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Friday / August 5.
HomemipatientContact Lens Fitting Post-ICRS

Contact Lens Fitting Post-ICRS

Intrastromal corneal ring segments technology has improved significantly in recent years, but should still be considered only after all options for contact lenses have been exhausted.

AM, a 48- year old book-keeper was referred to the practice for contact lens fitting. AM was diagnosed with keratoconus at age 19, and has worn rigid gas permeable (RGP) contact lenses since. Two years ago, he began to have difficulty with his right RGP, reporting problems of instability, variable vision and ghosting. He was referred for right intra-stromal corneal ring segments (ICRS). AM had two Kerarings implanted to his right cornea six months ago.

Following ICRS implantation, AM reported minimal improvement in his unaided vision, and complained of monocular right diplopia. He successfully wore a left RGP without problems.

Upon first presentation, vision unaided was R 6/95. Subjective refraction gave R -1.50/-4.50×114 (6/15=). Vision with his left contact lens was L 6/6=. His contact lens appeared well fitting.

Intrastromal corneal ring segments (ICRS) are comprised of either one or two semi-circular rings made from PMMA

Corneal topography of the right eye revealed flatter cornea over the ring segments, with relatively much steeper areas adjacent. (Figure 1). The elevation map shows an increase in elevation of the cornea above the ring segments, with an area of depression adjacent (Figure 2).

AM was initially prescribed an RGP lens with a reverse geometry design. On review he complained of discomfort, shadowy vision and monocular diplopia. Examination of the contact lens revealed excess bearing on the ring segments, and lateral decentration.

The lens fit was steepened and, on review, AM reported greater comfort and reduced diplopia, however now he experienced shadowy vision. Examination of the contact lens revealed a well centred lens with good alignment over the ring segments, but central pooling was causing bubble formation (Figure 3).

AM was subsequently refitted into a mini-scleral contact lens with a diameter of 17.50mm (Figure 4). AM returned for review, reporting excellent comfort and vision. Examination revealed complete clearance of the contact lens over the ring segments as seen with cross-section through the slit lamp (Figure 5) and anterior OCT imaging (Figure 6). However, AM was still aware of reflections off the ring segments in dim lighting when his pupil dilated.

Intrastromal Corneal Ring Segments

Intrastromal corneal ring segments (ICRS) are comprised of either one or two semi-circular rings made from PMMA. They are implanted into the corneal stroma, creating an ‘arc-shortening’ effect to flatten the central cornea. ICRS were originally developed to treat myopia, but they have been shown to be useful in keratoconus as they can reduce the corneal irregularity found in keratoconus.1 However, as keratoconic corneas have an irregular placement of corneal fibers, results may be less predictable.1,2

The amount of corneal flattening with ICRS is directly proportional to the thickness of the rings and inversely proportional to the diameter of the rings. Smaller diameters will result in the segments being closer to the visual axis, which can lead to glare and haloes if they encroach on the pupillary axis, which can be particularly a problem in dim lighting.3

In recent years, the popularity of ICRS has increased as it is a minimally invasive and reversible surgical option for keratoconus. ICRS often results in improvements in unaided vision, corrected visual acuities, manifest refractive error and can reduce topographical astigmatism.1,2 ICRS have been able to delay or avoid the need for keratoplasty for patients who are contact lens intolerant. However, the main limitation of ICRS is that results can be variable. Patients with mild to moderate disease produce more predictable results and better visual outcomes. Patients with advanced disease often show little improvement in vision.1,4

Contact Lenses for ICRS

Following ICRS, most patients will still require some form of visual correction.4 If the resultant astigmatism is fairly regular, spectacles or soft contact lenses can be prescribed. However, if the residual astigmatism is still highly irregular, RGP lenses will be required to achieve an adequate level of vision.

RGP contact lens fitting following ICRS can be challenging due to the shape changes arising from the ring segments. There will be an increase in corneal elevation directly above the ring segments and a depression just adjacent to it.5,6 As the ring segment is elevated, standard design contact lenses aligning with the central apex may lead to excess bearing on the ICRS, causing decentration, corneal insult and discomfort. If the contact lens aligns the ring segments, this can result in excess sagittal depth centrally leading to central bubble formation and or insufficient edge clearance, which may result in binding.

