ARTICLE

1-Year Follow-up of Phakic Implantable Collamer Lens for Low Myopia
Jos� F. Alfonso MD, PhD^1,2, Luis Fern�ndez-Vega PhD^1,2, Robert Mont�s-Mic� PhD³

ABSTRACT
PURPOSE: To evaluate the efficacy, predictability and safety of myopic phakic posterior chamber implantable collamer lens (ICL) to correct low myopia.
SETTING: Fern�ndez-Vega Ophthalmological Institute, Oviedo, Spain.
METHODS: In a prospective noncomparative interventional case series, outcomes in 50 eyes of 39 patients, myopia from –1.00 to –3.00 dioptres (D), were analyzed 12 months after the implantation of myopic ICLs (STAAR Surgical). They comprised uncorrected visual acuity (UCVA), best corrected visual acuity (BCVA), slit-lamp examination, refrac- tion, tonometry, endothelial microscopy and ICL vault.
RESULTS: The mean UCVA and BCVA after ICL implantation were 0.01±0.01 logMAR (range from 0.01 to 0) and 0.003±0.012 logMAR (range from 0.046 to 0), respectively. The efficacy index was 0.99. No eyes lost 1 o more than 1 lines, 44 eyes did not change after surgery, and 6 eyes gained 1 line of visual acuity. The safety index was 1.01. The BCVA after ICL implantation was statistically significantly better than the BCVA before surgery (P=0.00638). Spherical equivalent (SE) was within ±1.00D of the desired refrac- tion in all cases and 98% within ±0.50D. Mean postoperative SE was –0.09±0.12D at 12 months. No cases of anterior subcapsular opacities were detected. Postoperative endothe- lial cell count was 2828±461 cell/mm2 (range from 2050 to 4239 cell/mm²). Vaulting after 1 year of follow-up was 2.24±0.77 and postoperative intraocular pressure was 11.72±1.30 mmHg.
CONCLUSIONS: Myopic ICL implantation was a safe, effective, and predictable proce- dure for the correction of low myopia.
(J Emmetropia 2010; 1: 3-8 ©2010 SECOIR - Sociedad Espa�ola de Cirug�a Ocular Implanto-Refractiva)

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Submitted: November 23 2009
Revised: January 19, 2010
Accepted: March 18, 2010

1 Fern�ndez-Vega Ophthalmological Institute, Oviedo, Spain.
2 Surgery Department, School of Medicine, University of Oviedo, Spain.
3 Optics Department, Faculty of Physics, University of Valencia, Spain

 

Acknowledgements and Disclosure: The authors have no propri- etary interest in any of the materials mentioned in this article.
Address: Jos� F. Alfonso MD, PhD, Instituto Oftalmol�gico Fern�ndez-Vega, Avda. Dres. Fern�ndez-Vega 114, 33012 (Oviedo), Spain.
E-mail: [email protected]

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INTRODUCTION

The implantable collamer lens (ICL), has been used to correct high and moderate refractive errors. Several clinical studies have confirmed the good pre- dictability, safety and efficacy of this technique^{1, 2, 3, 4, 5, 6, 7}. However, up to now the use of ICLs to correct the spherical error in patients with low myopia has not been evaluated. Laser excimer corneal surgery may be used for correcting low myopic errors; although, in some cases this technique is contraindicated⁸. In these cases, the implantation of an ICL may be considered. In addition, different studies that compare the tech- nique of Laser in situ keratomileusis (LASIK) and ICL have concluded that the ICL was safer and more effec- tive than LASIK^{9, 10, 11, 12}.

The present study presents a series of 50 eyes of 39 patients with low myopia who were implanted a myopic ICL. The purpose of this study is to confirm the safety, efficacy and predictability of the surgical correction of low myopia after ICL implantation.

