic' range.

METHODS

Tomographic and topographic analyses of 670 eyes performed with a rotating Scheimpflug imaging system (Pentacam(®), Oculus Inc., Wetzlar, Germany) were retrospectively analysed. Based on the KISA% keratoconus classification system, eyes were assigned to a 'normal', 'keratoconus-suspect' or 'manifest keratoconus' group. In addition, a new group of 'subclinical keratoconus eyes' was analysed, comprising unsuspicious fellow eyes of patients with keratoconus. T-tests, Wilcoxon rank-sum test, receiver operating characteristics (ROC) and robust regression analyses were performed to correlate tomographic parameters with the increasing KISA% index.

RESULTS

KISA%-grouped keratoconus eyes showed robust tomographic changes. By adding the subclinical group, although the concurrent topography was unchanged, we were able to demonstrate statistically significant changes for almost all tomographic parameters (parameters with highest sensitivity/specificity: ART_max, [0.69/0.69], BAD_D [0.66/0.66]). The highest coefficient of determination (R(2)) with the KISA% index was demonstrated for Ele_f_max (R(2) = 0.70), Ele_f_TP (R(2) = 0.69), Ele_b_TP (R(2) = 0.69) and BAD_D (R(2) = 0.68).

CONCLUSION

We recommend the use of the expanded KISA% index (eKISA% index) as the basis for the definition of keratoconus and normal groups in future keratoconus research projects.

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.

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).

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.

Collagen copolymer toric posterior chamber phakic intraocular lens in eyes with keratoconus

PURPOSE

To assess the safety, efficacy, stability, and predictability of collagen copolymer toric phakic intraocular lens (pIOL) implantation to correct myopia and astigmatism in eyes with keratoconus.

SETTING

Fernández-Vega Ophthalmological Institute, Oviedo, Spain.

METHODS

This prospective study comprised keratoconic eyes that had implantation of a toric Intraocular Collamer Lens. Uncorrected (UDVA) and corrected (CDVA) distance visual acuities, refraction, and postoperative complications were evaluated 1, 3, 6, and 12 months postoperatively.

RESULTS

Preoperatively, the mean spherical equivalent in the 30 eyes (21 patients) was -5.38 diopters (D) +/- 3.26 (SD) (range -13.50 to -0.63 D) and the mean cylinder, -3.48 +/- 1.24 D (range -1.75 to -6.00 D). At 12 months, 86.7% of the eyes were within +/-0.50 D of the attempted refraction and all eyes were within +/-1.00 D. For the astigmatic components J0 and J45, 83.3% of eyes and 86.7% of eyes, respectively, were within +/-0.50 D. The mean Snellen UDVA was 0.81 +/- 0.20 and the mean CDVA, 0.83 +/- 0.18; CDVA was 20/40 or better in 29 eyes 96.7% of eyes and 20/25 or better in 22 eyes (73.3%). No eyes lost more than 2 lines of CDVA; 29 eyes (96.7%) maintained or gained 1 or more lines. The efficacy index was 1.07 and the safety index, 1.16. There were no complications or adverse events.

CONCLUSIONS

The results confirm that toric ICL implantation is a predictable, effective procedure to correct ametropia in eyes with keratoconus. Predictability and stability were achieved early and remained fairly stable up to 12 months.

Stability of LASIK in topographically suspect keratoconus confirmed non-keratoconic by Artemis VHF digital ultrasound epithelial thickness mapping: 1-year follow-up

PURPOSE

To determine the 1-year stability of LASIK in corneas with topographic suspect keratoconus confirmed as non-keratoconic by epithelial thickness mapping.

METHODS

This was a retrospective case/control comparative study. Eyes suspected of keratoconus using criteria based mainly on Atlas (Carl Zeiss Meditec AG) and Orbscan II (Bausch & Lomb) topography were scanned by Artemis very high-frequency digital ultrasound (ArcScan Inc). Keratoconus was confirmed if the epithelial thickness profile showed relative epithelial thinning coincident with an eccentric posterior elevation best-fit sphere apex. Laser in situ keratomileusis was performed in all eyes where keratoconus was excluded by finding relatively thicker epithelium or not finding localized thinning over the topographically suspected cone. Patients were followed for 1 year after LASIK. A control group was generated matched within 0.50 diopter (D) for sphere, cylinder, and spherical equivalent refraction (SEQ) to compare refractive stability.

