Article

CUSTOM SOFT

ARE WE TOO GENERAL WHEN IT COMES TO SOFT LENS FITTING?

When we determine soft lens wear candidacy, clinical considerations include, but are not limited to, patient age, spectacle refraction, ocular health, desired wear schedule, occupation, and lens care compliance history. Ironically, when it comes to which soft lens we place on a patient’s eye, we often generalize our selection to our favorite brand and a single base curve. Sure, this methodology appears to work on most of our patients, but what if there was another way to determine if failure was imminent and further, if custom soft lens parameters may be indicated?

Under the rationale that ocular sagittal height plays an important role in soft lens fitting (Young, 1992; van der Worp, 2013), my colleagues and I were interested in evaluating whether the sagittal height of a sample of commercially available soft lenses could be reported on.

Measuring Samples

The Optimec is830 is a spectral domain optical coherence tomography-based contact lens measurement system. It is capable of measurement in both air and saline for different samples. For measurement of samples in saline, steps were taken to control the temperature of the measurement fluid.

All soft lenses were immersed in the measurement fluid (0.9% saline) in a glass vial at least 24 hours prior to measurements. The sample was then placed in the wet cell and left to equilibrate for five minutes at 20°C. The lens was then measured, across a single meridian for the spherical lenses in the sample.

To measure the sagittal height of the contact lens, the lens edge was first detected. The geometric center of the lens was then found based on the edge-to-edge diameter, and the perpendicular distance from lens inner apex was calculated to give the posterior sagittal depth. The contact lens samples were selected at random; two identical parameters of each design were measured for comparison purposes.

In total, four different lens brands (8 lenses total), each at a power of –2.50D, were measured twice. Their known material, reported base curve (BC) and diameter (DIA), and measured sagittal heights (SH) are found in Table 1.

TABLE 1 STUDY RESULTS
LENS SAMPLE MATERIAL BC (mm) DIA (mm) AVERAGE SH (mm) STANDARD DEVIATION
1 Lotrafilcon A 8.4 13.8 3.606 0.009
2 Lotrafilcon A 8.4 13.8 3.604 0.008
3 Samfilcon A 8.5 14.2 3.824 0.016
4 Samfilcon A 8.5 14.2 3.852 0.006
5 Senofilcon A 8.8 14.0 3.483 0.024
6 Senofilcon A 8.8 14.0 3.474 0.003
7 Nelfilcon A 8.7 14.0 3.432 0.008
8 Nelfilcon A 8.7 14.0 3.429 0.008

Final Words

Could we use this information to match the sagittal height of an eye to that of a contact lens? If so, we may be able to adopt a more technical fitting philosophy to better fit our patients with soft contact lenses. Further studies are ongoing. CLS

For references, please visit www.clspectrum.com/references and click on document #SE2017.