Nancy K. Tripoli

Effect of Trephine Tilt on Corneal Button Dimensions

Wound disparity, mismatch between the size and shape of the donor corneal button and its wound, probably determines the direction and amount of postkeratoplasty astigmatism. Tilting a hand-held trephine is thought to contribute to an oval wound and to wound disparity. We examined the contribution of trephine tilt to wound size and shape. Eyebank eyes were hand trephined at 0, 5, 10, 15, 20, and 25 degrees of tilt. The button endothelial edges were analyzed by the photogrammetric index method. All index values were significantly different from those for a theoretically circular or symmetric button. Although the most oval buttons were at 20 and 25 degrees, buttons were similarly oval and asymmetric for trephine tilt from 0 to 15 degrees. Neither ovality nor asymmetry correlated with angle of tilt. Even when no attempt is made to tilt a hand-held trephine, oval and irregularly shaped wounds may result.

Automatic quantitative measurement of ocular hyperemia

Evaluation of ocular hyperemia has been an important assessment in research studies of effects of contact lenses, medications, and pollutants on the eye. Hyperemia has been difficult to quantitate objectively. The purpose of this study was to validate a computer based image analysis system to quantitate hyperemia automatically and objectively in pixelated images of the external eye using two measures, the percent of the red color, RR, and the fraction of pixels which are blood vessels, VA. Validation was against an established photographic reference scale of ocular hyperemia and against the clinical pharmacologic effects of 0.5% dapiprazole hydrochloride, known to increase hyperemia, and 2.5% phenylephrine hydrochloride, known to decrease hyperemia. Color transparencies from the reference scale were converted to digital images. Temporal and nasal regions of the external eye were imaged directly to magnetic disk before and after pharmacologic intervention. Custom software automatically excluded unwanted regions, and quantitative image analysis produced RR and VA. RR and VA were each correlated with the reference scale. For each region and for each pharmacologic intervention, the mean RR and the mean VA, respectively, were compared at time zero and at a mean elapsed time of 713 +/- 47 s. RR and VA consistently increased as the hyperemia in the reference scale increased. Pearson correlation coefficients were 0.98 and 0.99, respectively, (p < 0.01). At 713 +/- 47 s after each pharmacologic intervention, RR and VA increased and decreased as expected (p < 0.001). Thus, this study successfully validated the methodology against expert clinical judgment and was able to measure automatically and objectively clinical changes in ocular hyperemia.

Prospective Analysis of Photokeratoscopy for Arcuate Keratotomy to Reduce Postkeratoplasty Astigmatism

Seven eyes of seven patients with visually disabling postkeratoplasty astigmatism underwent arcuate keratotomy to reduce astigmatism. Keratotomy length was prospectively determined by comparing the corneal shape change needed by each patient with shape changes in cadaver eyes induced by arcuate keratotomy. Keratograph ring ovality quantified corneal shape change. Keratotomies were placed in the wound interface using a diamond knife with blade length set to 100% of corneal thickness. Prekeratotomy keratometric astigmatism was 9.27 +/- 2.14 D (mean +/- SD), and at 2.0 to 18.4 months after keratotomy, astigmatism was 2.75 +/- 2.25 D (mean +/- SD). All corneas had decreased keratometric astigmatism and less oval keratoscope rings. Five corneas had 3.00 D or less residual keratometric astigmatism. Change in ring ovality was significantly correlated with keratotomy length and keratometric astigmatism change. The utility of keratoscope ring ovality as a corneal topography metric was demonstrated by systematically investigating the response to arcuate keratotomy.

Cat Keratoplasty Wound Healing and Corneal Astigmatism

BACKGROUND A major contributor to postkeratoplasty astigmatism may be donor/recipient disparity. Deficient or excess cornea 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 Descemets membrane was embedded in the stroma were correlated with eccentricity (corneal astigmatism). Stromal thickness and the presence or absence of folded and fragmented Descemets 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 Bowmans layer in cats restricts application of our results to understanding the etiology of corneal astigmatism after penetrating keratoplasty in humans.

