Variations in corneal wound healing after radial keratotomy: possible insights into mechanisms of clinical complications and refractive effects.

Ultrastructural and histopathologic analysis was performed on three human corneal specimens for variable and complicated refractive outcomes 1-2 years after radial keratotomy. Specimens were obtained immediately postsurgery after microkeratome resection with homoplastic lamellar keratoplasty (two cases) and penetrating keratoplasty (one case) for correction of glare, severe astigmatism, overcorrection, and/or double vision. All three cases showed variability of wound healing and delayed corneal wound healing sites; epithelial retention cysts, and/or absence of stromal scar collagen that was not dependent on the length of time after surgery. Two of the three radial keratotomy specimens also contained extensive duplication of the superficial corneal epithelial basal lamina. When present, the thickened basal lamina (3-6 microns in thickness) was seen between all incisions evaluated and appeared to extend from the central optical zone out to the periphery of the lamellar button. The one full-thickness keratoplasty specimen showed focal loss of underlying endothelial cells with occasional migrating cells seen by scanning electron microscopy. These data support previous findings that delayed corneal wound healing with epithelial retention cysts remains the most common histopathologic alteration after radial keratotomy. The effects of variations and delay in wound healing between individuals could explain the lack of predictability of refractive outcome and continuing refractive instability in long-term follow-up after single or repeat radial keratotomy surgeries.

Comparison of ultrasonic corneal thickness measurements before and during surgery in the prospective evaluation of Radial Keratotomy (PERK) Study.

Central corneal thickness, determined by an ultrasonic pachymeter, was studied in one eye each of 395 patients enrolled in the Prospective Evaluation of Radial Keratotomy (PERK) Study, to determine the changes in central corneal thickness between preoperative and intraoperative measurements. There was no statistical difference between the preoperative and the intraoperative measurement. However, 9.4% of the corneas were 0.03 to 0.08 mm thinner intraoperatively and 3.3% were 0.03 to 0.06 mm thicker intraoperatively, indicating that clinically meaningful changes in corneal thickness occurred between the preoperative and intraoperative measurements in some eyes. We conclude that the most reliable way to use ultrasonic pachymetry readings to set the length of the knife blade for radial keratotomy surgery is to measure the corneal thickness intraoperatively.

Keratophakia and keratomileusis: histopathologic, ultrastructural, and experimental studies.

We present ultrastructural findings in two cases, one of keratophakia (9 months postoperatively) and one of keratomileusis (1 year, 7 months post-operatively), which best demonstrate the pathologic changes we observed in six cases of cryorefractive surgery. In addition, we studied a rabbit model of keratophakia which appears to exhibit similar features to that of human keratophakia. In the keratomileusis cases, there were marked abnormalities, including deposition of redundant basal lamina, loss of Bowman's membrane and deposition of a 6 nm fibrillar material in areas devoid of Bowman's membrane. In keratophakia lenticule we noted the absence of keratocyte regeneration, abnormal deposition of long-spacing collagen, and the presence of necrotic cellular debris. In experimental keratophakia, little to no evidence of keratocyte regeneration was evident 4 months after surgery. Keratophakia lenticules implanted into actively regenerating corneas induced by freeze injury exhibit only a slight increase in the number of keratocytes migrating into the donor tissue, suggesting that implants lack a primary factor necessary for keratocyte regeneration. Immunofluorescent localization of fibronectin and fibrinogen demonstrated absence of these factors in normal host stroma, implanted lenticules and freeze injured corneal stroma. Actively migrating fibroblasts, however, did react positively for fibronectin, suggesting that these cells synthesize and secrete fibronectin during regeneration. These results do not support a role for soluble fibronectin or fibrinogen in keratocyte repopulation.

Powderfree surgical gloves.

The first commercially available powderless glove was compared to other popular ophthalmic gloves. They were compared with scanning electron microscopy (SEM), the ease of donning, and tactile sensitivity. SEM revealed the new gloves to, in fact, be entirely powderfree. Customary washing procedures of the presently available commercial gloves revealed the inability to remove powder from the surfaces.

Evaluation and comparison of sources of variability in the measurement of corneal thickness with ultrasonic and optical pachymeters.

