Journal of Refractive Surgery

Original Articles 

Cat Keratoplasty Wound Healing and Corneal Astigmatism

Nancy K Tripoli, MA; Kenneth L Cohen, MD; Alan D Proia, MD, PhD

Abstract

ABSTRACT

BACKGROUND: A major contributor to postkeratoplasty astigmatism may be donor/recipient disparity. Deficient or excess comea at the wound is thought to influence the directions of the steep and flat meridians. Using an established model of penetrating keratoplasty in the cat, this study evaluated the morphometry of histopathologic wound features in the steep and flat meridians.

METHODS: Thirteen cats had successful penetrating keratoplasties after intentionally misshapen donor corneas were misaligned in misshapen recipient beds. At 9.50 ± 0.32 (mean ± 1 SEM) months after keratoplasty, photokeratography was performed and analyzed, corneas were sectioned along the steep and flat meridians, and four histologic sections were processed. Features of the wounds were measured using a Zeiss Videoplan®. The relationships between the morphometry of each feature and every other feature, between the morphometry of each feature and eccentricity, and between the steep and flat section morphometry of each feature were statistically evaluated.

RESULTS: Epithelial thickness, area of lamellar alteration, length of Descemets membrane produced postoperatively, and the depth that preoperative Descemet's membrane was embedded in the stroma were correlated with eccentricity (corneal astigmatism). Stromal thickness and the presence or absence of folded and fragmented Descemet's membrane were not correlated with eccentricity. Wound morphometry at the steep meridians was neither correlated with nor significantly different from wound morphometry at the flat meridians.

CONCLUSIONS: Differences between healing at the steep and flat meridians were not likely contributors to astigmatism. Disproportionate availability of tissue in wound regions may have affected healing throughout the entire wound over time. The absence of Bowman's layer in cats restricts application of our results to understanding the etiology of corneal astigmatism after penetrating keratoplasty in humans. [Refract Corneal Surg 1992;8:196-203.)

Abstract

ABSTRACT

BACKGROUND: A major contributor to postkeratoplasty astigmatism may be donor/recipient disparity. Deficient or excess comea at the wound is thought to influence the directions of the steep and flat meridians. Using an established model of penetrating keratoplasty in the cat, this study evaluated the morphometry of histopathologic wound features in the steep and flat meridians.

METHODS: Thirteen cats had successful penetrating keratoplasties after intentionally misshapen donor corneas were misaligned in misshapen recipient beds. At 9.50 ± 0.32 (mean ± 1 SEM) months after keratoplasty, photokeratography was performed and analyzed, corneas were sectioned along the steep and flat meridians, and four histologic sections were processed. Features of the wounds were measured using a Zeiss Videoplan®. The relationships between the morphometry of each feature and every other feature, between the morphometry of each feature and eccentricity, and between the steep and flat section morphometry of each feature were statistically evaluated.

RESULTS: Epithelial thickness, area of lamellar alteration, length of Descemets membrane produced postoperatively, and the depth that preoperative Descemet's membrane was embedded in the stroma were correlated with eccentricity (corneal astigmatism). Stromal thickness and the presence or absence of folded and fragmented Descemet's membrane were not correlated with eccentricity. Wound morphometry at the steep meridians was neither correlated with nor significantly different from wound morphometry at the flat meridians.

CONCLUSIONS: Differences between healing at the steep and flat meridians were not likely contributors to astigmatism. Disproportionate availability of tissue in wound regions may have affected healing throughout the entire wound over time. The absence of Bowman's layer in cats restricts application of our results to understanding the etiology of corneal astigmatism after penetrating keratoplasty in humans. [Refract Corneal Surg 1992;8:196-203.)

