Objective To assess anterior segment changes, including iridocorneal angle and vault, after toric and non-toric implantable collamer lens (ICL) V4c (STAAR Surgical AG) implantation under different lighting conditions.
Methods Longitudinal, prospective, case series. Patients with high myopia (>6 dioptres) underwent toric and non-toric ICL V4c implantation. Optical coherence tomography measurements were taken under different lighting conditions preoperatively and at 1 week and 1, 6 and 12 months of follow-up.
Results Seventy-six eyes of 42 patients underwent ICL V4c implantation. Mean age was 27.4 years (±5.14 years, range 20 to 39 years). The average iridocorneal angle showed a statistically significant decrease (p<0.05) in all mesopic, scotopic and photopic conditions after 1 week of surgery compared with the preoperative measurements; in mesopic conditions, it decreased 14.1°, in photopic conditions 14.8° and scotopic conditions 13.2°. The angle measurement had a statistically significant change only in mesopic conditions (p=0.01) over the 1-year follow-up. The average vault under mesopic conditions was 0.661±0.21 mm at week 1. The vault measurement change was statistically significant over the 1-year follow-up in mesopic conditions (p=0.01). Refractive results showed a significant improvement in both uncorrected and corrected distance visual acuity (p<0.001).
Conclusion There is a significant reduction in the iridocorneal angle after ICL V4c implantation. Furthermore, there is a change under mesopic conditions in both the iridocorneal angle and vault during long-term follow-up.
- Anterior Chamber
Statistics from Altmetric.com
Patients with high myopia encounter certain limitations with keratorefractive procedures because of the safety limits in pachymetry to avoid the risk of iatrogenic ectasia and the potential decline in optical quality with large ablations; both situations have a direct impact in quality of vision.1 2 Procedures like refractive lens exchange and phakic intraocular lens (pIOL) implantation are viable options for the correction of high ametropia.3 4 A commonly used pIOL is the Visian Implantable Collamer Lens (ICL—STAAR Surgical, CA, USA). The V4c model was designed with a small central opening of the lens to prevent pupillary block without degrading the optical qualities.5 Although pIOL implantation is a common and safe procedure, some complications have been reported, including over-correction/under-correction, lens rotation, angle-closure glaucoma, pigmentary dispersion syndrome, anterior capsular cataract and retinal detachment.6–10
The ICL lens calculation is a critical step for surgical planning since an undersized ICL will have a small vault, increased risk of central lenticular touch and decreased stability. An oversized ICL can produce mechanical stress to the sulcus by horizontal compression and anterior bending of the lens; an increase in peripheral pIOL touch with anterior displacement of peripheral iris may cause pigment dispersion.8–10 The size of the vault is determined by the difference between the size of the ICL and the horizontal sulcus-to-sulcus (STS) diameter.9
The objective of this study is to assess anterior segment changes, such as iridocorneal angle and vault, after toric and non-toric ICL V4c implantation under different lighting conditions, and to evaluate the refractive results of these patients.
Materials and methods
This is a prospective, longitudinal case-series study. Patients with high myopia (>6 dioptres) who underwent surgical implantation of toric ICL V4c between March 2013 and June 2014 at the Department of Cornea and Refractive Surgery, Instituto de Oftalmologia ‘Conde de Valenciana’ in Mexico City were included. Inclusion criteria were diagnosis of high myopia, anterior chamber depth over 2.8 mm obtained by Orbscan II Topography (Bausch & Lomb, Claremont, CA) and Pentacam (Oculus, Germany), age over 21 years, stable refraction for at least 12 months, clear lens and no pre-existing ocular pathology. Exclusion criteria were history of previous ocular surgery or trauma, uncontrolled systemic disease, corneal scarring or vascularisation, and pregnancy.
Calculation of the selected ICL V4c was based on the nomogram suggested by the company, using the refraction obtained by the surgeon and the preoperative information including the white-to-white measurement obtained with the Orbscan II (Bausch & Lomb) topography.
