When implanting a posterior chamber phakic intraocular lens (pIOL), it is crucial to maintain a safe distance. The patient was a 29-year-old man with high-degree bilateral myopia. In February 2021, posterior chamber acrylic pIOLs (Eyecryl Phakic TORIC; Biotech Vision Care, Gujarat, India) were implanted in both his eyes. After the surgery, the right eye vault was 6 μm, and the left eye vault was 350 μm. Moreover, the internal anterior chamber depth values were 2,270 and 2,220 μm for the right and left eyes, respectively. In our case, we found a fairly high crystalline lens rise (CLR) in both eyes, but it was greater in the right eye. The CLR value was +455 in the right eye and +350 in the left eye. In our patient, anterior segment anatomical parameters were higher in the right eye than in the left eye, and a greater pIOL length was calculated for the right eye, but the vault was very low. In our opinion, this was associated with the high CLR in the right eye. If an even larger pIOL had been implanted, there would have been a greater narrowing of the anterior chamber angle. This case would be contraindicated if those parameters were considered in selecting the indications and determination of the pIOL length.

© 2023 The Author(s). Published by S. Karger AG, Basel

Introduction

Posterior chamber intraocular lenses (IOLs) are widely used to correct high-degree myopia. Newer lens models have a central hole that contributes to the outflow of the aqueous humour and thus supports the metabolism of the epithelial cells of the crystalline lens [1], reducing the incidence of cataracts. However, it is important to maintain a safe distance (vault) between a phakic intraocular lens (pIOL) and the crystalline lens. Dynamic changes in the vault [2] and age-related thickening of the lens [3] can lead to contact of the pIOL with the epithelium of the crystalline lens. At the same time, a high vault can lead to pronounced narrowing of the anterior chamber angle, which impairs outflow of the aqueous humour and may increase pigment dispersion, resulting in a risk of higher intraocular pressure [4]. In addition, a high vault may impair the pupil’s response and result in the appearance of a halo, an optical phenomenon [5, 6].

With regard to the calculation of the most appropriate pIOL size by an ophthalmologist, manufacturers provide nomograms for determining the pIOL size based on the corneal diameter (white-to-white [WTW]) and the anterior chamber depth (ACD) [7]. However, these measurements do not accurately reflect the size of the posterior chamber space where the pIOL will be placed. Several investigators have attempted to calculate the optimal collateral lens size (implantable collamer lens (ICL) using various parameters [7, 8] and new technologies, such as anterior segment optical coherence tomography (AS-OCT) and ultrasound biomicroscopy (UBM). However, measurement errors and structural variability result in the implantation of inappropriately sized ICLs. Currently, there is no specific method for determining the optimal pIOL size, and the size of the arch is mainly determined by the relationship between the pIOL and anatomical factors. Moreover, we did not find any studies devoted to calculating the size of posterior chamber acrylic pIOLs. In our clinical case, we report the results obtained after implantation of posterior chamber acrylic pIOLs in both eyes.

Clinical Case

The patient was a 29-year-old man with high-degree bilateral myopia. His corrected distance visual acuity was 0.6 logMAR and 0.48 logMAR for the right and left eyes, respectively. The spherical equivalent (SE) of his right eye was 15.88D, and that of his left eye was 15.63D. His intraocular pressure (IOP) was 13.0/12.0 mm Hg, and the corneal endothelial cell density (ECD) was 2,516/2,556 mm2. In February 2021, posterior chamber acrylic pIOLs (Eyecryl Phakic TORIC; Biotech Vision Care, Gujarat, India) were implanted in both his eyes.

Patient signed a specific consent form that covers his privacy, and the data can be used for research and clinical purposes following the Declaration of Helsinki, which meets the requirements of the Republican Scientific and Practical Medical Center for Eye Microsurgery of Uzbekistan.

The patient underwent the following ophthalmological examinations: visual acuity check, autorefractometry (Multifunction Unit MR-6000; Tomey, Nürnberg, Germany), biometry (IOLMaster 700; Carl Zeiss Meditec, Jena, Germany), tonometry (Goldmann applanation tonometer and iCare tonometer; iCare, Helsinki, Finland), AS-OCT (CASIA II; Tomey), and ECD assessment (Tomey Specular Microscope 4,000; Tomey).

AS-OCT was used to measure the WTW distance, horizontal anterior chamber angle-to-angle (ATA) distance, anterior chamber width (ACW), crystalline lens rise (CLR), internal anterior chamber depth (ACDendo), and trabecular-iris angle at 500 μm from the scleral spur. The AS-OCT scan was performed along the horizontal meridian using a single scan centred at the pupil. Subsequently, a scan with high image quality under mesopic illumination (300 lux) was selected. The device was equipped with currently available prediction formulae: the NK formula version 2 [8] and the KC formula. It automatically calculated the predicted vault, but this time for the ICL. During a visit 1 month after the surgery, we measured the size of the pIOL vault using the same AS-OCT under the same conditions. The dioptric power and size of the Eyecryl Phakic TORIC lenses were determined using the manufacturer’s calculator, and the values were D −17.0 cyl +2.0 and 13.0 mm, respectively, for the right eye and D −16.0 cyl + 2.0 and 12.5 mm, respectively, for the left eye.