RESULTS

The average change in SEQ between 3 and 12 months was -0.10+/-0.30 D for the suspect keratoconus group and -0.10+/-0.28 D for controls. No statistically significant difference in shift from 3 months to 12 months in SEQ or cylinder between groups was noted. No statistically significant change in best spectacle-corrected visual acuity between groups was noted, with no eye losing 2 lines and 5% in the suspect keratoconus group and 2% of controls losing 1 line. No cases of ectasia were observed in either group.

CONCLUSIONS

Suspect keratoconus, confirmed to be non-keratoconic by epithelial thickness profile criteria demonstrated equal stability to control eyes 1 year after LASIK. Epithelial thickness profiles may enable LASIK to be performed in eyes that would otherwise have been excluded due to topographic suspect keratoconus. Further follow-up is being carried out.

Mild topographic abnormalities that become more suspicious on Scheimpflug imaging

PURPOSE

Although several screening methods exist, postoperative corneal ectasia after refractive surgery is a severe complication. One possibility for this might be the fact that screening methods may fail in detection of preoperative risk factors such as forme fruste keratoconus (FFKC).

METHODS

Retrospective evaluation of four cases that showed only mild changes of FFKC on placido-based topography but revealed indicative findings on Scheimpflug imaging (Pentacam).

RESULTS

While in placido-based topography evaluation of corneal topography did not show a clear FFKC, the evaluation of corneal topography on Scheimpflug imaging together with the data of spatial corneal thickness revealed distinctive FFKC in all cases presented.

CONCLUSIONS

Although both methods bear the risk of not detecting pre-existing FFKC, Scheimpflug imaging seems superior to placido-based corneal topography alone.

Myopic phakic STAAR collamer posterior chamber intraocular lenses for keratoconus

PURPOSE

To evaluate the efficacy, predictability, and safety of myopic phakic posterior chamber Implantable Collamer Lens (ICL) to correct myopia associated with keratoconus.

METHODS

In a prospective, noncomparative, interventional case series, outcomes in 25 consecutive keratoconus eyes of 16 patients, myopia from -3.00 to -18.00 diopters (D) and astigmatism from -0.50 to -3.00 D, were analyzed 12 months after implantation of myopic ICLs (STAAR Surgical). All eyes showed best spectacle-corrected visual acuity (BSCVA) > or =20/50, central keratometric values < or =52.00 D, and refractive cylinder < or =3.00 D. Myopic ICL implantation was performed through a corneal incision in the steepest meridian.

RESULTS

The mean uncorrected visual acuity and BSCVA after ICL implantation were 0.17+/-0.19 and 0.12+/-0.12 logMAR, respectively. The efficacy index was 0.98. No eyes lost 2 or more lines of visual acuity, 2 eyes lost 1 line, 18 eyes did not change after surgery, and 5 eyes gained 1 or more lines. The safety index was 1.05. Best spectacle-corrected visual acuity after ICL implantation was statistically significantly better than preoperative BSCVA (P=.0021). Spherical equivalent refraction was within +/-1.00 D of the desired refraction in all cases and 84% of cases were within +/-0.50 D. Mean postoperative spherical equivalent refraction was 0.32+/-0.55 D at 12 months.

CONCLUSIONS

Myopic ICL implantation was a safe, effective, and predictable procedure for the correction of myopia associated with keratoconus.

Risk Assessment for Ectasia after Corneal Refractive Surgery

PURPOSE

To analyze the epidemiologic features of ectasia after excimer laser corneal refractive surgery, to identify risk factors for its development, and to devise a screening strategy to minimize its occurrence.

DESIGN

Retrospective comparative and case-control study.

PARTICIPANTS

All cases of ectasia after excimer laser corneal refractive surgery published in the English language with adequate information available through December 2005, unpublished cases seeking treatment at the authors' institution from 1998 through 2005, and a contemporaneous control group who underwent uneventful LASIK and experienced a normal postoperative course.

METHODS

Evaluation of preoperative characteristics, including patient age, gender, spherical equivalent refraction, pachymetry, and topographic patterns; perioperative characteristics, including type of surgery performed, flap thickness, ablation depth, and residual stromal bed (RSB) thickness; and postoperative characteristics including time to onset of ectasia.

MAIN OUTCOME MEASURES

Development of postoperative corneal ectasia.

