Phototherapeutic keratectomy for decentration and central islands after photorefractive keratectomy

Phototherapeutic keratectomy: Indications, methods and decision making

Phototherapeutic keratectomy (PTK) involves treating anterior corneal lesions by superficial corneal ablation using an excimer laser (193 nm). Some of the commonly treated conditions include recurrent corneal erosions (RCE), corneal dystrophies, spheroidal degeneration, keratoconus, and corneal scars. We discuss various techniques of PTK including large area PTK, focal PTK, and multifocal PTK and alternatives to PTK. Masking agents like hyaluronate, methylcellulose, and dextran are recommended to help achieve a better outcome when ablating irregular corneal surfaces. Antifibrotic agents like mitomycin C reduce the chances of recurrence of the disease, apart from minimizing the postoperative scarring. Some of the complications include induced hyperopia and irregular astigmatism, haze, recurrence, and corneal thinning. However, earlier postoperative recovery, possibility of a repeat procedure, and ability to control the depth of ablation make PTK a promising, minimally invasive alternative to keratoplasty in cases with anterior corneal pathologies.

Phototherapeutic keratectomy

Phototherapeutic keratectomy is an excimer laser-based surgical procedure widely performed by corneal surgeons for treating anterior corneal stromal pathologies. Phototherapeutic keratectomy helps by ablating the corneal stroma, thereby improving corneal clarity and smoothening the surface. Transient discomfort and induced hyperopia from corneal flattening are the immediate postoperative concerns. The long-term course is often marked by the recurrence of original corneal pathology and corneal haze formation. Phototherapeutic keratectomy, however, allows for repeat stromal ablation for managing recurrences, as the corneal thickness permits, without affecting the outcome of future keratoplasty. Adjunctive methods such as topical mitomycin-C may be additionally used to reduce recurrence rates. Also, various masking agents such as carboxymethyl cellulose, sodium hyaluronate, and dextran are used in eyes with irregular corneal surface to allow for uniform stromal ablation. Overall, phototherapeutic keratectomy has provided corneal surgeons an additional surgical tool, particularly those residing in developing nations where the availability of donor corneal tissue is an important limiting factor.

Phototherapeutic Keratectomy: Science and Art

PURPOSE

To describe, with videos, the principles of excimer laser phototherapeutic keratectomy (PTK) for the treatment of corneal scars, corneal surface irregularity, and recurrent corneal erosions.

METHODS

Depending on the pathology in a treated cornea, the epithelium is removed either by transepithelial PTK ablation with the excimer laser or thorough scraping with a scalpel blade. Stromal PTK can be performed with or without photorefractive keratectomy (PRK), depending on the refractive status of both eyes. Residual surface irregularity is treated with masking-smoothing PTK. Typically, 0.02% mitomycin C treatment is applied for 30 seconds to corneas treated with PTK for scars and surface irregularity.

RESULTS

Transepithelial PTK with masking-smoothing typically improves corrected distance visual acuity in the eye even if the entire stromal opacity cannot be removed and can be used to debulk surface irregularity to facilitate subsequent therapeutic customized wavefront-guided or optical coherence tomography-guided PTK or PRK. PTK for recurrent erosion is performed after thorough mechanical epithelial debridement of redundant epithelial basement membrane (EBM) with a scalpel and should only include a dusting of excimer laser to remove residual EBM without inducing central irregular astigmatism or damaging limbal tissues. Meta-analyses are provided for PTK treatment for corneal scars, corneal dystrophies, and recurrent corneal erosions.

CONCLUSIONS

Excimer laser PTK is a highly effective treatment for superficial corneal scars, central corneal irregular astigmatism, and recurrent corneal erosions unresponsive to medical treatment or mechanical epithelial debridement alone. [J Refract Surg. 2017;33(3):203-210.].

Central island formation after cataract surgery in a laser in situ keratomileusis eye: New etiology

We report a case of central corneal steepness formation after cataract surgery in a post-laser in situ keratomileusis (LASIK) eye. A 51-year-old woman with traumatic cataract and a history of myopic LASIK surgery had uneventful phacoemulsification cataract surgery. Postoperatively, the corneal topography difference map showed a central island formation of 2.1 diopters (D) compared with the preoperative level, which correlated with a clinical myopic shift of 2.00 D from the targeted emmetropia. At 4 months, most of the central island had resolved spontaneously. At 15 months, topography returned to preoperative levels. We speculate that wound hydration in the flap interface during surgery resulted in a pond-like fluid accumulation in the center of the cornea, resulting in a myopic refractive shift. We report this case because of the high probability that this phenomenon could be confounded by an erroneous intraocular lens (IOL) calculation and the potential for a serious iatrogenic complication from a premature IOL exchange or touch-up procedure.

