Surgical correction of hyperopia: clear lens extraction and laser correction

Modern ophthalmology offers a series of surgical procedures to correct a wide range of hyperopia and hyperopic astigmatism. Varies excimer lasers and thermal lasers have been proven safe and effective. Phakic implants and clear lens extraction offers alternatives for moderate to high hyperopic patients. Indications, techniques, and clinical study results were reviewed and summarized.

Keratoconus detected by videokeratography in candidates for photorefractive keratectomy

BACKGROUND

Patients with corneal shape abnormalities should be identified prior to photorefractive keratectomy (PRK). We used videokeratography screening to detect subclinical corneal abnormalities, including keratoconus, which might have been missed by conventional clinical evaluation.

METHODS

One hundred forty-six apparently normal myopic eyes (-1.00 to -7.00 diopters [D] with less than 1.50 D of cylinder) of 91 consecutive patients who were candidates for PRK were screened by videokeratography.

RESULTS

In 6 of 91 patients (7 of 146 eyes), unsuspected corneal shape abnormalities were detected by videokeratography. Two patients had definite keratoconus and three were classified as keratoconus suspects by inferior corneal steepening (Rabinowitz I-S index ranging from 1.62 to 6.20 D). One patient had early pellucid marginal degeneration.

CONCLUSIONS

Keratoconus suspects and contact lens-induced changes resembling keratoconus are present in the "normal" myopic population that presents for refractive surgery. Videokeratographic screening is the only effective means of identifying these and other corneal shape abnormalities.

Irregular astigmatism after radial and astigmatic keratotomy

Eleven eyes of six patients, who had been referred for management of irregular astigmatism after receiving crossed incisions for myopic astigmatism, had moderate to marked irregular corneal astigmatism with marked flattening in the meridians of intersecting incisions. All six patients had a decrease in best-corrected visual acuity with spectacles after surgery. Visual acuity with spectacles was 20/40 in five of 11 eyes; with contact lenses it reached 20/40 in ten of 11 eyes. However, two patients could not wear the contact lenses because of lens decentration caused by the marked distortion in corneal topography. Even with contact lenses, visual acuity could only be improved to 20/25 or better in six of 11 eyes.

Preliminary study of keratomileusis in primates (Macaca speciosa)

Keratomileusis was investigated in five stumptail monkey eyes (Macaca speciosa). An arbitrary flattening of six diopters was selected and programmed in the computer for each eye. The actual flattening achieved two weeks after surgery ranged from -4.00 D to -6.00 diopters (D). One to 5 diopters of the initial effect was lost during the six-month observation period. Histopathology of two eyes demonstrated attenuation and/or loss of Bowman's membrane with overlying epithelial defects.

Radial keratotomy in fresh human cadaver eyes

Radial keratotomy in fresh human cadaver eyes produced corneal flattening varying from 6 to 11 diopters (D). There was no significant difference in the effectiveness of the incisions to the incisions to the limbus compared to incisions through the limbus. Eighty to ninety percent of the flattening effect was obtained after the first eight incisions. The preoperative keratotomy reading was not helpful in predicting the final result. Histopathology of the incised corneas revealed considerable variation in incision depth and demonstrates the difficulty in achieving deep incisions safely.

Modification of corneal curvature following radial keratotomy in primates

Radial keratotomy was performed on six stumptail monkey eyes (Macaca speciosa) and 22 owl monkey eyes (Aotus trivirgotus). Changes in keratometry, specular microscopy, and tonometry have been studied postoperatively for three to six months. Sixteen radial incisions in stumptail monkey eyes resulted in a significant mean corneal flattening of 2.75 diopters (P less than 0.005). This effect was stable with a mean 2.50 diopters flattening remaining six months after surgery. Sixteen radial incisions in ten owl monkey eyes resulted in a much greater short-term effect, with a mean 10.50 diopters of flattening present at two weeks postoperatively. This flattening deteriorated over the observation period, and no significant effect was noted three months after surgery. A comparison of 8 vs 16 incisions on owl monkey eyes demonstrated that these two procedures are equally effective in initially flattening the cornea. Complications and side effects encountered included perforations, irregular astigmatism, corneal neovascularization, transitory increase in pachometry, and decrease in central corneal endothelial cell density in isolated cases.

Radial keratotomy in non-human primate eyes

We performed a prospective study of the effects of radial keratotomy in the owl monkey. We compared a 16-incision and an eight-incision radial keratotomy, and followed the changes in corneal curvature, corneal thickness, endothelial cell counts, and intraocular pressure. We compared the results of the changes in these clinical factors with a histopathologic and ultrastructural analysis of the time-related changes after radial keratotomy in another group of animals. We found that the loss of initial corneal flattening following radial keratotomy corresponded with the contracture of the wound as demonstrated by histopathologic and ultrastructural study. This procedure results in a significant endothelial cell loss (14% to 15%), which is a result of the postsurgical inflammation associated with this surgery. Additionally, examination of the histopathologic structure of these corneas showed a high level of variability in the surgical incision depth, which we believe is responsible for the marked variations in the response to the surgical procedure.