Ocular examinations, including uncorrected distance visual acuity (UDVA) and corrected distance visual acuity (CDVA) with Snellen chart and analysed with logarithm of the minimum angle of resolution (logMAR), refraction with and without cycloplegia, intraocular pressure with the Goldmann applanation tonometer, slit-lamp biomicroscopy and anterior segment optical coherence tomography (AS-OCT) with an OCT Visante (Carl Zeiss Meditec AG, Germany), were performed before and after surgery at each of the predetermined visits scheduled at day 1, day 7 and 1, 3, 6 and 12 months. Angle and vault were evaluated using the images obtained from the anterior segment OCT taken by an expert technician. Visante OCT was performed under photopic, mesopic and scotopic lighting conditions. The iridocorneal angle was measured by tracing a line of 500 µm from the angle recess towards the Schwalbe line and another line on the surface of the iris to the point perpendicular to the first line, and the vault was measured by tracing a line from the centre of the anterior pole of the crystalline lens to the posterior pole of the ICL.11 The measurements under different lighting conditions were performed as described by others; briefly, scotopic measurements were performed with the lights of the room turned off after a period of dark adaptation (less than 1 lux).12 13 Then mesopic measurements were performed with the room luminance of 2 lux; for the photopic measurements, a direct ophthalmoscope (175 lux) was held in front of the contralateral eye. Three scans were taken and the image showing the best quality was chosen.
The study was approved by the institution’s ethics committee and institutional review board. Written informed consent was obtained from all patients prior to the procedure, and the study was performed according to the tenets of the Declaration of Helsinki.
Pupillary dilatation was achieved with tropicamide/phenylephrine (TP—Sophia Laboratories, Jalisco, Mexico) with 1 drop every 15 min, 30 min before surgery. After topical anaesthesia with tetracaine (PONTI—Sophia Laboratories), a marking at 0° and 180° was performed, a paracentesis was made at 90° and intracameral cohesive viscoelastic (Provisc—Alcon, Fort Worth, Texas, USA) was injected. A second paracentesis was made 180° from the first one, followed by a 3-mm corneal incision in the temporal region; an ICL V4c was inserted using the appropriate injector (STAAR Surgical) and placed in the posterior chamber, viscoelastic was removed, the main port was sutured with 10-0 nylon, intracameral acetylcholine (ILOC—Sophia Laboratories) was introduced and a drop of topical moxifloxacin (Vigamoxi—Alcon) was instilled at the end of the case.
Categorical variables were evaluated using percentages and numerical variables were assessed using measures of central tendency. A paired t-test was used to compare preoperative with 1-week iridocorneal angle measurements. A one-way repeated measures ANOVA was used to analyse the changes in iridocorneal angle and vault over time. A post hoc test, the Tukey multiple comparisons test, was performed to compare the iridocorneal angle vault at each of the time points. A p value <0.05 was considered statistically significant. Analysis was done using STATA V.13.1 (STATA).
Seventy-six eyes of 42 patients underwent either toric or non-toric ICL V4c implantation. Mean age was 27.4 years (±5.14 years, range 20 to 39 years) and 30 patients (71.4%) were women. Demographic data are shown in table 1.
Preoperative values of the anterior chamber depth (internal), white-to-white distance and the iridocorneal angle measured with Orbscan II, Pentacam and OCT are shown in table 2.
The anterior segment OCT angle and vault analysis in mesopic, scotopic and photopic conditions is presented in table 3.
The average iridocorneal angle showed a statistically significant decrease (p<0.05) in all mesopic, scotopic and photopic conditions after 1 week of surgery compared with the preoperative measurements; in mesopic conditions, it decreased 14.1°, in photopic conditions 14.8° and in scotopic conditions 13.2°.
