Effects of lamellar keratotomy on postkeratoplasty astigmatism

Post-penetrating keratoplasty astigmatism

Postoperative astigmatism is one of the common complications affecting visual outcomes after a penetrating keratoplasty. It can result from various factors related to host, donor and surgical technique, resulting in suboptimal visual outcome. While some of the measures taken during preoperative planning and during actual surgery can reduce the magnitude of postoperative astigmatism, postoperative correction of astigmatism is often required in cases with high degrees of astigmatism. When spectacles and contact lenses fail to provide optimal visual outcomes, various surgical techniques that include astigmatic keratotomy, compression sutures, toric intraocular lens placement, and laser refractive procedures can be considered. When none of these techniques are able to achieve a desired result with in the acceptable optical range, a repeat keratoplasty is considered a last option. We discuss the various causes and management of complication of postoperative astigmatism occurring after a full thickness corneal transplantation surgery.

Reversible femtosecond laser-assisted myopia correction: a non-human primate study of lenticule re-implantation after refractive lenticule extraction

LASIK (laser-assisted in situ keratomileusis) is a common laser refractive procedure for myopia and astigmatism, involving permanent removal of anterior corneal stromal tissue by excimer ablation beneath a hinged flap. Correction of refractive error is achieved by the resulting change in the curvature of the cornea and is limited by central corneal thickness, as a thin residual stromal bed may result in biomechanical instability of the cornea. A recently developed alternative to LASIK called Refractive Lenticule Extraction (ReLEx) utilizes solely a femtosecond laser (FSL) to incise an intrastromal refractive lenticule (RL), which results in reshaping the corneal curvature and correcting the myopia and/or astigmatism. As the RL is extracted intact in the ReLEx, we hypothesized that it could be cryopreserved and re-implanted at a later date to restore corneal stromal volume, in the event of keratectasia, making ReLEx a potentially reversible procedure, unlike LASIK. In this study, we re-implanted cryopreserved RLs in a non-human primate model of ReLEx. Mild intrastromal haze, noted during the first 2 weeks after re-implantation, subsided after 8 weeks. Refractive parameters including corneal thickness, anterior curvature and refractive error indices were restored to near pre-operative values after the re-implantation. Immunohistochemistry revealed no myofibroblast formation or abnormal collagen type I expression after 8 weeks, and a significant attenuation of fibronectin and tenascin expression from week 8 to 16 after re-implantation. In addition, keratocyte re-population could be found along the implanted RL interfaces. Our findings suggest that RL cryopreservation and re-implantation after ReLEx appears feasible, suggesting the possibility of potential reversibility of the procedure, and possible future uses of RLs in treating other corneal disorders and refractive errors.

Two-step LASIK after penetrating keratoplasty

PURPOSE

The point of interest of this retrospective case review is to study refractive changes caused by the hinged lamellar keratotomy and the refractive outcome after laser ablation in a second step within the scope of laser in situ keratomileusis (LASIK) in patients with penetrating keratoplasty.

METHODS

Data from eight patients obtained before lamellar keratotomy, before laser ablation, and three months later were evaluated. Keratotomies were performed with the Moria((R)) LSK one and the Amadeus((R)) 2 microkeratome, laser ablation was performed with the Schwind((R)) Keratome I and the Wavelight((R)) Allegretto WaveEyeQ.

RESULTS

Uncorrected visual acuity (UCVA) improved significantly from 1 [logMar] to 0.4 [logMar] at the last visit. Median gain of UCVA was 7.38 +/- 2.96 Snellen lines. Best spectacle-corrected visual acuity did not change significantly. Preoperative manifest refraction spherical equivalent decreased from -4.02 +/- 4.77 diopters (D) to -1.11 +/- 2.45 D after laser ablation. Mean preoperative manifest astigmatism was -7.27 +/- 3.65 D, after lamellar keratotomy -6.72 +/- 3.68 D, and after laser ablation -2.08 +/- 1.80 D. Manifest astigmatism did not change significantly after the keratotomy.

CONCLUSIONS

Lamellar keratotomy causes biomechanical changes to the cornea. We favor a two-step LASIK in penetrating keratoplasty patients in order to improve precision and predictability of the refractive outcome.

Flap-induced Refraction Change in LASIK After Penetrating Keratoplasty

PURPOSE

To further analyze the refractive and topographic changes occurring with microkeratome lamellar keratotomy and to investigate possible factors associated in eyes with previous penetrating keratoplasty (PK).

METHODS

The Hansatome microkeratome was used to create a lamellar corneal flap in 21 eyes of 19 patients after PK. The laser ablation was not performed in the first stage. Pre- and postoperative refractions and corneal topographies were compared to evaluate possible changes induced by the keratotomy.

