Comparison of deep lamellar keratoplasty and penetrating keratoplasty

To compare the topographic and refractive effects from the arcuate relaxing incisions in treating post-keratoplasty astigmatism after deep anterior lamellar keratoplasty (DALK), penetrating keratoplasty (PKP)

Keratoplasty

Post-Keratoplasty astigmatism is a significant challenge for surgeons after a successful keratoplasty surgery. Many measures have been studied for its management; starting from simple measures such as contact lenses, Spectacles, Selective Suture Removal (SSR) in interrupted or mixed sutures, and Suture sliding in single continues sutures (SCS). Others include Wedge resection, Excimer LASER ablation either photorefractive keratectomy (PRK) with Intraoperative Mitomycin C (MMC) or Laser-assisted in situ keratomileuses (LASIK). Moreover, wavefront-guided LASIK was effective in treating irregular astigmatism. Toric Intraocular Lens (IOL) Implantation for correction of regular astigmatism, and finally repeat keratoplasty.

Penetrating Keratoplasty

Penetrating keratoplasty (PKP) jeopardizes the intraocular anatomy and immunological integrity of the eye. Hence, it increases the risk of rejection and intraocular inflammation. Anwar et al. have described Deep Anterior Lamellar Keratoplasty (DALK) using the big-bubble technique as replacing only the stromal tissue and preserving recipient endothelium. It has many advantages over PKP such as preservation of the globe integrity, faster wound healing, earlier suture removal, faster visual rehabilitation, no risk of endothelial rejection and this leads to the rapid tapering of steroids and reduction of complications.

Arcuate keratotomy

Arcuate Relaxing Incisions “Arcuate keratotomy” (AK) provides for fast visual rehabilitation, as well as economical, easy, and a relatively safe procedure for the management of post-keratoplasty astigmatism. It is defined as creating one or more arc-shaped incision in the cornea; it can be constructed using the blade, arcuate Keratome or Femtolaser. Moreover, it can be combined with Excimer LASER, stress sutures, and during cataract surgery. Its main principle is flattening of the steep meridian, and that will also steepen the opposite un-incised meridian that is 90 degrees away, which is known as the coupling ratio. The coupling ratio can be one where the flattening of the steep meridian and the steepening of the opposite meridian is equal, and that will not change the spherical equivalent. However, if the coupling ratio is more than one, then that will result in more flattening of the incised meridian than the steepening of the un-incised opposite meridian leading to more flattening of the cornea and the spherical equivalent will be a hyperopic shift and vice versa. We hypothesize that the tightness of the graft in DALK being pushed by the host Descemet’s membrane might affect the outcome of the incision.

Keratoplasty surgery

This study is a retrospective review of Interventional consecutive case series in a single-center, Devers Eye Institute, Portland, Oregon, USA. Surgical consent for AK surgery was approved by our hospitals’ institutional review boards for patients. This study was divided into two groups: A DALK group and A PKP group, each group contains 20 eyes. We analyzed 40 consecutive eyes intervened upon at the Devers Eye Institute, cornea service in Portland, OR, USA. In the DALK group, only one patient was excluded, as there was an intraoperative wound gaping after the incision, which needed to be corrected by immediate suturing. All patients were adults and of any sex; three months after complete suture removal with astigmatism more than 4 Dioptres (D), all grafts were clear, central, with similar intraoperative trephination size, with no clinical edema at the slit-lamp examination. All patients have completed the follow-up visits, and the refractive and topographic data were recorded, preoperative and average 3 months’ postoperative. We excluded patients with irregular astigmatism that prevented proper estimation of the refraction, severe dry eye, signs of allograft reaction, any active infectious disease, visually significant cataracts, pregnancy, and collagen disease.

Technique

We adopt the Moorfields Eye Hospital standardized AK technique. The 6 O’clock position was marked while the patient is upright and looking straight ahead with both eyes open to avoid cyclotorsion. Under topical anesthesia, all eyes had at least one relaxing incision using a guarded, Thornton triple-edged arcuate blade (Duckworth & Kent), which was set at 90% depth of the thinnest point at the steepest hemi-meridian guided by the Oculus Pentacam®. The incision was placed 0.5 mm inside the donor’s cornea for a 60-degree arc. After surgery, a topical antibiotic and steroids were prescribed. Postoperative follow-up examinations were performed on the first post-operative day, at week 1, at months 1, 2, 3 and included: Manifest Refraction, Best spectacle- corrected visual acuity (BSCVA), Corneal topography, using the Oculus Pentacam®. Moreover, other routine ophthalmological exams were conducted. Statistics: At the end of this study, data was statistically described in terms of mean ± standard deviation (± SD), median, correlation, and percentages when appropriate, Comparison of numerical variables between the two study groups was made using Paired-Samples and Independent T-Test. In vector analysis, the data was not normally distributed, so the Mann-Whitney U test was used as a test of significance. Correlation between groups using Pearson correlation: All statistical calculations were made using computer programs IBM® SPSS® Statistics Version 22 (Statistical Package for the Social Science; SPSS Inc., Chicago, IL, USA) for Macintosh. P-values less than 0.05 were considered significant.

Refractive astigmatism

In our study, the mean Preoperative refractive astigmatism was 4.73 D improved to 2.88 D in PKP group and 6.38 D which improved to 3.46 D in the DALK group. The mean refractive astigmatism change showed an improvement of 1.6 D (34%) in PKP (p-value = 0.03) and an improvement of 2.9 D (45.4%) in DALK group (p-value = 0.01). In Kubaloglu et al.,’s study, the decrease in the refractive cylinder was 43% DALK group and 52% in the PK group, they also showed a change in refractive astigmatism from 6.24 D to 3.53 D (43%) in the DALK group(P = 0.001) and from 6.48 D to 3.31 D (53%) in the PK group (P = 0.001) . In our study, the improvement was more for the DALK group, results were statistically insignificant (p-value = 0.163), and that aligned with the results of Kubaloglu et al., study. In Loriaut et al.,’s study, the mean Preoperative refractive astigmatism decreased by 3.79 D ± 2.06 D.



What was Known Arcuate relaxing incision provides a safe method for reducing post keratoplasty astigmatism with no enough data that compares it in DALK versus PKP. It showed a difference in the outcome between DALK, and PKP which might be attributed to the difference in the biomechanics, and that will need further studies to support this conclusion. To read full article visit  International Journal of Forensic Science & Pathology . published by SciDocPublishers