Refractive results of successful penetrating keratoplasty, intraocular lens implantation with selective suture removal

The refractive outcome in 44 eyes that had combined penetrating keratoplasty and intraocular lens insertion, with at least 6 months follow-up, was analyzed. All patients were operated on by the same surgeon using two types of trephines in all but one eye, and one suturing technique with nylon or dacron sutures. The intraocular lens power was calculated using SRK II formula with an assumed average post-operative keratometry of 45 D. The first refraction showed that the mean spherical equivalent was -0.20 +/- 3.45 D, the mean refractive astigmatism was 5.11 +/- 2.48 D and the average keratometry had a mean of 44.42 +/- 3.19 D. Modulation of postoperative astigmatism was done by selective removal of tight interrupted sutures, taking out one suture or maximally two sutures per visit, based on refraction, keratometry, and keratography criteria. The total number of sutures removed had a mean of 2.5 +/- 2.2 with a mean total number of visits of 5.3 +/- 2.0. The interval between visits had a mean of 4.5 +/- 1.9 weeks and the total duration of the suture removal phase was about six months. At the end of the refractive rehabilitation period, 73% of cases had a spherical equivalent between +3.0 D and -3.0 D and 61% of cases had an average keratometry within 2.5 D from our assumed value of 45 D. The mean postoperative refractive astigmatism was 2.5 +/- 1.5; 55% of cases had 3.0 D or less of astigmatic error and 90% of cases were within 4.0 D of postoperative astigmatism.

Scanning slit delivery system

We describe the structure and function of a delivery system designed for use with an argon fluoride excimer laser for corneal surgery. The basic principle of the delivery system is to shape the laser beam with a slit mask to a defined configuration. The image of the slit is moved across the cornea in a mathematically defined pattern to ablate a given amount of tissue, creating a new anterior radius of curvature for the cornea. The location of the beam on the cornea is determined by a rotating dove prism and a translating spherical lens, each of which is controlled by computer-regulated servomotors. The system is versatile and can be used for laser myopic or hyperopic keratomileusis, for correction of astigmatism by surface ablation, for creation of radial or transverse linear cuts, for excision of corneal buttons, and for uniform lamellar corneal smoothing procedures. The delivery system is currently used in the laboratory for the ablation of nonhuman primate corneas.

Corneal stromal wound healing in rabbits after 193-nm excimer laser surface ablation

An argon fluoride excimer laser (193 nm) with a moving slit delivery system was used to perform anterior myopic keratomileusis in both eyes of 24 New Zealand white rabbits. Rabbits were killed immediately after ablation and at intervals up to 100 days. By slit-lamp microscopy, four rabbits at day 100 exhibited four clear corneas and four corneas had central, spotty, subepithelial haze. Light and electron microscopy documented corneal healing. In the early stages a transient acellular zone in the anterior stroma appeared over a period of three weeks, followed by an increased number of fibrocytes. In the corneas with opacification, focal areas of 20-microns-thick subepithelial scarring were present. An unexpected finding was transient damage to posterior stromal keratocytes and endothelial cells. The endothelium produced a layer of granular material that migrated anteriorly across Descemet's membrane. Immunochemistry at day 6 showed a marked staining for collagen IV, proteoglycans, fibronectin, and laminin.

Preliminary computer simulation of the effects of radial keratotomy

We created a computerized mathematical model of the eye for the simulation of refractive surgery. This model used a slightly prolate shape for a moderately myopic eye and an idealized aspheric profile for the cornea. The finite element method and the nonlinear Mooney-Rivelin law were used to analyze stress-strain relationships. Radial keratotomy changes stress distribution in the cornea and the anterior sclera, with major changes at the paracentral and peripheral ends of the incisions. The model predicted that there would be a flattening of the central cornea with a posterior displacement, which increased with an increase in intraocular pressure. A change in the length of the incision of 0.5 mm produced a significant change in correction. For small clear zones (3 to 4 mm), incisions of equal length produced comparable changes in refraction. We found that the effect of the corneal radius of curvature on the amount of refractive change was negligible. We studied the effect of elasticity coefficients and corneal anisotropia.

