Special Indications for the Use of Phakic IOLs
Phakic IOLs were relatively slow to gain wide acceptance among ophthalmic surgeons after the introduction of designs in the 1980s. In the past decade, however, factors including improvements in lens designs and implantation techniques, publication of longerterm clinical results, and the realization among surgeons that LASIK alone cannot address all refractive errors, have led to greater adoption and use of phakic IOLs for a variety of indications.
The principal indication for use of phakic IOLs is the correction of myopia or myopic astigmatism beyond the range of LASIK correction (ie, generally for myopic errors of -8.00 D or greater) but these lenses can also be useful in a number of other situations including correction of myopia or myopic astigmatism in eyes with less than -8.00 D error that are for some reason contraindicated for LASIK; in eyes with stable keratoconus; and in eyes with residual refractive errors after LASIK, corneal transplant, intrastromal corneal ring segment (ICRS) implantation, corneal collagen crosslinking (CXL), and pseudophakia.
Phakic IOLs fall into one of three broad categories; anterior chamber angle-fixated lenses, originally introduced by Baikoff and Joly;1,2 anterior chamber iris-fixated lens, introduced by Fechner and Worst;3 and posterior chamber sulcus- fixated lens introduced by Fyodorov4 and subsequently modified by STAAR Surgical (Monrovia, California) and other companies.5
Our first experience with phakic IOLs was in 1992; three designs were available at that time. Today, the posterior chamber phakic IOL is our preferred design, and our principal recent experience is with the sulcus-fixated lens. This article describes some of what we have learned about the use of the Visian ICL (STARR Surgical, Monrovia, California) for special indications, including patient selection, surgical techniques, and clinical results.
VISIAN ICL
The Visian ICL is a one-piece plate-haptic lens designed to
vault anteriorly over the crystalline lens. The lens material,
trade-named Collamer, is a hydrophilic collagen-polymer
combination with a water content of 34% and a refractive
index of 1.45. The lens is available in a toric version (Toric
ICL or TICL) designed to address myopic astigmatism.
BROADENED INDICATIONS
High myopia and high myopic astigmatism are the
most common indications for ICL and TICL implantation.
Patients with these conditions are generally not suitable
candidates for LASIK because of increased risk for
corneal ectasia, along with low visual quality and unpredictable
refractive results.6 Although there is no clear-cut
upper safety limit for LASIK, it is generally agreed to be
somewhere between 7.00 and 9.00 D of myopia. In a
prospective bilateral randomized study,7 we showed that
phakic IOLs were more effective, more predictable, and
safer than LASIK for myopia above 9.00 D. For this reason
we routinely perform ICL or TICL implantation for correction
of myopia of 8.00 D or more.
For lower degrees of myopia, we implant the ICL or TICL in candidates who present with any risk factors for post- LASIK ectasia or flap complications. Risk factors include eyes with relatively thin corneas, in which LASIK ablation would not leave a residual stromal bed of at least 300 µm; corneas steeper than 48.00 D or with expected post-LASIK keratometry readings flatter than 35.00 D; and corneas with topography indicating forme fruste keratoconus or keratoconus suspect.
Patients with stable keratoconus are also potential candidates for ICL and TICL implantation. In the past 2 years we have performed more than 80 ICL or TICL implantations in patients with stable keratoconus. Other indications for ICL and TICL include correction of residual refractive errors after LASIK, corneal transplant, ICRS implantation, corneal collagen crosslinking, and pseudophakia.
The ICL is available to correct hyperopia of up to 10.00 D. However, because hyperopes generally have shallower anterior chambers and narrower angles than myopes, hyperopic ICLs are less commonly used.
There are no published data on long-term results after ICL implantation in children; because the implants can be surgically exchanged the ICL might be a good option for children with anisometropia. Long-term prospective clinical trial results are needed to confirm the efficacy, predictability, and safety of ICL implantation in children.
PATIENT SELECTION
Candidates for ICL implantation must have documented
stable refraction for at least 1 year, sufficient anterior chamber
depth, a central endothelial count of greater than 2,200
cells/mm2, appropriate pupil size, and an open anterior
chamber angle. Manifest refraction is usually sufficient in
low and moderately high myopes (12.00 D and less), but in
extreme myopia contact lens over-refraction is recommended.
In hyperopes, cycloplegic refraction is advisable, especially
in younger patients. In all cases, the vertex distance of the
refraction should be recorded for use in ICL power calculation.
A 1.00 mm error in vertex distance corresponds to a
1% miscalculation of ICL power.8
The ICL and TICL sit further away from the corneal endothelium than anterior chamber phakic IOLs. An anterior chamber depth of 2.7 mm from the endothelium to the anterior surface of the crystalline lens is estimated as the lower limit for safe ICL implantation. Anterior chamber depth can be measured using optical devices such as the IOLMaster (Carl Zeiss Meditec, Jena, Germany), anterior segment imaging devices such as the Pentacam (Oculus Optikgeräte GmbH, Wetzlar, Germany) or Orbscan II (Bausch & Lomb, Rochester, New York), or A-scan ultrasound.
