EyeWorld India March 2019 Issue

52 March 2019 EWAP REFRACTIVE Toric phakic IOLs in keratoconus by Stefanie Petrou Binder, MD EyeWorld Contributing Writer Specialist provides guidelines on the use of toric phakic IOLs in keratoconus patients T he 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. 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).