Results of Photorefractive Keratectomy in Keratoconus Suspects at 4 Years

Laser In Situ Keratomileusis (LASIK) Combined with Prophylactic Corneal Cross-Linking for Correction of Myopia: Regional Analysis of Corneal Morphology

Introduction

Methods

Results

Conclusions

[Excimer laser in keratoconus management]

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

Toric Artisan after transepithelial topography-guided photorefractive keratectomy for higher-order aberrations following intrastromal corneal ring segments in keratoconus - Trioptics

We report a case of a 40-year-old female with keratoconus and high myopia who had previous ICRS implantation in both eyes (OU) and was intolerant to contact lenses. Manifest refraction was -8.50 -1.50 × 95 (20/25--) in right eye (OD) and -9.50 -2.50 × 60 (20/70--) in left eye (OS). A topography-guided transepithelial-photorefractive keratectomy (ttPRK) was performed to correct high-order aberrations on OS, resulting in corneal surface and coma improvement, and CDVA achieved 20/30. Correction of residual ametropia was performed with an iris-fixated toric phakic lens in OU. CDVA improved to 20/20- (Plano) in OD and 20/20- (Plano -1.00 90°) in OS. In conclusion, it is possible to rehabilitate a patient with keratoconus and high ametropia after intrastromal corneal ring segments (ICRS) implantation associating ttPRK and phakic lens ("Trioptics").

Outcomes of photorefractive keratectomy in patients with posterior corneal steepening

PURPOSE

To assess post-operative outcomes following photorefractive keratectomy (PRK) in patients with posterior corneal steepening compared to an age, gender and refraction matched control group.

METHODS

A retrospective matched case-control study that analysed outcomes of PRK in eyes with posterior corneal steepening as shown by the Sirius tomography (Sirius, CSO, Italy), versus normal eyes. Both groups were age, gender and refraction matched. Data collected include: demographic data, pre-operative and post-operative refraction, uncorrected distance visual acuity (UDVA) and corrected distance visual acuity (CDVA), maximal ablation depth. Inferior-superior ratio, central corneal thickness (CCT), mean posterior keratometry (K), Baiocchi Calossi Versaci index for the front (BCV_f) and back (BCV_b) cornea, the symmetry index of front (SI_f) and back (SI_b) corneal curvature were assessed pre- and postoperatively.

RESULTS

Overall, 89 study eyes and 954 normal myopic eyes were included. Compared to the control group, corneas with posterior steepening demonstrated significantly reduced CDVA (p < 0.0001 and p = 0.007) and lower CCT (p < 0.0001 and p = 0.03), before and following the operation, respectively. Pre-operative BCV_f, BCV_b, SI_f and SI_b were significantly higher in corneas with posterior steepening (p < 0.0001) and remained higher following the surgery except for BCV_f. Ectasia occurred in one eye (1.1%). The safety and efficacy indices at 12 months were comparable for both groups.

CONCLUSION

PRK on corneas with posterior steepening results in similar refractive outcomes compared to normal eyes, 1 year following the surgery. Keratectasia is a rare, however a possible complication.

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

RATIONALE

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

PATIENT CONCERNS

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

DIAGNOSES

Bilateral keratectasia.

INTERVENTIONS

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

OUTCOMES

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

LESSONS

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

A Novel Corneal Remodeling Technique for the Management of Keratoconus

PURPOSE

To describe a novel technique to reshape the ectatic cornea by means of crescent keratectomy performed with an excimer laser using a mask.

METHODS

A crescent-shaped perforation at the base of the mask allowed the laser ablation to be directed only to the intended region, shielding the remaining cornea. This technique was performed in 3 eyes of 3 patients with keratoconus grade 2 to 3. Arcs of 180° and 360° had been performed depending on the severity of the keratoconus. The edges of the crescent were closed by 10-0 nylon interrupted sutures.

RESULTS

At 1 year postoperatively, all cases showed improvement in visual acuity, keratometry, and corneal topography. The treatment also reduced optical aberrations and shortened the anterior chamber depth.

CONCLUSIONS

Although the preliminary results are promising, there is a need to standardize a nomogram of this technique for treating keratoconus. [J Refract Surg. 2017;33(12):854-856.].

Photorefractive keratectomy in mild to moderate keratoconus: outcomes in over 40-year-old patients

Background:

Keratoconus is a contraindication for photorefractive keratectomy (PRK). In the recent decade, some efforts have been made to perform PRK in patients with keratoconus whose corneas are stable naturally or by doing corneal collagen crosslinking. These studies have suggested residual central corneal thickness (CCT) ≥450 μm.