Phakic Intraocular Lens and Surgical Procedure

Eyecryl Phakic IOL is a foldable hydrophilic acrylic one-piece posterior chamber IOL. It is available in 4 lengths (12.0, 12.5, 13.0, and 13.5 mm) to correct myopia in a dioptric power range of −3.00 to −23.00 D. It provides spherical optics with zero aberration. The diameter of the optical part ranges from 4.65 to 5.50 mm. A 320-µm hole is present at the centre of the optical part. The same surgeon performed all operations. Before the surgery, mydriasis was induced with 1% Mydriacyl injected 30 min before the surgery. Incision positioning, centring, and the location of the toric pIOL component were monitored using the ZEISS CALLISTO eye intraoperative navigation system integrated with a ZEISS OPMI LUMERA 700 microscope (Carl Zeiss Meditec).

After three times drip anaesthesia with 1% proparacaine hydrochloride, 3% povidone-iodine was injected into the conjunctival cavity, and a profile self-sealing 2.8-mm corneal incision was made in the horizontal (temporal) meridian. The anterior chamber was filled with 2% viscoelastic methylcellulose, and two paracenteses were performed at 6 and 12 h. The Eyecryl Phakic IOL was implanted behind the iris through the incision using the cartridge and injector supplied by the manufacturer. With this approach, the position of the pIOL was horizontal immediately after the implantation. The pIOL supports were tucked behind the iris using a manipulator, and the lens was centred and rotated. On gently placing the Eyecryl Phakic IOL into the ciliary sulcus, the remaining viscoelastic methyl cellulose was completely flushed out from the anterior chamber with a balanced saline solution, and 0.01% miotic carbachol was instilled. The anterior chamber was sealed by hydration with a balanced saline solution.

One month after the surgery, the patient’s vision was as follows: eyes had an uncorrected distance visual acuity of 0.4 logMAR, the right eye had a SE of +0.25D, and the left eye had a SE of −0.25D. Moreover, the IOP was 15.0/13.0 mm Hg, and the corneal ECD was 2,510/2,525 mm2. According to Figure 1, after the surgery, the right eye vault was 6 μm, and the left eye vault was 350 μm. Moreover, the ACDendo values were 2,270 and 2,220 μm for the right and left eyes, respectively. Because of the very low vault in the right eye, we analysed the preoperative anatomic parameters of the anterior segments of both eyes.

Fig. 1.

AS-OCT image of the vault measurement.

The findings for the right eye from Figure 2 were as follows: WTW distance, 11.82 mm; ATA distance, 11.88 mm; ACW, 12.05 mm; CLR, 455 μm and ACDendo, 2.86 mm. The findings for the left eye were as follows: WTW distance, 11.69 mm; ATA distance, 11.43 mm; ACW, 11.41 mm; CLR, 350 μm; ACDendo, 2.84 mm. UBM was also performed to exclude neoplasms and iris cysts. The STS (sulcus-to-sulcus diameter) size was 12.04 mm in the right eye and 11.43 mm in the left eye.

Fig. 2.

AS-OCT image before pIOL implantation.

After pIOL implantation, the anterior chamber angle in the right eye narrowed. In the right eye, the minimum opening angle (trabecular-iris angle at 500 μm from the scleral spur) was 18° postoperatively and 38° preoperatively. In the left eye, this angle was 27° postoperatively and 30° preoperatively.

The patient underwent a yttrium aluminium garnet laser iridotomy. But no pIOL changes were observed after that.

Discussion

Calculating the exact pIOL size and predicting a safe vault size remain unsolved problems. The manufacturer’s nomogram considers anatomical parameters, such as WTW distance and ACDendo. High variability of WTW measurements (using manual callipers or automatic grey-scale steps devices) and their weak correlation with sulcus-to-sulcus distance support the idea of choosing other internal distances, such an ATA – the horizontal anterior-chamber angle-to-angle distance, in order to minimize the above-mentioned variability and increase inter-parameter correlation. CLR-the perpendicular distance between the line of angle recess and the anterior crystalline lens surface, is an important reference index for the implantation of the pIOL. According to Kang et al. [9], these two measurements do not accurately reflect the size of the posterior chamber space in which the lens will be placed. The study by Xu et al. [2] showed that although ATA distance does not use the sulcus diameter, it may be more accurate and reliable than other biometric parameters measured in the horizontal dimension. According to Igarashi et al. [4], ATA measurements had higher reproducibility than WTW measurements on AS-OCT, making them a more important predictor of a postoperative vault.

