Faculty Bibliography

Epikeratophakia is a surgical technique initially developed for the correction of aphakia, and later adapted for the correction of keratoconus and myopia. The concurrent development of color-coded computerized corneal topography has greatly assisted in the evolution of epikeratophakia. Corneal topography has demonstrated the importance of both accurate centration of the epikeratophakia lenticle over the visual axis and the size of the optical zone on the final refractive results. Corneal topographic changes associated with correction of aphakia are primarily the result of steepening of the anterior radius of curvature of the cornea, in contrast to myopic correction which results in flattening of the anterior cornea. Correction of keratoconus results from a physical compression of the cone thereby flattening both the anterior and posterior radii of curvature. Preoperative topography in patients with keratoconus permits the precise position and extent of both regular and irregular astigmatism mation may assist in designing the optimal lenticle size and amount of graft decentration necessary to achieve the maximal surgical effect. Corneal topographic mapping has also been helpful in the management of postoperative astigmatism following epikeratophakia. Topography identifies the location and extent of both regular and irregular astigmatism which assists in planning of both surgical and nonsurgical intervention. Corneal topographic mapping has also been extremely helpful in the management of postoperative astigmatism following epikeratophakia. Topography identifies the location and extent of both regular and irregular astigmatism which assists in planning of both surgical and nonsurgical intervention

Twelve eyes undergoing penetrating keratoplasty with a double-running suture technique had corneal topographical analysis immediately before and one month after 10-0 suture removal. Substantial changes in astigmatism were evident following suture removal. Twenty five percent of eyes showed a decrease of 1 D, 33% of eyes showed a decrease of 3 D, 8.3% of eyes showed an increase of 1 D, 8.3% of eyes showed an increase of 2 D, 16.6% of eyes showed an increase of 3 D, and 8.3% of eyes showed an increase of 4 D of astigmatism following suture removal. The mean corneal astigmatism did not show a significant change from a mean of 5.3 D after suture removal. There was less individual variation of spherical corneal power following suture removal. Thirty three percent of eyes showed a decrease of 1 D, 33% of eyes showed a decrease of 2 D, 8.3% of eyes showed a decrease of 3 D, 18.3% of eyes showed an increase of 1 D, and 6.6% of eyes showed an increase of 2 D of spherical power following suture removal. The surface asymmetry index (SAI), a centrally weighted measure of corneal surface irregularity, decreased significantly (P less than 0.04) from a mean of 1.17 before suture removal to a mean of 0.93 after suture removal. These results suggest that surface irregularity may be decreased following the removal of a single running 10-0 nylon suture following penetrating keratoplasty

In the Prospective Evaluation of Radial Keratotomy (PERK) study, the symmetry of refractive and visual acuity outcome was analyzed in 269 patients with bilateral radial keratotomy with a single operation in each eye. Patients were required to wait 1 year after surgery on the first eye before having surgery on the second eye. At 1 year after surgery on the second eye, 98% of patients had 3.00 diopters or less difference between their two eyes in the spherical equivalent of the cycloplegic refraction (100% before surgery), and 96% of patients had 3.00 D or less difference between their two eyes in the amount of refractive power in the vertical meridian (100% before surgery). Thus, surgically induced refractive anisometropia was not a major complication in the PERK study. However, 14% of patients had four to eight Snellen lines difference in the uncorrected visual acuity between their two eyes (1% before surgery), emphasizing that induced asymmetry of refraction is a potential clinical problem for some patients

Surgical keratometers were conceived as an aid that would help anterior segment surgeons minimize postoperative astigmatism, a major obstacle along the road to rapid visual rehabilitation. Two classes of surgical keratometers are commercially available at present. The first class of devices produces a keratoscopic image from which the surgeon must make a qualitative assessment of both the amount and location of astigmatism based upon distortion present in the keratoscopic image. The second class of devices quantitates corneal power at a chosen meridian and providing the surgeon with either an analogue or digital readout. Usually it is up to the surgeon to identify the meridian of greatest corneal power based on qualitative alterations of the keratoscopic image. These keratoscopes are based either on the optical principles of the von Helmholtz keratometer, or on nonparallel electronic image digitization. In this article we critically review commercially available surgical keratometers emphasizing their attributes and limitations

In the Nationwide Study of Epikeratophakia, 22 eyes underwent penetrating keratoplasty (PKP) after epikeratophakia for keratoconus. Reasons for PKP included visual acuity unsatisfactory to the patients (6 eyes), recipient corneal scarring (4 eyes), recipient Descemet's folds (3 eyes), scarring in the tissue lens (2 eyes), vascularization of the tissue lens (2 eyes), astigmatism (2 eyes), failure of the tissue lens to reepithelialize (1 eye), corneal ulcer (1 eye), and scarring of the donor and recipient cornea (1 eye). After PKP, all patients had clear grafts and 20/40 or better visual acuity. Average follow-up was 17 months. Three of the 22 patients (13.6%) had graft reaction episodes, all of which were treated successfully, resulting in clear grafts. The authors conclude that previous epikeratophakia does not adversely affect the outcome of subsequent PKP for keratoconus

Hyperopic hydrogel intracorneal lenses were successfully implanted into 27 of 33 primate eyes. All eyes were evaluated preoperatively and postoperatively at monthly intervals for clinical appearance and refractive alteration. In a preliminary surgical series, several factors, such as tight sutures and implant design, resulted in a poor refractive yield. The final surgical series used a microkeratome with a pediatric microkeratome ring for smooth interface cuts, interrupted suturing with sufficient tension to align the wound without compression, a suture through the lens to prevent its dislocation, and intraoperative keratometry to reduce postoperative cylinder. The predicted vs measured refractive alteration for a range of 6 to 20 diopters had a correlation coefficient of .95. Keratometry changes correlated to the refractive changes with a coefficient of .97 but understand the change in refraction created by the surgery