Aims:

The aim was to evaluate the long-term outcomes of PRK in patients with mild to moderate keratoconus in patients older than 40 with residual CCT ≥ 400 μm.

Settings and Design:

This prospective study was conducted in our Cornea Research Center, Mashhad, Iran.

Materials and Methods:

Patients over 40 years old, with a grade I/II keratoconus without progression in the last 2 years were recruited. Patients with a predicted postoperative CCT < 400 μm were excluded. PRK with tissue saving protocol was performed with Tecnolas 217 Z. Mitomycin-C was applied after ablation. The final endpoints were refraction parameters the last follow-up visit (mean: 35 months). Paired t-test and Chi-square were used for analysis.

Results:

A total of 38 eyes of 21 patients were studied; 20 eyes (52.6%) with a grade I and 18 eyes (47.4%) with grade II keratoconus. The mean uncorrected visual acuity, best corrected visual acuity (BCVA), spherical equivalent, cylindrical power and keratometric readings were significantly improved at the final endpoint compared to preoperation measurements (P < 0.001). Two eyes (5%) lost two lines of BCVA at the final visit. No case of ectasia occurred during the follow-up course.

Conclusions:

PRK did not induce keratoconus progression in patients older than 40 with a grade I/II keratoconus. Residual CCT ≥ 450 μm seems to be sufficient to prevent the ectasia.

Long-Term Clinical Outcomes of Myopic Patients Having Thin Residual Corneal Thickness after Excimer Laser Surface Ablation

PURPOSE

To investigate and compare the long-term safety, efficacy, and accuracy of PRK (photorefractive keratectomy) and LASEK (laser epithelial keratomileusis) in myopic corneas having residual corneal thickness less than 400 micron meters (µm).

METHODS

The medical reports of the patients who had undergone excimer laser surface ablation between 2007-2011 and had a residual corneal thickness less than 400 µm were retrospectively reviewed.

RESULTS

Forty-two eyes of 42 patients with a mean age of 28.79±7.76 years were enrolled into the study. Twenty-two PRK and 20 LASEK procedures were performed. The mean follow-up time was 45.00±11.80 months. At the end of follow-up, no ectasia was detected. Nineteen percent of eyes had trace haze. No eyes lost any lines in corrected distance visual acuity. Eighty-one percent of the patients had an uncorrected distance visual acuity better than 20/40. The regression rate was 16.7%. Sixty-two percent of eyes were within ±1.00 D. The safety and efficacy indexes were 1.19±0.42 and 1.00±0.40, respectively. There was not any difference between LASEK and PRK regarding achieved spherical equivalent refraction, haze ratio, visual acuity, safety, efficacy, and regression.

CONCLUSIONS

Both PRK and LASEK are safe and effective in myopic corneas having thin residual thickness.

Collagen cross-linking: when and how? A review of the state of the art of the technique and new perspectives

Since the late 1990s corneal crosslinking (CXL) has been proposed as a new possibility to stop progression of keratoconus or secondary corneal ectasia, with the promising aim to prevent progressive visual loss due to the evolution of the pathology and to delay or avoid invasive surgical procedures such as corneal transplantation. The possibility of strengthening corneal tissue by means of a photochemical reaction of corneal collagen by the combined action of Riboflavin and ultraviolet A irradiation (UVA), radically modified the conservative management of progressive corneal ectasia. This is a review of the state of the art of CXL, reporting basic and clinical evidence. The paper describes basic principles, advantages and limits of different CXL techniques and possible future evolution of the procedure.

Non-topography-guided PRK combined with CXL for the correction of refractive errors in patients with early stage keratoconus

PURPOSE

To evaluate the safety and clinical outcome of combined non-topography-guided photorefractive keratectomy (PRK) and corneal collagen cross-linking (CXL) for the treatment of mild refractive errors in patients with early stage keratoconus.

METHODS

A retrospective, nonrandomized study of patients with early stage keratoconus (stage 1 or 2) who underwent simultaneous non-topography-guided PRK and CXL. All patients had at least 2 years of follow-up. Data were collected preoperatively and postoperatively at the 6-month, 1-year, and 2-year follow-up visit after combined non-topography-guided PRK and CXL.

