Soft lenses provide excellent comfort and vision to patients worldwide, with 100 million people wearing them (Nichols et al, 2013).¹ Although many patients can wear disposable lenses, there is still a great need for custom soft designs. 

For example, custom lenses may be created to correct for high ametropias or for those who have irregular corneal shapes, and/or to treat and manage ocular surface diseases. As such, custom designs are available in extended lens parameters such as variable diameters (Figure 1), base curves, and peripheral curves.

Custom soft lenses are designed by matching the contact lens sagittal depth (CL-SAG) to the ocular surface sagittal depth (OC-SAG). The CL-SAG defines the height of a lens and depends largely on the base and intermediate curves, and the lens diameter. 

The corneal sag for a chord equivalent to the horizontal visible iris diameter (HVID) can be measured from corneal topography. This information is important in fitting custom soft lenses, because there is a correlation between lens centration and corneal sagittal height, with greater sagittal height leading to greater decentration (Young, 2014).² 

An over-calculated OC-SAG value, therefore, may lead to a steep lens design with poor centration, excessive movement, and poor patient comfort and vision.

Case Description

A 14-year-old African American male presented with pathological myopia due to Stickler Syndrome. This young patient was referred for a specialty contact lens fitting to improve his vision, only correctable to 20/40 in both eyes through his spectacles. Originally, he was fitted into hybrid contact lenses, which improved his vision to 20/25 in both eyes. 

Nevertheless, the patient was dissatisfied due to peripheral glare and vision distortion from the limited size of the front optic zone and uncorrected residual astigmatism. Instead, the patient was fitted into Concise Custom Soft Definitive SiHy (ABB Optical Group).

Discussion

The patient’s manifest refraction was -13.50-4.25 x 010 OD and -13.00-4.25x165 OS. His keratometry values from corneal topography were 41.64 @ 001 / 44.78 @ 091 OD, and 41.54 @ 168 / 44.64 @ 78 OS.  To create a custom-fit lens, the patient’s HVID was measured as 11.70mm OD and 11.97mm OS via the caliper ruler present on topographer software.

Using the ABB Concise Perfect Fit Calculator, the patient’s silicone hydrogel custom toric lens parameters were as follows: 8.6/ -11.50-3.25 x010/ 14.5 OD, and 8.6/-11.00-3.25x180 OS, which the patient was able to wear all day with good VA and comfort.

Conclusion

There is medical and visual necessity for custom soft lenses. Using ocular sagittal depth information is helpful when designing a custom soft lens.

Melanie Frogozo, OD, is the owner of Alamo Eye Care in San Antonio, Texas, where she directs the Contact Lens Institute. She is a consultant to CooperVision, Essilor Contact Lens, Lentechs, and SynergEyes.

Katia Garza-Mejia, NCLE is clinical manager and contact lens fitter specializing in scleral and rigid gas permeable contact lenses at Alamo Eye Care in San Antonio, Texas.

REFERENCES

1. Nichols, JJ., et al. The TFOS International Workshop on Contact Lens Discomfort: executive summary. Invest Ophthalmol Vis Sci, 2013. 54(11):TFOS7-TFOS13.

2. Young, G., Mathematical model for evaluating soft contact lens fit. Optom Vis Sci, 2014. 91(7):167-176.