RESULTS

Twenty-one eyes were analyzed in this study. Mean time between PK and lamellar keratotomy was 36.63 +/- 28.23 months (range: 12 to 120 months). No microkeratome-related flap complications occurred. Previous to the keratotomy, the mean spherical equivalent refraction was -4.26 +/- 3.41 diopters (D), mean refractive astigmatism was -4.71 +/- 2.27 D, and mean topographic astigmatism was 5.28 +/- 2.94 D. After keratotomy, eyes showed statistically significant changes in spherical equivalent refraction from preoperative values (P = .025), with 3 eyes showing changes > 2.00 D. Average refractive and topographic astigmatism did not change significantly from before to after keratotomy. However, surgically induced astigmatism (SIA) calculated through vector analysis was > 1.01 in 11 (52.4%) eyes. A statistically significant correlation was found between the SIA values and preoperative refractive astigmatism (P = .025).

CONCLUSIONS

Lamellar keratotomy as part of two-stage LASIK in eyes with prior PK led to refractive changes that justify the use of this technique, especially in eyes with high degrees of preoperative astigmatism.

Two-step laser in situ keratomileusis to correct high astigmatism after corneal autograft

We report a case in which significant anisometropia and astigmatism after an autograft by rotation was treated by a 2-step laser in situ keratomileusis (LASIK) procedure. Six weeks after the lamellar keratotomy, photoablation was performed using the LADARVision 4000 excimer laser. The ablation depth was 87.2 mum on a 6.0 mm optical zone. One day postoperatively, the uncorrected visual acuity (UCVA) was 7/10 and the refractive error was -0.25 -0.25 x 67. Two months later, the UCVA was 5/10 and the best corrected visual acuity, 8/10 Parinaud 2 with a refractive error of +1.75 -1.25 x 16. The case demonstrates the effectiveness of 2-step LASIK for the correction of astigmatism induced by a corneal autograft. The significant reduction in autograft-induced astigmatism, together with stabilization of the higher-order aberrations, resulted in restoration of satisfactory functional vision.

Correction of post-keratoplasty astigmatism with keratotomies in the host cornea

We evaluated the effects of astigmatic keratotomy performed in the host cornea to treat astigmatism after penetrating keratoplasty. In 11 patients with high post-keratoplasty astigmatisms (mean 9.02 diopters [D]; range 5.5 to 17.4 D), an arcuate keratotomy was performed in the host cornea. The mean incision depth was 575 mum (range 500 to 600 mum). The refractive data were analyzed using the Alpins method for vector analysis. The mean keratometric cylinder decreased to 3.41 D (range 0.9 to 5.3 D). The mean surgically induced astigmatism achieved was 7.3 +/- 3.89, with a mean correction index of 0.82 +/- 0.34. No microperforations were observed, and neither graft decompensation nor rejection occurred. Astigmatic keratotomy performed in the host cornea was a safe procedure to reduce post-keratoplasty astigmatism. The procedure offers the potential for correction of the astigmatism and has satisfactory predictability.

Laser in situ keratomileusis outcomes following radial keratotomy, astigmatic keratotomy, photorefractive keratectomy, and penetrating keratoplasty

PURPOSE

To evaluate the safety and efficacy of laser in situ keratomileusis (LASIK) to enhance refractive status following other corneal surgical procedures.

SETTING

Clinical office-based practice.

METHODS

Seventy-one eyes of 57 patients had LASIK for refractive errors following radial keratotomy (n = 22), astigmatic keratotomy (n = 13), photorefractive keratectomy (n = 18), and penetrating keratoplasty (n = 18). A Moria LSK-1 microkeratome was used with a Visx S2 or Wavelight Allegretto excimer laser. Data were acquired by retrospective chart review of all appropriately qualified patients.

RESULTS

The mean preoperative manifest refractive spherical equivalent (MRSE) was -3.93 diopters (D) +/- 2.83 (SD) in myopic eyes and +1.43 +/- 1.79 D in hyperopic eyes. The mean time from the initial corneal surgical procedure to LASIK was 65.0 months. The mean post-LASIK follow-up was 9.40 months (range 1 to 42 months). Postoperatively, the mean MRSE was -0.85 +/- 1.42 D in myopic eyes (P<.0001) and -0.16 +/- 1.09 D in hyperopic eyes (P<.0001). Enhancement by LASIK was required in 14% of eyes.

CONCLUSION

In eyes that have had a variety of previous corneal surgeries, LASIK offers a safe and predictable method for enhancing refractive results.

Repeat keratoplasty for correction of high or irregular postkeratoplasty astigmatism in clear corneal grafts

PURPOSE

To evaluate the functional results of repeat penetrating keratoplasty in clear corneal grafts with high/irregular postkeratoplasty astigmatism.

DESIGN

Retrospective, longitudinal, single-center, consecutive clinical case series.