Two studies were carried out to determine and compare the effects of several sources of variation on the measurement of corneal thickness using the standard optical pachymeter and three ultrasonic pachymeters. Sources of variation included: intra- and inter-session variation, inter-observer variation, left/right eye variation, and variations due to alternate settings of ultrasonic sound frequencies. It was found that the optical pachymeter had a) two to three times as much intra-session variation as that of the ultrasound pachymeters, b) significant inter-observer variation (P = 0.015), and c) significant differences between left and right eye thickness determinations (P less than 0.005). On the other hand, ultrasonic pachymeters demonstrated a) high reproducibility, b) no inter-observer variation, and c) no left/right eye variation. These results have implications for the use of pachymetry in measuring corneal thickness for radial keratotomy and other refractive surgery.

Keratophakia. Long-term results.

Thirty-three keratophakias were performed at Holy Cross Hospital in Mission Hills, California between August 1979 and October 1982. Nineteen were primary, combined with cataract surgery; 14 were secondary, performed on aphakic eyes. Data on the 23 cases that had a minimum follow-up time of one year were analyzed by an independent observer. Best visual acuity obtained at seven months was 20/40 or better in 62% of the patients. Induced keratometric astigmatism averaged 1.0 diopter and manifest refractive astigmatism 2.0 diopters. The results of secondary keratophakia vs keratophakia combined with cataract extraction were compared. Accuracy, complication rate and final visual recovery suggest that the combined procedure is safe and effective, and that primary keratophakia does not add a significant risk to cataract surgery.

Analysis of incision depth following experimental radial keratotomy.

Eight-incision radial keratotomy was performed on a series of cadaver eyes using ultrasonic pachymetry and both metal and diamond blades. There were no statistically significant differences in mean corneal flattening (approximately 9.5 diopters) obtained with either the diamond or metal blades. Short diamond knife incisions produced less flattening that was statistically significant (5.8 diopters). Histologic analysis of incision depth revealed similar results with both the diamond (84%) and metal (86%) blades.

Epithelial inclusion cysts following radial keratotomy.

A 26-year old woman underwent radial keratotomy combined with concentric trephination (6.5 and 8 mm) six months prior to development of multiple epithelial inclusion cysts. A biopsy specimen from one enlarging cyst showed an absence of scarring in addition to the retention of epithelium within a radial incision wound. Adjacent keratocytes were abnormal and seemed to be undergoing degenerative changes. To our knowledge, this is the first report of a failure in corneal wound healing associated with microcystic degeneration of the epithelium following radial keratotomy.

Evaluation of sources of variation on the accuracy and reproducibility of microkeratome sections with the modified artificial anterior chamber.

A study was carried out to evaluate effects of various sources of variation on the accuracy and reproducibility of the modified artificial chamber in obtaining lamellar sections from rabbit cornea. Sources of variation included a) measurement error, inter-cornea and inter-session variation, b) length of storage time M-K medium, and c) choice of preselected values of thickness and diameter. The findings indicated tha a) measurement error, inter-cornea, and inter-session variations were of nominal magnitude; b) the length of storage time up to 10 days did not effect the precision of the procedure; c) the precision of diameter determinations did not depend on the preselected value of the diameter; d) the precision of thickness determinations did depend on preselected parameter values; and e) parameter values tended to be underestimated. Regression equations therefore are provided to adjust for the underestimation of thickness and diameter. Based on these findings, it was concluded that the modified artificial anterior chamber is adequate for use in experimental refractive keratoplasty since it provides adequate diamter values and is reproducible.

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.

A modified artificial anterior chamber for use in refractive keratoplasty.

We devised a modified artificial anterior chamber that enables Barraquer microkeratome keratectomies on corneas preserved in McCarey-Kaufman medium. It consists of a hydraulic system, which creates a positive pressure of 60 mm Hg or more. An added rotating ring serves as a base to the microkeratome's tracks and varying diameters of lamellar sections can be obtained. This device allows the surgeon to use readily available corneas with scleral rims preserved in McCarey-Kaufman medium rather than whole eyes to obtain precise lamellar sections.

Correction of induced astigmatism after cataract surgery with introduction of an intraocular lens.

1. The induced astigmatism is most frequently due to corneal scleral suturing and not tilting of the pseudophakos. 2. A simple method of reducing postoperatively induced corneal astigmatism after implantation of intraocular lens has been presented.