Download Scleral Contact Lens - Managing the Midday Fog

Scleral Contact Lens - Managing the Midday Fog
Jessica H Mathew, OD, PhD
Visiting Assistant Professor
Texas Eye Research and Technology Center
University of Houston College of Optometry
505 J Davis Armistead Building
4901 Calhoun Rd
Houston, Texas 77204-2020
Modern scleral gas permeable contact lenses (SGP) are rapidly becoming the preferred choice for
correcting corneas with irregular astigmatism from post-surgery, trauma, keratoconus and pellucid
marginal degeneration. Today the SGP is our most profitable contact lens modality and patients fitted
with this device our most loyal ones!
Unfortunately, not every patient is able to wear such lenses uninterrupted for a full day in spite of
what appears to be a “good fit”. These patients may report ‘hazy’, “foggy” or “cloudy” vision after a
few hours of wear, which requires removing and reapplying the lens after rinsing and refilling the lens
shell with fresh unpreserved physiological saline solution. To date, this unique to SGP phenomenon
has not been defined nor systematically investigated. This presentation, based on research
conducted at the Texas Eye Research and Technology Center, will in some detail describe this
condition while discussing factors most important in the successful conversion of the patient into an
uninterrupted all day wearer of SGPs.
Texans like things of generous proportions and when it comes to SGPs there is no exception to this
rule. Therefore, our SGP is using an OAD of 18mm and a high Dk material with an ultraviolet
radiation blocker. The anatomical, physiological and physical reasons for this design approach will be
provided.
Because many of the eyes we fit with an SGP lens have compromised corneas that had its nerve
fibers severed or have dry eyes we present our patients with a Texas Eye Research and Technology
Center Dry Eye Questionnaire (DEQ) to complete. The DEQ will give you a score telling whether your
patient has normal, marginally dry or severely dry eyes. In this manner we routinely will have a
subjective dry eye score on each patient to aid our decision making.
Our routine SGP assessment also involves a lens fit assessment with biomicroscopy and, if needed,
a Visante OCT. Lens fit is described as aligned, steep or flat by assessing the vault, or lack thereof,
over the cornea using an optic section and white light with a biomicroscope. The fit is considered
aligned when the back surface of the lens is approximately parallel to the front surface of the cornea.
Patients able to wear their lenses 8 hours or more per day are typically referred to as “uninterrupted”
wearers while those that can only wear their lenses less than 8 hours per day without removal are
termed “interrupted” wearers. We have found that interrupted wear is more associated with foggy or
cloudy vision than with comfort, at least as long as no uncorrected or residual refractive error exists.
After initial fit, approximately 33% of our SGP patients report being unable to wear their lenses all day
without interruption. Our research shows that the wearing time ranges from 1.75 to 6 hours with an
average of 4.45 hours before lens removal. Wearing time for the uninterrupted patients (67%) ranges
from 8 to 16 hours with an average of 11.75 hours.
We have found that the average DEQ score for the uninterrupted SGP wearer are 28 while the
interrupted wearer’s average was 54. There is a moderate correlation between DEQ scores and
average daily wear times (r = -0.528).
Most of our fits (60%), uninterrupted and interrupted lens wearers, will achieve an alignment fit, which
is our preferred SGP fit. Peripheral fit is important too and we have found that in interrupted wearers,
80% exhibit a tight edge fit while only 40% of uninterrupted wearers have a tight fitting edge.
Our research demonstrated that the average corneal vault for uninterrupted lens wearers was
0.29mm while interrupted wearers averaged 0.71mm. There is a moderate correlation between
corneal vault and average daily wear times (r = -0.509).
Midday cloudy or foggy vision, occurring in one third of scleral contact lens wearers, is a multifactorial
phenomenon unique to these ocular devices. Important factors appear to involve a predisposition to
“dry eye” and significantly greater central corneal vault combined with lens edge tightness that may
impede tear exchange from beneath the lens. To address this unique SGP wearing challenge, it is
recommended that adjusting the fit to reduce corneal vault and edge tightness may provide
increased, uninterrupted wearing time. Furthermore, ocular dryness, when present, also must be
attended. Any existing blepharitis must be eliminated and tarsal gland deficiencies, such as MGD,
needs to be addressed. Aqueous deficiencies may be resolved with punctual plugs and we apply
punctual plugs more often in SGP wearers than any other contact lens modality.