By Brett Jenkinson
BOptom GradCertOcThera GAICD FAAO
Myopia is the most common refractive error being treated with orthokeratology but there are options to correct various levels of hyperopia and astigmatism. It also has the advantage of slowing the progression of myopia.
AB, a 27-year-old female, attended for ortho-K fitting in 2007 because she did not want to wear spectacles or contact lenses during waking hours. She had a history of moderate myopia corrected by spectacles and various monthly disposable contact lenses. She had a family history of glaucoma and ocular surface neoplasia and was in good general health.
Her refraction was R-2.00/-0.25x100 L-2.00 and VA was R6/5 L6/5. Her refraction was stable and had been for several years prior. Corneal topography was regular (Figure 1) and her flattest Ks were R 44.1 D L 44.5 D. Ocular health examination was normal, in particular there were no anterior segment contraindications to ortho-K lens wear and there were no signs of glaucoma. Her IOP was R 11 mmHg L 12 mmHg.
Figure 1. Original topography
AB was fitted with a CRT lens (Paragon Vision Sciences) according to their nomogram which indicated an initial lens for the right eye with a base curve of 8.2 mm a return zone depth of 525 µm and an edge angle of -33 deg (8.2 525 33); the indicated lens for the left eye was 8.1 550 34. After assessing the fit, ultimately the lenses dispensed were R 8.2 525 34 L 8.1 525 34 in Menicon Z material.
With the CRT lens, an ideal fit is a lens that centres well, with a treatment zone of about 4 mm and an edge clearance of about 1 mm. In adjusting the fit, altering the return zone depth will adjust the centration of the lens and adjusting the edge angle will adjust the edge thickness primarily but also the centration.
Adjusting the base curve will obviously affect centration but will also adjust the refractive change so is generally not altered to optimise the fit.
AB was instructed on the safe insertion and removal lenses and the lens care regimen (Menicon Menicare Plus daily and Progent weekly).
She was reviewed after her first night of lens wear and she reported no complaints, apart from having to remove the lenses on waking. Relevant findings were:
Finding RE LE
Unaided vision 6/24 6/24
Refraction -0.75/-0.50x100 -1.25
VA 6/6 6/6
Slitlamp findings Normal, no corneal Normal, no corneal
oedema staining and oedema staining and
conjunctiva white conjunctiva white
Topography Forming bull’s eye Forming bull’s eye
AB was given R -1.00 L -1.25 monthly disposable lenses and instructed to wear them on that day, with the expectation that her refraction would be about plano on day 2, to continue with nightly ortho-K lens wear and to return for review again in one week.
At one week review, AB was happy with her unaided vision (6/5 in each eye) and her refraction was R +0.25/-0.25x100 L Plano. The lenses were well centred with a good NaFl pattern. Topography was a normal bull’s eye pattern.
Further reviews at one month and three months were normal. AB reported having to wear her lenses every second night to maintain good vision all day.
AB has been successfully wearing ortho-K lenses since and in that time the right lens has remained unchanged and the left has been altered to 8.2 525 34 because of a slight increase in her myopia. Her most recent visit was in 2016 and images of the lens fit and her corneal topography are shown in Figures 2, 3, 4A and 4B. The topographic patter of the right eye is slightly high but adequate.
Figure 2. 2016 topography RE
Figure 3. 2016 topography LE
Figure 4A. Fit RE
Figure 4B. Fit LE
This case illustrates a fairly simple ortho-K fitting. Points to note are:
- A well-centred treatment zone is the key to success in ortho-K fitting
- A well-centred topographic image is important to determine how well the treatment zone is centred
- It is important to emphasise the need for scrupulous attention to hygiene to minimise the risk of contact lens complications