By Lucy Liu
BOptom(Hons) SpecCertMCLP SpecCertMMP
A 66-year-old retired engineer, who had undergone radial keratotomy about 26 years ago, presented to this clinic complaining of monocular diplopia, variable vision and glare with his spectacles.
Good visual acuity but poor visual quality could be obtained with spectacles three hours after waking, but was ‘inadequate’ early morning and in the evening.
Consultation with various ophthalmologists resulted in several management suggestions but as the patient did not wish to undergo surgery, contact lens fitting was sought to provide him with better visual quality and usable vision over a longer period of the day.
Radial keratotomy involves making radial incisions of 85-95 per cent depth, terminating greater than or equal to 1 mm inside the limbus and leaving a central zone of 3-4 mm. These incisions cause weakening and protrusion of the peripheral cornea, thereby flattening the central cornea. Scarring and irregularity of the cornea has been known to cause glare sensitivity and several studies have found fluctuations in refraction due to changes in corneal topography during the day.
Best spectacle corrected visual acuity was R 6/6++ L 6/7.5 with R +2.50/-1.75 x 110 L +2.25/-2.00 x 040 at 8:30 am. At 5:30 pm this changed to R 6/6++ L 6/7.5++ with R +2.50/-2.25 x 108 L +3.00/-2.00 x 040.
Slitlamp examination revealed eight radial cuts and two transverse cuts at 12 and 6 o’clock, with a 3.5 mm optic zone in both eyes. Areas of peripheral corneal neovascularisation, mild posterior blepharitis and meibomian gland dysfunction were also noted. Corneal topography revealed a flat central zone surrounded by mid-peripheral steepening with distinct areas of elevation bilaterally. The left eye was more irregular with higher wavefront aberrations.
Contact lens options and dry eye advice were discussed during the initial consultation. ACL twin curve (reverse geometry) and Capricornia KATT miniscleral lenses were then trialled. Better vision, with alleviation of monocular diplopia was obtained by the twin curve lenses. Lenses were ordered based on the trial lens fitting.
The first right lens ordered was 8.2/10.40/-3.00 giving 6/6= visual acuity. This lens fits well, avoiding excessive pooling centrally and unacceptable touch on the elevated areas in the mid periphery. The more irregular left lens was harder to fit.
The first lens trialled (8.2/10.4/-3.00) resulted in good vision but excessive mid-peripheral bearing inferiorly and superiorly. For the second lens, the back optic zone radius was flattened by 0.1 mm and the first reverse geometry peripheral curve was made steeper to reduce mid-peripheral bearing and avoid dimple veiling centrally.
Excessive bearing in the mid-periphery was alleviated, resulting in a delicate balance between the flat central zone and steep mid-periphery. Vision was 6/7.5+. After the two-week trial, the patient reported good comfort and crisp vision with relief of monocular diplopia and fluctuating vision. There was no corneal staining.
The diversity of vision problems in the post-RK patient presents a complex management challenge to the clinician. Although there are numerous suggested treatment options including collagen cross-linking and keratoplasty, RGP lenses is a minimally invasive, affordable and reversible method well worth exploring.
Research evidence to guide management is scarce, so clinical judgement and close follow-up of the patient are often required.
Topography: right eye
Topography: left eye