Clinical Outcomes of Toric Implantable Collamer Lens (T-ICL) and Toric Implantable Phakic Contact Lens (IPCL) for High Myopia with Astigmatism: A Comparative Study

1. INTRODUCTION

Myopia is the most prevalent refractive error in children and adults around the world, causing defective vision [1]. Myopia correction is required to avoid vision impairment. During the last 2 decades, various surgical procedures have been emerged and approved for treatment of different degrees of myopia. Refractive lens exchange, corneal ablation surgery, and phakic intraocular lens implantation (pIOL) are among these procedures. Ablative corneal operations like; laser-assisted in situ keratomileuses (LASIK), photorefractive keratectomy (PRK), laser-assisted subepithelial keratectomy and epi-LASIK, are not appropriate for correcting higher degrees of myopia because it has a higher risk of postoperative complications and poor visual outcomes [2]. Refractive lens surgery is not a suitable treatment option for patients aged less than 40 years due to a higher incidence of retinal detachment and loss of accommodation [3]. Alternatively, phakic intraocular lens implantation (pIOL) can treat significantly higher degrees of myopia that are beyond the range of refractive corneal surgery. Good visual outcomes, higher efficacy, reversibility, preservation of accommodation, long-term predictability, and stability are among the advantages of this procedure [4, 5]. But as pIOL implantation is an intraocular surgery, it may result in problems such as uveitis, pigment dispersion syndrome, cataract, pupillary block glaucoma, and endophthalmitis [6].

Nowadays, the Implantable Collamer Lens (ICL) (Staar Surgical, Nidau, Switzerland) and the Implantable Phakic Contact Lens (IPCL) (Care Group Sight solutions, India) are the available posterior chamber pIOLs on the market. Due to long-term complications, other PC pIOLs such as the phakic refractive lens (PRL, Zeiss Meditec, Jena, Germany) were phased out of the market [7].

Long-term follow-up has shown that the Visian ICL is a safe and effective treatment choice for moderate to high myopia with astigmatism. However, the financial cost of the implant, particularly in developing nations, is a big issue. The toric IPCL is a novel PC pIOL that may be used for the correction of refractive errors as a cost-effective alternative to the ICL implant, which costs 2.5 times as much as the IPCL implant [8, 9].

Our study aimed to compare the clinical, visual outcomes, and efficacy of T-ICL and toric IPCL in patients with high myopia with astigmatism over a follow-up period of 6 months.

2. MATERIALS AND METHODS

2.2. T-ICL Design

The ICL is a biocompatible hydrophilic collagen hydroxyethyl methacrylate copolymer with an ultraviolet light filtering chromophore. It's a foldable lens that can be injected through a corneal incision of 3.2 mm or smaller. In 2018, the FDA approved the toric version for correcting myopia with astigmatism. It has the potential to correct myopia and astigmatism up to -18.0 D and -6.0 D, respectively. The V4c, commonly known as the EVO variant, features a 360 um central port (KS-Aquaport) that precludes the necessity for iridectomy or iridotomy with Nd: YAG [10] (Fig. 1).

2.3. Toric IPCL Design

The IPCL is a foldable injectable to be injected through a 2.8 mm corneal incision. It has a unique design with 2 holes in the peripheral part from the upper zone and 4 holes outside the optical zone to facilitate loading in the cartridge and unfolding inside the eye, as well as 6 haptics for added stability. The toric design has the potential to correct myopia up to -30 D and astigmatism up to -10 D. The V2.0 design features a central opening of approximately 380 um, which is aimed to minimize glare and light scattering while also facilitating aqueous circulation, hence alleviating the need for peripheral iridectomy (Fig. 2) [11].

2.3.1. Surgical Procedure

All surgeries were performed under general anesthesia by the same surgeon (M.S). Preoperatively, the pupil was dilated by tropicamide 1% every 10 minutes for a minimum of 30 minutes. To prevent cyclotorsion in the supine position with lens misalignment, the eye was marked with a corneal marker at the horizontal axis at the slit-lamp in the upright position before the surgery. Loading of T-ICL and toric IPCL was done before the corneal incision construction.