RESULTS

There were 171 ectasia cases, including 158 published cases and 13 unpublished cases evaluated at the authors' institution. Ectasia occurred after LASIK in 164 cases (95.9%) and after photorefractive keratectomy (PRK) in 7 cases (4.1%). Compared with controls, more ectasia cases had abnormal preoperative topographies (35.7% vs. 0%; P<1.0x10(-15)), were significantly younger (34.4 vs. 40.0 years; P<1.0x10(-7)), were more myopic (-8.53 vs. -5.09 diopters; P<1.0x10(-7)), had thinner corneas before surgery (521.0 vs. 546.5 microm; P<1.0x10(-7)), and had less RSB thickness (256.3 vs. 317.3 microm; P<1.0x10(-10)). Based on subgroup logistic regression analysis, abnormal topography was the most significant factor that discriminated cases from controls, followed by RSB thickness, age, and preoperative corneal thickness, in that order. A risk factor stratification scale was created, taking all recognized risk factors into account in a weighted fashion. This model had a specificity of 91% and a sensitivity of 96% in this series.

CONCLUSIONS

A quantitative method can be used to identify eyes at risk for developing ectasia after LASIK that, if validated, represents a significant improvement over current screening strategies.

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

PURPOSE

To evaluate patients who developed ectasia with no apparent preoperative risk factors.

METHODS

Potential cases of patients who developed ectasia without apparent risk factors were identified by contacting participants in the Kera-Net (n = 580), ASCRS-Net (n = 450), and ISRS/AAO ISRS-Net (n = 525) internet bulletin boards from April to October 2003. Cases were included if ectasia developed after laser in situ keratomileusis in the absence of apparent preoperative risk factors. Reported cases were excluded for the following reasons: (1) calculated residual stromal bed less than 250 microm, (2) preoperative central pachymetry less than 500 microm, (3) any keratometry reading greater than 47.2 diopters (D), (4) a calculated inferior-superior value greater than 1.4, (5) more than 2 retreatments, (6) attempted initial correction greater than -12.00 D, (7) an Orbscan II "posterior float" (if obtained) greater than 50 microm, and (8) surgical/flap complications.

RESULTS

A total of 27 eyes of 25 patients were submitted for consideration. Eight eyes (8 patients) met our inclusion criteria. Mean age was 27.7 years (range, 18-41 years). Preoperative manifest refraction spherical equivalent was -4.61 D (range, -2.00 to -8.00 D); steepest keratometric reading was 43.86 D (range, 42.50-46.40 D); keratometric astigmatism was 0.93 D (range, 0.25-1.90 D); and preoperative central pachymetry was 537 microm (range, 505-560 microm). The mean calculated ablation depth was 82.8 microm (range, 21-125.4 microm), and mean calculated residual stromal bed was 299.5 microm (range, 254-373 microm). Mean time to recognition of ectasia onset was 14.2 months (range, 3-27 months) postoperatively. At the time of ectasia diagnosis, the mean manifest refraction spherical equivalent was -1.23 D (range, +0.125 to -3.00) with a mean of 2.72 D (range, 0.75-4.00 D) of astigmatism.

CONCLUSIONS

Ectasia can occur after an otherwise uncomplicated laser in situ keratomileusis procedure, even in the absence of apparent preoperative risk factors.

Keratectasia after Laser in situ Keratomileusis

PURPOSE

To describe the morphological features of a prominent ectasia of the cornea after laser in situ keratomileusis (LASIK).

METHODS

The morphology of the ectatic corneas was examined using corneal topography, light microscopy and transmission electron microscopy in 2 cases who underwent penetrating keratoplasty due to poor visual acuity induced by progressive corneal ectasia after LASIK.

RESULTS

On topographic examination, the apex of the corneal surface was observed within the central 3-mm zone, and the smallest thickness was 0.116 and 0.271 mm in each case. On histological examination, the epithelial layer became thinner and detached easily. Bowman's membrane was broken down and folded. An irregular arrangement of the stromal lamellae with fibroblastic keratocytes was found. The fulled fiber cell, a transformed epithelial cell, was visible in a plane on Bowman's layer in the central region. In contrast, the corneal endothelium was intact, and no abnormality was found in both cases.

CONCLUSION

On morphological examination of 2 cases with corneal ectasia, a forward protrusion of both the anterior and posterior corneal surfaces occurred, and epithelial detachment, Bowman's membrane breakage and folding and irregular lamellae were found. The 2 cases had greatly thinned and protruding corneas, yet there was no abnormality in the corneal endothelium.