The optic diameter of the ICL ranges from 4.65 to 5.50mm depending on lens power; the effective optic diameter at the corneal plane ranges from 6.17 to 7.30 mm. Patients with scotopic pupil diameter larger than the effective optic diameter may experience night glare or halos.
Corneal topography is essential for patients undergoing any type refractive surgery, primarily to identify early keratoconus. Abnormal topography is not an absolute contraindication for ICL surgery. Many patients who are not good candidates for LASIK can safely undergo ICL implantation; these include patients with steep or flat corneas and keratoconus suspect. Cases with stable keratoconus and good BCVA can also benefit from ICL surgery.
Gonioscopy should be performed to identify narrow or abnormal angles, as ICL implantation in these eyes may lead to further narrowing of the angle and secondary glaucoma.
Proper sizing of the ICL is key for successful surgery. The length of the ICL should ideally be equal to the horizontal ciliary sulcus diameter. The conventional method for ICL sizing, white-to-white distance as measured with calipers, IOLMaster, or Orbscan, does not accurately reflect the diameter of the sulcus.9 However, this method is good enough; the rate of ICL replacement for long or short size is less than 0.8%.10 High-frequency ultrasound showed that the ICL can safely sit on the ciliary sulcus, ciliary processes, or the zonules without complications. This, together with the flexible material of the lens, may at least partially explain the forgiveness in lens position.
In eyes with limbal pigmentation, Orbscan can over-estimate the white-to-white measurement, so in these cases caliper measurement is more reliable.
SURGICAL CONSIDERATIONS
Many surgeons perform two peripheral iridotomies, 90°
apart, 1 or 2 weeks before surgery with the Nd:YAG laser to
prevent postoperative pupillary block. At the start of surgery
the pupil must be widely dilated. We routinely perform
ICL surgery under topical anesthesia (0.5% bupivacaine HCl).
It is advisable to double check the white-to-white measurement
with calipers before beginning surgery.
The size of the clear corneal temporal incision can vary from 2.6 to 3.2 mm depending on surgeon preference; we use a 2.8-mm incision, which enables smooth injection with negligible effect on postoperative astigmatism.
The anterior chamber is filled with an ophthalmic viscosurgical device (OVD) before the lens is injected using the MicroSTAAR injector (STAAR Surgical). The injection should be slow enough to allow the leading footplate to unfold in the anterior chamber before the trailing footplate is pushed out of the cartridge (Figure 1). This prevents the lens from unfolding upside-down in the anterior chamber. Once the lens unfolds and the marks on the footplates are checked for proper orientation, the footplate near the main incision is tucked under the iris using an ICL manipulator.
If laser iridotomies were not performed before surgery, a miotic agent is injected to constrict the pupil and surgical iridectomies are performed. We use a vitrector to perform iridectomy because we have found it more cosmetic and reproducible, easier, and effectively done through the main incision. It also saves an extra procedure as compared with laser iridotomy. However, forceps and scissors can also be used. Thorough irrigation and aspiration of the remaining OVD is then performed to prevent postoperative intraocular pressure spikes. At the completion of the procedure we inject an intracameral preservative-free antibiotic. Implantation of the TICL is basically the same, with the exception that the axis of cylinder must be aligned correctly to correct the patient's preoperative astigmatism.
We perform bilateral same-session ICL surgery in most patients; each eye is treated as a separate case with separate sets of instruments.
LOW TO MODERATE MYOPIA
AND ASTIGMATISM
The safety and efficacy of the Visian ICL and TICL for high
myopia and myopic astigmatism have been well established
in published reports, including the results of phase 3 clinical
trials for US Food and Drug Administration (FDA)
approval.10-13
In the past 2 years, we have performed more than 270 cases of spherical ICL and more than 230 cases of TICL implantation. ICL is our procedure of choice for eyes with myopia greater than 8.00 D. We use the TICL in cases with compound myopic astigmatism when the cylindrical component of the refraction is greater than 1.00 D.
In myopia of 8.00 D or less, we perform LASIK provided corneal topography is not suspect and corneal thickness allows a stromal bed of at least 300 µm after a 6.5-mm ablation. The ICL is our procedure of choice for correction of myopia less than 8.00 D in cases contraindicated for LASIK.
In a series of 35 consecutive eyes that received ICL for myopia between -2.00 and -8.00 D; mean patient age was 28 years, mean baseline manifest refraction spherical equivalent (MRSE) was -4.69 D (range, -8.00 to -2.13 D), and mean refractive cylinder was 0.42 D (range, 0.00 to 1.00 D). Emmetropia was the target in all eyes.
In 29 eyes (82.9%) examined at 1 year postoperative, mean MRSE was -0.14 ±0.27 D (range, -0.75 to 0.25 D); 86.2% eyes were within ±0.50 D, and all eyes were within ±1.00 D of emmetropia. Mean refractive cylinder was 0.43 ±0.28 D (range, 0.00 to 1.25 D). At 1 year postoperative, UCVA in four eyes (13.8%) was 20/16 or better, in 25 eyes (86%) was 20/20 or better, and in all eyes was 20/32 or better. Two eyes (6.9%) lost 1 line of UCVA.
