October 2018

REFRACTIVE

Presentation spotlight
Toric phakic IOLs in keratoconus


by Stefanie Petrou Binder, MD, EyeWorld Contributing Writer


Line diagram showing the effect of corneal shape in normal and keratoconic eye and corrective modalities; (a) normal cornea with a regular focus of rays from optical infinity; (b) keratoconic cornea (scattering and lack of clear focus of rays from optical infinity); (c) keratoconus with glasses (improved focus of some rays); (d) keratoconus with implanted collamer lens (almost similar optical effect as with glasses, however, reduced minification as the ICL is closer to nodal point than the spectacles); (e) keratoconus with specialized contact lenses (improved focus in more irregular cases of keratoconus as the contact lens/air interface now acts as the first refracting surface)

OCT image with ICL in situ in a keratoconic eye
Source (all): Gaurav Prakash, MD

 

Specialist provides guidelines on the use of toric phakic IOLs in keratoconus patients

The implantation of toric phakic IOLs in eyes with keratoconus is complex. Ophthalmic surgeons have understandable concerns about potentially inducing higher order aberrations due to the complicated interplay of the phakic IOL’s toricity and the corneal irregularity in these patients. The key to using toric artificial lenses, according to Gaurav Prakash, MD, FRCS, cornea and refractive surgery services, NMC Eye Care, NMC Specialty Hospital, Abu Dhabi, United Arab Emirates, is having the right refractive information to identify who the true beneficiaries are.
“Only a subset of keratoconus patients will benefit truly from phakic IOLs, and it is very important to choose the correct ones,” Dr. Prakash said in a presentation he gave on the subject at the 2018 World Ophthalmology Congress.

Where do toric phakic IOLs fit in?

Refractive challenges abound in eyes with keratoconus, leaving it up to the eye surgeon to understand and weigh the risks and benefits. Ablative laser procedures can jeopardize the already weak cornea in keratoconus. Phakic IOL implantation is advantageous in such cases because it is a cornea sparing procedure. According to Dr. Prakash, phakic IOLs offer a large range of combination options for keratoconic eyes, which often have both astigmatism and high myopia to contend with. Mostly it is the stability of cornea ectasia that is the surgeon’s greatest concern, however, phakic IOL implantation is reversible and lens explanation is always an option if necessary.
Previous studies on safety and efficacy revealed that toric phakic IOLs either in combination with corneal crosslinking (CXL) or intracorneal ring segments (ICRS) could achieve good safety and efficacy. One retrospective study that evaluated ICL implantation after CXL in 30 progressive keratoconus eyes revealed that toric ICLs were an effective option for improving visual acuity for up to 2 years.1 A second, unrelated investigation in which the Visian toric ICL (STAAR Surgical, Monrovia, California) was implanted for the treatment of residual refractive error 6 months after ICRS and CXL in stable keratoconus showed good safety and efficacy in seven patients with moderate to severe keratoconus.2
Despite the positive outcomes, Dr. Prakash noted the small sample sizes in these studies as a possible limiting factor.

Who stands to benefit?

The most critical factor for the insertion of toric phakic IOLs in keratoconus patients is the presence of stable, non-progressive ectasia. According to Dr. Prakash, in patients under 30 years of age, his protocol would be to perform CXL first and wait for at least 1 year to evaluate the patient’s corneal topography before considering a toric phakic IOL. In patients who are older than 30 years of age, he requires documented topographic corneal stability, usually three scans over at least 1 year, before he would consider a toric phakic IOL correction.
Ectasia progression strongly influences the surgeon’s choices.
In an evaluation of current quantitative criteria for keratoconus progression, Dr. Prakash maintained that it was important for change to be lower than the statistical limits and not progressive. His study included 100 eyes of 100 patients with keratoconus who underwent Sirius Scheimpflug topography (CSO, Florence, Italy).3
In the case studies that Dr. Prakash presented, he described his best outcomes with toric phakic IOLs in patients in their mid-30s whom he followed for at least 1 year, those with non-central keratoconus, or in which ectasia was stable for 2 years, as opposed to those with progressive ectasia.
“The corneal shape in keratoconus plays a role in refraction,” Dr. Prakash explained. “The more irregular the cornea, the poorer the best spectacle corrected distance visual acuity (BSCVA) and the more central the cone, the poorer the BSCVA as well. You can count on good results with toric phakic IOLs in keratoconic eyes if the patient experiences good vision with glasses. Otherwise, the visual improvement primarily depends on the type and fit of specialized contact lenses,” he said.

Contact lenses vs. phakic IOL and glasses


Dr. Prakash explained that when using specialized contact lenses for keratoconus, the contact lens air interface becomes the anterior refracting surface. The comparative beneficial effect of contact lenses increases with increasing corneal irregularity in keratoconic eyes, smoothly rounding out the surface irregularities in simulation of a more normal corneal shape. Hard contact lenses can “ignore” the surface of the keratoconic cornea, which can be well visualized on OCT, he said.
The effect of a lens placed inside the eye, however, has a different refractive effect that is more complicated to gauge. “When you have an implantable lens inside the eye, by contrast, it is like a myopic glass being shifted inside the eye near the focal point. You still have to consider the interface, therefore, typically patients who do well with glasses preoperatively are the ones who will do well with the implantable lens postoperatively,” he said.
Refractive correction with phakic IOLs should be limited to cases with good glasses-corrected refraction, stable ectasia, and also to those who have repeatable and verifiable subjective refraction. Dr. Prakash personally prefers to have a perceivable, subjective improvement in excess of BSCVA (with glasses) 20/40 or UDVA to BSCVA with at least three lines of improvement.
“Preoperatively, do not try to treat the autorefraction. We are trying to treat the subjective refraction in these patients,” he said. “A repeatable subjective refraction is the best guide. Also, keep the targeted postoperative refraction slightly myopic, as a hyperopic end result is usually poorly tolerated. Always inform the patient that reduced spectacle dependence is the target, not spectacle independence.”
The IOL implantation is fairly straightforward, the only variation being a slightly larger incision at the limbus, he explained. The alignment marks are crucial. “We use slit lamp based markings, as they mimic the position in refraction,” he said. “Don’t overfill the chamber with viscoelastic and therefore avoid too much irrigation post-implantation. Postoperatively, be aware that a good guide for visual outcomes is the 1-month and 3-month refraction. Do not shy away from giving a temporary glasses correction if necessary. Redial only in cases of significant residual astigmatism; a small amount of astigmatism is not a problem. The stepwise planning for posterior chamber phakic IOL implantation in keratoconus needs patience and should include corneas that are stable and have subjective improvement with glasses. There should be no systemic or ocular contraindications to posterior chamber phakic IOLs,” he said.

References

1. Antonios R, et al. Safety and visual outcome of Visian toric ICL implantation after corneal collagen crosslinking in keratoconus: up to 2 years of follow-up. J Ophthalmol. 2015:514834.
2. Dirani A, et al. Visian toric ICL implantation after intracorneal ring segments implantation and corneal collagen crosslinking in keratoconus. Eur J Ophthalmol. 2014;24:338–44.
3. Prakash G, et al. Evaluation of the robustness of current quantitative criteria for keratoconus progression and corneal crosslinking. J Refract Surg. 2016;32:465–72.

Editors’ note: Dr. Prakash has no financial interests related to his comments.

Contact information

Prakash
: drgauravprakash@gmail.com

Toric phakic IOLs in keratoconus Toric phakic IOLs in keratoconus
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