November 2018

REFRACTIVE

Presentation spotlight
Indications for toric phakic IOLs


by Stefanie Petrou Binder, MD, EyeWorld Contributing Writer


Patient suffering a sport-fishing trauma to the left eye that has caused a corneal scar

Nine months following PTK treatment. The improvement allowed toric IOL implantation
Source (all): Jorge Alio, MD

 

Toric phakic IOLs offer visual improvement in astigmatic eyes, even in more complex case scenarios

Phakic IOLs offer a viable method of adjusting the eye’s refraction without removing the natural lens and are a highly effective alternative to LASIK and PRK surgery for the correction of moderate to severe myopia. These lenses are designed to correct high myopia between –5 D and –20 D in patients with a residual anterior chamber depth of at least 3 mm. Irregular corneas can also strongly benefit from phakic IOL placement, according to Jorge L. Alio, MD, PhD, professor and chairman of ophthalmology, Miguel Hernandez University, and scientific director, Vissum-Instituto Oftalmologico de Alicante, Spain.
“Phakic IOLs are designed to correct regular astigmatism. In our hands, toric phakic IOLs are a remarkable tool, even in eyes with irregular astigmatism. We have specific indications for their use in eyes with irregular corneas and categorize and treat these eyes as either standard or special cases,” Dr. Alio said in a presentation at the 2018 World Ophthalmology Congress.
Phakic devices are either supported by the iris or placed in the posterior chamber. Posterior chamber phakic IOLs are easier to implant and have a shorter learning curve and shorter surgical time, but they have rotated in some cases. Iris-fixated phakic IOLs have no rotation or vaulting issues, but they are associated with a longer, more cumbersome surgery and a longer learning curve.

Standard cases

According to Dr. Alio, standard cases for phakic IOLs include corneas with regular astigmatism. “Our general indications for phakic toric IOLs include first and foremost a stable refraction for at least 1 year in patients who are poor candidates for corneal refractive surgery,” Dr. Alio explained. “One of the major advantages of astigmatism correction with phakic IOLs is the opportunity to correct both myopia and astigmatism, or hyperopia and astigmatism, in one surgery. A second surgery to correct the astigmatism (bioptics) is avoided in most of the cases. Toric IOLs can correct higher levels of astigmatism than lasers, and the IOL calculation is relatively easy as it is based on refraction, which is far easier than in pseudophakic toric IOLs,” he said.
To be considered for a toric phakic IOL, the endothelium/crystalline lens distance must be greater than or equal to 2.85 mm, the anterior chamber angle greater than or equal to 35 degrees, and the crystalline lens rise should be below 20 µm. In addition, Dr. Alio stipulated a flat iris configuration, a refractive cylinder greater than or equal to 1.25–1.5 D, and an endothelial cell count (ECC) in excess of 3,000 cells in patients under 25 years, an ECC of more than 2,500 cells in patients between 25 and 30 years, and an ECC of more than 2,200 cells in those older than 30 years of age.

