SCLERAL LENSES
Fitting
Scleral Lenses
Scleral
lenses can offer excellent comfort and vision for both compromised and normal corneas.
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By Mitchell M. Loftin, OD
That
necessity is sometimes the mother of invention is born out in how modern scleral
lenses developed. Seeking a protective system to deliver medication to eyes ravaged
by inflammation, Dr. Perry Rosenthal seized upon the work of Australian optometrist
Don Ezekiel, who in 1983 reported success with an air-ventilated silicone acrylate
scleral lens. Their pioneering work began in the late 1980s and led to the development
of the Boston Scleral Lens (Dk 100, Boston Foundation for Sight [501c3]).
Utilizing spline curves, diameters between
15.0mm to 24.0mm and a unique tear channel system, the Boston Scleral Lens is like
a liquid corneal bandage to treat severe conditions such as severe dry eyes, ocular
cicatricial pemphigoid, Stevens-Johnson syndrome, persistent epithelial defects,
keratoconus, pellucid marginal degeneration and penetrating keratoplasty. The lens
is supported almost entirely by the sclera, and the central optic zone (12mm) is
designed to completely vault the cornea. The Boston Scleral Lens provides a protective
shell and therapeutic reservoir, and it has improved vision and symptoms in patients
for whom nothing else has worked.
In
addition to the Boston Scleral Lens, other scleral lenses of similar designs are
also available. These include the Jupiter Mini-scleral and Scleral (Innovations
in Sight), the Macrolens Elite and O series (C&H Contacts) and the Semi-Scleral
(Abba) lens. These designs are available in various diameters from just beyond the
limbus (corneal-scleral) to sizes well onto the sclera (18.0mm to 24.0mm).
The
following cases illustrate the therapeutic uses of two of these scleral lens designs.
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Figure 1. Apical clearance with the Boston
Scleral lens.
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Case 1
A 21-year-old African-American male who had moderate
keratoconus was referred for contact lens fitting because of corneal apical staining
and early apical scarring. The patient was wearing GP lenses that had been fit elsewhere.
Fluorescein analysis demonstrated a large apical-bearing zone of 5mm to 6mm in diameter.
Entering aided acuities were OD 20/25 and OS 20/30, which were two to three lines
better than best-correctable spectacle acuity because of the irregular astigmatism
created by the ectasia. Corneal topography including axial curvature and direct
elevation mapping demonstrated a central cone OD and a slightly nasally eccentric
cone OS. Simulated keratometry yielded values of OD 48.96/59.15 @ 128 and OS 38.26/52.22
@ 079. We advised the patient to discontinue lens use for two weeks and to return
for lens fitting.
After
two weeks of not wearing the lenses, we fit the patient into Rose K (Blanchard Contact
Lens, Inc.) GP lenses. We informed him that corneal changes would likely occur over
the next few weeks because of the molding effects from his previous lenses. Over
the next four months the corneas continued to remold, with each eye increasing approximately
0.50D in steepness each month. With each change, we made a corresponding change
in the lenses to stay ahead of the cone and to maintain feather touch
fit. The peripheral clearance
required adjustments to prevent seal off and to maintain adequate movement.
During the next five years,
the patient's keratoconus continued to progress bilaterally, requiring lens changes
and peripheral curve adjustments every six months. By 2003, the patient's contact
lens prescription was OD base curve 4.38mm (77.05D), diameter 9.90mm, maximum peripheral
flattening, power of –24.75D, Boston XO and OS base curve 4.60mm (73.37D),
diameter 9.90mm, maximum peripheral flattening, power of –24.00D, Boston XO.
At this point apical bearing was apparent, yet steepening the lens made it difficult
to fabricate appropriate peripheral curves and powers.
We suggested alternatives of a piggyback
lens system, a full-thickness corneal graft or scleral contact lens fitting. The
patient opted to be fit with the Boston Scleral Lens, so we referred him to the
Boston Foundation for Sight.
On follow-up examination after the
patient received the lenses, slit lamp examination demonstrated a well-centered
lens with 1mm to 2mm of apical clearance (Figure 1). The lens showed no movement
at all and we found significant blanching of perilimbal conjunctival vessels. The
blanching pattern exhibited bands of blanching and engorgement, denoting decreased
conjunctival capillary perfusion due to compression (Figure 2). We instilled sodium
fluorescein three times and found no evidence of tear flow under the lens after
15 to 30 minutes.