RESULTS

Seventy-nine patients (140 eyes) were included in the study. Combined non-topography-guided PRK and CXL induced a significant improvement in both visual acuity and refraction. Uncorrected distance visual acuity significantly improved from 0.39 ± 0.22 logMAR before combined non-topography-guided PRK and CXL to 0.12 ± 0.14 logMAR at the last follow-up visit (P <.001) and corrected distance visual acuity remained stable (0.035 ± 0.062 logMAR preoperatively vs 0.036 ± 0.058 logMAR postoperatively, P =.79). The mean spherical equivalent decreased from -1.78 ± 1.43 to -0.42 ± 0.60 diopters (D) (P <.001), and the mean cylinder decreased from 1.47 ± 1.10 to 0.83 ± 0.55 D (P <.001). At the last follow-up visit mean keratometry flat was 43.30 ± 1.75 vs 45.62 ± 1.72 D preoperatively (P = .03) and mean keratometry steep was 44.39 ± 3.14 vs 46.53 ± 2.13 D preoperatively (P = .02). Mean central corneal thickness decreased from 501.74 ± 13.11 to 475.93 ± 12.25 µm following combined non-topography-guided PRK and CXL (P < .001). No intraoperative complications occurred. Four eyes developed mild haze that responded well to a short course of topical steroids. No eye developed infectious keratitis.

CONCLUSIONS

Combined non-topography-guided PRK and CXL is an effective and safe option for correcting mild refractive error and improving visual acuity in patients with early stable keratoconus.

Characterization of corneal structure in keratoconus

The increasing volume of patients interested in refractive surgery and the new treatment options available for keratoconus have generated a higher interest in achieving a better characterization of this pathology. The ophthalmic devices for corneal analysis and diagnosis have experienced a rapid development during the past decade with the implementation of technologies such as the Placido-disk corneal topography and the introduction of others such as scanning-slit topography, Scheimpflug photography, and optical coherence tomography, which are able to accurately describe not only the geometry of the anterior corneal surface but also that of the posterior surface, as well as pachymetry and corneal volume. Specifically, anterior and posterior corneal elevation, corneal power, pachymetry maps, and corneal coma-like aberrometry data provide sufficient information for an accurate characterization of the cornea to avoid misleading diagnoses of patients and provide appropriate counseling of refractive surgery candidates.

FINANCIAL DISCLOSURE

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

Photorefractive keratectomy in patients with suspected keratoconus: five-year follow-up

PURPOSE

To assess the long-range outcomes of photorefractive keratectomy (PRK) using functional and topographic criteria in myopic eyes with suspected keratoconus.

SETTING

Rothschild Foundation, Paris, France.

DESIGN

Retrospective interventional case series.

METHODS

Eyes of patients classified as keratoconus suspects or keratoconus by the Corneal Navigator software of the OPD-Scan II device were included. They were treated with myopic PRK using an EC-5000 excimer laser between 2004 and 2007. The main outcome measures were refractive stability, mean corneal keratometry, mean central pachymetry, mean thinnest point value, and the occurrence of postoperative complications such as corneal ectasia.

RESULTS

The study evaluated 62 eyes of 42 patients. The mean patient age was 34.6 years ± 15.1 (SD) and the mean spherical equivalent (SE), -3.96 ± 3.05 diopters (D). The mean central pachymetry was 529.4 ± 32.8 μm and the mean simulated keratometry, 45.75 ± 1.75 D. The percentage of similarity to keratoconus suspects or keratoconus was positive in all 62 eyes and exceeded a 50% similarity score in 30 eyes (48.4%). The mean follow-up was 4.8 ± 1.4 years. The mean magnitude of the SE was -0.53 ± 1.35 D over the follow-up. Two patients required glasses postoperatively because of significant myopic regression. No case of corneal ectasia was reported.

CONCLUSION

Photorefractive keratectomy in eyes with suspected keratoconus based on a Placido neural network may be safe and effective for myopia and astigmatism in carefully selected patients.

Corneal biomechanical properties in normal, forme fruste keratoconus, and manifest keratoconus after statistical correction for potentially confounding factors

PURPOSE

To evaluate the difference in corneal biomechanical properties, after controlling for potentially confounding factors, along the spectrum of keratoconic disease as measured by the keratoconus severity score.

METHODS

The corneal biomechanical properties of 73 keratoconic (KCN) eyes of 54 patients, 42 forme fruste keratoconic (FFKCN) eyes of 32 patients, and 115 healthy eyes of 115 age- and sex-matched patients were reviewed retrospectively. The main outcome measures were corneal hysteresis (CH) and corneal resistance factor (CRF).