PATIENTS AND METHODS

A prospective assessment was made of 50 eyes of 39 patients with low myopia who underwent implanta- tion of myopic ICLs to correct myopia at the Fern�ndez-Vega Ophthalmological Institute (Oviedo, Spain) between September 2003 and September 2005. Table 1 shows the demographic characteristics of par- ticipants. Mean spherical and cylindrical refractive errors were �2.32�0.63D (range �1 to �3) and �0.31�0.30D (range from 0 to �1), respectively.

The inclusion criteria were best corrected visual acuity (BCVA) of 20/30 or better, stable refraction and laser corneal surgery contraindication. The exclu- sion criteria included age below 21 years, anterior chamber depth under 3.0 mm, endothelial cell densi- ty under 2000 cell/mm², escotopic pupil diameter over 6.5 mm, cataract, history of glaucoma or retinal detachment, previous corneal or intraocular surgery, macular degeneration or retinopathy, neuro-oph- thalmic diseases and history of prior ocular inflamma- tion.

Before the ICL implantation, patients had a com- plete ophthalmologic examination, including manifest and cycloplegic refraction, keratometry, corneal topo- graphy, endothelial cell count, pachymetry, slit-lamp biomicroscopy, Goldmann applanation tonometry, and binocular indirect ophthalmoscopy through dilat- ed pupils. Subjective vault was assessed using an optical section during routine slit-lamp examination and clas- sified in five levels by comparing the separation between the lens anterior surface and the posterior sur- face of the ICL to the corneal thickness. This classifica- tion system has showed good reliability in terms of comparison with anterior segment Optical Coherence Tomography measurements¹³. All vault measures, were taken under cycloplegic effect in order to avoid poten- tial influence of accommodation-induced changes in the position of the anterior surface of the crystalline lens or the ICL itself on the estimation of the vault value, and above all to make the assessments more repeatable between visits.

The ICMV4 STAAR Visian (STAAR Surgical, Monrovia, CA) lens is a phakic posterior chamber ICL made of collamer to correct myopia. All surgeries in this study were performed by one experienced surgeon (J.F.A.) through a 3.2 mm clear corneal tunnel incision in the steepest meridian using peribulbar anesthesia. 30 minutes before surgery, cyclopegic and phenilephrine eyedrops were instilled. 5 minutes before surgery, povi- done-iodine 5% (Betadine�) was instilled. The anteri- or chamber was filled with sodium hyaluronate 1% (Provisc, Alcon), which was completely removed at the end of the surgery. Tobramicin and dexamethasone 0.1% (Tobradex�) eyedrops were used 4 times a day for 7 days, after which diclofenac sodium eyedrops (Voltaren�) were started 3 times a day for 2 weeks. In cases of bilateral implantation, second eye was operat- ed within the first postoperative week. The ICL power was calculated using the software ICL power choice of STAAR Surgical. Laser iridotomy was performed 1 week before the surgery.

The tenets of the Declaration of Helsinki were followed in this research. Informed consent was obtained from all patients after explaining the nature and possible consequences of the study. Institutional Review Board approval was obtained. Follow-up was 12 months postoperatively. It comprised uncorrected visual acuity (UCVA), BCVA, slit-lamp examination, refraction, fundoscopy and tonometry. Following the power vector method the refractions obtained before and 12 months after ICL implantation were assessed for astigmatism analysis. Any spherocylindrical refractive error was expressed by three dioptric pow- ers: SE, J₀, and J₄₅; with SE being a spherical lens equal to the SE of the given refractive error, and J₀ and J₄₅ two Jackson crossed cylinders equivalent to the conventional cylinder. These numbers are the coordinates of a point in a three-dimensional diop- tric space, being the power vector the vector originat- ed from the origin of this space to the point (SE, J₀, and J₄₅). Manifest refractions in conventional script notation [S (sphere), C (cylinder), j (axis)] were con- verted to power vectors coordinates and overall blur- ring strength by the following formulas: SE = S + C/2; J₀ = (-�C/2) cos (2j); J₄₅ = (�C/2) sin (2j) and B = (M² + J₀² + J₄₅²)^1/2.