Corneal topography after cataract surgery using a clear corneal incision closed with one radial suture

BACKGROUND AND OBJECTIVE To determine whether corneal topography and visual recovery are affected by suturing a temporal, clear corneal incision for cataract surgery. PATIENTS AND METHODS Forty-one consecutive phacoemulsification patients (39 eyes) had a 3.2-mm incision sutured with one 10-0 nylon, radial suture removed after 1 postoperative week. Visual acuity (VA) and corneal topography, including best fit sphere (BFS), best fit cylinder (BFC), principle meridian, topographic irregularity (TI), and vector-corrected astigmatism (VCA), were measured preoperatively and 1 day, 1 week, and 1 month postoperatively. Two-tailed t tests and Pearson correlations were calculated. RESULTS From the preoperative measurement to 1 week postoperatively, VA improved, BFS (P = .005) and TI (P = .033) increased, and VCA shifted with-the-rule. From 1 week to 1 month postoperatively, BFS (P = .012) and TI (P = .002) decreased. BFC and its direction did not change. Almost all measures were significantly correlated. CONCLUSION The benefits of sutureless surgery on corneal topography and visual recovery are not degraded by using a suture to prevent wound leakage.

Cat endothelial morphology after corneal transplant

The cat has been suggested as a superior model to evaluate penetrating keratoplasty and corneal endothelial damage and repair. Morphologic change is felt to be a sensitive indicator of endothelial stress response. We documented corneal thickness and endothelial morphometric parameters of eight cats before and after homograft penetrating keratoplasty using an Eisner contact glass. One-hundred-cell samples from preoperative and 6.18 +/- 0.57 weeks and 9.25 +/- 0.84 months (means +/- standard errors of the means) postoperative photomicrographs were computer analyzed. Cell density (cells/mm2), coefficient of variation of cell area, percent hexagonal cells, and mean figure coefficient were measured. Values are given as means +/- standard errors of the means. Preoperative coefficient of variation for area, 19.1 +/- 0.4, was significantly greater (22.0 +/- 1.0) six weeks after surgery. At nine months, cell density (1487 +/- 114) and percent hexagonal cells (59.6 +/- 2.1) were significantly less than six week values (cell density = 2053 +/- 201, percent hexagonal cells = 68.1 +/- 1.5) and preoperative values (cell density = 2395 +/- 94, percent hexagonal cells = 69.3 +/- 1.1). Thus there is evidence of polymegethism six weeks after surgery and persistent decreased cell density and pleomorphism nine months after surgery.

Necessity of the Honan intraocular pressure reducer in cataract surgery using topical anesthesia

PURPOSE To assess the use of the Honan intraocular pressure reducer (HIPR) for clear corneal cataract surgery using topical anesthesia. SETTING University of North Carolina Hospitals Ambulatory Care Clinic outpatient operating rooms. METHODS Of 51 consecutive candidates for surgery (excluding those with uncontrolled glaucoma), 26 were randomly assigned to wear the HIPR (Honan group) for 10 minutes before surgery. The remainder were placed in a control group. Intraocular pressure (IOP) was measured before (T1) and after (T2) HIPR application and after patient preparation for surgery (T3). RESULTS Mean IOP was the same in the Honan and control groups at T1 and T3. At T2, the groups had a significantly different mean IOP (P = 1.8 x 10(-5)). In the Honan group, mean IOP decreased significantly (P = 2.8 x 10(-7)) between T1 and T2, and there was a significant correlation among patients at T1 and T2 (P < .0005). Between T2 and T3, the Honan group experienced a significant recovery (P = 3.5 x 10(-9)); there was a significant correlation between the decreases from T1 to T2 and the increases from T2 to T3 (P < .0005). Mean IOP in the control group did not change between T1 and T2 but increased significantly between T2 and T3 (P = .004). CONCLUSION When using topical anesthesia, the HIPR transiently reduced IOP. However, the IOP-reducing effect resolved by the time of surgery, negating any reason to use the HIPR with topical anesthesia for cataract surgery.

Photogrammetric Index Method (PIM) System of Astigmatism Analysis and Its Use in Surgery for Astigmatism

Keratorefractive surgical practice has led to a need for corneal measurement that can evaluate surgical techniques. Surgical results have been quantitated by refraction, a measure of the net diopter power of the eye, and keratometry, which estimates corneal curvature in an annular region approximately 3 mm from an undefined corneal center. Keratometry fits the complex curvature of the cornea to a spherocylindrical model and does not respect irregular astigmatism.