The one-way repeated ANOVA showed that the angle measurement changed statistically significantly over the 1-year follow-up in mesopic conditions (p=0.01). A Tukey post hoc test revealed that significant changes were not present within any continued time points; however, a significant change was evident between month 1 and 12 (p=0.006). On the other hand, the angle measurement did not have a significant change over the 12-month follow-up in scotopic (p=0.07) nor photopic (p=0.18) conditions, without significant changes between the various time periods.
The average vault under mesopic conditions was 0.661±0.21 mm at week 1. The vault decreased to 0.650±0.18 mm under scotopic light and to 0.502±0.17 (24.1%) under photopic light conditions.
The one-way repeated ANOVA showed a statistically significant change in vault measurement over the 12-month follow-up in mesopic conditions (p=0.01). A Tukey post hoc test revealed that a significant change was not present within any two consecutive time periods; however, it was evident between week 1 and 12 months (p=0.025). The vault measurement did not show a significant change over the 12-month follow-up in scotopic (p=0.09) nor photopic (p=0.36) conditions.
Refractive results showed a preoperative UDVA of 1.65±0.4 logMAR and postoperative 0.12±0.12 logMAR (p<0.001). Mean preoperative CDVA was 0.11±0.12 logMAR and postoperative 0.05±0.08 logMAR (p<0.001). Preoperative spherical equivalent was −11.94±3.51 D (−7.5 to −22.88) and −0.06±0.77 D (−1.62 to 1.25) postoperatively (p<0.001).
At 12 months of follow-up, 99% of eyes had an UCVA of 20/40 or better (figure 1A). Thirty-seven (48.6%) eyes maintained the same CDVA postoperatively, four eyes (5.2%) lost 1 line and one eye lost 2 lines (1.3%) of CDVA, where the aetiology of the loss was attributed to the presence of pathological or degenerative myopia (figure 1B). A good correlation was found between attempted versus achieved spherical equivalent refraction (R2=0.95393) (figure 1C). Eighty-six per cent of eyes were within 1.00 D of target spherical equivalent (figure 1D). Preoperative mean refractive astigmatism was −2.87 D and decreased to −0.28 D postoperatively (p<0.001). Seventy-eight per cent of eyes had <1.00 D of refractive astigmatism after surgery (figure 1E). Eighty-five per cent of eyes remained within 0.5 D of spherical equivalent refraction at last visit (figure 1F).
The ICL V4c model includes a central orifice for the passage of aqueous humour thereby minimising the risk of pupillary block and avoiding the need for an iridectomy. The ideal postoperative vault must create a space between the anterior lens surface and posterior surface of the pIOL; a vault between 500 and 750 μm is recommended. A smaller vault (<250 μm) can cause cataracts while a larger vault (>750 μm) can cause angle closure, pupillary block and subsequent glaucoma. The vault is affected by the shape of the ICL, white-to-white measurement and age. Previous studies have shown that the toric and non-toric ICL V4c vault is comparable with previous models of ICL. Schmidinger and colleagues showed that there is a reduction of the central vault after a 10-year period, recommending a minimum size of 230 μm for long-term safety; however, considering the dynamic changes of the vault during accommodation and an average increase in lens thickness of 20 μm per year, a vault of at least 500 μm is recommended to avoid complications in a period of 25 years.14
Different studies have focused on determining the best way to calculate the size of the ICL, the estimated and the achieved vault. Lee et al determined that the most important factor to estimate the vault is the disparity between the ICL and the diameter of STS.12 Others, like Kamiya et al, have studied factors influencing the achieved vault, such as patient age, and they observed that the achieved vault decreases about 10 μm per year of age, a statistically significant result; other factors were found to have greater influence on the vault such as the ICL size, anterior chamber amplitude and a positive correlation of the latter with keratometric average.15
We had four complications in our case series: one patient with ocular hypertension secondary to ocular viscoelastic device retention, one patient with corneal oedema that resolved within 20 days with topical treatment, one patient with Descemet detachment during corneal incision creation that required an intracameral air bubble to resolve and one patient that after toric ICL V4c implantation required repositioning for a greater than 20° rotation; all these resolved during follow-up.
