Transepithelial photorefractive keratectomy for the management of hyperopic regression after conductive keratoplasty

Abstract

Several refractive techniques are available for the treatment of hyperopia. Conductive keratoplasty (CK) is a safe and non-ablative procedure suitable for the treatment of low hyperopia and presbyopia. Due to the high rate of regression, it is not a commonly used technique. There is minimal literature about the use of refractive procedures for the treatment of hyperopic regression after CK. We report a case of a 49-year-old man who had undergone bilateral CK 15 years before for the correction of his hyperopia. He experienced a regression, with sph +2.75 cyl −0.50(20) in the right eye and sph +2.50 cyl −0.75(170) in the left eye. Transepithelial photorefractive keratectomy (tPRK) was performed with Schwind Amaris 750 s. After 12 months, his best-corrected visual acuity was 20/20, with −0.25 sph in both eyes. To the best of our knowledge, this is the first reported case of tPRK performed after CK.

Background

The surgical treatment of hyperopia represents a great challenge for ophthalmologists, as the refractive error progresses with age and affects the visual acuity more and more according to the loss of accommodation. There are several options, including lens procedures and corneal ablative and non-ablative techniques.

Phakic intraocular lens (pIOL) implantation allows treating high hyperopia with good predictability, fast rehabilitation, stable refraction and it is a reversible technique. However, pIOL implantation can lead to serious complications like corneal decompensation, angle-closure glaucoma, cataract, retinal detachment, uveitis and endophthalmitis.¹

Clear lens extraction and refractive lensectomy are terms used to describe the removal of the crystalline lens followed by IOL implantation for refractive purpose, in spite of the fact that there are no lens opacities. It appeared to be an effective alternative to other techniques especially in presbyopic patients, although it is not free from the complications of an intraocular procedure.^{2 3}

Corneal ablation techniques like photorefractive keratectomy (PRK) and laser-assisted in situ keratomileusis (LASIK) are frequently used to correct hyperopia or presbyopia and involve the use of an excimer laser. LASIK requires the creation of a corneal flap with a femtosecond laser, rather than with a microkeratome, followed by excimer laser ablation and flap repositioning. This technique allows a fast and almost painless recovery, with a minimal tissue reaction and reduced risk of corneal haze. Nevertheless, LASIK can induce worsening of a pre-existing dry eye and lead to possible flap-related complications.

PRK is a surface ablation technique in which the epithelium is mechanically scraped off, either with a previous exposure to 20% alcohol solution or directly removed with excimer laser in a single step procedure (transepithelial PRK). Bowman’s membrane and anterior stroma are then ablated. PRK is a technically easy procedure, suitable for thinner corneas to reduce the risk of ectasia. The disadvantages include the longer recovery time and discomfort for patients and the risk of corneal haze.⁴

LASIK and PRK have shown comparable results in terms of efficacy and safety for the treatment of hyperopia.⁵

The small-incision lenticule extraction (SMILE) is a novel refractive procedure and consists in the shaping of a lenticule within the cornea with a femtosecond laser followed by the extraction through a very small corneal incision. This technique allows the change of corneal curvature preserving the structure of front corneal tissue inducing minimal inflammation and discomfort. Nonetheless, it could be more technically challenging. Regarding the efficacy in hyperopic eyes, it appears that SMILE is a feasible and effective procedure, although further research is needed to evaluate predictability and effectiveness. At present, SMILE is unsuitable for the correction of hyperopic astigmatism.⁶

Photorefractive intrastromal crosslinking (PiXL) is a recent non-ablative technique to achieve the steepening of the central cornea by applying crosslinking in an annular shape in the midpheripheral cornea. According to Stodulka et al, it is a promising alternative to conventional refractive techniques for low hyperopia.⁷

Conductive keratoplasty (CK) is a minimally invasive and non-ablative procedure, used for the correction of hyperopia and presbyopia. In April 2002, the US Food and Drug Administration (FDA) granted approval of the ViewPoint CK System for the treatment of mild to moderate spherical hyperopia (0.75 D to 3.00 D) with less than +0.75 D coexisting astigmatism, and for presbyopia in 2004. In CK, radiofrequency energy is delivered at 8–24 locations inserting a thin probe in the peripheral corneal stroma in order to shrink collagen and consequently steepen the central cornea.^8–10

CK was shown to be safe, but it is not without complications. In a multicentre clinical trial performed in 2005, 400 eyes were treated and followed up to 2 years. Only one eye experienced corneal perforation. Other mild adverse events were one case of iritis and three cases of intraocular pressure increase, all resolved without sequelae.⁸ Compared with LASIK and PRK, CK preserves the optical zone and does not induce haze or flap complications.¹¹

Concerning stability of refraction, Ehrlich et al observed that the refractive effect of CK regresses significantly over a long-term follow-up (mean 73 months). Particularly, the rate of regression in their study appeared to be significantly greater than that typically reported for hyperopic LASIK.¹² Although, CK is an option to retreat the hyperopic overcorrection and astigmatism after LASIK or PRK.^13–15 Moshirfar et al stated that CK is a safe procedure but results in inevitable regression. In particular, they demonstrated that patients with previous LASIK or PRK showed a greater treatment response to CK but regressed at a similar rate as those eyes without prior LASIK or PRK.¹⁶

As CK has been replaced by more popular and modern laser techniques, finding a patient with a regression of hyperopia after CK is not frequent. We report our experience about a case of regression of hyperopia after CK treated with transepithelial photorefractive keratectomy (tPRK).