In our case, there was no great difference in the WTW distance between the right and left eyes. The values for the right and left eyes were 11.83 mm and 11.71 mm, respectively, on measurement by CASIA II (AS-OCT), and 11.9 mm and 11.7 mm, respectively, on measurement by IOLMaster. The difference in the ATA distance between the right (11.88 mm) and left (11.43 mm) eyes was greater.

The NK formula developed by Nakamura et al. [5] for ICL is probably the most accurate prediction formula to date. The formula considers the scleral spur distance (ACW) and CLR as independent variables. The mean vault was achieved in 92.1% of cases in which the formula was applied. Our patient had a difference in the ACW between the right (12.05 mm) and left (11.41 mm) eyes.

The effect of CLR protrusion on the vault has been reported in various studies [9–12]. Gonzalez–Lopez et al. [12] analysed the dynamic behaviour of the vault and reported that the CLR was lower in eyes having a high vault (>750 μm in mydriasis) than in eyes having a low vault (<100 μm in myosis) (CLR: +73 μm vs. +352 μm). The study’s results by Cerpa Manito et al. [11] show an important relationship between the CLR and the presence of a low vault. The probability of having a vault ≤250 μm increased by 0.5% for each CLR (μm), and the number of eyes with a low vault gradually increased among those with a CLR above 150 μm, suggesting that high protrusion of the anterior lens represented by CLR is a major contributing factor to a low vault.

In our case, we found a fairly high CLR in both eyes, but it was greater in the right eye. The CLR value was +455 in the right eye and +350 in the left eye.

When implanted with a similar ICL, eyes with similar anterior segment anatomy can have differences in the vault size of up to 240 μm [13]. In our case, the sizes of the anatomical structures of both eyes were also different.

Dioptric power of the ICL was another factor associated with suboptimal vaults. However, while a low myopia ICL was a risk factor for a low vault, it was a protective factor for a high vault. The intrinsic sagittal depth of the ICL depends on its dioptric power; for the ICL-V4 model, the sagittal depth increased from 1.04 to 1.94 mm for a dioptric interval of −3.00 to −23.00 DS [14]. In our case, there was no significant difference in dioptric power between the two eyes.

Takagi et al. [6] reported that the pupil diameter and the vault are affected by the illumination level in the examination room [15]. Therefore, we performed the measurements under the same mesopic light conditions (300 lux).

Although various formulae determine lens size based on STS measurements with UBM, surgeons do not use these UBM-based formulae often because of the invasiveness and low reproducibility of UBM. A Packer [16] meta-analysis showed that the STS-based formula is not superior to the WTW-based formula. Some additional factors, including investigator error, eye position, and anatomic changes in the ciliary sulcus, may affect the measurements [2]. In our patient, the horizontal STS size was 12.04 mm in the right eye and 11.43 mm in the left eye.

According to Mahmoud et al., implantable phakic contact lens implantation is a safe method for myopia correction, with stable narrowing of the AC (anterior chamber) angle within 6 months after surgery under AS-OCT control [17]. Our patient showed marked narrowing up to 18° in the right eye.

Conclusion

In our patient, anterior segment anatomical parameters were higher in the right eye than in the left eye, and a greater pIOL length was calculated for the right eye, but the vault was very low. In our opinion, this was associated with the high CLR in the right eye. If an even larger pIOL had been implanted, there would have been a greater narrowing of the anterior chamber angle. This case would be contraindicated if those parameters were considered in selecting the indications and determination of the pIOL length.

The CARE Checklist has been completed by the authors for this case report, attached as online supplementary material (for all online suppl. material, see www.karger.com/doi/10.1159/000530008).

Acknowledgments

This manuscript was edited for English language by Enago Editing Service.

Statement of Ethics

This study followed the tenets of the Helsinki Declaration and was approved by the Republican Specialized Center of Eye Microsurgery Ethics Board, Тashkent, Uzbekistan (protocol No. 12) Written informed consent was obtained from the patient for publication of the details of their medical case and any accompanying images.

Conflict of Interest Statement

The authors have no conflicts of interest to declare.

Funding Sources

The authors report no funding was received.

Author Contributions

Saliev Ikbol Fazilovich: patient management and data collection, and manuscript writing and editing. Yusupov Azamat Farhadovich: patient management and manuscript editing. Mukhamedova Nazokat Ismailovna: patient management and data collection. All co-authors read and approved the final version of the manuscript.

Data Availability Statement

This case report did not result in any data generation or analysis. Given the need for patient confidentiality, further information about the case cannot be openly available. Please direct any further enquiries to the corresponding author.

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