There are limited studies reporting changes in the iridocorneal angle and vault measured by AS-OCT after ICL implantation; however, none of these studies analyses changes under different light conditions with the toric ICL V4c model. A study evaluating the central vault of patients with the ICL V4 model with OCT, taken with a dilated pupil and under cycloplegic effect, showed a significant central vault dropping from 510±238 μm to 439±231 μm after 6 months (decrease of 71±58 μm), with a trend to a further reduction after this period.16 In the same manner, we found a decrease in vault after 12 months of follow-up in the different lighting conditions, changing from 661±21 μm to 596±23 μm in mesopic conditions, 653±19 μm to 593±23 μm in scotopic conditions and 495±18 μm to 475±20 μm in photopic conditions; however, only the mesopic changes were statistically significant. In another group of 36 eyes undergoing ICL implantation, the authors noted a statistically significant decrease in vault at 1 and 3 months after surgery, after which the values stabilised.17
The iridocorneal angle was assessed in a study in patients after the ICL V4c implantation using a Fourier-domain OCT; the authors found a considerable angle narrowing in different quadrants, and this narrowing remained stable at 3 months postoperatively.11 In the same way, we found important angle narrowing as soon as the first week after surgery in all lightning conditions, but this measurement remained stable in the follow-up in scotopic and photopic conditions, and changing in the mesopic measurement.
In the present study, we demonstrate that the ICL V4c implantation is safe, stable, predictable and efficient for high myopia correction during a 12-month follow-up. It has been reported that ICL implantation is effective for correction of moderate to high myopia. Sari et al reported that after toric ICL implantation with a 3-year follow-up, 17.6% did not show any changes in CDVA, while the remaining 76.5% earned 2 lines of vision and 5.9% lost 1 line of vision.18 They also reported that 52.9% had a spherical equivalent of ±0.5 D and 82.4% of ±1.00 D.18 However, the risks of complications such as cataract formation, loss of endothelial cells, pigment dispersion syndrome, pigmentary glaucoma and pupillary block have to be taken into account. From the previous, the endothelial cell loss/change is a variable that could be assessed in future studies and included in the safety evaluation.
The current study has some limitations. The first is the short follow-up of 12 months since a long-term monitoring is needed to determine if changes following ICL V4c implantation have a significant impact. The second limitation is that measurements with AS-OCT are operator dependent; however, measurements were performed in our study by the same expert operator to avoid further bias. The third limitation is the lack of pupilometry under different lighting conditions, as this variable can help analyse the change in the iridocorneal angle being different in each eye.
The ICL V4c implantation seems to be predictable and stable for correction of myopia and astigmatism. A decrease of the vault is noted after 12 months of follow-up, and this varies under different lighting conditions; measuring the vault in photopic conditions may help in determining the minimal vault size. Immediately after ICL V4c implantation, a significant decrease in the iridocorneal angle was observed and must be taken into consideration during preoperative planning.
Contributors Design of the study: GGD, AOP, JCSO and EOGH. Conduct of the study: GGD, AOP, JCSO and MSSR. Collection and management of the data: GGD, AOP, JCSO and MSSR. Analysis and interpretation of the data: GGD, AOP, JCSO, MSSR, AL, AGB, ARM, AN and EOGH. Preparation of the manuscript: GGD, AOP, JCSO and MSSR. Review and approval of the manuscript: GGD, AOP, JCSO, MSSR, AL, AGB, ARM, AN and EOGH.
Funding This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.
Patient consent Detail has been removed from this case description/these case descriptions to ensure anonymity. The editors and reviewers have seen the detailed information available and are satisfied that the information backs up the case the authors are making.
Ethics approval The Institutional Review Boards of Research, Ethics and Biosecurity from The Instituto de Oftalmologia Conde de Valenciana approved the study protocol.
Provenance and peer review Not commissioned; externally peer reviewed.
If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.