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Friday / August 19.
HomemipatientBilateral Radial Keratotomy and CLs

Bilateral Radial Keratotomy and CLs

Radial keratotomy was widely used for correcting myopia, however has since fallen out of favour due to complications. Patients who have had radial keratotomy can present unique challenges for contact lens fitting.

MR, a 42-year old male, was referred by his corneal specialist for contact lens fitting. He’d had bilateral radial keratotomy (RK) in 2000, which had given him excellent unaided vision for years. However, in the past five years, his right eye had become increasingly blurry.

Prior to surgery his refractive correction was approximately R -3.25DS and L -2.75DS. MR’s specialist reported mild corneal irregularity but topography was stable over the past two years. MR reported excellent unaided vision in the left eye, but poor in the right. He also complained of glare with night time driving.

Examination revealed eight radial scars in his right cornea (Figure 1) and four in the left (Figure 2). Two of the scars in the right eye encroached the inferior pupil margin. Ocular health was otherwise unremarkable.

Prescribing contact lenses for patients who have undergone RK can be challenging

Unaided vision was R 6/60 and L 6/6.

Subjective refraction gave R +6.00/-1.00×97 (6/7.5), L plano/-0.25×37 (6/6=). N5 could be seen at near.

Videokeratoscopy with Medmont E300 revealed central flattening and mid-peripheral steepening over the incisions (Figure 3).

Spectacles were not a suitable option, due to the significant aniseikonia that would be induced, as well as being aesthetically unpleasing. Thus, contact lenses were the best option for MR. Various options were discussed, including rigid gas permeable contact lenses and soft contact lenses.

Johnson and Johnson Oasys-1 Day 9.0/14.3/+6.00 was trialled. This lens was chosen for its flatter BOZR so it would drape over MR’s post-surgical flatter cornea. This lens showed good lens movement and centration. Over-refraction was R -2.00(6/7.5).

MR was dispensed Oasys-1 Day R 9.00/14.3/+4.00. He returned one week later and reported excellent comfort, improved vision and reduced symptoms of flaring at night. The lens appeared well fitting (Figure 4) and contact lens acuity was R 6/7.5.

Discussion: Radial Keratotomy

Radial keratotomy (RK) is a refractive surgery procedure for correcting myopia. It involves deep corneal incisions, to approximately 90 per cent of the corneal depth, in a spoke-like pattern, resulting in mid-peripheral corneal steepening and central corneal flattening. Uniform incisions are made in the mid peripheral cornea, leaving a central clear optical zone. The amount of incisions depends on the level of myopia – normally between four to eight.1

RK results in significant pain 24–48 hours following the surgery and photophobia, which can last for several weeks. Vision may fluctuate for the first few weeks until the refraction stabilises. Following, some patients may be left with residual refractive error.2

Under-correction can occur, due to miscalculations resulting in insufficient surgery. This is more common when higher degrees of myopia are treated. Astigmatism may be residual (i.e. pre-existing astigmatism that is not corrected by the procedure) or may be induced, which may be regular or irregular.

The Prospective Evaluation of Radial Keratotomy (PERK) study found at the ten year follow-up, only 38 per cent of patients had a refractive error within 0.5 D of emmetropia and 60 per cent were within 1.00 D. 30 per cent of patients still required spectacles for distance. While vision-threatening complications were rare, 3 per cent of eyes had a reduction of more than two lines of best corrected Snellen spectacle acuity following surgery.2

The PERK study also revealed the long-term instability of the refractive error with a shift toward hyperopia being reported in 43 per cent of eyes at the 10 year follow-up.2 This refractive shift can occur years following the procedure, as was the case for MR.

RK was popularised by Russian ophthalmologist Svyatoslav Fyodorov in 1974 and was used extensively in the 1970s and 1980s.1 In the 1990s, RK was largely superseded by newer refractive surgery techniques – photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK), which provide more predictable and more stable results with fewer complications.

