Management of Compound Myopic Astigmatism Using Toric Implantable Collamer Lens after

Keratoconus is an ectatic disorder of the cornea that usually manifests during puberty. It is a bilateral, asymmetrical, noninflammatory ectatic disorder that causes conical anterior bulging and thinning of the cornea [1]. This abnormal shape of the cornea causes a steepening which results in a high astigmatism which increases as the disease progresses. This astigmatism can initially be corrected by glasses and contact lenses [2]. In advanced cases with severe myopic astigmatism and corneal opacity the patients become intolerant to contact lenses as fitting becomes difficult or visual acuity may not improve. In this group invasive procedures like penetrating or deep anterior lamellar keratoplasty are required for restoring the visual function [2]. Most of these patients are young and therefore lesser invasive procedures should be considered. Corneal ablative procedures like laser in situ keratomileusis and photorefractive keratectomy are usually contraindicated as they may cause worsening of the disease by causing further thinning of the cornea [3]. Intra stromal corneal ring segments have been used to correct the induced astigmatism and reinforce the cornea but they do not halt the progression of the disease [4]. Corneal collagen crosslinking using riboflavin (C3R) and ultraviolet (UV) light has been increasing used to halt the progression of keratoconus [5]. In our study our primary aim was to provide a glass-free vision to the patient of keratoconus by correcting the refractory error with the means of a toric collamer phakic intraocular lens (toric pIOL) placed in the ciliary sulcus (STAAR surgicals). This procedure was undertaken 3-6 months post-C3R which served to stabilize the myopic astigmatism.


Introduction
Keratoconus is an ectatic disorder of the cornea that usually manifests during puberty. It is a bilateral, asymmetrical, noninflammatory ectatic disorder that causes conical anterior bulging and thinning of the cornea [1]. This abnormal shape of the cornea causes a steepening which results in a high astigmatism which increases as the disease progresses. This astigmatism can initially be corrected by glasses and contact lenses [2]. In advanced cases with severe myopic astigmatism and corneal opacity the patients become intolerant to contact lenses as fitting becomes difficult or visual acuity may not improve. In this group invasive procedures like penetrating or deep anterior lamellar keratoplasty are required for restoring the visual function [2]. Most of these patients are young and therefore lesser invasive procedures should be considered. Corneal ablative procedures like laser in situ keratomileusis and photorefractive keratectomy are usually contraindicated as they may cause worsening of the disease by causing further thinning of the cornea [3]. Intra stromal corneal ring segments have been used to correct the induced astigmatism and reinforce the cornea but they do not halt the progression of the disease [4]. Corneal collagen crosslinking using riboflavin (C3R) and ultraviolet (UV) light has been increasing used to halt the progression of keratoconus [5]. In our study our primary aim was to provide a glass-free vision to the patient of keratoconus by correcting the refractory error with the means of a toric collamer phakic intraocular lens (toric pIOL) placed in the ciliary sulcus (STAAR surgicals). This procedure was undertaken 3-6 months post-C3R which served to stabilize the myopic astigmatism.

Study population
The inclusion criteria were age ≥18 years, best corrected visual acuity (BCVA) of 6/12 or better on Snellen's visual acuity chart, presence of unilateral / bilateral keratoconus as proven on Orb scan and a history of undergone C3R ≥3 months in the same eye. The exclusion criteria were anterior chamber depth < 2.8mm, presence of corneal opacity / cataract / macular degeneration, history of ocular hypertension or glaucoma or retinal detachment. Data recovered from the case records of these patients at baseline included age, gender, BCVA with refraction, slit lamp bio microscopy and fundus examination, IOP by Goldmann applanation tonometry, gonioscopy and corneal topography by Orb scan. The patients were followed-up at 1 month, 3-6 months and 1 year. At each follow-up visit, the visual outcome was assessed by means of BCVA with refraction and the safety analysis was performed by noting down any adverse events, anterior and posterior segment examination, vaulting of the toric pIOL, IOP measurements and gonioscopy. Repeat orb scan was done at the end of 1 year follow-up.

Surgical technique
All patients were operated under topical anesthesia. All patients were dilated with tropicamide plus phenylephrine and cyclopentolate eye drops one hour prior to surgery. A temporal incision was preferred in all cases. The ICL was inserted into the anterior chamber and placed in the sulcus and rotated into the required axis. The pupil was constricted with pilocarpine and a peripheral iridectomy was made. A representative example is shown in Figure 1.

Statistical Analysis
The mean and standard deviation were calculated for the age and follow-up of the patients.

Results
Twelve eyes of seven patients were evaluated. Five patients had bilateral implantation and two patients had unilateral implantation. The mean age of the study group was 24±3.1 years (Figure 2). There were 4 females and 3 males in the study group. The median follow-up period was 8 months (minimum 1 month, maximum 30 months). All eyes completed the one month follow-up. Six of the twelve eyes completed the 6 month and 12 month follow-up respectively. At the end of one month, all eyes maintained a UCVA of 6/9 or better, with 5 eyes having a UCVA of 6/6 ( Table 1). Of the six eyes that completed the six month and the one year follow-up, two eyes maintained a UCVA of 6/6 and four eyes maintained a UCVA of 6/9 respectively (Table 2 & 3). Out of the four eyes with UCVA of 6/9, three eyes had a mean residual spherical equivalent of +1.25 D and one eye had a residual spherical equivalent of -1.50 D. The mean residual cylindrical power was -1.25±(-1.54) D for the four eyes. There were no intra-or post-operative complications. No incidence of any rise in IOP, cataract formation or retinal detachment was noted.

Discussion
The purpose of our study was to analyze whether toric pIOL's could be used safely to correct myopic astigmatism which was stabilized by C3R in patients with keratoconus. The assessment of our data has shown satisfactory visual and safety outcomes. The predictability was very good as at the end of one year, two eyes were emmetrope, and four eyes had a mean residual cylindrical power of -1.25±(-1.54) D and mean residual spherical equivalent of +1.25 D (3 eyes) and -1.50 D (1 eye) respectively. To our knowledge, there have been only two studies that have analyzed the efficacy of toric pIOL in patients of keratoconus [6,7]. Alfonso et al. [6], have reported good stability and predictability with toric pIOL in patients of keratoconus for 12 months. Many other studies have been done to treat the refractive error of keratoconus by means of spherical anterior chamber pIOLs [8], iris fixated pIOLs [9], anterior and posterior chamber toric IOL's [10] as well as by refractive lens exchange [11] and multifocal IOL's [12]. Of all these, only the refractory lens exchange and multifocal IOL's have shown good results.
Phakic IOL's have been associated with complications like anterior sub capsular cataracts and increased IOP [13,14]. In our study though, we did not report any incidence of adverse event till the end of one year. However, one year may be a short duration of follow-up to evaluate the refractive stabilization as well as to gauge the development of any adverse reactions. This is one of the short-coming of our study. In conclusion, our results show that toric pIOL's can be used safely and predictably to correct the refractive error in keratoconus patients once the power has been stabilized by means of C3R. We recommend longer follow-up of the patient for at least 3-5 years along with a larger sample size to propose guidelines for refractive correction of keratoconus patients.