RESULTS

In the normal group, the mean CH was 11.0 ± 1.4 mm Hg and mean CRF was 11.1 ± 1.6 mm Hg. The FFKCN mean CH was 8.8 ± 1.4 mm Hg and mean CRF was 8.6 ± 1.3 mm Hg. The KCN mean CH was 7.9 ± 1.3 mm Hg and mean CRF was 7.3 ± 1.4 mm Hg. There were statistically significant differences in the mean CH and CRF in the normal group compared with the FFKCN and the KCN groups (P < 0.001) after statistically controlling for differences in central corneal thickness, age, and sex.

CONCLUSIONS

There is a significant difference in the mean CH and CRF between normal and FFKCN corneas after controlling for differences in age, sex, and central corneal thickness. However, there is a significant overlap in the distribution of CH and CRF values among all groups. The biomechanical parameters CH and CRF cannot be used alone but may be a useful clinical adjunct to other diagnostic tools, such as corneal tomography, in distinguishing normal from subclinical keratoconic corneas.

Topography-guided transepithelial surface ablation followed by corneal collagen cross-linking performed in a single combined procedure for the treatment of keratoconus and pellucid marginal degeneration

PURPOSE

To evaluate a combination of topography-guided custom ablation and corneal collagen cross-linking (CXL) in a single procedure for the treatment of keratectasia.

METHODS

Twelve eyes of 12 patients with keratectasia were treated with topography-guided custom ablation and CXL. Topography-guided custom ablation was performed using a transepithelial technique with the iVIS Suite 1 kHz flying spot excimer laser. Collagen cross-linking was performed immediately after topography-guided custom ablation, according to standard protocol. Postoperative follow-up examinations were performed at 1, 3, 6, and 12 months. Uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), refractive change, corneal topography, and pachymetry were analyzed pre- and postoperatively.

RESULTS

Mean UCVA increased from 20/1000 preoperatively to 20/125 12 months postoperatively. Mean BSCVA increased from 20/57 to 20/35, with no loss of lines of visual acuity. Mean astigmatism was reduced from 5.40+/-2.13 diopters (D) to 2.70+/-1.44 D, and keratometric asymmetry decreased from 6.38+/-1.02 D to 2.76+/-0.73 D. Only minor changes in posterior corneal surface elevation and stability of refraction were found, confirming that no progression of ectasia occurred during the observation time.

CONCLUSIONS

A combination of topography-guided custom ablation and CXL improved patients' visual, refractive, and topography outcomes and halted the progression of keratectasia within the observation period of 12 months. This method may postpone or eliminate the need for corneal transplantation in suitable cases with keratectasia.

Current trends in advanced surface ablation

PURPOSE OF REVIEW

Since their introduction in the mid-1990s, surface ablation techniques have continued to evolve, enabling surgeons to give patients better quality of vision with less postoperative pain. The purpose of this chapter is to discuss that evolution, the common techniques used today, and how to address potential complications.

RECENT FINDINGS

Advanced surface ablation techniques offer advantages over laser in situ keratomileusis, including expanded potential patient profiles, reduced haze and pain postoperatively, and increased quality of vision. Haze reduction via preserved epithelial flaps, smoother stromal beds, and introduction of mitomycin-C intraoperatively have all improved safety outcomes of advanced surface ablation.

SUMMARY

Experience has shown us that virtually all patients who are candidates for laser in situ keratomileusis can be candidates for surface ablation, but patients with specific ocular conditions, such as epithelial basement membrane dystrophy, superficial corneal scars, and previous radial keratotomy will have the best outcomes with surface ablation. Surface ablation and laser in situ keratomileusis are comparable in terms of safety and quality of vision. Wavefront-guided photorefractive keratectomy offers better acuity and less induction of higher order aberrations than wavefront-guided laser in situ keratomileusis.

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

PURPOSE

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

DESIGN

Retrospective review.

METHODS

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

RESULTS

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

CONCLUSIONS

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

Customized photoastigmatic refractive keratectomy using combined topographic and refractive data for myopia and astigmatism in eyes with forme fruste and mild keratoconus

PURPOSE

To examine the outcomes of photoastigmatic refractive keratectomy using corneal and refractive parameters for myopia and astigmatism in eyes with forme fruste and mild keratoconus.

SETTING

Private practice, Melbourne, Australia.

METHODS

Photoastigmatic refractive keratectomy was performed with a Star 1 or Star 2 laser (Visx) in 45 eyes with forme fruste or mild keratoconus using the Alpins vector planning technique. Inclusion requirements were best corrected visual acuity (BCVA) 20/40 or better, no slitlamp signs of keratoconus, mean keratometry less than 50.00 diopters (D), and corneal and refractive stability for at least 2 years.