3. RESULTS

Thirty eyes in group A were implanted with T-ICL, while 30 eyes in group B were implanted with toric IPCL. Patients demographic data are summarized in Table 1.

Both spherical and cylindrical errors were significantly reduced during the follow up period in both groups, without statistically significant difference between the two groups either pre-operatively or during the follow-up period (Table 2).

A statistically significant improvement of LogMAR UCDVA was observed in both groups during the follow-up period. While, LogMAR BCDVA showed non-statistically significant change during the follow-up period (Table 3).

A statistically significant increase in IOP was found in both groups during the early follow up, and a significant decrease after 6 months postoperatively (p=0.036) was reported in group A (Table 4).

In both study groups, the mean central corneal endothelial cell count was significantly decreased after 1 month and improved to reach near pre-operative values after 6 months postoperatively (Table 5).

4. DISCUSSION

The prevalence of high myopia with astigmatism is high in Egypt. In a study conducted on 3442 students in their first academic year at Assiut University, Upper Egypt, refractive error was found in 360 of them. Compound myopic astigmatism was found in 257 out of 360 (71.39%) [12].

A large number of myopic persons have been able to improve their quality of life by removing their glasses or contact lenses since the introduction of corneal ablation surgery. Regardless of the fact that current photorefractive corneal surgeries have been demonstrated to be predictable and safe, they are still not appropriate for patients with thin corneas or high myopia [13].

In these cases, phakic IOLs are an acceptable treatment choice since they have a greater ability to correct higher degrees of refractive errors than LASIK and have no risk of corneal ectasia. pIOLs could be used in patients with stable keratoconus after corneal cross-linking [14, 15].

T-ICL is an FDA approved pIOL for the correction of myopia with astigmatism and many studies have confirmed the safety of T-ICL [16-21]. But the cost-effective burden of T-ICL is considered a major concern in our locality. The toric IPCL is a good alternative implant for the correction of high myopia with astigmatism.

Our study aimed to compare the efficacy and safety of both implants (T-ICL and Toric IPCL) over 6 months follow-up period. To our knowledge, this is the first study to evaluate the clinical outcomes of toric IPCL for correction of high myopic astigmatism over 6 months follow-up period.

The current study included 60 myopic eyes, half of them were implanted with T-ICL and the other half were implanted with toric IPCL. Included patients were age-matched (age ≥ 21 years), had stable refraction with normal ocular examination, except for high myopia with astigmatism, who were unfit for keratorefractive surgeries. The included patients had myopia less than -18 D and astigmatism less than -6 D, as T-ICL could correct up to -18 D myopia and -6 D astigmatism while toric IPCL could correct up to -30 D myopia and -10 D astigmatism.

The primary efficacy outcome for the current study is the significant reduction in both spherical and cylindrical refractive errors with good predictability in both groups compared with preoperative values. In T-ICL group (A), the median spherical and cylindrical errors were significantly improved from (-10 D & -4.5 D) pre-operatively to (-0.3 D & - 0.3 D) at the end of a 6-month follow up period (Table 2). Similarly, in the toric IPCL group (B), the median spherical and cylindrical errors were significantly improved from (-11 D & -4.5 D) pre-operatively to (-0.3 D & - 0.3 D) by the end of follow up period (Table 2). Good predictability was achieved with both types of implants, as the mean residual spherical and cylindrical errors were (-0.3 D & - 0.3 respectively) at the end of follow-up period. Similar results were obtained from Sachdev et al. in their comparative study on two different implants (ICL, V4c and IPCL, V1), as residual spherical equivalent error ranged between 0.5 D and 1.0 D of the attempted correction in both groups, at the 12 months postoperative visit, although their study included toric and non-toric implantation with different implants designs [22].

A statistically significant improvement of UCDVA at 6 months postoperatively was another efficacy parameter for the two implants, as median preoperative LogMAR UCDVA was 1.1 and 1.3 in the ICL and IPCL groups, which was significantly improved to 0.3 in both groups at the end of follow-up period (Table 3). Similar results were reported from a study on two toric implants (Eyecryl Phakic Toric IOL or Visian Toric ICL) for myopic astigmatism correction. There was no significant difference between both groups along the 2 years follow up [23].