Reversal of laser in situ keratomileusis–induced ectasia with intraocular pressure reduction

A 40 year-old woman had laser in situ keratomileusis for --7.75 --0.75 x 20 in the right eye. Preoperative examinations, including topography, pachymetry, and intraocular pressures (IOPs), were normal, and best spectacle-corrected visual acuity (BSCVA) was 20/20 in each eye. By 4 months postoperatively, the uncorrected visual acuity and BSCVA in the right eye had decreased to 20/40. Corneal topography of that eye was consistent with ectasia. One drop per day of timolol 0.5% (Timoptic XE) was prescribed. Five months postoperatively, the IOP had decreased and BSCVA and topography had improved. At 11 months, BSCVA returned to 20/20 and corneal topography normalized. Topographic difference maps were used to monitor corneal shape changes. In this case, early reduction in IOP completely reversed the ectasia.

Long-term follow-up of ultrathin corneas after surface retreatment with phototherapeutic keratectomy

PURPOSE

To evaluate visual acuity and long-term stability after phototherapeutic keratectomy (PTK) in patients with corneal thickness less than 400 microm and cornea-related vision problems.

SETTING

Department of Ophthalmology, Istituto Clinico Humanitas, Rozzano-Milan, Italy.

METHODS

This retrospective study comprised 48 eyes that had PTK for complications after photorefractive keratectomy that removed more than 200 microm of tissue. Phototherapeutic keratectomy was performed with the Nidek EC-5000 excimer laser with 10 Hz frequency, intraoperative topography, and masking fluid over an ablation diameter of 10.0 mm. The follow-up was 5 years. The mean preoperative best spectacle-corrected visual acuity (BSCVA) was 0.2 +/- 0.09 (SD) with -2.53 +/- 2.34 diopters (D), and the mean pachymetry was 390 +/- 38 microm. The efficacy parameters were pachymetry and visual acuity at 1 year and the stability parameters, optical refraction, corneal curvature (calculated as the mean curvature over the entire 3.0 mm and 5.0 mm central zones), and pachymetry from 1 to 5 years.

RESULTS

At 1 year, the mean BSCVA was 0.6 +/- 0.72 with -2.15 +/- 1.67 D and the mean pachymetry, 341 +/- 40 microm. At 5 years, the mean BSCVA was 0.7 +/- 0.15 with -2.33 +/- 1.12 D and the mean pachymetry, 339 +/- 48 microm. In all patients, there was an improvement of 4 or more Snellen lines. Statistical evaluation of refraction and corneal curvature values at 1 and 5 years indicated no statistically significant differences.

CONCLUSIONS

After PTK in eyes with ultrathin corneas, there was significant improvement in BSCVA and long-term stability of the optical refraction, corneal curvature, and pachymetry. In selected cases, 10.0 mm ablation zone PTK may be an alternative to penetrating keratoplasty, offering long-term corneal stability.

Pachymetric evaluation prior to laser in situ keratomileusis

PURPOSE

To determine whether deviations in the localization of the cornea's thinnest point or the magnitude and localization of posterior corneal ectasia is associated with deviations in the spherical equivalent, the astigmatism, or the magnitude of an anterior corneal ectasia and whether corneas at risk for iatrogenic keratectasia can be identified without a pachymetry map of the cornea.

SETTING

University hospital eye clinic.

METHODS

Three hundred eight eyes of 156 healthy volunteers with various refractive errors were examined with Orbscan II and autorefractometer-keratometer. The corneal thickness was registered at the fixation point, at the geometrical center, and at the thinnest point of the cornea. Keratometry and refraction were determined for all subjects.

RESULTS

The thinnest point of the cornea was predominantly located in the inferotemporal quadrant, and was significantly thinner than the fixation point (539.6 +/- 35.8 microm and 548.0 +/- 35.4 microm, respectively, P<.001). Interestingly, the larger this difference was, the longer the distance between these points. No relationship was found between the refractive or external surface measurements and the internal surface measurements.

CONCLUSIONS

The absence of a clear relationship between the shape of the anterior corneal surface or the refractive error, and the shape of the posterior corneal surface, necessitates a thorough pachymetric evaluation of the cornea before a laser in situ keratomileusis procedure, with special attention to the inferotemporal area.

Le kératocône : options chirurgicales actuelles

The treatment of keratoconus is in part dependant on the severity of the disease process. When contact lenses fail because of patient intolerance or insufficient acuity to meet the patient's needs, penetrating keratoplasty is the usual surgical modality considered for satisfactory visual rehabilitation. Keratoconus is considered to be a contraindication for incisional refractive surgery such as radial keratotomies or LASIK because of the corneal instability conferred by these procedures. When the cornea is transparent, INTACS implantation is a refractive modality that may improve visual function and in some instances prevent the need for corneal transplantation in select patients with keratoconus.

