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Patient
EW presented with a longstanding history of keratoconus OU. He had
undergone an epikeratophakia procedure on the right eye in 1988, which
today is correctable to 20-50 with a spectacle Rx of -2.75 -2.25 x 47, VA
20/50. He subsequently underwent a penetrating keratoplasty to the
left eye in 1999 (figure 1).
Postoperatively, his left cornea stabilized with K reading of 44.25 @
144/47.12 @ 54. Computerized corneal mapping showed an asymmetrical
distribution to the topography with significant mid-peripheral nasal
steeping from 7 o'clock to 11 o'clock and temporal flattening from 1
o'clock to 6 o'clock (figure 2).
An asymmetrical corneal topography, or graft tilt, is a common
postoperative complication in penetrating keratoplasty. The
mechanisms for the tilting include improper suture tension, uneven
trephination of the donor button or recipient bed and pre-existing corneal
topography (figure 3).
The presence of graft tilt may complicate the fitting of rigid contact
lenses depending on the location of the tilt (steepest portion). If
the tilt is inferior, design an RGP to align the flatter superior cornea,
which allows the lens to lift off inferiority (similar to a keratoconus
pattern). However, if the tilt is nasal or temporal, the lens will
exhibit significant edge lift over the steepest area of the mid-peripheral
cornea. This can result in excessive lens decentration and
inconsistent VA.
The lens we selected was the Post-Graft Design from Lens Dynamics in
Denver. The design incorporates a large overall  diameter of 10.4 mm
to aid in centration on these often asymmetrical or irregular corneal
topographies. The design also incorporates a large 9.0 mm optical
zone which can be adjusted (made smaller) especially in cases in which the
central portion of the graft has steepened.
Our fitting objective was to select a diagnosis lens with a base curve
that would be steep enough to clear the apex of the cornea and land on the
flatter
temporal mid-peripheral cornea from 1 o'clock to 6 o'clock (Figure 4). 
Ultimately, the patient was fit with a lens of 46.00 diopters, -3.25 D,
10.4 mm, visual acuity 20/25, with a comfortable wearing schedule of 14 to
16 hours a day.
Patrick
Caroline is an associate professor of optometry at Pacific University and
an assistant professor of ophthalmology at the Oregon Health Sciences
University. Mark André is director of contact lens services at the
Oregon Health Sciences University. |