Both used pIOLs, in the current study, V4c T-ICL and IPCL V2.0 toric were implanted with no need for preoperative iridotomy or intraoperative peripheral iridectomy, as IPCL V2.0 TORIC was designed with a unique central hole (380 μm) in the optic for proper aqueous flow. V4c T-ICL, also has a central hole (360 μm) with two additional holes outside the optic helping aqueous outflow. In a previous study by Kawamorita et al., who evaluated aqueous humor dynamics in patients implanted with V4c model, they reported that the presence of a central hole in Hole-ICLs was beneficial in preventing cataract development due to sufficient aqueous diffusion and nutrients reaching the anterior surface of the lens that maintains adequate lens nutrition [24]. This could be applied to current study results, as no eye in both groups developed cataract by the end of the follow-up period. Although cataract formation was the major complication of pIOLs in many previous studies, that could be referred to as longer follow-up periods and different pIOL designs.[10 & 25]

Over the 6 months follow-up period, IOP was maintained below 21 mm Hg in both groups, and no significant difference was reported between the two groups concerning IOP stability, which could be ascribed to the presence of a central hole within the optic of the two implants that maintained proper aqueous flow, reducing the possibility of the pupillary block and pigmentary glaucoma. A mild statistically significant increase in the IOP was reported in the first month postoperatively in both groups (p-value = 0.017 and 0.001, respectively), possibly due to some retained viscoelastic material, postoperative inflammation, or steroid-induced glaucoma which is more common in highly myopic patients, and was managed by topical antiglaucoma medications, this was in agreement with previous study reports . [26]

Though the materials of both toric pIOLs used in this study were different, as T-ICL is manufactured from Collamer®, a proprietary hydroxyethyl methacrylate (HEMA)/porcine-collagen-based biocompatible polymer material, while T-IPCL is formed from a reinforced hybrid hydrophilic acrylic material, both lenses showed good biocompatibility with intraocular tissues. Lens biocompatibility was assessed in our study by two factors: effect on corneal endothelium and the incidence of adverse events (intense postoperative inflammation, hypopyon, or hyphema). Regarding the effect on the corneal endothelium, we observed a similar effect on the corneal endothelium for both lenses, as the central endothelial cell count was significantly reduced in the early postoperative period, possibly due to surgical trauma, and returned to near preoperative values after 6 months (Table 5). This agreed with results from previous studies held on ICL [27] and IPCL [28]. Sachdev et al. also reported no effect on ECD for both lenses; T-ICL (V4c) and toric IPCL (V1) over a 1-year follow-up period [22].

In current study, none of the eyes demonstrated excessive postoperative inflammatory reaction (endophthalmitis or hypopyon) or hyphema in both groups, and topical steroids were tapered gradually during the first month postoperatively, which indicates good compatibility for both implants. No cases of lens rotation or cataract were recorded during the follow up period.

Toric IPCL has some advantages over T-ICL in terms of surgical technique. We found that toric IPCL loading was much easier than T-ICL loading, which requires special instrumentation and a learning curve. For the implantation of both lenses, a temporal corneal incision was constructed, but the T-ICL had a longer incision length (3.2 mm) than the toric IPCL (2.8 mm), which could impact the final cylindrical error results due to induced astigmatism. The T-ICL had a diagram for axis detection after implantation, while the toric IPCL is customised for a 0-180 degree axis with no rotation. Toric IPCL can also correct a broader range of compound myopic astigmatism (myopia up to-30 D and astigmatism up to-10 D) than T-ICL (myopia up to-18 D and astigmatism up to-6 D).

Limitations to the current study are: the smaller sample size, the shorter follow up period, as longer follow up period may highlight certain adverse effects (ex; decentration), and finally lack of vault evaluation by ultrasound biomiscroscopy (UBM).

CONCLUSION

In conclusion, Toric IPCL provided refractive correction, stability, and visual acuity improvement comparable with T-ICL results for correction of high myopia with astigmatism over 6 months follow-up period, with good biocompatibility. Toric IPCL is a suitable alternative to T-ICL for the management of high myopia with astigmatism, especially in developing countries. However, data over longer follow-up periods are needed to confirm its safety and stability.

REFERENCES