Influence of Flap Thickness on Results of Laser in situ Keratomileusis for Myopia

PURPOSE

To study whether flap thickness influences laser in situ keratomileusis (LASIK) results.

METHODS

This comparative, non-randomized, retrospective study comprised 421 LASIK eyes (233 patients) with spherical equivalent refraction between -0.60 and -6.00 diopters (D). Laser in situ keratomileusis was performed with the Moria One manual microkeratome and the Chiron Technolas 217C laser. Depending on the flap thickness, the eyes were divided into three groups (group 1, flap thickness < or =100 microm; group 2, flap thickness > 100 microm and < 130 microm; and group 3, flap thickness > or = 130 pm). For each group uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity, residual spherical equivalent refraction, and keratometric power (D) were measured 1 day, 1 week, 1 month, and 6 months after LASIK. Complications, retreatment, and correlation between flap thickness and preoperative corneal thickness and keratometric power were also analyzed.

RESULTS

One month postoperatively, UCVA was > or = 20/20 in 76% (96 eyes), 56% (79 eyes), and 61% (93 eyes) of eyes in the three group, respectively (P = .015). One month postoperatively, UCVA was > or = 20/25 in 88% (111 eyes), 76% (108 eyes), and 76% (116 eyes) of eyes in the three groups, respectively (P = .015). Complication rate and retreatment rate were not statistically different among the groups. At 6-month follow-up, no statistically significant differences were noted in UCVA between the groups. Significant correlations between flap thickness and preoperative corneal thickness (P < .0001) and between flap thickness and preoperative keratometric power (P < .05) were found.

CONCLUSION

Patients with flaps < or = 100 pm had better functional results at 1 month than those with thicker flaps. It may be important to perform LASIK with thin flaps to save corneal tissue in the stromal bed.

Topographic Patterns in Refractive Surgery Candidates

PURPOSE

To evaluate the prevalence of different topographic patterns in refractive surgery candidates and to estimate the extent of candidate rejection based on topography alone.

METHODS

We performed a retrospective evaluation of videokeratographies of previously unoperated refractive surgery candidates. The defined topographic patterns of their corneas and the indices computed by the videokeratographer software were registered. The data were evaluated by SPSS/PC statistical software.

RESULTS

One hundred candidate electronic topography records were evaluated. The candidates included 41 women and 59 men whose average age was 32 years (range 17.5-63.5). Their topographic patterns were: spherical (36/200 evaluated eyes), spherocylindrical (60), upper steep (32), lower steep (43), irregular astigmatism (9), decentered (3), suspected keratoconus (11), and probable keratoconus (6 eyes). Rejection from undergoing the procedure was based on topography alone in 27 of the 200 eyes. It was difficult to decide what to do with the 43 eyes with a lower steep pattern, and they were eventually rejected. Of the nine software-calculated indices, only one, "keratoconus index," could distinguish between the spherocylindrical and the lower steep patterns.

CONCLUSIONS

More than one-half of corneal topographies of refractive surgery candidates did not comply with the assumed "normal" spherical or spherocylindrical patterns. The possible continuum of keratoconus-suspected keratoconus-lower steep pattern raises the question of where to draw the line between reasonable and risky when considering corneal refractive surgery.

Contact Lens Management of Keratectasia After Laser In Situ Keratomileusis for Myopia

PURPOSE

To present a case in which rigid gas-permeable contact lenses were fit for a patient in whom keratectasia developed after laser in situ keratomileusis (LASIK).

METHODS

Case report.

RESULTS

A 21-year-old man underwent bilateral LASIK for myopia and astigmatism. The left eye was only partially corrected because of high myopia and corneal thickness restrictions. Eight months after LASIK, visual acuity was reduced in the right eye; the central cornea had steepened; and pachymetry showed central corneal thinning. Keratectasia was diagnosed, and rigid contact lenses were fitted. Four years later, the patient achieved satisfactory visual acuity and all-day lens wear with minimal complications.

CONCLUSIONS

The options for management of iatrogenic keratectasia include contact lenses, intracorneal ring segments, and penetrating keratoplasty. This case report shows that rigid contact lenses offer a safe, reversible option for improving visual acuity in such patients by delaying or avoiding the need for further surgical intervention.

Residual bed thickness and corneal forward shift after laser in situ keratomileusis

PURPOSE

To prospectively assess the forward shift of the cornea after laser in situ keratomileusis (LASIK) in relation to the residual corneal bed thickness.