METHODS

We studied 17 eyes (16 keratoconus, 1 Fuchs' dystrophy) of 16 patients (age, 54.9 +/- 12.6 years). They were treated with repeat PK, performed using the 193-nm Zeiss-Meditec MEL-60 excimer laser using round metal masks (diameter, 7.5-8.0 mm), and employing double running sutures. main outcome measures: Subjective refractometry, standard keratometry, and corneal topography (Tomey TMS-1) were used to assess best-corrected visual acuity (BCVA), spherical equivalent (SEQ), keratometric and topographic central corneal power (CP), refractive, keratometric and topographic astigmatism, surface regularity index (SRI), surface asymmetry index (SAI), and potential visual acuity (PVA) preoperatively, before and after first suture removal (1.1 year), and after second suture removal (1.8 years).

RESULTS

Visual acuity improved significantly (BCVA from 0.2-0.5, P = .04 or better) for all postoperative measurements. CP decreased significantly, but SEQ did not change. All measures of astigmatism and SRI and SAI values showed postoperative improvement with sutures in place; however, astigmatism increased significantly after second suture removal.

CONCLUSIONS

With all-sutures-in, BCVA and astigmatism improve significantly after repeat PK for high/irregular astigmatism. However, to present significant increase in astigmatism, final suture removal should be postponed as long as possible in such eyes.

Standardized arcuate keratotomy for postkeratoplasty astigmatism

PURPOSE

To assess the effect of standardized, paired arcuate keratotomy (AK) on the change in astigmatism in postkeratoplasty eyes.

SETTING

Moorfields Eye Hospital, London, United Kingdom.

METHODS

A retrospective review was conducted of 20 eyes of 19 patients having the same AK procedure regardless of the magnitude of the preoperative astigmatism. Each eye had a pair of 60-degree arc length incisions placed in the corneal stroma. The incisions were 600 mum deep and 6.0 mm apart. The preoperative and postoperative refractions and complications were analyzed. Astigmatic change was analyzed without regard to axis, as surgically induced refractive change, and using a modified polar plot of change in astigmatism.

RESULTS

The mean cylinder was reduced from -10.99 diopters (D) +/- 4.26 (SD) to -3.33 +/- 2.18 D. There was no significant change in the mean spherical equivalent. There was a strong correlation between the magnitude of the preoperative cylinder and the magnitude of the change in astigmatism (R2 = 0.76). In 3 eyes, the surgically induced axis of astigmatism was more than 15 degrees from that expected.

CONCLUSIONS

In postkeratoplasty eyes, the change in the magnitude of astigmatism induced by standardized AK was proportional to the preoperative magnitude of astigmatism. Arcuate nomograms for congenital astigmatism have no role in the management of astigmatism in postkeratoplasty eyes.

Corneal first-surface aberration analysis of the biomechanical effects of astigmatic keratotomy and a microkeratome cut after penetrating keratoplasty

Astigmatic keratotomy (AK) was performed in a patient after penetrating keratoplasty (PKP) for keratoconus to reduce high post-PKP astigmatism. The procedure led to a significant decrease in astigmatism, but corneal higher-order aberrations (HOAs) increased. After PKP, the patient was scheduled for 2-step laser in situ keratomileusis (LASIK) to correct myopia and astigmatism. One day after the microkeratome cut, a decrease of -2.75 diopters in the spherical equivalent (SE) was noted. Although subjective manifest cylinder and corneal spherical aberrations were marginally affected, a marked decrease in coma and other HOAs could be observed. One month after the cut, the SE was unchanged. Excimer laser ablation was not performed as the patient was satisfied with the result and refused further treatment. This case shows that AK cuts can induce HOAs and a single microkeratome cut performed in corneal grafts can have strong biomechanical effects on lower-order aberrations and HOAs. If LASIK is planned after PKP, a 2-step approach is recommended to anticipate biomechanical effects and avoid overcorrection or undercorrection.

Contact Lens Prescribing in a Specialist Medical Contact Lens Clinic Based in an NHS Hospital

PURPOSE

To describe the range of indications for contact lenses and the types of lenses being used in an NHS hospital-based specialist medical contact lens clinic and contrast this with information from 12 years ago.

METHODS

A retrospective audit of 596 clinic attendances was performed in the contact lens clinic at the Western Eye Hospital between April 2002 and March 2003. The results were compared with a similar audit performed in 1991. We used the hospitals electronic records, and information on contact lens prescribing was obtained directly from the receipts generated by the contact lens department and the accounts department.

RESULTS

We saw 392 patients with 88.5% of patients requiring 2 or less visits per year. The majority of referrals are for high myopia (28.6%) closely followed by aphakia (25.2%) and keratoconus (24.7%). This is in contrast to 1991 when 68% of referrals were for aphakia and twice as many myopes (17%) were seen as keratoconus patients (8%). A total of 560 lenses were prescribed with 68 different types of lens in use. The seven most commonly used lens types accounted for 61% of all lenses prescribed.

CONCLUSIONS

Medical contact lens clinics provide a specialist service and also provide an important training resource for junior ophthalmologists. Safer cataract surgical techniques have had a significant impact on the case mix seen in our clinic, with the emphasis moving away from aphakic and myopic patients and toward the more challenging to fit eyes with keratoconus or postcorneal surgery.