A 36-year-old female had a history of keratoconus since 2009. She underwent bilateral corneal transplants first on the left eye in 2014 and then on the right eye in 2016. The right eye also underwent a tube shunt with a subsequent filtering bleb. The patient was referred to our clinic by her corneal surgeon for bilateral contact lens fitting. Slit lamp examination showed trace corneal clouding in both eyes. The patient was on topical and oral 10mg prednisolone. Unaided visual acuities were right eye 20/200 and left eye 20/70.
The patient’s left eye was fitted with a scleral lens with parameters of sag 4,400µm, base curve (BC) 8.25mm, power –0.75D, diameter 16.3mm, limbal clearance zone (LCZ) +10, and peripheral central clearance zone (PCCZ) +10. Visual acuity with this lens is 20/20. A scleral lens could not be fitted on the right eye due the elevation and position of the filtering bleb. At this point, we decided to fit the patient’s right eye with a custom soft contact lens.
The custom soft lens was designed with the assistance of an online arc length calculator. The patient’s horizontal visible iris diameter (HVID), central keratometric readings, spectacle Rx, and desired lens diameter (in this case 13.0mm) were entered into the calculator (Figure 1). The calculator determined that the optimum lens parameters should be BC 7.2mm, power –4.50 –4.00 x 097, and diameter 13.0mm. The patient’s visual acuity with the custom soft contact lens was 20/25.
Slit lamp examination of the right eye showed that the soft lens was in an excellent position and had 0.25mm of movement in primary gaze. The soft lens had adequate corneal coverage of 360o and minimal interaction with the superior bleb (Figures 2 and 3). She was advised to use a hydrogen peroxide disinfection system for both the right and left lenses.
Custom Soft Versus Scleral
While scleral lenses with notches and vaults have been successfully used in cases of conjunctival elevations (filtering blebs, pingueculas, etc.), our clinical experience has shown that they often fail to create a tight enough “seal” and frequently result in post-lens fluid loss and subsequent bubbles. Additionally, there is always the risk of the scleral lens suction forces interfering with the function of the bleb. Therefore, we like to avoid the bleb altogether, and when possible, use an alternative lens design.
This case is an excellent example of how an online arc length calculator can be used to determine the initial base curve, power, and diameter of a custom soft contact lens. CLS