Corneal astigmatism is a major complication of penetrating keratoplasty which can interfere with visual rehabilitation. Suggested contributors to excessive postkeratoplasty astigmatism include trephination, suturing and other surgical techniques, timing of suture removal, wound healing, and recipient disease.1"9 A major contributor to postkeratoplasty astigmatism may be donor/ recipient disparity which produces deficient or excess cornea at the wound.10,32 This concept has been supported by a study that used an established model of penetrating keratoplasty in the cat. When intentionally misshapen donor corneas were misaligned in misshapen recipient beds to induce donor/ recipient disparity, the directions of the steep and flat meridians after keratoplasty were influenced by the deficiency or excess of cornea at the wound. 12

To our knowledge, the model of penetrating keratoplasty in the cat has not been used to study wound healing and to evaluate a possible relationship between wound healing and astigmatism. We intentionally created donor/recipient disparity to promote the development of corneal astigmatism after penetrating keratoplasty.12-13 The amount of and the directions of the steep and flat meridians after keratoplasty were compared with morphometry analyses of histopathologic wound features measured at the steep and flat meridians.

MATERIALS AND METHODS

Surgical Technique

The same surgeon performed penetrating keratoplasties on the right eyes of 13 young adult, domestic cats. The animals had no preoperative, anterior segment abnormalities as assessed by biomicroscopy, and preoperative keratometric astigmatism was less than 0.50 D. Animal care and surgical technique adhered to the AKVO Resolution on the Use of Animals in Research. Before surgery, recipient cats received 20 mg of intramuscular gentamicin sulfate and 1000 units of subcutaneous heparin sodium. The keratoplasties were oversized (7.5millimeter recipient/7. 7-millimeter donor). New, disposable trephines (Edward Week and Company, Ine, Research Triangle Park, NC) were centered on the epithelial surfaces of the donor and recipient corneas. No obdurator was used. To increase the likelihood of out-of-round donor corneas and recipient beds, all trephines were tilted 20° in the 12, 3, 6, or 9 o'clock directions according to a random schedule, and the intraocular pressures and the pressures of the trephines on the eyes were not controlled.

The anterior chambers were entered by hand trephination, and excision of the corneas was completed with razor blade knives and corneal scissors. Silk marking sutures (9-0) identified the 12 o'clock in vivo positions on donor corneas which were aligned with the 12 o'clock positions of the recipient corneas. During surgery, anterior chamber depths were maintained with 1% sodium hyaluronate. Wounds were closed with 16, evenly spaced, interrupted, 9-0 nylon sutures, and an additional suture was placed at each 8 o'clock position, a region which is vulnerable to rubbing by cats. At the conclusion of surgery, operated eyes received 1% atropine sulfate drops, bacitracin ointment, and 1 mg of subconjunctival triamcinolone acetonide. Ib reduce corneal edema, topical bacitracin-neomycin-polymyxin with 1% hydrocortisone acetate ointment and 1 nig of subconjunctival triamcinolone acetonide were administered as needed throughout the postoperative course.

All sutures were removed after 2 weeks. Postoperative examinations were performed weekly for 6 weeks, monthly for the next 3 months, and at 6 and 9 months and included biomicroscopy, intraocular pressure measurement (MacKay Marg® electronic tonometer, Berkeley Bio-Engineering, San Leandro, Calif), and measurement of central corneal thickness using an optical pachymeter (Haag Streit AF, Bern, Switzerland) with Mishima Hedbys modification.

Keratography

For each cat, photokeratograpby was performed at 9.50 ± 1.15 (mean, ± SD) months after penetrating keratoplasty using a nine-ring photokeratoscope (CorneaScope®, Kera Corporation, Santa Clara, CaHf). The keratoscope rings were centered on each keratoplasty such that the most peripheral ring image(s) was symmetrically distorted by the wound (Fig 1). The configuration of the second-ring image was processed by the Photogrammetric Index Method (PIM) which measured the lengths and directions of the longest and shortest chords across the ring.14 The directions of the longest and shortest chords were considered to be the directions of the flattest and steepest meridians. Eccentricity of the second ring, defined as the shortest chord length divided by the longest chord length, was used as a quantitative assessment of corneal astigmatism. A circular ring has an eccentricity of one. The lower the eccentricity, the greater the astigmatism. At the time of keratography, the 13 cats had clear keratoplasties, and no retrocorneal fibrous tissue, peripheral anterior synechiae, or wound abnormalities were observed by biomicroscopy.