The patient returned to the Boston
Foundation for Sight for lens fit adjustments. On subsequent examination, flattening
of the peripheral curves demonstrated an improved bearing relationship between the
lens and the scleral haptic. Decreased blanching of perilimbal conjunctival vessels
denoted minimal bearing peripherally. The lenses continued to demonstrate little
to no movement and an apical clearance pattern was still evident. Most importantly,
the lenses demonstrated adequate tear exchange by the observance of fluorescein
under the lens some 15 minutes after instillation. The Boston Scleral lens specifically
avoids fenestration through the use of channels designed to prevent seal off while
also preventing bubble formation. Desiccation is a potential significant cause of
treatment failure in inflammatory disease and must be avoided in cases of severe
pathology. The patient's visual acuity continued to hover in the 20/25 to 20/30
range, which he deemed acceptable.
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Figure
2. Pronounced blanching and engorgement from poor-fitting scleral lens. |
Over the past year the patient's cornea
has well tolerated a daily-wear schedule, with no increase in apical staining or
scarring and no evidence of corneal edema or anterior chamber reaction. Only recently
has the patient's right eye started to demonstrate negative tear flow under the
lens again. He will return to Boston Foundation for Sight for follow up.
Case 2
A 30-year-old white male presented with a history
of keratoconus OD and a full-thickness corneal graft OS, performed three years prior.
He presented to be fit with a contact lens OS. His right eye had previously been
fit with a lens that yielded excellent visual acuity of 20/25. He wore no lens in
his left eye. Best-corrected spectacle acuity in this eye was 20/40, resulting from
uncorrected irregular astigmatism inherent in many corneal grafts. Biomicroscopy
evaluation OD demonstrated slight apical thinning, with minimal to no other signs
of keratoconus. The GP lens OD centered well, with an acceptable three-point touch,
good tear exchange and good movement.
The left eye demonstrated a crystal clear
graft with normal pachymetry in the four major quadrants. Keratometry revealed the
expected mild distortion of mires, with readings of OD 48.37 @ 057/ 50.00 @ 148
and OS 42.75 @ 175/43.00 @ 086. Placido disc topography revealed an inferiorly displaced
cone OD with simulated Ks of OD 51.92/ 47.46 and OS 44.00/41.56. The corneal graft
was oblate in appearance and, by topography, had steeper host tissue than donor
tissue.
We
performed a diagnostic fitting and ordered a Dyna Intralimbal Lens (Lens Dynamics)
of large diameter design to increase stabilization. Parameters OS included a 10.4mm
diameter, 7.34mm base curve, power of –6.75D, periphery 1.00D flatter than
standard, Korb edge, Boston XO material. We instructed the patient to limit wear
time and to return within one to two weeks with the lens in place so we could discern
what adjustments might be needed.
Seven months later the patient
returned for his first follow-up examination. He had been out of the country on
an archeological dig and had been unable to respond to our attempts to schedule
a follow-up appointment. Fortunately, the patient hadn't been wearing the lens because
of discomfort and thus no corneal damage had occurred. Examination revealed significant
inferior decentration of the lens most likely because of its excessive mass. Dyna
Intralimbal lenses usually center exceptionally well, but when they don't, attempt
to correct the problem by decreasing the mass.
We decided to pursue other lens designs.
We made attempts to fit the patient with Rose K, Post Graft (Lens Dynamics), Aspheric
(Boston), reverse geometry and Polycon II (CIBA Vision) lens designs. All were unstable,
with most decentering laterally as often occurs with corneal graft patients. Bitorics
were incompatible with the corneal toricity, and the patient didn't prefer countersunk
and piggyback lenses.
These difficulties left only scleral
GP lenses as an option. Nearly one year after initially presenting to our cornea
clinic, we fit the patient with the Jupiter lens (Innovations in Sight). This lens
is available to all practitioners and is manufactured in Boston XO material in a
variety of custom parameters. Designed to provide good central alignment while resting
on the sclera for support, you can also fit the Jupiter lens with apical clearance.
As with the Boston Scleral Lens, the Jupiter lens must avoid peripheral seal off
to provide adequate physiology through use of appropriate peripheral curves or fenestration.
Thus, movement of the lens is desired but not absolutely necessary for success on
a daily wear basis. However, it is important to avoid excessive corneal bearing
and bubble formation. In addition, adequate tear exchange must occur even if movement
isn't obvious.
This lens yielded excellent centration,
central clearance and almost complete absence of perilimbal blanching as we'd seen
with the Boston Scleral lens in Case 1 (Figure 3). The most obvious exchange occurred
at the site of fenestration, which is always placed outside of the donor tissue
interface, as close to perilimbal as possible, to prevent desiccation of donor tissue.
Carefully monitor fenestration to ensure that significant desiccation does not occur.
The patient continues to wear the lens successfully, with acuities of OD 20/25 and
OS 20/20.
