By Ho Wah Ng
Adrian S Bruce
BScOptom PhD FAAO
Australian College of Optometry
A 30-year-old man had a right penetrating eye injury when aged 12 years in Somalia. Due to a chronic retinal detachment, there was no longer useful vision in the eye but surgeons at the Royal Victorian Eye and Ear Hospital determined there was no indication for enucleation.
When the patient presented to the hospital contact lens clinic, there was a right band keratopathy, marked cataract and superior iridodialysis. He used plano glasses with a mild tint to cover the right eye and protect the left. The patient wanted an improved cosmetic appearance for the right eye and presented for prosthetic lens fitting.
We fitted a Capricornia EyColours PRBLK 8.8/14.3/plano lens. The patient was happy with the appearance and there was good centration and 0.3 mm movement. A 3 mm black pupil was ordered, because the eye had no vision.
The EyColours lens has a patterned iris colour pigment on the front surface and is available only in 38 per cent water content material. Figures 1A and 1B show the diseased eye and with the new lens. A maximum wearing time of eight hours/day was advised due to the limited oxygen transmissibility (Dk/t) of the lens.
Figure 1A. Diseased eye
|Figure 1B. Appearance with prosthetic lens
Five months later, the patient presented for delivery of a spare right contact lens. The current contact lens was comfortable and he was pleased with cosmetic appearance but he noted the eye did get red. When the lens was removed there was corneal neovascularisation extending 4 mm or more into the cornea in all quadrants. Anterior OCT scans showed right corneal oedema with central thickness of about 900 µm (Figures 2A and 2B).
The patient was cautioned to reduce wearing time to six hours/day or less. The effect of hypoxia causing the redness was explained, and the need to remove the contact lens if the hyperaemia was excessive. Review was scheduled for four weeks.
Figure 2A. Marked corneal neovascularisation
|Figure 2B. Corneal oedema
Hospital-based contact lens work can differ from usual clinical practice. In this instance vision was not an issue as the eye was blind, and complications were considered in the context of the cornea already being diseased. However, the corneal neovascularisation observed at after-care was a graphic example of the effect of hypoxia, although it is likely that there were pre-existing blood vessels within a cornea that was already decompensating.
The hypoxic issue with the current prosthetic contact lenses arises because they are made from 38 per cent water content hydrogel, a material known for low (< 12) Dk/t lenses.1 The original Holden-Mertz2 criterion found a critical Dk/t value of 24 for a lens worn under open-eye conditions to induce zero lens-induced corneal swelling. Almost half of all documented contact lens complications relate to hypoxia.3
With Alcon releasing Australia’s first silicone hydrogel colour contact lens, we look forward to addressing the issue of corneal hypoxia in selected patients.
The Air Optix Colours (lotrafilcon B) claims to maintain a Dk/t of 110 at -3.00 DS. For cases requiring a cosmetic improvement post trauma, it may be possible to prescribe for both eyes, ensuring a ‘perfect’ colour match, especially in the presence of refractive error.
Further benefit over the EyColours conventional lens option is the monthly replacement schedule, ensuring better hygiene and reducing replacement cost with lost or torn lenses.
We are yet to see how effective the Air Optix Colours may be in cases of blown pupils, or those requiring a solution for glare, as unlike the EyColours prosthetic range, there is no opaque black backing. For patients similar to the one detailed in this case report with an opaque cornea, we will also need to consider the absence of a black pupil option. Prescribing the Air Optix Colours in this patient may give the appearance of leukocoria, more prominent with darker irides, although it may soften the overall appearance.
- Bruce AS. Local oxygen transmissibility of disposable contact lenses. Contact Lens Anterior Eye 2003; 26: 189-196.
- Holden BA, Mertz G. Critical oxygen levels to avoid corneal edema for daily and extended wear contact lenses. Invest Ophthalmol Vis Sci 1984; 25: 1161-1167.
- Bruce AS, Brennan NA: Corneal pathophysiology with contact lenses. Surv Ophthalmol 1990: 35: 1: 25-58.