OM t of c.iii - Vision Research Coordinating Center - Washington ...

2/1/99 Chapter 1 Background page 1-12
the early stages of the disease. These optometrists often work in association with
ophthalmology centers or refer regularly to ophthalmologists for necessary medical
therapy including surgery. Surgery is required by only about 10% - 20% of keratoconus
patients (Kennedy et al., 1986; Smiddy et al., 1988), and 11% of penetrating
keratoplasties performed in the United States are for keratoconus (Eye Bank Association
of America statistics, 1992).
Most keratoconus patients require the primary mode of successful management:
rigid contact lenses. Several recent retrospective studies have demonstrated good
success following the refitting of contact lenses in patients who were being considered
as possible surgical candidates due to presumed intolerance of contact lenses (Smiddy
et al., 1988; Kastl et al., 1987; Belin et al., 1988; Fowler et al., 1988; Dana et al., 1990).
Most practitioners avoid surgery in the early stages of keratoconus because of the risks
of surgical complications, corneal graft rejection, or post-surgical corneal distortion, and
because contact lens fitting in keratoconus has a high success rate (Kastl et al., 1987).
Surgery—in the form of penetrating keratoplasty or epikeratoplasty—is required when
contact lenses can no longer be tolerated due to either discomfort or poor vision
associated with scarring (Sharif and Casey, 1991).
Epikeratoplasty is a procedure where an on-lay graft of lyophilized lamellar
tissue is sewn to Bowman’s membrane of the keratoconic cornea. The ideal
epikeratoplasty candidate has no corneal scarring and is contact lens intolerant but can
achieve 20/40 visual acuity with a contact lens in place (Lembach et al., 1989; Dietze
and Durrie, 1988). This procedure has significant advantages in that it is not an
intraocular procedure and does not require donor tissue that might be immunologically
rejected. This procedure represents a recent advancement in the surgical management
of keratoconus, and its early success has been reported from several centers (Dietze and
Durrie, 1988; Kaufman and Werblin, 1982; McDonald et al., 1983; McDonald et al., 1986;
McDonald et al., 1987; Lass et al., 1987). The long term follow-up data for this
procedure, however, are demonstrating that many of these patients with a successful
surgical result still require the use of contact lenses to maximize visual improvement
(Lembach et al., 1989). The role of epikeratoplasty compared to penetrating keratoplasty
has not been clearly identified at this time (McDonald et al., 1987; Steinert and Wagoner,
1988). There is a growing opinion that rapid identification of those patients with
changing keratometric readings and marked disease progression may benefit from
earlier surgery with epikeratoplasty before a penetrating keratoplasty is necessary.
There is some suggestion that the use of moist-pack nonlyophilized tissue may improve
the rehabilitation and quality of vision achieved in these patients.
Although the rate of success with penetrating keratoplasty is higher for
keratoconus than for most other indications for corneal grafts (Steinert and Wagoner,
1988; Sharif and Casey, 1991), significant risks and costs are associated with
keratoplasty. Immunological rejection episodes, sometimes irreversible, are reported to