All examinations were performed at 12 months after implantation by one ophthalmic technician who was unaware of the objective of the study. Data analy- sis was performed using SPSS for Windows version 12.0 (SPSS Inc., Chicago, IL). Normality was checked by the Shapiro-Wilk test, and the monovariate t-test was used for SE analysis. Differences were considered to be statistically significant when the P value was <0.01 (i.e., at the 1% level).

RESULTS

No complications occurred during the surgery. No eye needed explantation or repositioning of the ICL. De-centering of the ICL lens was not observed and no patients reported halos and glare under daylight con- ditions. In the postoperative period no case of pupil- lary obstruction and anterior subcapsular opacities was detected.

Visual Acuity

The mean UCVA after ICL implantation was 0.01±0.01 logMAR (range from 0.01 to 0). UCVA was 20/40 or better in 45 eyes (90%) and 20/20 in 5 eyes (10%). The mean BCVA after ICL implantation was 0.003±0.012 logMAR (range from 0.046 to 0). BCVA was 20/40 or better in 4 eyes (10%) and 20/20 or bet- ter in 46 eyes (90%). The overall efficacy index (mean postoperative UCVA/mean preoperative BCVA) at 12 months was 0.99. None of the eyes lost 1 o more than 1 lines, 44 eyes did not change after surgery, and 6 eyes gained 1 line of visual acuity (figure 2). The safety index (ratio of postoperative and preoperative BCVA) at 12 months was 1.01. The BCVA after ICL implan- tation was statistically significantly better than the BCVA before surgery (P=0.00638).

Refractive Errors

The deviation of the achieved SE refractive error from the calculated SE refractive error was calculated. Figure 3 shows the attempted versus achieved plot for SE (top) and for both components of astigmatism: J₀ (middle) and J₄₅ (bottom). In the case of SE all eyes were within �1.00D of the desired refraction and 98% with- in �0.50D. The mean postoperative SE was �0.09�0.12D at 12 months [sphere: -0.05�0.11D (from 0 to �0.50) and cylinder �0.10�0.18 (from 0 to �0.50)]. Results for both J₀ and J₄₅ were 100 % of cases within �0.50D. Figure 4 shows the astigmatic compo- nent of the power vector as represented by the 2- dimensional vector (J₀, J₄₅). The origin of this graph (0,0) represents an eye without astigmatism. The spread in the pre-surgical data is converted into a con- centrated data set around the origin after ICL implan- tation. There was a reduction in SE after implantation, showing that a relatively wide range of refractive errors was reduced to a narrow distribution near emmetropia. The power vector magnitude was reduced after surgery and a compression of the overall refractive error data was observed by the reduction in the standard devia- tions. A monovariate t test was performed to test the hypothesis that the SE component of the power vector analysis had a mean that was not statistically different from zero; that is, the refractive error was adequately correct by the ICL (P<0.0001).

Endothelial Cell Count, ICL Vault and Intraocular Pressure

Postoperative endothelial cell count was 2828±461 cell/mm², ranging from 2050 to 4239 cell/mm², at 1 year of follow-up. Mean vaulting of the ICL at 1 year of follow-up was 2.24±0.77, ranging from 1.00 to 4.00. Before ICL implantation the mean intraocular pressure (IOP) was 12.68±1.54 mmHg (10 to 19 mmHg), and at 1 year of follow-up was 11.72±1.30 mmHg (9 to 16 mmHg).

DISCUSSION

In this prospective study of 50 eyes, a new approach for low myopic eyes was evaluated, i.e., the implanta- tion of of a low power myopic ICL. To our knowledge, there are no studies evaluating ICL implantation in eyes with myopia between �1.00 to �3.00D. The aim of the present study was to show the refractive and visual out- comes found after ICL implantation in these patients.