Computer simulation of arcuate and radial incisions involving the corneoscleral limbus

We have created a computer model of the eye that improves upon previous models with two assumptions: (1) the cornea is considered anisotropic, and (2) the strain tensor is non-linear for large displacements. Values used include those for Young's modulus, Poisson's ratio, and three coefficients of anisotropia. A finite element computer program was used to stimulate the behaviour of the eye. Four simulations were done: (1) a full thickness arcuate limbal cataract incision, (2) a partial thickness arcuate corneal relaxing incision, (3) a partial thickness radial incision extending across the limbus, (4) a partial thickness radial incision confined to the cornea. A full thickness corneal arcuate incision for cataract induced more change in corneal shape than a limbal incision. However, the gaping is more important in the limbal incision. Partial thickness arcuate corneal relaxing incisions were found to be more effective with a clear zone 3-5 mm in diameter. Radial incision simulation demonstrated little enhancement of the effect of the incisions when across the limbus.

Symmetry of refractive and visual acuity outcome in the Prospective Evaluation of Radial Keratotomy (PERK) study

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.

Development of a system for excimer laser corneal surgery

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Effect of excimer laser radiant exposure on uniformity of ablated corneal surface

The argon fluoride (193 nm) excimer laser is being used to change the anterior corneal curvature for correction of refractive errors. Uniformity of the surface following laser ablation may play an important role in the rate of epithelial healing and amount and type of stromal scarring. To test the effect of radiant exposure (fluence) on surface smoothness, we ablated rabbit corneas with the 193 nm argon fluoride excimer laser at nine radiant exposures from 50 to 850 mJ/cm2. A total energy of 100 J/cm2 was used for each ablation at a frequency of 1 Hz. Scanning electron microscopy demonstrated progressive improvement of surface smoothness with increasing radiant exposures. Transmission electron microscopy demonstrated no consistent increase in thickness to the surface condensate (pseudomembrane) with increasing radiant exposure. Improvement in surface quality associated with increasing radiant exposures may result from a more uniform depth of ablation per pulse in the corneal lamellae that absorb laser wavelengths differently. Radiant exposures at levels where the depth of ablation is the same regardless of increasing energy densities achieve a more uniform surface because inhomogeneities in the beam and variation in energy from pulse to pulse do not affect the ablation rate.

The effect of selective suture removal on astigmatism following penetrating keratoplasty

We retrospectively evaluated selective removal of interrupted nylon sutures to reduce astigmatism following penetrating keratoplasty in 68 eyes with eight or 12 interrupted sutures and one running suture. Following removal of one to four interrupted sutures at one visit (N = 234 visits), corneal astigmatism had changed 2 to 3 diopters (range 0 to 12 D) by the next visit. The astigmatism decreased greater than or equal to 1 D in 54%, changed 0 to .87 D in 28%, and increased greater than or equal to 1 D in 18%. When a total of five or six sutures were removed during the 5 months following surgery, less than 3 D of residual astigmatism was present in 50 eyes (74%). The axis of astigmatism changed less than or equal to 40 degrees in 74% (n = 65). In a second group of 20 eyes with double running sutures, removal of the 10-0 running suture in all 20 eyes produced an average change of 1.8 D (range = 0 to 3.75 D), with an equal number of increases and decreases. Vector analysis showed the total induced change in astigmatism was approximately twice the absolute keratometric change.

Histopathology of traumatic corneal rupture after radial keratotomy

Two patients (three eyes) had previously undergone technically successful radial keratotomy procedures and subsequently sustained blunt injury to the eyes in motor vehicle accidents one and two years after surgery, respectively, with rupture of the cornea along the keratotomy scars. One case subsequently required penetrating keratoplasty to recover 20/50 visual acuity. The second patient died, but had he survived, the extensive ocular injuries would have required significant surgical and medical care to restore vision. Histologic and ultrastructural studies demonstrated incomplete wound healing in the three corneas. Individuals who have had radial keratotomy, like those who have had penetrating keratoplasty, are at increased risk of corneal rupture after direct ocular trauma.