FIGURE 1: The CorneaScope® photokeratograph show$ the nine-ring pattern centered on the keratoplasty as determined by symmetrical distortion of the peripheral rings. The steep and flat meridians are selected from 180 measurement positions at 2-degree intervals on the second ring.

FIGURE 1: The CorneaScope® photokeratograph show$ the nine-ring pattern centered on the keratoplasty as determined by symmetrical distortion of the peripheral rings. The steep and flat meridians are selected from 180 measurement positions at 2-degree intervals on the second ring.

Morphometry

Within 1 week after photokeratography, at each corneal limbus, the 12 o'clock position and both ends of the flat and steep meridians identified by PIM were located with a Méndez® degree marker (Katena Products, Ine, Denville, NJ) and marked with color-coded sutures. Each cornea was excised at the limbus, and the cats were killed. Corneas were fixed in 3.7% phosphate-buffered neutral formaldehyde and cut along the steep and flat meridians (Fig 2). To represent the wounds at the steep and flat meridians, corneas were sectioned as close as possible to the sutures that identified these meridians. From each cornea, four histologic sections were processed, one at each end of the steep meridian and one at each end of the flat meridian. Ine sections were dehydrated with serial alcohols, embedded in Paraplast (Fisher Scientific, Pittsburgh, Pa), and stained with either hematoxylin and eosin or periodic acid-Schiff reagent.

Sections were examined histopathologically by an observer with no knowledge of the corneal astigmatism. Wounds were identified by discontinuous Descemet's membrane, altered stromal lamellae, thickened epithelium, and thinned stroma. Seven histopathologic features were measured at the wound and two features were measured in donor and recipient cornea on each section using a Zeiss Videoplan® (Carl Zeiss, Oberkochen, Federal Republic of Germany).

FIGURE 2: Within 1 week after photokeratography, at each corneal limbus, the 12 o'clock position and both ends of the steep and flat meridians identified by the Photogrammetrlc Index Method, were marked by color-coded sutures.'4 Excised corneas were fixed in 3.7% formaldehyde, embedded in Paraplast, and sections were stained with hematoxylin and eosin or periodic acid-Schiff reagent. Each cornea was represented by four sections. Sections 1 and 3 were taken along the steep meridian and sections 2 and 4 along the flat meridian.

FIGURE 2: Within 1 week after photokeratography, at each corneal limbus, the 12 o'clock position and both ends of the steep and flat meridians identified by the Photogrammetrlc Index Method, were marked by color-coded sutures.'4 Excised corneas were fixed in 3.7% formaldehyde, embedded in Paraplast, and sections were stained with hematoxylin and eosin or periodic acid-Schiff reagent. Each cornea was represented by four sections. Sections 1 and 3 were taken along the steep meridian and sections 2 and 4 along the flat meridian.

Five features were analyzed using continuous measurements. Three of these were measured perpendicular to the epithelial surface: maximal epithelial thickness in the wound (Fig 3A) and in donor and recipient cornea approximately 1 mm from the wound, stromal thickness at the same location as maximal epithelial thickness (Fig 3A), and the distance from the endothelial surface to the locations in the stroma of the most deeply embedded portion of either preoperative donor or recipient Descemet's membrane (Fig 3B). A fourth feature, the length of Descemet's membrane produced postoperatively, was measured in sections stained with periodic acid-Schiff reagent (Fig 3B). The fifth feature, the area of lamellar alteration, was measured by enclosing its region with the cursor (Fig 3A).