RESULTS

Thirty-two eyes had follow-up of 5 years and 9 eyes, of 10 years. Preoperatively, the mean refractive astigmatism was -1.39 DC +/- 1.08 (SD) (range 0.45 to -5.04 DC) and the mean corneal astigmatism was 1.52 +/- 1.18 D (range 0.35 to 4.75 D) by manual keratometry and 1.70 +/- 1.42 D (range 0.32 to 5.32 D) by topography. Twelve months postoperatively, the mean refractive astigmatism was -0.43 +/- 0.40 D and the mean corneal astigmatism was 1.05 +/- 0.85 D by keratometry and 1.02 +/- 0.83 D by topography. At 12 months, the uncorrected visual acuity was 20/20 or better in 56% of eyes and 20/40 or better in all eyes. The BCVA was 20/20 or better in 89% of eyes and 20/30 or better in all eyes. Seven eyes had a loss of BCVA, and 16 eyes had a gain. There were no cases of keratoconus progression.

CONCLUSIONS

Photoastigmatic refractive keratectomy in eyes with forme fruste and mild keratoconus was safe and effective for myopia and astigmatism in carefully selected patients with refractive and corneal stability. The incorporation of the corneal astigmatism data into the applied treatment parameters may improve visual and total astigmatism results.

Identification of scanning slit-beam topographic parameters important in distinguishing normal from keratoconic corneal morphologic features

PURPOSE

To identify morphologic parameters obtained using scanning slit-beam topography that help distinguish normal from keratoconic corneal morphologic features.

DESIGN

Observational, retrospective, cross-sectional study.

METHODS

This retrospective review examined 207 normal eyes of patients undergoing an initial consultation for primary refractive surgery and 42 eyes with clinical keratoconus (KCN). The following parameters were examined and compared between the two groups: astigmatism, central corneal power, irregularity indices at 3 mm (II3) and 5 mm (II5), maximal posterior elevation (MPE) magnitude and location, thinnest optical pachymetry (TOP) magnitude and location, anterior elevation best-fit sphere (ABFS), posterior elevation best-fit sphere (PBFS), the ratio of ABFS to PBFS, the difference between average inferior and average superior K values at 3 mm and 5 mm in both keratometric (I-S K3 and I-S K5) and tangential (I-S T3 and I-S T5) topographic maps, and skewed radial axis at 3 mm (SRAX3) and 5 mm (SRAX5) of the keratometric topography map.

RESULTS

The II3, II5, MPE magnitude, TOP magnitude, ABFS, PBFS, ABFS-to-PBFS ratio, I-S K at both 3 mm and 5 mm, I-S T at both 3 and 5 mm, and SRAX at 3 mm and 5 mm values were significantly different among the two groups (P < .001). The least-correlated parameters were SRAX3, TOP magnitude, and II3 in the KCN group and I-S K3, amount of astigmatism and MPE magnitude in the normal group.

CONCLUSIONS

Parameters obtained using scanning slit-beam topography may allow improved differentiation of keratoconic from normal corneal shapes, especially when the poorly correlated intragroup parameters are used.

Corneal ectasia after photorefractive keratectomy

BACKGROUND

Corneal ectasia after photorefractive keratectomy (PRK) has only been occasionally reported, and its incidence has not been assessed.

METHODS

In a retrospective, non-comparative case series, incidence of corneal ectasia was evaluated in a personal consecutive 6453-case series of myopic PRK with a minimum follow-up of 18 months. Features and prognosis were evaluated in all patients with ectasia after PRK (in both personal and referred cases).

RESULTS

Ectasia was detected in three eyes of two patients (patients 1 and 2) 3 years and 1 year after PRK performed elsewhere. In addition, in the personal PRK series, two eyes of two patients (patients 3 and 4) developed corneal ectasia 5 months after surgery (incidence: 0.03%). Pre-operatively, forme fruste keratoconus was present in patients 1, 3 and 4; keratoconus in the fellow eye in patient 2; pachymetry <500 micron in patients 2 and 3. In patient 1, rigid contact lenses were prescribed, and in patient 2 deep anterior lamellar keratoplasty was needed; in patients 3 and 4, low induced astigmatism resulted, requiring driving spectacles in patient 3.

CONCLUSIONS

PRK induced corneal ectasia in predisposed eyes, even after low myopic ablations. Forme fruste keratoconus and keratoconus in the fellow eye were the main pre-operative findings. Prognosis varies according to severity.

