Article

CONTACT LENS CASE REPORTS

USING ONLINE CALCULATORS TO DETERMINE THE BEST LENS

Our patient is a 35-year-old female who has a longstanding history of myopia. Her entering visual acuities with correction were OD 20/20 and OS 20/100. Her manifest refraction was OD –1.00 –2.50 x 007, 20/20 and OS –17.00 –6.50 x 175, 20/40. Corneal topography revealed –3.87D of with-the-rule corneal astigmatism in both eyes (Figure 1). Axial length measurements were right eye 23.8mm and left eye 29.9mm, with the left eye being 6.1mm longer than the right. As a rule of thumb, each 1.0mm greater than 24.0mm (normal) is equal to 2.87D. Therefore, 6.1 x 2.87 equals 17.50D. This is almost identical to the myopia manifested in the left eye.

Figure 1. The corneal topography showing –3.87D of with-the-rule astigmatism.

A dilated exam showed that the right eye was normal with no defects. The left eye had a large area of peripapillary atrophy surrounding the disc, with dense 360º of lattice degeneration and an old peripheral retinal hole with overlying pigmentation (Figure 2).

Figure 2. The retinal imaging and axial length measurements of the patient’s right and left eyes.

The patient’s right eye was fitted with an “off-the-shelf” 14.5mm toric soft lens with an 8.7mm base curve, –1.00D sphere power, and –1.75D cylinder power at 10º axis, with a resultant visual acuity of 20/20. The left eye was fit with a custom 14.4mm toric soft lens with a 7.70mm base curve, –14.00D sphere power, and –4.25D cylinder power at 175º axis, with a visual acuity of 20/40 (Figure 3). The custom lens may seem to be numerically quite steep; however, the manufacturing and labeling of these particular custom soft lenses are such that the steeper base curve radius is indeed appropriate for this high-minus toric lens design.

Figure 3. The soft lens fit of the right and left eyes.

Calculating the Solution

Figure 4 shows an Arc Length Calculator that uses the central keratometric readings and the horizontal visible iris diameter to estimate the sagittal height of the anterior eye at any given soft lens diameter.

Figure 4. The online Arc Length Calculator for calculating the base curve, power, and diameter of any custom soft contact lens.

This case report highlights the use of an online, sagittal height calculator designed to aid practitioners in selecting the initial base curve, power, and diameter of any custom soft contact lens. CLS