Two features were analyzed with binary counts (presence = 1, absence = 0). Folds and fragments in either preoperative donor or recipient Descemet's membrane were scored for their presence or absence (Fig 3C). A fold was present if Descemet's membrane turned back on itself more than 90°. A fragment was present if discontinuous Descemet's membrane was seen in the wound.

Statistics

Histologic data were processed in two ways. First, to represent the wound morphometry of a feature for each cornea, measurements of the feature in all four sections were combined; continuous measurements were averaged and binary counts were summed. Second, to represent the wound morphometry of a feature at the steep and flat meridians separately for each cornea, measurements of the feature in the steep meridian were combined by averaging continuous measurements and summing binary counts, and measurements of the feature in the flat meridian were combined using the same calculations.

Spearman correlations evaluated the relationships between each feature and every other feature as represented by wound morphometry. For each feature, Spearman correlations evaluated the relationships between the wound morphometry and eccentricity, between the wound morphometry at the steep and flat meridians and eccentricity, and between the wound morphometry at the steep and flat meridians. For each feature, Wilcoxon rank sums evaluated the differences between the wound morphometry at the steep and flat meridians. In all evaluations, random probability of less than 0.05 was reported as significant. Confidence intervals were constructed for the Wilcoxon analyses.

RESULTS

General Observations

In all specimens, wounds were identified by thickened epithelium, thinned stroma, disorganization of the normal stromal lamellar pattern, and discontinuity of Descemet's membrane. Lamellar disruption varied both in extent and severity, but in all cases it was manifested by hypercellularity and altered staining intensity with hematoxylin and eosin. In all wounds, ends of either preoperative donor or recipient Descemet's membrane, or both, extended from the endothelial surface into the stroma, indicating that new connective tissue had been formed at the wound. In many wounds, the new connective tissue was barely distinguishable from the stroma away from the wound. All stroma posterior to preoperative donor and recipient Descemet's membrane was covered with a thin layer of Descemet's membrane produced postoperatively (Figs 3A-3C). Close apposition or overlapping of preoperative donor and recipient Descemet's membrane occurred in sections of only two corneas (Fig 4). Descemet's membrane was folded in at least one section of 12 wounds (92.3%) and fragmented in at least one section of 11 wounds (84.6%) (Fig 3C). For each feature, means and standard deviations of all measurements, measurements from the steep sections, and measurements from the flat sections are shown in Table 1. Correlations that compared the wound morphometry of each feature with every other feature are shown in Table 2.

Correlations Between Wound Morphometry and Eccentricity

The wound morphometry of epithelial thickness, the area of lamellar alteration, the depth that preoperative Descemet's membrane was embedded into the stroma, and the length of Descemet's membrane produced postoperatively were all significantly negatively correlated with eccentricity (Table 3). Stromal thickness, fragmentation of Descemet's membrane, and folds in Descemet's membrane were not significantly correlated with eccentricity.

FIGURE 3: Histopathologic wound features were measured using a Zeiss Videoplan®. (A) Wound epithelial thickness (WP) was measured at its thickest point, and wound stromal thickness (WS) was measured at the same location. The area of lamellar alteration (LA) was measured by enclosing its region with the cursor. (B) The distance from the endothelial surface fo fhe most deeply embedded portion of either preoperative donor or recipient Descemet's membrane (DP) and the length of Descemet's membrane produced postoperatively (NW) were measured.

FIGURE 3: Histopathologic wound features were measured using a Zeiss Videoplan®. (A) Wound epithelial thickness (WP) was measured at its thickest point, and wound stromal thickness (WS) was measured at the same location. The area of lamellar alteration (LA) was measured by enclosing its region with the cursor. (B) The distance from the endothelial surface fo fhe most deeply embedded portion of either preoperative donor or recipient Descemet's membrane (DP) and the length of Descemet's membrane produced postoperatively (NW) were measured.