Refractive complications are not the only downfall of RK. Due to the depth of the incisions, corneal perforations may occur during surgery, with incidence of micro-perforations being 2-10 per cent and macro-perforations rarer, occurring in up to 0.045 per cent. Perforations can lead to endothelial damage, Descemet membrane scarring, iridocorneal adhesions, laceration of the lens, epithelial ingrowth and endophthalmitis. Following, patients are subjected to ongoing increased risks of perforation, infection and sutural neovascularisation.1

Common symptoms reported by patients include fluctuating visual acuity, reduced night vision, reduced contrast sensitivity, and glare.

Contact Lenses for RK

Prescribing contact lenses for patients who have undergone RK can be challenging. The normal cornea is ‘prolate’ in shape, i.e. steepest centrally and progressively flattening towards the periphery. During RK, the resultant cornea is an ‘oblate’ shape, i.e. a flatter centre and steeper mid-periphery.3 Oblate shapes can be difficult to fit as conventional contact lenses are designed for prolate shapes, and will either be excessively steep centrally or excessively flat peripherally. Some patients may require reverse geometry contact lens designs or similar.4

Caution should also be taken due to the corneal incisions. Contact lens wear can lead to epithelial erosion, infiltrative keratitis, incisional neovascularisation, and oedema.3 Care should be taken to ensure there is minimal physiological insult to the cornea and highly oxygen permeable materials should be used to reduce the chance of incisional neovascularisation.

Soft contact lenses with a low modulus and flatter base curve may adequately drape the flattened corneal surface. However, if there is there substantial central depression, standard soft contact lenses may buckle over the centre of the cornea, which can lead to fluctuating vision. Aspheric soft contact lenses may mask low levels of astigmatism, but significant amounts may require soft toric contact lenses. Soft toric lenses have limited success on these oblate corneas as they may result in atypical rotations and instability.

When astigmatism is significant and or irregular, soft lenses will be insufficient and rigid gas permeable (RGP) lenses will be required to achieve optimal vision. However, the altered corneal shape will present a challenge. When fitting a corneal RGP lens, a reverse geometry design will often be indicated to align the oblate surface.4 The mid-peripheral area, where the incisions occurred, is steepened and weakened by RK, and is subject to abrasions by contact lenses, which can lead to discomfort and further complications. Mini-scleral and hybrid contact lens designs may be used when corneal RGPs are not suitable or when there are tolerance issues.

Given MR’s low level of irregularity, he was fitted with a soft daily disposable contact lens. While the lens fit well over MR’s cornea, the relative central depression created a tear film meniscus between the lens and the central cornea, resulting in a different refractive result compared to the spectacle prescription. In the past, soft contact lenses were not a great option for RK patients as lenses were low dK, which could lead to hypoxia and subsequent incisional neovascularisation. Fortunately today, with a wealth of silicone hydrogel lens options to choose from, soft contact lenses can be an excellent solution for RK patients with low levels of astigmatism, as was the case for MR.

Jessica Chi is the director of Eyetech Optometrists, an independent specialty contact lens practice in Melbourne. She is the current Victorian and most recent 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, a member of the Optometry Victoria Optometric Sector Advisory Group, a fellow of the Australian College of Optometry. Jessica writes ‘mipatient’ on alternate months with Margaret Lam.

References
1. Mounir Bashour. Radial Keratotomy Myopia Treatment & Management. USA: Hampton Roy, March 2014
2. Waring GO 3rd, Lynn MJ, and the PERK Study Group. Results of the Prospective Evaluation of Radial Keratotomy (PERK) Study 10 Years After Surgery. Arch Ophthal. 1994;112:1298-1308
3. Shivitz IA, Arrowsmith PN, Russell BM; Contact Lenses in the Treatment of Patients with Overcorrected Radial Keratotomy. Ophthalmology. 1987;94(8):899¬903
4. Lim L, Siow KL, Sakamoto R, Chong JS, Tan DT; Reverse geometry contact lens wear after photorefractive keratectomy, radial keratotomy, or penetrating keratoplasty. Cornea. 2000 May;19(3):320¬4.

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