Scleral Contact Lens Fog
BY WILLIAM L. MILLER, OD, MS, PHD, FAAO
Scleral GP lenses are an increasingly more popular vision correction option for the management of selected patient populations such as keratoconus and post-surgical corneas. However, there may be issues to address. One scleral-related complaint occurring in between 25 percent to 33 percent of these patients is foggy vision, which occurs sometime during their daily wearing cycle. Causes may be poor tear exchange, corneal edema due to a decreased Dk/t, or increased mucin production from massaging of the conjunctival tissue.
Eliminating or minimizing these complaints may take several preventative steps, which begin with an accurate assessment of the lens fit.
Depending on the size of the lens, start by making sure that conjunctival vessel impingement is not occurring. The impingement may not be visible for several minutes after application, but becomes more evident later as the lens settles on the easily moldable conjunctival tissue. This results from an edge that does not have enough clearance. Edge modification can be accomplished inhouse by adding a flat peripheral curve to the posterior edge of the lens, or the lens can be sent to the lab for an increase in clearance.
By increasing the peripheral flange from the conjunctival tissue, either in-house using a very flat diamond and tape tool (around 15mm) or by sending to the lab for an increase of between 50 and 150 microns, you may eliminate vessel impingement and also increase tear exchange. The latter is important to circumvent eventual foggy vision complaints from the patient. Observing sodium fluorescein move out from under the lens during a blink can be helpful in judging whether the edge clearance is adequate.
Optimizing the Tear Reservoir
The next observation should include an assessment of the tear reservoir beneath the scleral contact lens. This reservoir should assume a plano lens shape, avoiding either a plus lens configuration (excessive tear reservoir) or a minus lens configuration.
Ideally, you should compare the thickness of the tear reservoir with the known center thickness of the scleral contact lens rather than the likely altered corneal thickness. The thickness should approximate 150 to 200 microns, with a suitable targeted thickness that is less than 200 microns (Michaud et al, 2012).
Other management strategies can include mid-day breaks from wear. Although not popular with patients, this option can lessen the effect of mid-day fogging. Patients can also be cautioned against using a more viscous solution on the eye when applying or wearing the lens. In our practice, the use of Menicon’s Unique pH, Opti-Free GP (Alcon) or Clear Care (Alcon) have been helpful as care system options, along with the use of Unisol 4 (Alcon) unpreserved saline for the application of the lenses.
Some practitioners prescribe inhalation saline, which is also unpreserved and comes in a unit-dose package. However, the pH of this solution trends toward acidity and may cause some stinging. Other drops that can be used during the day should be preservative-free and contain important electrolytes necessary for a healthy epithelium. These include Unisol 4, Refresh Optive and Refresh Contacts (Allergan), and Blink Contacts (Abbott Medical Optics).
Out of the Fog
As we await the definitive cause for scleral contact lens mid-day fogging, the above steps should allow your patients to increase their wear time and improve symptoms to increase comfort and vision. CLS
For references, please visit www.clspectrum.com/references.asp and click on document #214.
Dr. Miller is an associate professor and chair of the Clinical Sciences Department at the University of Houston College of Optometry. He is a consultant or advisor to Alcon and Vistakon and has received research funding from Alcon and CooperVision and lecture or authorship honoraria from Alcon and B+L. You can reach him at firstname.lastname@example.org.