In another series, the TICL was implanted in 68 consecutive eyes. Mean age was 26 years, mean baseline MRSE was -7.07 D (range, -13.38 to -2.25 D), and mean refractive cylinder was 2.34 D (range, 1.25 to 4.75 D).
In 58 eyes (85.3%) examined at 1 year postoperative, mean MRSE was -0.16 (range, -1.75 to 1.13 D); 49 eyes (84.5%) were within ±0.50 D of emmetropia, five eyes (8.6%) between -1.00 and -0.51 D, and three eyes (5.2%) between -2.00 and -1.10 D. One eye (1.7%) was overcorrected by 1.13 D.
Mean refractive cylinder at 1 year was 0.38 D (range, 0.00 to 1.75 D). From 1 month to 1 year postoperative, refractive cylinder changed by less than 1.00 D in all eyes and by less than 0.50 D in more than 95.5% of eyes. The mean difference was less than 0.05 D at each reporting interval. Vector of cylinder was stable from the 1-month examination and changed by less than 1.00 D in more than 98.3% of eyes and less than 0.50 D in more than 94.8% of eyes at each interval.
At 1 year postop, UCVA was 20/16 or better in seven (12.1%) eyes, 20/20 or better in 39 (67.2%) eyes, and 20/32 or better in 50 eyes (86.2%). All eyes were 20/40 or better uncorrected.
Axis misalignment was less than 5° at 1 year in 89.6% of eyes, less than 10° in 98.3%, and less than 20° in all eyes. One eye with axis misalignment of more than 10° was diagnosed at 1 week postop. Realignment was performed on postoperative day 8, and no rotation was observed afterwards; at 1 year the axis misalignment of this eye was 2°.
STABLE KERATOCONUS
The ICL and TICL can be used to correct myopia and
compound myopic astigmatism in eyes with stable keratoconus.
We are conducting a prospective randomized clinical
trial to assess the efficacy, predictability, and safety of TICL for correction of compound myopic astigmatism associated
with stable keratoconus.
The study includes patients with stable keratoconus, clear central cornea, MRSE between -4.00 and -15.00 D, BCVA of 20/40 or better, stable refraction for at least 1 year, and other previously mentioned selection criteria for ICL implantation. All patients were intolerant of rigid contact lenses. Each eye received a myopic TICL through a temporal clear corneal incision.
In 23 eyes seen for 1 year follow-up, mean baseline MRSE was -9.62 D (range, -15.00 to -4.38 D). At 12 months postop, it was -0.32 (range, -1.50 to 0.13 D). UCVA was 20/40 or better in 20 eyes (90%) and 20/20 or better in 11 eyes (55%); four eyes (20%) eyes gained 2 or more lines of BCVA.
Due to the nature of the disease, longer follow-up and larger series are needed; however, based on our 1-year results we believe that TICL implantation is effective, predictable, and relatively safe for the correction of compound myopic astigmatism associated with stable keratoconus.
OTHER INDICATIONS
In progressive keratoconus treated with implantation of ICRS (Figure 2) or CXL, implantation of a TICL is possible to correct residual refractive error. A TICL was implanted 1 year after the primary procedure to correct residual refractive error.
Another important indication for the TICL is correction of residual refractive errors after corneal transplantation in which keratorefractive techniques are not a viable option. In a prospective study we evaluated the predictability, efficacy and safety of TICL implantation to correct compound myopic astigmatism after deep anterior lamellar keratoplasty (DALK). Twenty-eight eyes of 28 patients with previous DALK received a TICL. All eyes had stable refraction for 6 months after removal of corneal sutures. Mean baseline MRSE was -9.4 D (range, -16.0 to -5.0 D). UCVA was 20/40 or better in all eyes and 20/20 or better in 14 eyes (50%)
One year after surgery in 24 eyes (85.7%), MRSE was -0.30 ±0.50 D; 14 eyes (58.3%) eyes had 20/20 UCVA; and six eyes (25%) gained 2 or more lines of UCVA. No visually threatening complications were observed.
ICL and TICL can also be implanted in eyes with penetrating corneal graft provided the endothelial cell count is acceptable and the anterior chamber is deep enough.
Future improvements to ICL design will hopefully include more accurate means of lens sizing, better ways to assess the position of the ICL in relation to the ciliary sulcus and zonules, and the introduction of aspheric and wavefrontoptimized customized lenses to minimize and/or compensate for higher-order aberrations in highly aberrated eyes.
The excellent predictability and efficacy of the ICL and TICL, combined with their low incidence of postoperative complications and high degree of patient satisfaction, make these phakic IOLs valuable tools for comprehensive refractive surgeons.
Alaa El Danasoury, MD, FRCS, is Chief of Refractive Surgery at Maghrabi Eye Hospital, Saudi Arabia. Dr. El Danasoury states that he is a paid consultant to STAAR Surgical. He may be reached at e-mail: malaa@magrabi.com.sa.
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