Morning-to-evening change in refraction, corneal curvature, and visual acuity 2 to 4 years after radial keratotomy in the PERK Study

The authors previously reported morning-to-evening changes in ophthalmic measurements at 3 months and at 1-year after radial keratotomy in a self-selected group of patients in the Prospective Evaluation of Radial Keratotomy (PERK) study. Fifty-two patients included in the earlier study were examined again between 2 1/2 and 4 years after surgery before 10:00 AM and after 5:30 PM on the same day to determine if the changes persisted beyond 1 year after surgery. Between the morning and evening examinations, 31% of the eyes had an increase in minus spherical equivalent power of the manifest refraction of 0.50 to 1.50 diopters; 12% had a change in cylinder power of 0.50 to 1.00 D; 19% had a decrease in uncorrected visual acuity of two to five Snellen lines; and 29% showed central corneal steepening by 0.50 to 1.00 D. Thus, in some patients, morning-to-evening fluctuation persisted until 2 1/2 to 4 years after radial keratotomy.

Late bacterial and fungal keratitis after corneal transplantation. Spectrum of pathogens, graft survival, and visual prognosis

The authors reviewed 108 bacterial and fungal corneal ulcers that developed 1 to 72 months after penetrating keratoplasty in 79 eyes of 78 patients. Graft hypesthesia, topical corticosteroid and antibiotic treatment, exposed sutures, epithelial defects, and poor visual acuity commonly predated infectious keratitis. There were 69 bacterial, 34 fungal, and 5 combined infections. Candida albicans and Staphylococcus epidermidis were the most common pathogens. Follow-up after infection averaged 23 months (range, 1-80 months). Despite hospitalization and fortified topical antibiotic treatment, complications such as wound dehiscence and corneal perforation necessitated emergency regraft in 38 (35%) cases. Of 73 previously clear grafts, only 29 (40%) retained clarity. Median visual acuity, 20/200 before infection, fell to counting fingers at last follow-up; 12 eyes lost light perception.

Configuration of corneal trephine opening using five different trephines in human donor eyes

In this laboratory study, we used five different corneal trephines on 60 fresh human donor eyes with controlled intraocular pressure to study the variation in the size and shape of the trephine openings. With all trephines, the average diameter of the button was larger than the diameter of the trephine at the epithelial side (mean difference, 0.21 mm; range, 0.06 to 0.35 mm) and the endothelial side (mean difference, 0.42 mm; range, 0.13 to 0.79 mm), presumably because the corneal tissue protruded into the trephine during cutting. The trephines that produced the most uniform opening were a nondisposable suction trephine and a freestanding disposable blade, but they caused some undercutting.

Results of anterior segment reconstruction for aphakic and pseudophakic corneal edema

The authors studied prospectively 59 eyes with corneal edema after cataract surgery that required reconstructive surgery; penetrating keratoplasty in 59 (100%), anterior vitrectomy in 42 (71%), intraocular lens removal or exchange in 33 (56%), gonioplasty in 32 (54%), and iridoplasty in 30 (51%). With an average follow-up of 9.9 months, the corneal transplant was clear in 56 eyes (95%). The corrected visual acuity was improved in 49 eyes (83%) and was the same in seven eyes (12%). Intraocular pressure was less than or equal to 21 mmHg in 47 eyes (80%) and 22 to 29 mmHg in nine eyes (15%). The peripheral anterior synechiae score was the same or improved in 56 eyes (95%). Cystoid macular edema was absent to mild in 52 eyes (88%). Anterior segment reconstruction improved both anatomic integrity and visual acuity of most eyes without increasing complications.

Effect of diameter and depth on the response to solid polysulfone intracorneal lenses in cats

Impermeable, solid polysulfone intracorneal lenses (ICLs) can change corneal refractive power but will not allow diffusion of nutrients from the aqueous to the anterior stroma. Lenses of 4, 5, 6, and 7 mm in diameter were implanted in 50 cat eyes at depths ranging from 45% to 95% of corneal thickness to determine the effect of depth and diameter. Two types of stromal opacities occurred during follow-up: peripheral amorphous opacity (100%) and crystalline-granular lipid central opacity (79%). No eyes implanted with a 4-mm ICL ulcerated, but ulceration occurred in 28% of the eyes overall. Because opacification occurred with all lens diameters and implantation depths, metabolic demands of the cornea are not met. No safe limit exists at which these ICLs can be predictably used in cat eyes.

