|Elevation map (A) of a patient with keratoconus with a corneal elevation
difference of 655 microns. The corneal gas permeable lens fit with
a large apical bubble (B) and a scleral lens (C) fit on the same eye.
Advances in materials and the ability to manufacture large diameter scleral GP lenses for patients makes it easy to add these specialty lenses to your practice.
The use of scleral contact lenses has increased dramatically over the past 10 years. The advantages of a scleral lens to vault an irregular cornea or to provide a moisture chamber to a dry eye has led many practitioners to embrace this contact lens type where other modalities may have failed. The ability to offer this lens option has helped to widen the services provided to the patient.
ANATOMY OF A SCLERAL
The anatomy of a scleral lens consists of a central base curve, peripheral zone, limbal zone and scleral landing zone. Each zone of the lens can be altered to change the fitting relationship of the lens on the eye. The fit of a scleral lens is specified in terms of sagittal depth or how close or far the posterior portion of the contact lens sits from the cornea. The ideal sagittal depth apically will allow for approximately 200 microns of tear lens between the back surface of the contact lens and the front surface of the cornea. Oftentimes the diagnosis can be used as a guide to select the initial depth of the diagnostic lens.
Interaction between the contact lens and the limbus is discouraged. Using sodium fluorescein in the bowl of the lens is imperative when fitting to ensure that there is a layer of tears between the contact lens and the limbus. Since the weight of the lens is primarily distributed on the sclera, it is important to view the blood vessels at the edge of the lens to rule out impingement of blood flow or excessive lift off of the lens edge.
Not all corneas will require a scleral lens. In a recent study, an elevation display topographical map was used to determine the elevation change along the meridian of greatest elevation difference. The results indicated that a difference of greater than 350 microns may necessitate a scleral contact lens.
TIPS FOR PRACTITIONERS
With new technology come changes in cost. These lenses are much larger than the typical corneal gas permeable lens, thus material cost of the scleral lens is greater. Professional fees may also increase as sclerals are specialty lenses and sometimes require more follow-up than the typical gas permeable or soft contact lens.
If you are ready to give scleral lenses a go, begin by developing a relationship with a specialty lens lab (see Where to Find It) and requesting a fitting set. Many companies offer consultation services and are happy to help you with your first few patients or with troubleshooting.
If you are already fitting scleral lenses, seek out specialty contact lens conferences to gain more experience in fitting complex cases, such as the Global Specialty Lens Symposium, or visit the Scleral Lens Education Society website. There is a wealth of information out there to assist in your venture of this exciting lens modality!
Beth T. Kinoshita, OD, is an assistant professor at Pacific University College of Optometry.
WHERE TO FIND IT:
ABB Optical Group
800.852.8089 | ABBOptical.com
Art Optical Contact Lens Inc.
800.253.9364 | ArtOptical.com
Bausch + Lomb Specialty Vision Products
Bausch.com | Info@BauschSVP.com
Blanchard Contact Lens, Inc.
800.367.4009 | BlanchardLab.com
800.547.8815 | ValleyContax.com