Keratectasia After LASIK But Not After PRK in One Patient

PURPOSE

To report a case of keratectasia in a patient who underwent LASIK in the right eye and photorefractive keratectomy (PRK) in the left eye for correction of compound myopic astigmatism.

METHODS

A 30-year-old man underwent LASIK in the right eye and PRK in left eye for refraction of -1.75 -1.50 x 48 degrees and -1.00 -1.75 x 100 degrees, respectively. Preoperative corneal thickness was 447 microm in the right eye and 446 microm in the left eye.

RESULTS

Postoperative corneal thickness decreased to 341 microm and 384 microm in the right and left eye, respectively. Uncorrected visual acuity in the left eye was 20/20, but the right eye developed keratectasia, which led to severe visual loss (20/400).

CONCLUSIONS

Photorefractive keratectomy may be better than LASIK for ablative refractive surgery for low myopic astigmatism in eyes with low central corneal thickness.

Corneal Ectasia after Photorefractive Keratectomy for Low Myopia

OBJECTIVE

To alert ophthalmologists of the possibility of an aggravation of forme fruste keratoconus after photorefractive keratectomy (PRK).

DESIGN

Clinical case report.

INTERVENTION

Standard bilateral PRK for low myopia.

MAIN OUTCOME MEASURES

Corneal topography, corneal thickness, and visual acuity.

RESULTS

Corneal ectasia occurred bilaterally after PRK. Retrospective analysis of preoperative videokeratography indicated the existence of forme fruste keratoconus on the left eye.

CONCLUSIONS

This article is the first case report of a bilateral corneal ectasia after PRK for low myopia. Even if there is no direct proof to demonstrate that PRK has worsened the evolution of keratoconus, the safety of the PRK procedure in forme fruste keratoconus must be considered.

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.

Photorefractive keratectomy versus laser in situ keratomileusis to prevent keratectasia after corneal ablation

A 27-year-old man had excimer photoastigmatic keratectomy in the right eye and laser in situ keratomileusis in the left eye for the treatment of equivalent myopia. Preoperative slitlamp examination did not reveal evidence of keratoconus, central corneal pachymetry was 485 microm in the right eye and 500 microm in the left eye, and corneal topography revealed asymmetric bow-tie astigmatism with inferior steepening in the right eye and a small area of inferior steepening in the left eye. Twenty-two months after surgery, the patient complained of poor vision in the left eye. Slitlamp examination of the left eye revealed central corneal thinning and protrusion, with a Fleischer ring within the flap. Corneal topographic evaluation revealed a stable map in the right eye and central corneal steepening indicative of keratectasia in the left eye.

Morphologic Characteristics of Lamellar Channel Deposits in the Human Eye

OBJECTIVE

To report the histologic characteristics of lamellar channel deposits after polymethyl methacrylate intrastromal corneal ring segments in a human eye.

METHODS

A 34-year-old man previously diagnosed with keratoconus received photorefractive keratectomy in his left eye that exacerbated his corneal ectasia. To delay or possibly prevent corneal transplant, the patient elected to have intrastromal corneal segments implanted in the left eye. One year later the patient underwent corneal transplant. Before transplant, lamellar channel deposits were noted on clinical microscopic examination of the left eye. We performed histologic evaluation to assess changes to the patient's excised corneal tissue and to further characterize the observed lamellar channel deposits.

RESULTS

Lamellar channel deposits in humans are histologically similar to our previous descriptions of deposits in rabbits. These deposits primarily consist of intracellular lipid accumulations that stain positively with oil red O and filipin but not periodic acid Schiff reaction. Immunohistochemistry of cells located in the deposit region stained positively with vimentin, suggesting that these cells were keratocytes. Stains for cytokeratins 3 and 12 and for CD68 were both negative, indicating that epithelial cells and macrophages were not present in the deposit region.

CONCLUSION

Lamellar channel deposits are a common clinical finding after intrastromal corneal implants. This case provides further evidence to support our hypothesis that lamellar channel deposits in humans are a tissue response to corneal implants that consist of intracellular lipid accumulations. We use this case to propose a theoretical construct for the observation of stromal lipid accumulation in response to corneal injury.

Microkeratome-assisted lamellar keratoplasty for keratoconus: stromal sandwich

PURPOSE

To evaluate microkeratome-assisted lamellar keratoplasty for the treatment of keratoconus when it is not possible to correct the astigmatic ametropia with contact lenses.

SETTING

Ophthalmology Department, School of Medicine, Gazi University, Ankara, Turkey.