Our study shows that ICL implantation is an effec- tive procedure for the correction of low myopia. Other previous published series of ICL implantation showed similar outcomes. Specifically, in the FDA study, the ITM study group¹ observed 523 eyes of 291 patients with myopia between 3 and 20D. They divided their study in several groups considering the preoperative SE. Focusing on the <7D group (range from -2.01 to -7.00D), they reported that the spherical error was corrected in 96.4% of the eyes within �1.00D of the attempted correction, and 75% of eyes within �0.50D range. We have obtained similar refractive outcomes with slightly differences. Our study shows that, after ICL implantation, predictability was also good, with 98% of eyes within the �0.50D range of SE (Figure 3 top) and 100% of cases whitin �0.50D range of both components of astigmatism (J0 and J45) (Figure 3 mid- dle and bottom). About safety and efficacy, they found that after 1 year follow-up 60.1% of patients with myopia between �3 to �20D had a BCVA of 20/20 or better, and 92.5% had an UCVA of 20/40 or better. In our case, 90% of eyes had a BCVA of 20/20 or better and an UCVA of 20/40 or better in 45 eyes (90%). In summary, our efficacy index was good too (0.99). On the other hand, they found 41 cases (9.6%) that gained 2 or more lines of BCVA. We have observed satisfactory visual outcomes in relation to safety index (1.01), with 12% of eyes gaining 1 lines of BCVA (Figure 2).

Other authors have concluded that the ICL implan- tation is a safe procedure for the surgical correction of high myopia ^{2, 3, 4, 5, 6, 7}. They presented similar refractive out- comes than those reported in our study. For example, Jimenez-Alfaro and coathors² had studied 20 eyes to 10 high myopic patients after ICL implantation. After sur- gery the percentage of eyes with a SE between �1.00D was 45%, less than our study where 100% of the eyes were between �1.00D range. On the other hand Lackner et al³ found that the safety index was 1.31 for myopic eyes (65 eyes) of 45 patients. In this case the safety index was also less than our results (1.01) more approaching the unit. We could summarize that ICL implantation in eyes with low myopia (range from �1.00 to �3.00D) is comparable or more effective, safer and predictable than high myopic ICL implantation.

When laser corneal surgery for low myopia correc- tion is contraindicated⁸ (cases of insufficient corneal thickness or corneal irregularity) the implantation of an ICL may be considered. In our study we couldn�t com- pare LASIK and ICLs, but previous studies compared these techniques to analyze which is the most effective and safer ^{9, 10, 11, 12}. The ITM study group⁴ included in their 3-year study a comparison of ICL with FDA-approved LASIK clinical studies. In this summary the FDA study group found that the efficacy and predictability out- comes were better or comparable after ICL surgery than to all approved LASIK clinical study results. Sanders and coauthors¹⁰ have described a comparison of ICL and standard LASIK for myopia of -4.00 to �7.88D in a total of 1678 LASIK eyes and 144 ICL eyes, after 6 months follow-up. They observed that 11% of eyes lost more than 1 line of BCVA after LASIK surgery and 4% after ICL implantation. 15% of LASIK eyes gained more than 1 line versus 46% of ICL eyes. Mean preoperative SE was -5.60 � 0.03D in LASIK eyes and �6.40�0.09D in ICL eyes. After 6 months follow-up the SE was �0.35�0.02D after LASIK surgery and -0.08�0.03D after ICL implanta- tion. Finally, 70% of LASIK eyes were within �0.50D of predicted refraction while 79% of ICL eyes were within �0.50D range. If we observe the results report- ed by Sanders, ICL has been effective alternative to LASIK for the range of myopia between �4 to �7.88D. In a previous report by Sanders and Vukich9, the authors compared the results of LASIK and ICL in the correction of myopia �3 to �7.88D and found similar outcomes. They concluded that ICL was safer and more effective than LASIK.

Complications to ICLs have been well described previously^{2, 3, 5, 14, 15, 16}. However, in our study we haven�t reported any complication during the surgery and over the entire follow-up period. Even so, the possible for- mation of cataracts probably represents the most con- troversial issue of the ICL implantation. After an ICL implantation, central and peripheral contact between the ICL and the crystalline lens may be responsible for the high prevalence of cataract formation⁵. The circu- lation of aqueous humor between the ICL and the anterior crystalline lens capsule is necessary to diminish the risk of touch between the 2 structures. The opti- mum vault size is when it represents 10% of the ante- rior chamber depth, which is equivalent to a lens slight- ly than the horizontal diameter of the ciliary sulcus². In our case there were no statistically significant changes in vaulting over the lens crystalline at 1 year follow-up (P=0.1269), therefore the probability of appearance of opacities is smaller.

