Evaluation of the central vault following implantable phakic contact lens and its correlation to horizontal white to white corneal diameter by anterior segment optical coherence tomography

INTRODUCTION

In those cases where corneal refractive surgery is contraindicated, phakic intraocular lenses (PIOLs) are a well-established method of correcting moderate to high refractive errors. ¹

Reversibility, high optical quality, and potential gain in visual acuity owing to retinal magnification are all features of PIOLs, which are also unaffected by corneal thickness or topography.²

However, because it is an intraocular surgery, it carries a higher risk of complications, including anterior segment damage, retinal detachment, and infections such endophthalmitis. ^{3, 4}

Over a long period of time, the Visian Implantable Collamer lens has been shown to be safe and effective for moderate and high ametropia. ^5-7

The cost of treatment, particularly in developing countries, would be a constraint of the ICL. The Implantable Phakic Contact Lens was developed as a cost-effective alternative option for refractive correction. ³

IPCL can correct ametropia up to - 30.0 D. In addition, the earlier design V1 was replaced with

V2.0, which features a central hole (380 µ) to reduce scattering and glare while also facilitating alignment and aqueous humour circulation. ⁸

The most important parameters for determining patients' eligibility for phakic posterior chamber intraocular lens surgery and selecting the right lens size are anterior chamber depth (ACD) and white to white (WTW) corneal diameter. ICL surgery is not recommended if the ACD value is less than 3.00 mm.  ⁹

The vault is the distance between the posterior IPCL surface and the anterior crystalline lens pole, which is important for determining the safety of surgery. ¹⁰

An ideal vault has been recommended to be between 250 and 750 µ. The contact between the IPCL and the anterior lens capsule might cause anterior sub-capsular cataract if the vault is insufficient. Also, excessive vaulting can result in angle closure, pupillary blockage, or pigmentary dispersion syndrome, all of which can raise intraocular pressure and therefore the risk of glaucoma. ^11-14

Anterior segment optical coherence tomography (AS-OCT) is a non-invasive method for obtaining high-resolution images of the anterior segment, which can be used for both quantitative and qualitative analysis. As a result, an assessment of IPCL's central vault to guarantee its safety.¹⁵

This work aimed to evaluate the central vault of IPCL and its correlation to horizontal (WTW) corneal diameter using anterior segment optical coherence tomography.

PATIENTS AND METHODS

A non-randomized prospective study was carried out from February 2020 to February 2022 on thirty eyes of patients with moderate to high myopia with or without Astigmatism. The patients were selected from the outpatient Ophthalmology clinics of Al-Azhar university hospitals. All patients were informed about the details & risk of the procedure and were asked to provide written informed consent.

Inclusion criteria: Patient age (18 - 40 years). Myopia between -1.50 and – 18.00 DS. Astigmatism between 0 and – 4.00 DC. Stable refraction for a minimum period of 1 year. Endothelial cell count ≥ 2,500 cells/mm2. Anterior chamber depth ≥ 3.00 mm.

Exclusion criteria: Eyes with prior ocular surgery. Comorbidities including cataract, glaucoma, uveitis or corneal ectasia. Patients with systemic diseases.

Full medical history has been taken and ocular examination was done to exclude any other pathology. Uncorrected distant visual acuity (UDVA) and corrected distant visual acuity (CDVA) were measured using a landolt’s C chart and expressed in decimal scoring. Manifest and cycloplegic refraction were measured using (Topcon KR Auto-refractometer). Intraocular pressure was measured using Goldmann applanation tonometer. Slit-lamp biomicroscopic examination and dilated fundus examination were done. Corneal tomography was assessed using (Siirus, CSO, Italy). Anterior chamber depth was measured using (Siirus, CSO, Italy). Horizontal white to white corneal diameter was measured using (IOL master, Zeiss).

IPCL power and size:

The phakic intraocular lens power was calculated using a modified vertex formula as per the manufacturer’s recommendation, with a target refraction of emmetropia. The variables in the formula included preoperative manifest spherical and cycloplegic refractions, keratometric power, central corneal thickness and central ACD. The size (length) of the implanted ICL was determined based on the patient’s WTW and ACD.

Surgical procedure:

Pupillary dilatation was done by tropicamide 1% and phenylephrine hydrochloride 2.5% 30 minutes before operation. General or peri-bulbar anaesthesia. Sterilization with betadine 10 % for the eye lids and surgical field. Betadine 5% eye-drops were used for the conjunctival cul-de-sac. Application of sterile drapes. Loading the IPCL before opening the eye. Implantation was done through 2.8 mm clear temporal corneal incision after viscoelastic substance injection, with 2 side ports at 90 degrees. Important land mark on the side of IPCL was noted and must be to the left side during implantation to prevent upside down of IPCL. After implantation, the footplates were tucked under the iris. Removal of viscoelastic substance and finally wound hydration was done.