METHODS

This prospective study comprised 9 eyes of 7 keratoconus patients with contact lens intolerance. The donor cornea was prepared with a microkeratome and punched with a 7.25 mm or 7.50 mm trephine. Following the creation of a standard 9.0 mm corneal flap in the host cornea, the donor stromal button was implanted under this corneal flap like a sandwich. Transepithelial photorefractive keratectomy or laser in situ keratomileusis was performed when the corneal topography and refraction stabilized by the end of the sixth postoperative month. Follow-up ranged from 7 to 22 months.

RESULTS

All patients gained 5 or more lines (mean 7.2 lines +/- 1.6 [SD]), and no patient lost a line of vision. The mean corneal thickness was 432.7 +/- 36.1 micrometers preoperatively and 578.1 +/- 45.1 micrometers after refractive surgery.

CONCLUSION

The early visual results of this surgical technique are promising and seem to be comparable to those with penetrating keratoplasty.

Intacs for keratoconus

PURPOSE

To evaluate the efficacy and safety of placement of Intacs in subjects with keratoconus.

DESIGN

Retrospective, nonrandomized comparative trial.

INTERVENTION

Intrastromal corneal ring segment implantation.

PARTICIPANTS

Seventy-four eyes of 50 subjects (41 male and 9 female) were evaluated. The mean age of subjects in the study was 35 years, ranging from 20 to 73 years. Twenty-six subjects underwent single-eye treatment, and 24 subjects had both eyes treated.

METHODS

A modified Intacs procedure was performed on subjects with keratoconus. Pachymetry was measured at the incision site, and the incision was made at 66% of the corneal thickness. A thicker ring segment was typically placed inferiorly, and a thinner segment was placed superiorly on the basis of a refractive nomogram.

MAIN OUTCOME MEASURES

Differences between preoperative and postoperative uncorrected visual acuity, best spectacle-corrected acuity, and spherical equivalent. Changes in irregular astigmatism were evaluated with the inferior-superior value from comeotopographic maps, and differences in refractive cylinder groups were studied.

RESULTS

Preoperative mean best-corrected logarithm of the minimum angle of resolution (LogMAR) visual acuity was 0.41 (20/50 - 1) (standard deviation [SD], +/-0.48), which improved to a postoperative mean of 0.24 (20/32 - 2) (SD, +/-0.31) (two lines of improvement). Preoperative mean uncorrected LogMAR visual acuity was 1.05 (20/200 - 2 1) (SD, +/-0.48), which improved to a mean of 0.61 (20/80-) (SD, +/-0.52) (four lines of improvement) at postoperative follow-up. Preoperative mean best-corrected LogMAR acuity in the corneal scarring group was 0.96 (20/200 + 2) (SD, +/-0.72), which improved to a mean of 0.54 (SD, +/-0.43) (20/63 - 2) (five lines of improvement). Uncorrected mean LogMAR acuity in the eyes with corneal scarring was 1.42 (20/400 - 4) (SD, +/-0.27), which improved to a mean of 1.03 (20/200 - 1) (SD, +/-73) (three lines of improvement). The mean spherical equivalent before surgery was -3.89 diopters (D) (SD, +/-5.16), which was reduced to a mean of -1.46 D (+/-4.11) at the postoperative follow-up.

CONCLUSIONS

Asymmetric Intacs implantation can improve both uncorrected and best spectacle-corrected visual acuity and can reduce irregular astigmatism in corneas with and without corneal scarring.

Six-year Experience With Excimer Laser Surgery for Primary Keratoconus in Russia

PURPOSE

To report our results using PRK combined with PTK to treat keratoconus.

METHODS

Forty-one patients (70 eyes) underwent PRK+PTK with a Nidek EC-5000 excimer laser. PRK included spherical or cylindrical ablations, or both. PRK ablation zone diameter was 6.00 mm. PTK was performed with an ablation zone diameter of 8.00 mm and a transition zone of 9 mm. PTK ablation zone was decentered toward the cone apex, according to corneal topography.

RESULTS

Refractive results: UCVA increased from 0.07 +/- 0.003 to 0.76 +/- 0.03 (69.2% of eyes had uncorrected visual acuity of 1.0); mean BSCVA increased from 0.70 +/- 0.03 to 0.83 +/- 0.04; myopia decreased from a mean 5.32 +/- 0.62 D to 1.55 +/- 0.30 D and astigmatism decreased from a mean 3.25 +/- 0.53 D to 1.75 +/- 0.25 D. Therapeutic results: Keratoconus progression was stopped in 91.43% of eyes with a mean follow-up of 3.5 years and maximum follow-up of 6 years.