The wound morphometry at the steep meridians for only epithelial thickness was significantly negatively correlated with eccentricity (r = 0.857; p < .01). The wound morphometry at the flat meridians for only the area of lamellar alteration (r = 0.549; p < .05) and length of Descemet's membrane produced postoperatively (r = 0.654; p < .05) was significantly negatively correlated with eccentricity.

Comparisons Between Wound Morphometry of Steep and Flat Sections

There were significant correlations between the wound morphometry at the steep meridians and the flat meridians for epithelial thickness, stromal thickness, area of lamellar alteration, length of Descemet's membrane produced postoperatively, and depth that preoperative Descemet's membrane was embedded into the stroma. There were no significant differences between the wound morphometry at the steep and flat meridians for any feature. Table 4 shows the 95% confidence intervals for the Wilcoxon assessment of the differences between the wound morphometry for each feature at the steep and flat meridians.

FIGURE 3 continued:(C) For each comea, folds (FOLD) and fragments (FRAG) in either preoperative donor or recipient Descemet's membrane, were scored for presence (1) or absence (0) in each of the four wound sections. A fold was present if Descemet's membrane fumed back on itself more than 90°. A fragment was present If a section of discontinuous membrane was in the wound site.FIGURE 4: Donor and recipient Descemet's membrane were closely apposed or overlapped in at least one section in only 2 of the 13 corneas sampled.

FIGURE 3 continued:

(C) For each comea, folds (FOLD) and fragments (FRAG) in either preoperative donor or recipient Descemet's membrane, were scored for presence (1) or absence (0) in each of the four wound sections. A fold was present if Descemet's membrane fumed back on itself more than 90°. A fragment was present If a section of discontinuous membrane was in the wound site.

FIGURE 4: Donor and recipient Descemet's membrane were closely apposed or overlapped in at least one section in only 2 of the 13 corneas sampled.

DISCUSSION

There is evidence that corneal astigmatism can be caused by the addition or deletion of cornea along the affected meridian. Recent studies of human and monkey corneas after radial keratotomy correlated a histopathologic wound feature, addition of cornea as quantitated by separation of the ends of Bowman's layer and wound gape, with the amount of corneal flattening.15'16 Several studies have suggested that placement of a round donor cornea in an oval recipient bed produces donor/recipient disparity that can lead to corneal astigmatism after penetrating keratoplasty.10-11 The deficiency or excess of cornea at the wound is thought to cause the steep and flat meridians, respectively.17 A previous study using the cat model provided evidence to support this proposed mechanical effect of disparity.12 Intentionally misaligning misshapen donor corneas in misshapen recipient beds produced a correspondence between the directions of deficient and excess cornea at the wound and the directions of the steep and flat corneal meridians, respectively, 9 months after transplantation.

Table

TABLE 1Means of Zeiss Videoplan® Measurements of Histopathologic Wound Features of 13 Postkeratoplasty Cat Corneas*TABLE 2Strength and Significance of Spearman Correlations Between Pairs of Histopathologic Wound Features*

TABLE 1

Means of Zeiss Videoplan® Measurements of Histopathologic Wound Features of 13 Postkeratoplasty Cat Corneas*

TABLE 2

Strength and Significance of Spearman Correlations Between Pairs of Histopathologic Wound Features*

Table

TABLE 3Strength and Significance of Spearman Correlations Between Histopathologic Wound Features*TABLE 4Confidence Intervals (95%) for the Differences Between Mean Measurements of Histopathological Wound Features*

TABLE 3

Strength and Significance of Spearman Correlations Between Histopathologic Wound Features*

TABLE 4

Confidence Intervals (95%) for the Differences Between Mean Measurements of Histopathological Wound Features*

In the current study, we attempted to determine whether wound healing at the steep and flat meridians of successful penetrating keratoplasties contributed to the directions and amount of corneal astigmatism after penetrating keratoplasty. The keratoplasty wounds were sampled at both ends of the steep and flat meridians to allow comparisons between measurements of histopathologic features of the wound and astigmatism.