SETTING

Miyata Eye Hospital, Miyazaki, Japan.

METHODS

Laser in situ keratomileusis was performed in 164 eyes of 85 patients with a mean myopic refractive error of -5.6 diopters (D) +/- 2.8 (SD) (range -1.25 to -14.5 D). Corneal topography of the posterior corneal surface was obtained using a scanning-slit topography system before and 1 month after surgery. Similar measurements were performed in 20 eyes of 10 normal subjects at an interval of 1 month. The amount of anteroposterior movement of the posterior corneal surface was determined. Multiple regression analysis was used to assess the factors that affected the forward shift of the corneal back surface.

RESULTS

The mean residual corneal bed thickness after laser ablation was 388.0 +/- 35.9 microm (range 308 to 489 microm). After surgery, the posterior corneal surface showed a mean forward shift of 46.4 +/- 27.9 microm, which was significantly larger than the absolute difference of 2 measurements obtained in normal subjects, 2.6 +/- 5.7 microm (P<.0001, Student t test). Variables relevant to the forward shift of the corneal posterior surface were, in order of magnitude of influence, the amount of laser ablation (partial regression coefficient B = 0.736, P<.0001) and the preoperative corneal thickness (B = -0.198, P<.0001). The residual corneal bed thickness was not relevant to the forward shift of the cornea.

CONCLUSIONS

Even if a residual corneal bed of 300 microm or thicker is preserved, anterior bulging of the cornea after LASIK can occur. Eyes with thin corneas and high myopia requiring greater laser ablation are more predisposed to an anterior shift of the cornea.

Wavefront Aberrations From Corneal Ectasia After Laser in situ Keratomileusis Demonstrated by InterWave Aberrometry

PURPOSE

To report a case of corneal ectasia after laser in situ keratomileusis (LASIK). The patient presented with minimal alterations in manifest refraction but had obvious distortions in the wavefront error of the eye, as demonstrated by InterWave aberrometry.

METHODS

Retrospective case report and literature review.

RESULTS

Three years following uneventful and initially successful LASIK and two subsequent enhancement procedures, a patient experienced a decrease in uncorrected and best spectacle-corrected visual acuity with only minor changes in manifest refraction and initially subtle changes on corneal topography. InterWave aberrometry showed a wavefront distortion consistent with progressive steepening of the anterior cornea, reflecting possible development of corneal ectasia.

CONCLUSIONS

InterWave aberrometry in conjunction with corneal topography was useful for early recognition of the development of corneal ectasia after LASIK.

Ectasia after laser in situ keratomileusis

Eighty-five cases of post laser in situ keratomileusis ectasia were reviewed and analyzed. Cases of keratoconus or forme fruste keratoconus were eliminated; many remaining case reports lacked key information. The current literature is unable to define a specific residual corneal thickness or a range of preoperative corneal thickness that would put an eye at risk for developing ectasia. The most logical cause for eyes without preexisting pathology to develop ectasia is a postablation stromal thickness that is mechanically unstable; this "minimal" thickness is probably specific to each eye. The preoperative and postoperative corneal thickness, measured flap thickness, and microkeratome and laser parameters used in a given case are required to determine the range of residual corneal thickness that puts the eye at risk for developing ectasia. Other as yet undetermined factors may play a role in the development of this complication.

Penetrating keratoplasty for iatrogenic keratoconus after repeat myopic laser in situ keratomileusis: Histologic findings and literature review

We report a patient with a sufficiently thick cornea (593 microm) and no topographic signs of keratoconus preoperatively who developed iatrogenic keratoconus 2 months after repeat laser in situ keratomileusis (-4.00 -1.00 x 20) performed 5 months after the primary procedure (-10.50 -1.00 x 55). After penetrating keratoplasty, macrophotography showed severe multidirectional "macrostriae" of the stromal bed. On histologic evaluation, excessive thinning of the residual stromal bed to a minimum of 75 microm in the valleys and a maximum of 200 microm at the peaks of the macrostriae were documented. The flap thickness was 225 microm in the center. The thicker-than-intended flap (160 microm) is thought to be the cause of the severe complication of the LASIK procedure.