To reduce these events, a reverse geometry design can be applied; i.e. a lens with a peripheral curve steeper than the back optic zone radius.6 However these can be difficult to fit, particularly over a cornea with such an irregular shape.

In some cases, piggybacking a rigid lens with a soft contact lens can be successful. The soft contact lens can avoid some of the mechanical irritation of the lens over the cornea, and can also help to smooth over some of the irregularity.7 Many patients will be resistant to having the inconvenience of managing two lenses for one eye. In addition, piggybacking can result in dryness or hypoxia.

Mini-scleral lenses have the advantage that they are able to vault the cornea and rest entirely on the sclera. This avoids all the corneal irregularity in complex cases such as this one. These lenses centre well and have larger optic zones compared to corneal RGP designs, reducing problems with shadowing and ghosting from decentred lenses.8 As mini-sclerals completely avoid corneal touch, this will avoid corneal insult and discomfort.

ICRS Candidates

ICRS are a promising alternative option for keratoconus, but still they still have their limitations. It is important to carefully select patients for this procedure. If the patient is willing and able to wear a contact lens, then contact lens options should first be exhausted.

Most papers currently report that ICRS implantation makes contact lens fitting easier, however, as a contact lens practitioner this is not what I have found in clinical practice. ICRS can improve unaided acuities and corrected spectacle acuities, but only makes contact lens fitting easier if the patient can wear soft contact lenses with acceptable acuity.

Patients should be informed that corrected acuities after ICRS implantation may be inferior to contact lens acuities. Additionally, although ICRS is minimally invasive, implantation is still surgery. This makes it important to set realistic expectations so that patients who endure the time and cost of surgery are not disappointed with their resultant vision. As alluded to previously, this technique should be reserved for cases where contact lens options have been exhausted and for patients who cannot wear contact lenses.

Fortunately, with the scope of contact lens technology today, and in particular mini-scleral lenses, there are few corneas that cannot be fitted with contact lenses, even highly irregular corneas such as AM’s. One would argue that AM could have been prescribed a mini-scleral lens in the first instance, which would have avoided surgery and the ongoing problems of reflections off his ring segments.

Jessica Chi is the director of Eyetech Optometrists, an independent specialty contact lens practice in Melbourne. She is the current Victorian and past National President of the Cornea and Contact Lens Society, and an invited speaker at meetings throughout Australia and beyond. She is a clinical supervisor at the University of Melbourne, and has served on the continuing education committee for the Australian College of Optometry and the Therapeutics Advisory Board for the Optometry Australia

Jessica writes ‘mipatient’ on alternate months with Margaret Lam.

References
1. Rabinowitz YS. INTACS for Keratoconus and Ectasia after LASIK. Int Ophthalmol Clin. 2013 Winter;53:27-39.
2. Haddad W, Fadlallah A, Dirani A, et al. Comparison of 2 types of intrastromal corneal ring segments for keratoconus. J Cataract Refract Surg 2012; 38:1214–1221
3. Burris TE, Baker PC, Ayer CT, Loomas BE, Mathis ML, Silvestrini TA. Flattening of central corneal curvature with intrastromal corneal rings of increasing thickness: an eye-bank eye study. J Cataract Refract Surg. 1993;19(Suppl):182–7.
4. Alfonso JF, Lisa C, Fernandez-Vega L, et al. Intrastromal corneal ring segment implantation in 219 keratoconic eyes at different stages. Graefes Arch Clin Exp Ophthalmol 2011; 249:1705–1712
5. Hladun L, Harris M. Contact lens fitting over intrastromal corneal rings in a keratoconic patient. Optometry 2004;75:48 –54.
6. Nepomuceno R, Boxer Wachler BS, Weissman BA. Feasibility of contact lens fitting on keratoconus patients with INTACS inserts. Cont Lens Anterior Eye 2003;26:175–180.
7. Smith KA, Carrell JD. High-Dk piggyback contact lenses over Intacs for keratoconus: A case report. Eye Contact Lens. 2008;34:238–241.
8. Alipour F et al. Mini-scleral Contact Lens for Management of Poor Visual Outcomes after Intrastromal Corneal Ring Segments Implantation in Keratoconus. J Ophthalmic Vis Res. 2016 Jul-Sep; 11(3): 252–257.

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