We found no statistically significant differences between the wound morphometry at the steep and flat meridians. This suggests that the wound healing was similar along these meridians. However, the sizes of the 95% confidence intervals for the Wilcoxon statistic that tested the differences between samples of the wound morphometry at the steep and flat meridians (Table 4) imply that only large differences between the populations would have produced significance. It is possible that the wounds contained morphometrically disparate regions that were not selected by our analysis method or that measurement with a Méndez® degree marker and marking of the steep and flat meridians with sutures were insufficiently accurate to section the corneas along the desired regions. Although all sections from the same wound had similar bistopathology, a different histopathologic appearance of the wound at locations other than the steep and flat meridians cannot be ruled out.

We did find statistically-significant relationships between the wound morphometry and decreased PIM eccentricity, a measure of increased astigmatism. Increased epithelial thickness, increased area of stromal lamellar alteration, increased length of Descemet's membrane produced postoperatively, and increased depth that preoperative Descemet's membrane was embedded into the stroma were significantly related to astigmatism. To our knowledge, these are the first findings in any species that relate histopathologic wound morphometry to the magnitude of corneal astigmatism after penetrating keratoplasty.

Because of PIM's advantages over keratometry, PIM was used to measure corneal astigmatism and to locate the astigmatic meridians along which the wound was sectioned.12·14 Unlike the keratometer, PIM selects the steepest and flattest meridians from numerous measurement positions, and the steep and flat meridians are not necessarily orthogonal to one another. For nonfixating subjects, the ring pattern can be centered on the keratoplasty by viewing distortion of the images of the peripheral rings and documenting this distortion with a photograph (Fig 1). If PIM's identification of the steep and flat meridians had been inadequate, the amount of the measured astigmatism would be incorrect, and it is unlikely that correlations between the wound morphometiy and astigmatism would have exceeded chance.

The association between donor/recipient disparity and the directions of postkeratoplasty astigmatism is thought to be mediated by meridional distortion produced by the deficiency and excess of donor cornea available to meet at the wound which cause steep and flat meridians respectively.17 In the current study, it does not appear that localized, mechanical effects of donor/recipient disparity led to localized, measured histopathologic differences in the wound since wound morphometry was similar in sections taken along steep meridians and those taken along flat meridians. However, it is possible that disproportionate availability of tissue in wound regions could have affected healing throughout the entire wound over time.

Our findings in the cat were similar, but not identical to previously described histopathologic features in successful, human penetrating keratoplasty wounds.18-25 Only three studies contain information on more than two keratoplasties with long-term follow up.2325 In two of the three studies, the number of successful keratoplasties is unknown.23"24 In both cats and humans, preoperative Descemet's membrane was folded and extended into the stroma, and isolated pieces were embedded in the stroma.2325 One of the human studies found an overriding wound edge with incarceration of preoperative Descemet's membrane in 73.3% of the wounds.25 However, overlapping of preoperative donor and recipient Descemet's membrane, typical of an overriding wound edge, was seen in only 2 of 13 cat wounds. In the remaining cat wounds, the ends of preoperative donor and recipient Descemet's membrane were separated, and the posterior stroma was covered by Descemet's membrane produced postoperatively. Regions of thickened epithelium and thinned stroma, similar to those in our study, can be seen in the photomicrographs of the human keratoplasty wounds.23-25

Ib our knowledge, there is only one study of penetrating keratoplasty wounds in any species that related histopathologic wound morphology to the amount of corneal astigmatism after penetrating keratoplasty.25 In this study of humans, incarceration of Bowman's layer into the stroma was more frequently found in corneas with greater than 5.00 diopters of astigmatism than in corneas with less than 3.00 D of astigmatism. However, Bowman's layer is absent in cat corneas, which are also larger, flatter, and thicker than human corneas. Any relationships between donor/recipient disparity and wound healing that alter corneal curvature by affecting the entire wound may be restricted to the cat species. These factors may restrict application of our results to understanding the etiology of corneal astigmatism after penetrating keratoplasty in humans.