CONCLUSION

PRK+PTK with the Nidek EC-5000 excimer laser was an excellent option for patients with primary keratoconus.

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.

Phototherapeutic keratectomy: 12 years of experience

BACKGROUND

Phototherapeutic keratectomy (PTK) has been employed as a surgical tool to treat corneal disease for more than 10 years. The laser has made it possible to remove superficial corneal opacities and thereby restore vision. The 193 nm ultraviolet light separates molecules and splits molecules in biological tissue, thereby ablating it. About 0.25 microm of tissue is ablated by each pulse. The development of the excimer laser technique has been fast. It has principally focused on refractive surgery but has also benefited PTK.

CORNEAL DYSTROPHIES

The ability to delay or postpone corneal grafting in superficial corneal dystrophies represents a very important achievement. Map-dot-fingerprint dystrophy or basal membrane dystrophy is a common indication for PTK. Other dystrophies such as Meesman's, Reis-Bückler's, Thiel-Benke's, granular, macular, lattice and Schnyder's can be treated, although with differing degrees of success and varying rates of recurrence. Subepithelial scarring in Fuchs' dystrophy has been ablated. Other trials have involved the removal of substantial parts of the stroma in order to reduce the load on the endothelium. Recurrent dystrophic changes can likewise be removed from corneal grafts and thus prevent the need for regrafting.

RECURRENT EROSIONS

Laser treatment has made it possible to manage wound-healing problems better after recurrent erosions. Recurrent erosions are the most common indications for PTK: several studies show good and persistent effects with this type of treatment. Persistent epithelial defects of various origins, among them corneal ulcers resulting from allergic disease, can likewise be treated.

SCAR TISSUE

Scars after surgery such as pterygeum excision can be removed. Smooth muscle actin containing fibroblasts in old scars should be given special consideration in PTK. Excimer laser surgery can be successfully combined with conventional surgery to remove excessive scar tissue, Salzmann's nodules and very flaky and coarse band keratopathy. Irregular corneal surfaces following ulcers and injuries pose problems that have so far proved difficult to overcome. Thinning is often seen after bacterial corneal ulcers or after herpes simplex keratitis. A rough or uneven surface can be made smoother by using modulators during treatment by casting a new surface under a hard contact lens (PALM technique), a surface that is then projected into the stroma by laser ablation. Modern techniques linking the excimer laser with computerized corneal topography and wavefront analysis promise to further improve the smoothing capacities of lasers and to increase the quality of optical results.

COMPLICATIONS

The most feared complication of PTK is the postoperative infection. These are rare. Haze is usually not prominent but scar tissue formation of a more persistent type has been noted after laser surgery in eyes with pre-existing surgical scars. Keratectasia has been described after PTK. Failure due to deep opacities or a surface that is too uneven is a more common frustration. This paper reviews advances in excimer laser treatment of corneal disease.

Intracorneal Ring Segments for Iatrogenic Keratectasia After Laser in situ Keratomileusis or Photorefractive Keratectomy

PURPOSE

Intrastromal corneal ring segments (Intacs) were inserted in four eyes with iatrogenic keratectasia, 12 to 44 months after laser in situ keratomileusis (LASIK) in two patients and photorefractive keratectomy (PRK) in two patients, in order to avoid penetrating keratoplasty and to improve quality of vision.

METHODS

A modified asymmetrical Intacs micro-thin prescription inserts implantation technique was used in three eyes where a 1.0-mm temporal incision and a superior-inferior dissection were performed. A thicker segment was implanted in the lower stromal channel and a thinner one was placed in the superior channel. In the fourth eye, because of the severity of the corneal bulging after PRK, two 5.0-mm optical zone symmetrical Ferrara Ring segments were implanted.

RESULTS

Ten months after surgery, all eyes experienced a significant improvement of uncorrected and best spectacle-corrected visual acuity. The topographical indices showed an overall surface regularization with increased corneal uniformity and potential corneal visual acuity. No intraoperative or postoperative complications occurred.

CONCLUSIONS

Asymmetrical or symmetrical corneal ring segment implantation in eyes with keratectasia after LASIK or PRK resulted in safe, fairly predictable corneal regularization, with significant improvement of aided and unaided vision. In the short term, these techniques seem to be helpful in reducing the progression of corneal ectasia after excimer laser surgery, delaying or avoiding the need of penetrating keratoplasty.

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.