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Figure 3. Minimal
to no vessel compression or engorgement.
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Discussion
These two cases illustrate some of the issues
that you must consider when selecting scleral contact lenses for patients who have
such disorders as keratoconus and irregular astigmatism. Patients that previously
were unlikely to achieve stable clear vision now can enjoy this benefit as well
as improved comfort.
Scleral contact lenses have come full circle
thanks to new technology that allows a lens modality once considered harmful to
be beneficial. The question remains as to their future beyond therapeutic uses.
Scleral lenses have a role in the treatment of persistent epithelial defects and
inflammatory degenerations of the ocular adnexa. These lenses offer much, but we
must modify our thinking if we are to add these lenses to our armamentarium. The
following are some of the issues we must resolve before these lenses can become
more widely used.
How important is lens movement?
Historically, lens movement has been of paramount importance in fitting contact
lenses. However, we now have clinical experience showing that, in some circumstances,
obvious clinically observable lens movement may not only be unnecessary, but may
also be undesirable.
For instance, movement of the Boston
Scleral Lens may have a deleterious effect on the healing of persistent epithelial
defects. The advantage of this lens is that it vaults the cornea and reduces cornea-lens
friction as compared to the friction associated with soft lens bandages. While vaulting
or clearance may reduce acuity in some cases, its benefits are very important in
other cases. For example, I believe the vaulting effect was beneficial in our
keratoconus patient because it subjected his already scarred corneas to less trauma.
He also demonstrated no adverse corneal effects, even a year later, from a lens
that doesn't move.
Even the Jupiter lens, which is smaller
in diameter than the Boston Scleral Lens, appears to require less movement than
most GP or soft lenses do. In general, the greater the tear film reservoir between
the cornea and posterior lens, the less movement is required. Therefore, movement
in corneal-scleral lenses may be more critical than movement with larger scleral
lenses that vault the cornea. You can facilitate movement by increasing mass and
fenestration. I believe placing the fenestration over the limbal region is critical.
We're currently working at Mason Eye Institute (supported by Research to Prevent
Blindness) with PAR corneal topography (Figure 4) to create a scleral curvature
database, which may provide a more efficient method of fitting sclerals in the future.
How
important is tear exchange? Stagnated tear film is associated with the potential
for build up of epithelial and inflammatory cells, so it's important to carefully
watch for the development of tear stagnation and post-lens debris. Radial channels
allow for adequate exchange in the Boston Scleral Lens, while in the Jupiter lens,
peripheral curve design and fenestration are important. Lens adherence can be problematic
and must be guarded against in the smaller diameters. Christine Sindt, OD, of the
University of Iowa recommends rinsing the lens with unpreserved saline just before
lens application. Dr. Sindt suggests using larger diameter lenses and sagittal depth
calculations when fitting these lenses.
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Figure 4. Temporal limbus sclera viewed with
PAR corneal topography. |
What about entrapment
of air bubbles? Entrapment of air bubbles under scleral lenses is a relative,
not an absolute, indicator of poor physiological performance. Air bubbles are ubiquitous
in scleral lens fitting. Large, confluent, centrally located air bubbles are obviously
not only optically debilitating, but can also cause corneal desiccation. These types
of air bubbles are absolute contraindications for continued use of the lens. On
the other hand, smaller-diameter bubbles may pose less of a risk. If the bubbles
are tiny (no greater than 1mm to 2mm), transient, mobile and peripheral, a non-inflamed
cornea may tolerate one or two air bubbles without difficulty. Inflammatory conditions,
however, may be less forgiving. To discourage bubble formation, retrain patients
on lens application to decrease the likelihood of air bubbles. Patients must apply
the lenses while they look downward.
Any contraindications for scleral
lenses? Patients whose corneas demonstrate significant edema because of
reduced endothelial cell count may be poor scleral lens candidates. However, scleral
lenses do present an opportunity to dramatically increase comfort and decrease apical
scarring in some keratoconic and corneal graft patients.
Don't feel that you must limit scleral lenses
to compromised corneas. These lenses eliminate lid-lens interactions, which are
a major source of discomfort for some GP lens wearers, especially in situations
where unstable dynamics occur with patients who have irregular astigmatism. You
can also use scleral lenses to avoid the hypoxia induced by some piggyback lens
systems and hybrid lens designs.
Dr. Loftin is a clinical assistant professor
at Mason Eye Institute, Department of Ophthalmology, University of Missouri School
of Medicine, Columbia, MO.
For references, please visit
www.clspectrum.com/references.asp
and click on document #125.
Contact Lens Spectrum, Issue: April 2006