By Jillian Campbell
Australian College of Optometry
Initially miniscleral lenses seem more intimidating to fit than standard gas permeable (GP) lenses because they are fitted based on sagittal height rather than on keratometric values. Patients may find the size daunting in terms of lens insertion and removal.
Despite the differences in procedure, miniscleral lenses have their uses and fitting can be simpler than anticipated. Here I describe a case in which miniscleral contact lenses provided an improved outcome over the previous GP lenses.
A 35-year-old male with keratoconus presented to the Australian College of Optometry with an uncomfortable right GP lens. His working environment had not been conducive to the use of GP lenses. He reported instances of the lenses dislocating or filling with dust when he was drilling holes. Given his unaided visual acuity was 6/60, this posed a considerable safety hazard. After a discussion with the patient, it was agreed that a miniscleral lens may best suit the patient’s occupational needs.
The KATT/ICD trial set by Capricornia was used for the fitting process. The lens is a 16.50 mm miniscleral lens with four distinct zones. All lenses are manufactured in Boston XO2 because the lens is sealed and requires a high oxygen permeable material.
The Visante anterior segment optical coherence tomography was used to measure the central depth (CD), which is the anterior chamber depth plus corneal thickness for a 15 mm chord. This was found to be 3.87 mm.
The diagnostic trial lens was selected by adding 0.4 mm to the CD. This allows the lens to settle back by 0.1 mm, giving the suggested 0.3 mm apical clearance. A modification was made to flatten the edge profile by two steps to prevent blanching of conjunctival vessels. The edge profile of this trial lens is shown in Figure 1.
Figure 1. Anterior OCT of the KATT 4200 after flattening the edge profile by two steps. Flattening the peripheral curve profile improved the comfort of the lens by preventing impingement, conjunctival staining and compression.
There were no bubbles or touch, and clearance was assessed using a narrow beam cross-section seen in Figure 2 and also documented using anterior OCT.
The final parameters of the right miniscleral lens were:
4200 Katt 7.46/16.5/-7.00
T1 = 50; T2 = 45; SLZ + 2 steps
Boston XO2 (VA 6/6)
Figure 2. Cross-section of trial lens KATT 4200 in situ. The miniscleral lens completely covers the cornea, neutralising much of the irregular astigmatism. The red arrow indicates the anterior surface of the lens, the white arrow indicates the posterior surface of the lens.
Because keratoconus is a chronic, long-standing condition, patients usually require optical correction for the rest of their lives. Giving patients a safe, manageable, cost-effective correction modality to suit their optical and lifestyle needs is imperative. Miniscleral lenses offer several advantages including better comfort and lens stability and may require less artificial lubrication.1
Larger lenses have larger optical zones and are less prone to decentre, benefitting patients while playing sports. The sealed system is valuable as it prevents dust seeping under the lens, although special patient instruction is required for lens removal. I am cautious about fitting corneal grafts, as sealed lenses may place more strain on the graft if undue force is used in lens removal.
This case study demonstrates that larger diameter lenses such as miniscleral lenses provide an alternative correction for patients who require GP lenses but cannot tolerate them.
- Barnett M, Mannis MJ. Contact lenses in the management of keratoconus [Review]. Cornea 2011; 30: 12: 1510-1516