Bilateral keratectasia after unilateral laser in situ keratomileusis: A retrospective diagnosis of ectatic corneal disorder

We present a case of iatrogenic keratectasia in the left eye after laser in situ keratomileusis (LASIK) with 14 microm of stromal ablation. Preoperative evaluation did not show significant evidence of keratoconus or forme fruste keratoconus in either eye. Twenty months postoperatively, in addition to postoperative ectasia in the left eye, the right eye developed mild changes in manifest refraction and on corneal topography. A retrospective diagnosis of ectatic corneal disorder was made in a patient who had no obvious findings of corneal pathology prior to LASIK.

Difference map or single elevation map in the evaluation of corneal forward shift after LASIK

PURPOSE

Forward shift of the cornea after excimer laser refractive surgery has been assessed on a difference map generated from two elevation maps of the scanning-slit corneal topography. The current study was conducted to test whether similar evaluation is possible on a postoperative color-coded elevation map alone.

DESIGN

Prospective, noncomparative case series.

PARTICIPANTS

One hundred sixty-three eyes of 86 patients with myopic refractive errors of -1 to -13.50 diopters.

INTERVENTION

LASIK was performed. Corneal topography of the posterior corneal surface was obtained with the scanning-slit topography system before and 1 month after surgery.

MAIN OUTCOME MEASURES

The amount of forward shift of the posterior corneal surface was determined at the center of the difference map generated from preoperative and postoperative elevation maps. For surface alignment in the difference map, the 3-mm wide peripheral annular fit-zone was used. The eyes were classified into two groups depending on the amount of forward shift, using 50 micro m as the threshold. Next, on the single postoperative color-coded elevation map, which is drawn relative to the individual best-fit sphere, the eye was judged to be abnormal (with significant forward shift) when more than three colors (discriminant number) were found within the central 3-mm area, and sensitivity and specificity were calculated. By varying the discriminant number from 3 to 9, receiver operator characteristic (ROC) curves were created.

RESULTS

The ROC curve analyses demonstrated that sufficient true positive ratio (sensitivity) and false-positive ratio (100-specificity [%]) could not be obtained with any discriminant color number when judgments were made on a single color-coded map. There was a weak, but significant, correlation between the amount of corneal forward shift and the radius of curvature of the posterior best-fit sphere (Pearson r = -0.170; P = 0.030), indicating that a cornea with greater forward shift tended to be drawn on a steeper best-fit sphere, and thus the forward protrusion of the posterior surface failed to be depicted.

CONCLUSIONS

Forward shift of the cornea after excimer laser surgery should be evaluated on the difference map generated from two elevation maps, such as preoperative and postoperative maps.

Histological and immunohistochemical findings after laser in situ keratomileusis in human corneas

PURPOSE

To describe histopathological and immunohistochemical findings in human corneas after myopic laser in situ keratomileusis (LASIK) followed by iatrogenic keratectasia and after hyperopic LASIK.

SETTING

Department of Ophthalmology, University of Innsbruck, Innsbruck, Austria.

METHODS

Clinical, histological, and immunohistochemical investigations were performed of 1 human cornea with iatrogenic keratectasia following myopic LASIK and 1 human cornea with irregular astigmatism and central scar formation after hyperopic LASIK. Corneal buttons were obtained during penetrating keratoplasty in both patients.

RESULTS

Histopathological examination showed thinning of the central stroma with a posterior residual thickness of 190 microm in the patient with iatrogenic keratectasia after myopic LASIK and significant midperipheral thinning in the patient who had hyperopic LASIK. However, this characteristic ablation profile of the stroma after hyperopic LASIK was partially mitigated and compensated by the epithelium, which was significantly thinned in the center and markedly thickened in the midperiphery. Traces of wound healing with minimal scar tissue were present at the flap margin after myopic and hyperopic LASIK. In a few sections of the cornea with keratectasia after myopia LASIK, only a few collagen lamellae were visible crossing between the posterior residual stroma and the superficial flap. Immunohistochemical examination revealed minimally increased staining of dermatan sulfate proteoglycan within the stroma adjacent to the interface of the microkeratome incision. Increased staining of hepatocyte growth factor was found on keratocytes/fibroblasts at the flap margin in both corneas.

CONCLUSIONS

The wound-healing response is generally poor after LASIK, which may result in significant weakening of the tensile strength of the cornea after myopic LASIK, probably due to biomechanically ineffective superficial lamella. After LASIK in patients with high hyperopia, compensatory epithelial thickening in the annular midperipheral ablation zone might be partly responsible for regression.