Predicting transepithelial phototherapeutic keratectomy outcomes using Fourier domain optical coherence tomography

PURPOSE

The aim of this study was to use Fourier domain optical coherence tomography to predict transepithelial phototherapeutic keratectomy outcomes.

METHODS

This is a prospective case series. Subjects with anterior stromal corneal opacities underwent an excimer laser phototherapeutic keratectomy (PTK) combined with a photorefractive keratectomy using the VISX S4 excimer laser (AMO, Inc, Santa Ana, CA). Preoperative and postoperative Fourier domain optical coherence tomography images were used to develop a simulation algorithm to predict treatment outcomes. Main outcome measures included preoperative and postoperative uncorrected distance visual acuities and corrected distance visual acuity.

RESULTS

Nine eyes of 8 patients were treated. The nominal ablation depth was 75 to 177 μm centrally and 62 to 185 μm peripherally. Measured PTK ablation depths were 20% higher centrally and 26% higher peripherally, compared with those for laser settings. Postoperatively, the mean uncorrected distance visual acuity was 20/41 (range, 20/25-20/80) compared with 20/103 (range, 20/60-20/400) preoperatively. The mean corrected distance visual acuity was 20/29 (range, 20/15-20/60) compared with 20/45 (range, 20/30-20/80) preoperatively. The MRSE was +1.38 ± 2.37 diopters (D) compared with -2.59 ± 2.83 D (mean ± SD). The mean astigmatism magnitude was 1.14 ± 0.83 D compared with 1.40 ± 1.18 D preoperatively. Postoperative MRSE correlated strongly with ablation settings, central and peripheral epithelial thickness (r = 0.99, P < 0.00001). Central islands remained difficult to predict and limited visual outcomes in some cases.

CONCLUSIONS

Optical coherence tomography measurements of opacity depth and 3-dimensional ablation simulation provide valuable guidance in PTK planning. Post-PTK refraction may be predicted with a regression formula that uses epithelial thickness measurements obtained by optical coherence tomography. The laser ablation rates described in this study apply only to the VISX laser.

Central Island Treatment Using Technolas 217 Based on Orbscan II Assessment

PURPOSE

To present a case of central island after myopic laser in situ keratomileusis and the treatment technique using Technolas 217 laser based on topography findings.

METHODS

Serial corneal topographies with Orbscan were taken and an ablation profile was generated with subsequent treatment using the phototherapeutic keratectomy mode and surface ablation technique.

RESULTS

Marked reduction was noted in the height of central island and the best spectacle-corrected visual acuity improved from 20/40 to 20/25.

CONCLUSIONS

Ablation profile based on corneal topography can provide a possible treatment option for patients with central island.

Circinate corneal scarring

A 56-year-old man presented with symptoms of monocular diplopia and reduced vision in his left eye. Visual acuities were R6/6, L6/12. At his previous visit left visual acuity was 6/6. An irregular area of anterior corneal stromal scarring was evident, encroaching on the visual axis of the left eye. Rigid lens fitting improved left visual acuity to 6/6, however, lens wear caused a corneal abrasion over the lesion after one to two hours of wear. Several other contact lens and surgical strategies were employed to successfully address the visual requirements of the patient.

LASIK complications: etiology, management, and prevention

Laser in situ keratomileusis (LASIK) is a rapidly evolving ophthalmic surgical procedure. Several anatomic and refractive complications have been identified. Anatomic complications include corneal flap abnormalities, epithelial ingrowth, and corneal ectasia. Refractive complications include unexpected refractive outcomes, irregular astigmatism, decentration, visual aberrations, and loss of vision. Infectious keratitis, dry eyes, and diffuse lamellar keratitis may also occur following LASIK. By examining the etiology, management, and prevention of these complications, the refractive surgeon may be able to improve visual outcomes and prevent vision-threatening problems. Reporting outcomes and mishaps of LASIK surgery will help refine our approach to the management of emerging complications.

Surgically induced topographical abnormalities after LASIK: management of central islands, corneal ectasia, decentration, and irregular astigmatism

Proper preoperative evaluation is critical for avoiding many postoperative complications associated with laser in-situ keratomileusis (LASIK). Proper nonsurgical management includes careful monitoring of patients during the recovery period using various testing procedures, including corneal topography. When surgical intervention is required, a stepwise approach often is used as a conservative treatment, allowing further treatment if necessary. Many complications after LASIK are amenable to further treatment. However, it often is advisable to monitor patients until improved instrumentation is developed. The authors review the etiology and management of several complications after LASIK by reviewing the literature and relaying their own clinical experiences.