Case presentation

A 49-year-old Caucasian man presented to us for surgical correction of his refractive error. The patient had undergone a CK procedure in both eyes 15 years before, to correct his hyperopia of +4.25 in the right eye and +4.75 in the left eye. After 5 years, he experienced a regression, and at the moment of our examination, his best-corrected visual acuity (BCVA) was 20/20 with sph +2.75 cyl −0.50(20) in the right eye and sph +2.50 cyl −0.75(170) in the left eye.

Investigations

On slit lamp examination, the eight CK spots 7.00 mm from the corneal centre were clearly visible (figure 1). The lens was clear and fundus examination was normal in both eyes. The central corneal thickness was 561 µm in the right eye and 556 µm in the left eye. Preoperatively, corneal topography was performed.

Figure 1.

Conductive keratoplasty corneal spots.

Treatment

After informed consent was obtained, aberration-free single-step tPRK was performed with Schwind Amaris 750 s. An optical zone of 7.00 mm was treated, with a transition zone of 1.78 mm in the right eye and 1.66 mm in the left eye, the total ablation zone was of 8.78 mm and 8.66 mm, respectively. Postoperatively, a therapeutic contact lens was worn for 1 week, and topical associated steroids and antibiotic therapy were prescribed for 4 weeks. Tapering regimen of topical steroids was continued for 3 months.

Figures 2 and 3 show the preoperative and postoperative topography.

Figure 2.

Corneal tomography showing the saggital power map before and after transepithelial photorefractive keratectomy in the right eye, showing a flat cornea with some astigmatism before treatment and a large area of increased corneal power after treatment.

Figure 3.

Corneal tomography showing the saggital power map before and after transepithelial photorefractive keratectomy in the left eye, showing a flat cornea with some astigmatism before treatment and a large area of increased corneal power after treatment.

Outcome and follow-up

After 12 months, no adverse events were reported and his BCVA was 20/20, with −0.25 sph in both eyes.

Discussion

Regression of refractive effect means the tendency of the eye to return towards the original refraction after a period of desired refraction achieved with a surgical procedure. The rate of regression after hyperopic refractive treatment is difficult to determine due to different definitions of regression, follow-up periods and methods. High hyperopia, increasing age, smaller optical ablation zone, lenticular shift and corneal modifications involving biomechanics and epithelial remodelling appear to influence regression.¹⁷

Recently, corneal crosslinking has been combined to refractive procedures like hyperopic LASIK in order to strengthen the cornea and prevent regression, with promising results.^18–20

Several options for hyperopic retreatment are available, depending on the primary refractive procedure. For example, the regression after LASIK can be approached with flap re-lift and excimer laser application, according to a sufficient residual stromal bed thickness. Otherwise, surface ablation methods like PRK and laser-assisted subepithelial keratectomy are alternative choices.¹⁷

There is minimal literature about the use of refractive procedures after CK. Both Klein et al and Kymionis et al presented cases of patients in whom residual hyperopia with astigmatism after CK was successfully treated with LASIK.^{21 22} Furthermore, Felipe et al conducted a prospective case series to evaluate the efficacy and safety of PRK to treat regression in eyes with previous CK for presbyopia. They evaluated 20 eyes of 20 patients until 6 months postoperatively and found out that only 13% of the patients were within ±0.50 D of the intended refraction, whereas 73% were within ±1 D. They attributed the overcorrection to numerous factors, including the old age of patients, the small optical zone treated (5.5 mm) and the unpredictable refractive results in patients who underwent previous refractive surgery, especially in early retreatment. The procedure showed to be safe as no patient developed perioperative complications or adverse events during the follow-up and no eye lost more than 2 lines of distance BCVA.²³

To the best of our knowledge, this is the first reported case of tPRK performed after CK.

Our choice to treat the hyperopic regression with tPRK followed several considerations.

Bilateral lensectomy was excluded because there were no lens opacities, and the refractive error was low and suitable for a corneal ablation refractive technique. Therefore, we preferred avoiding the well-known safety issues of intraocular surgery.

The previous CK makes it necessary to treat a smaller optical zone, as the ablation should be made between the corneal scars. In Klein’s case, an optical zone of 6.00 mm was treated with the LASIK technique.²¹ Felipe et al treated a 5.5 mm zone with the conventional PRK and it resulted in an overcorrection.²³ We managed to treat a total ablation zone of 8.78 mm and 8.66 mm, respectively, in the right and left eyes, and we achieved a promising outcome until the last follow-up.

Second, surface ablation techniques like tPRK resulted in more predictable, more stable and safer results, and with less regression indices for the treatment of low hyperopia (up to +3 D) when compared with moderate and high hyperopia.^{24 25}

Finally, tPRK is generally cheaper than other procedures (eg, LASIK) in most settings, which is another consideration in the choice of treatment.

In conclusion, the management of hyperopic regression is challenging. The approach should be customised according to the previous refractive procedure and the characteristics of each patient.

Learning points.

• The refractive treatment of hyperopia includes several corneal ablative and non-ablative procedures, none of which is free from regression.

• The management of hyperopic regression is challenging.

• The approach should be customised according to the previous refractive procedure and the characteristics of each patient.

• Transepithelial photorefractive keratectomy is an option to treat the regression of low hyperopia after conductive keratoplasty, allowing the ablation of a large optical zone.