REFERENCES

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6. Olson RJ, Mattingly TP, Waltman SR, et al. Aphakic keratoplasty. Visual acuity and optical errors. Ophthalmology. 1980;87:680-686.

7. Troutman RC, Swinger CA, Belmont S. Selective positioning of the donor cornea in penetrating keratoplasty for keratoconus. Postoperative astigmatism. Cornea. 1984;3:135-139.

8. Cohen KL, Holman RE, Tripoli NK, et al. Effect of trephine tilt on corneal button dimensions. Am J Ophthalmol. 1986;101:722-725.

9. Kaufman HE. Astigmatism after keratoplasty - possible cause and method of prevention. Am J Ophthalmol. 1982;94:556-557.

10. Perlman EM. Analysis and interpretation of refractive errors after penetrating keratoplasty. Ophthalmology. 1981;88:39-45.

11. Troutman RC, Gaster RN. Effects of disparate-sized graft and recipient opening. Symposium on medical and surgical diseases of the cornea. In: Transactions of the New Orleans Academy of Ophthalmology. St Louis, Mo: CV Mosby; 1980:386-405.

12. Cohen KL, Tripoli NK, Pellom AC, et áL Effect of tissue fit on corneal shape after transplantation. Invest Ophthalmol Vis Sci. 1984;25:1226-1231.

13. Bahn CF, Meyer RF, MacCallum DK et al. Penetrating keratoplasty in the cat. A clinically applicable model. Ophthalmology. 1982;89:687-699.

14. Cohen KL, Tripoli NK, Pellom AC, et al. A new photogrammetric method for quantifying corneal topography. Invest Ophthalmol Vis Sci. 1984;25:323-330.

15. McDonnell PJ, Sawusch MR, Wan LW. Tissue addition accounting for corneal flattening with radial keratotomy. Invest Ophthalmol Vis Sci. 1990;31(suppl):300.

16. Jester JV, Petroli WM, Feng W, et al. In vivo modulation of corneal curvature during wound healing in radial keratotomy (RK). Invest Ophthalmol Vis Sci. 1990;31(suppl):300.

17. Troutman RC. Microsurgery of the Anterior Segment of the Eye. Volume II. The Cornea: Optics and Surgery. St Louis, Mo: CV Mosby; 1977: 23-27.

18. Filatov VP. Transplantation of the cornea. Arch Ophthalmol. 1935;13:321-347.

19. Thomas JWT. The clinical record and histology of two successful corneal grafts in man. Transactions of the Ophthalmologic Society of the United Kingdom. 1935;55:114-136.

20. Morpurgo F, Ferrata L. Histopathologic observations on keratoplasty in man. Am J Ophthalmol. 1951;34:786-787.

21. Vejdovsky PV, Mazanec K Examen histologique d'un greffon de cornée transparent après la kératoplastie. Ophthalmologica. 1955;130:344-353.

22. Henderson JW, Reimer WJ. Separation of Descemet's membrane in keratoplasty. Am J Ophthalmol. 1968;65:375-378.

23. Morrison JC, Swan KC. Bowman's layer in penetrating keratoplasties of the human eye. Arch Ophthalmol. 1982;100:1835-1838.

24. Morrison JC, Swan KC. Descemet's membrane in penetrating keratoplasties of the human eye. Arch Ophthalmol. 1983;101:1927-1929.

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TABLE 1

Means of Zeiss Videoplan® Measurements of Histopathologic Wound Features of 13 Postkeratoplasty Cat Corneas*

TABLE 2

Strength and Significance of Spearman Correlations Between Pairs of Histopathologic Wound Features*

TABLE 3

Strength and Significance of Spearman Correlations Between Histopathologic Wound Features*

TABLE 4

Confidence Intervals (95%) for the Differences Between Mean Measurements of Histopathological Wound Features*

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