Special cases

The challenge is knowing which more complex corneas stand to benefit from phakic IOL placement. According to Dr. Alio, the special cases would include corneas with a combination of regular and irregular astigmatism. He considers phakic IOLs in special cases with post-keratoplasty surgery after stitch removal, stable keratoconus eyes, stable pellucid marginal degeneration (PMD), and in eyes with corneal scars due to traumatic events or infectious keratitis.
“Regular astigmatism is a naturally and symmetric occurring cylinder due to the difference between the steepest and flattest meridian power. It can be totally corrected with a toric lens. Irregular astigmatism occurs secondary to a corneal disease or injury, and it is not symmetric. A corneal procedure to modify the corneal shape needs to be performed in order to correct it or an RGP to compensate it,” Dr. Alio said.
In an irregular cornea, refraction is a key factor to decide on whether to implant or not implant a phakic IOL. If the patient has good visual acuity with spectacles, usually over 0.5 D, this can be a good indicator of success with a toric phakic IOL. Dr. Alio pointed out that in contrast, refraction is not helpful in cataract patients with irregular corneas when a pseudophakic toric IOL is considered. Higher order aberrations, like coma, are also good indicators of the outcomes with phakic IOLs. High ametropia associated with the correction of high astigmatism usually leads to the best visual outcomes, he said.
To treat the regular component in an irregular astigmatism, Dr. Alio thinks that higher order aberrations can be telling. Dr. Alio, the coinvestigator of a study, explained that keratoconus patients treated in the study had coma-like aberrations that correlated well with the degree of corneal irregularity, usually coma- like, non-radial aberrations lower than 2 µm (RETICS classification for keratoconus grade I and some with grade II).1 He explained, however, that brain aberration compensation could differ significantly among patients.
In another study, he and his coinvestigators tried to qualify variables involved in the degradation of vision in 776 eyes of 507 keratoconus patients. They found that there could be acceptable levels of vision in highly aberrated corneas. Vision could be adequate for functional purposes in many patients and visual limitations could be explained by different alterations in these corneas, according to the retrospective case series.2
“Based on our experience, we can say that to successfully treat regular astigmatism with toric PIOLs in an irregular cornea, only cases with stable astigmatism should be considered,” he said. “We perform a thorough analysis of the central 4 mm of the topography and avoid corneas with high irregularity. Patients whose BCVA is 20/40 or better can qualify for this operation. For keratoconus patients, usually grades I and II qualify. It is better to include cases with not very high coma aberration, not more than 1.5–2 µm, and to avoid patients who need RGPs to achieve good VA. All these factors need to be considered together in order to make the right decision,” he explained.
Patients who fit the bill for toric phakic IOL implantation have a number of choices. Two options—the Artiflex toric IOL (Ophtec, Groningen, the Netherlands) and the toric ICL (STAAR Surgical, Monrovia, California)—were part of a study carried out by Dr. Alio, who compared them as part of a retrospective, comparative study for visual outcomes, predictability, and stability in keratoconic eyes. The toric iris claw lens (Artiflex) was implanted in 20 keratoconic eyes and the toric ICL, a collagen copolymer posterior chamber phakic IOL, in 28 keratoconic eyes. The study patients had stable keratoconus grade I and II (Amsler-Krumeich). The outcomes revealed that both phakic IOLs achieved a remarkable index of refraction, with an efficacy index of 0.90±0.26 and a mean safety index of 1.19±0.29. The efficacy index was not statistically different between the two lenses (P=.058), and refraction was stable during the follow up.3
“Our study showed that both of the phakic IOLs did an excellent job with a remarkable similarity. There was a small trend toward undercorrection in the ICL, but we learned this was due to the abnormal surface to sulcus distance especially in moderate to advanced keratoconus. Therefore, we think that the indications for toric PIOLs in irregular corneas include patients with stable astigmatism, patients with a low grade of irregular astigmatism, HOA <2.5 µm in the central 4 mm of the cornea, patients whose BSCVA is >20/40, cases with coma aberration lower than 1.5 µm, usually grade I and II (RETICS) maximum keratoconus, and the same guidelines for post-keratoplasty. A careful endothelial evaluation is mandatory,” he said.

References

1. Vega-Estrada A, et al. Outcome analysis of intracorneal ring segments for the treatment of keratoconus based on visual, refractive, and aberrometric impairment. Am J Ophthalmol. 2013;155:575–584.
2. Alio JL, et al. Keratoconus-integrated characterization considering anterior corneal aberrations, internal astigmatism, and corneal biomechanics. J Cataract Refract Surg. 2011;37:552–68.
3. Alio JL, et al. Comparison of iris-claw and posterior chamber collagen copolymer phakic intraocular lenses in keratoconus. J Cataract Refract Surg. 2014;40:383–94.

Editors’ note: Dr. Alio has financial interests related to his comments.

Contact information:

Alio
: jlalio@vissum.com

Indications for toric phakic IOLs Indications for toric phakic IOLs
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