Current surgical options for keratoconus

The treatment of keratoconus is partly dependent on the severity of the disease process. When contact lenses fail because the patient is intolerant or they do not provide sufficient acuity to meet the patient's needs, penetrating keratoplasty is the usual surgical modality for adequate visual rehabilitation. Keratoconus is considered a contraindication to incisional refractive surgery such as radial keratotomy and laser in situ keratomileusis because of the corneal instability conferred by these procedures. When the cornea is transparent, intrastromal corneal ring implantation is a refractive modality that may improve visual function and, in select keratoconus patients, obviate the need for corneal transplantation.

Risk factors and prognosis for corneal ectasia after LASIK

PURPOSE

To review cases of corneal ectasia after laser in situ keratomileusis (LASIK), identify preoperative risk factors, and evaluate methods and success rates of visual rehabilitation for these cases.

DESIGN

Retrospective nonrandomized comparative trial.

PARTICIPANTS

Ten eyes from seven patients identified as developing corneal ectasia after LASIK, 33 previously reported ectasia cases, and two control groups with uneventful LASIK and normal postoperative courses: 100 consecutive cases (first control group), and 100 consecutive cases with high myopia (> 8 diopters [D]) preoperatively (second control group).

METHODS

Retrospective review of preoperative and postoperative data for each case compared with that of previously reported cases and cases with uneventful postoperative courses.

MAIN OUTCOME MEASURES

Preoperative refraction, topographic features, residual stromal bed thickness (RSB), time to the development of ectasia, number of enhancements, final best-corrected visual acuity (BCVA), and method of final correction.

RESULTS

Length of follow-up averaged 23.4 months (range, 6-48 months) after LASIK. Mean time to the development of ectasia averaged 16.3 months (range, 1-45 months). Preoperative refraction averaged -8.69 D compared with -5.37 D for the first control group (P = 0.005). Preoperatively, 88% of ectasia cases met criteria for forme fruste keratoconus, compared with 2% of the first control group (P < 0.0000001) and 4% of the second control group (P = 0.0000001). Seven eyes (70%) had RSB <250 microm, as did 16% of eyes in the first control group and 46% of the second control group. The mean RSB for ectasia cases (222.8 microm) was significantly less than that for the first control group (293.6 micro m, P = 0.0004) and the second control group (256.5 microm; P = 0.04). Seven eyes (70%) had enhancements. Only 10% of eyes lost more than one line of BCVA, and all patients eventually achieved corrected vision of 20/30 or better. One case required penetrating keratoplasty (10%), while all others required rigid gas-permeable contact lenses for correction.

CONCLUSIONS

Significant risk factors for the development of ectasia after LASIK include high myopia, forme fruste keratoconus, and low RSB. All patients had at least one risk factor other than high myopia, and significant differences remained even when controlling for myopia. Multiple enhancements were common among affected cases, but their causative role remains unknown. We did not identify any patients who developed ectasia without recognizable preoperative risk factors.

Keratectasia after laser in situ keratomileusis (LASIK): evaluation of the calculated residual stromal bed thickness

PURPOSE

To report corneal histopathology associated with keratectasia after laser in situ keratomileusis (LASIK) and to evaluate the thickness of the calculated residual stromal bed in two cases and those in the literature.

DESIGN

Interventional case reports.

METHODS

Three eyes of two patients developed keratectasia after LASIK. Corneal specimens after penetrating keratoplasty in one eye of each patient were studied histopathologically, and the residual stromal bed was directly measured. For comparison, residual stromal bed thicknesses were calculated from published cases of keratectasia.

RESULTS

Two eyes of a 26-year-old woman and one eye of a 22-year-old woman developed keratectasia after LASIK. Calculated residual stromal bed thicknesses were 210, 213, and 261 microm. Histologic sections revealed focal scarring in the flap plane. The cornea specimens measured 75 and 118 microm thinner than calculated values immediately after LASIK. Transmission electron microscopy of one case revealed an average lamellar thickness of 0.94 microm. In 28 (49%) of 57 previous cases of keratectasia, the calculated residual stromal bed thicknesses were greater than 250 microm.

CONCLUSIONS

Both the flap and the stromal bed of the cornea may thin after LASIK. A residual stromal bed thickness of 250 microm does not preclude the development of keratectasia after LASIK.

Utilization of refractive surgery technology in keratoconus and corneal transplants

Keratoconus is considered a contraindication for refractive surgery because of the potential corneal instability following surgery. On the other hand, penetrating keratoplasty is the usual surgical modality when the keratoconic patient cannot tolerate a contact lens. In some selected cases, when the central cornea is still transparent, refractive surgical procedures, particularly Intacs implantation, may be used to help the patient to improve visual function.