Several authors have found cataract formation in their studies. Gonvers et al⁵ reported at 36 months follow-up period that 27% of eyes with an ICL induced anterior subcapsular cataract. They found that the cataract development was more common in older patients and the number of cataracts increased with the duration of the follow-up. Sanders¹⁴ reached the same conclusion, patient age (>40 years) was a significant fac- tor in the development of cataract. But Sanders includ- ed a new correlation between cataract formation and very high preoperative myopia (>12D). But only 1% to 2% of 526 eyes progress to clinically significant opaci- ties at more than 7 years follow-up. Before Sanders study, Lackner and coauthors¹⁵ studied ICLs in 76 myopic eyes and found that lens opacification occurred in 14.5% of the eyes. According to Lackner risk factors for lens opacification after implantation of ICL includ- ed intraoperative trauma to the lens and older age. However, in our series, no anterior subcapsular lens opacities were detected, after 1 year follow-up.

Another complication is the possibility that the IOP could increase. Cases with an elevated IOP after ICL implantation was detailed in previous reports^2,16. According to Jimenez-Alfaro and coauthors² the IOP could increase in the immediate postoperative period because the retention of viscoelastic material or the appearance of a pupillary obstruction by the lens resulting from impervious iridotomies. Also they have found that the IOP could increase progressively during the follow-up period because of a narrowed angle originated by the lens or because of pigmentary dispersion that can result in pigmentary glaucoma. In their study the IOP had normal values after the first post-operative month. In addition, Chung et al16 had ana- lyzed several studies and reviewed the cases with elevated IOP and found that the elevated IOP had been associated with acute pupillary obstruction, chronic pigment dispersion and other mechanisms not specified. The elevated IOP in cases of pupillary obstruc- tion was normalized by additional iridotomy. According to Chung, inadequate preoperative irido- tomies and a high ICL vault due to inaccurate sizing of the ICL could be considered as primary causes of the elevated IOP in these cases. In the same study they concluded that iridocorneal angle became significanly narrowed in all eyes immediately after surgery. They analyzed changes in trabecular pigmentation in 48 eyes of 29 patients after 2 years follow-up. They con- cluded that there was no general increase in trabecular pigmentation or IOP over a mean follow-up of 33.2 months, and recommended careful monitoring of iridocorneal angle and IOP during the early postoperative period, especially for 1 month.

In our postoperative period no case of pupillary obstruction was detected. We have observed IOP variation in 60% of the eyes. There were statistically significant changes in IOP measurements after 1 year follow- up (P=0.00087). Increased IOP occurred in 9 eyes (18%) after all follow-up investigations, but one should be considered that there was a minimal change and this was not clinically relevant.

Another complication is the possibility of a postop- erative decrease of endothelial density. The decrease of endothelial density is proportional to the surgical time and manipulation² (attributed to the traumatic effect of surgery). In our study we have obtained statistically significant changes at 1 year follow-up (P<0.0001). 6% of eyes (3 cases) have suffered a loss of endothe- lial cells exceeding 500 cell/mm² after 1 year follow- up, but in any case the endothelial cell count was critical.

In conclusion, our study shows that ICL implanta- tion is a safe and reliable surgical method for correcting low myopia (range from �1.00 to �3.00D), specially in cases where other procedures are contraindicated. We believe that long-term randomized comparative prospective studies are necessary to evaluate this tech- nique and its complications. In subsequent studies long term safety of the presence of an ICL for low myopia on the posterior chamber of a phakic eye must be eval- uated. Moreover, future studies should include ICL evaluation in low hyperopic eyes.