Post-operative treatment consisted of topical antibiotic Moxifloxacin, topical anti-inflammatory prednisolone acetate 1% in tapering doses. Anti-glaucomatous drugs were used in cases of IOP elevation.

At 1week, 1month, 6 months and 12 months post-operatively: Visual acuity and spherical equivalent were measured. IOP was measured using Goldmann applanation tonometer. Central vault was measured using Topcon DRI OCT Triton anterior segment OCT.

Statistical analysis:

Recorded data were analyzed using the statistical package for social sciences, version 20.0 (SPSS Inc., Chicago, Illinois, USA). Quantitative data were expressed as mean ± standard deviation (SD). Qualitative data were expressed as frequency and percentage. The confidence interval was set to 95% and the margin of error accepted was set to 5%. So, the probability value (P-value) was considered significant as the following:  P-value < 0.05 was considered significant. P-value < 0.001 was considered as highly significant. P-value > 0.05 was considered insignificant.

RESULTS

Thirty eyes of nineteen patients were selected. They were five males and fourteen females.

Eighteen eyes were right and twelve eyes were left.

Table 1: summarize demographic data of age, sex and affected eyes.

Visual acuity, Spherical equivalent and IOP were analyzed in all eyes at first.  

Visual acuity:

VA improved from 0.24 ± 0.14 pre-operatively to 0.45 ± 0.18 at the end of 12 months post-operatively with P value < 0.01 indicating highly statistically significant difference (Table 2 & Fig. 1)

Table 2: Differences between pre and post-operative VA.

Fig. 1 : Diagrammatic representation of pre and post-operative VA.

Spherical equivalent:

SE improved markedly from – 12.4 ± 4.91 pre-operatively to – 0.5 ± 0.63 at the end of 12 months with P value < 0.01 indicating highly statistically significant difference (Table 3 & Fig. 2)

Table 3: Differences between pre and post-operative spherical equivalent.

Fig. 2: Diagrammatic representation of pre and post-operative spherical equivalent.

Intraocular pressure:

IOP measured by Goldmann applanation tonometry increased maximally at 1 week and 1 month post operatively but declined at 6 and 12 months with P value < 0.01 indicating highly statistically significant difference as shown in (Table 4 & Fig. 3) 

Table 4: Differences between pre and post-operative IOP.

Fig. 3: Diagrammatic representation of pre and post-operative IOP.

After analysis of all data, two groups were divided according to the pre-operative horizontal WTW corneal diameter and central vault was measured to compare between the 2 groups: Group 1 Include eyes with horizontal white to white diameter < 12 mm. Group 2 include eyes with horizontal white to white diameter ≥ 12 mm.

Table 5: Differences between pre-operative WTW in the two groups.

Group 1 central vault:

Central vault in group 1 decreased from 642 ± 129 µ at 1 week post-operative to 634 ± 134 µ at the end of 12th months with P value < 0.05 indicating statistically significant difference (Table 6 & Fig. 4)

Table 6: Group 1 post-operative central vault and its difference from the 1st week.

Fig. 4: Diagrammatic representation of post-operative central vault in group 1.

Group 2 central vault:

Central vault change in group 2 from the 1st week to the end of 12th month showed P value > 0.05 indicating statistically insignificant difference (Table 7&Fig. 5).

Table 7: Group 2 post-operative central vault and its difference from the 1st week.

Fig. 5: Diagrammatic representation of post-operative central vault in group in group 2.

Comparison between Groups:

Comparison between the 2 groups showed mild difference in all visits with P value > 0.05 indicating statistically insignificant difference (Table 8 & Fig. 6).

Table 8: Difference between post-operative central vault in the two groups.

Fig.6: Diagrammatic representation of post-operative vault in the two groups.

Complications: 4 eyes developed IOP rise up to 30 mmHg. This IOP rise was due to retained viscoelastic and steroid responsiveness. This IOP rise decreased with anti-glaucomatous drugs and returned to normal after one month and with discontinuation of steroids. 2 eyes developed rotation of IPCL but no decentration occurred with no visual affection or IOP rise. 2 eyes developed increased vault > 750 µ (868 µ in group 1 & 854 µ in group 2) but no IOP rise occurred along all periods of follow up with no narrowing of the angle neither by gonioscopy or by Sirius tomography. However these 2 eyes need long term follow and close observation.