Effect of donor epithelium on corneal transplant survival

Two hundred thirty-two penetrating keratoplasties in 228 eyes were performed with or without the removal of donor corneal epithelium in a prospective, randomized clinical trial to determine the effect of epithelial removal on graft survival. The removal of epithelium did not reduce the likelihood of graft failure, irreversible allograft reaction, or reversible allograft reaction.

Ultrastructural analyses of enzyme-treated microfibrils in rabbit corneal stroma

Microfibrils have been identified within and between corneal collagen lamellae in a number of vertebrate species in a variety of developmental and pathological conditions, but they are relatively rare in normal adult animals. The present study was undertaken to analyze corneal microfibrils in adult rabbits using enzymatic digestion techniques. Transmission electron microscopy (TEM) showed clusters of 10-15 nm microfibrils arranged in quasi-parallel bundles within or between orthogonally arranged stromal collagen lamellae. When corneas were fixed with tannic acid/glutaraldehyde, the entire stroma showed increased electron density and microfibrillar bundles were heterogeneously stained. Peripheral fibrils were more electron-dense than those located more centrally. Following sequential detergent solubilization of unfixed corneas, all cellular elements were removed and collagen lamellae were distorted. Microfibrillar bundles remained intact, however, and resembled untreated controls. Subsequent treatment with pepsin, trypsin or elastase resulted in swollen corneal tissues in which collagen lamellae were no longer distinguishable but individual collagen fibrils maintained their morphological integrity. In these tissues microfibrillar bundles were rarely identifiable and were reduced to randomly oriented fragments or clusters of filamentous material. Testicular hyaluronidase or chondroitinase ABC did not affect the fibrils. These data indicate that rabbit corneal microfibrils are proteinaceous and that the tannic acid-staining component of the bundles is not glycosaminoglycan. The fibrils are indistinguishable from those identified as oxytalan in cornea and other ocular tissues. Moreover, their sensitivity to elastase and preferential staining with tannic acid/glutaraldehyde strongly suggest they may be related to the elastic system of fibrils.

Prospective evaluation of radial keratotomy. Photokeratoscope corneal topography

Preoperative and postoperative corneascope photographs of 368 myopic patients undergoing radial keratotomy in the Prospective Evaluation of Radial Keratotomy (PERK) study were optically scanned and digitized. A high-resolution scanning system was developed in order to quantify the preoperative and postoperative corneal shape accurately. Careful analysis of the 72 data points in the nine representative rings demonstrated that corneal topography is best represented by radius of curvature from the center to the periphery. The normal myopic cornea flattens approximately +0.28 mm from the center to the periphery, demonstrating the cornea's aspheric nature. More highly myopic patients in the PERK population (-4.50 to -8.00 diopters [D]) demonstrated corneas that are 0.08 to 0.10 mm steeper than the less myopic population (-2.00 to -3.12 D). Optical zone, patient age, and gender are all correlated to changes in corneal topography after radial keratotomy. In more myopic populations, men have corneas which are flatter than those of women by 0.09 to 0.11 mm in all rings represented on corneoscopy. Highly myopic males also experience more corneal flattening after 3.0-mm optical zone radial keratotomy. Regardless of the optical zone used in radial keratotomy, the resulting corneal topography flattens in all rings. However, the ratio of millimeters of radius of curvature change to diopters of correction is consistent for each ring. The dioptric change observed after radial keratotomy corresponds closely with the millimeters of flattening at the respective rings being examined. The central rings flatten 0.166-mm radius of curvature per diopter of refractive alteration obtained. The largest degree of corneal flattening occurs centrally, 0.72 mm, in the more highly myopic patients who underwent 3-mm optical zone radial keratotomy. The use of smaller optical zones in radial keratotomy produces larger changes in the radius of curvature and, consequently, in the amount of refraction than when larger optical zones are used. When compared with younger patients, older patients with 3.0, 3.5, and 4.0 optical zone radial keratotomies experience more central and peripheral corneal flattening. This study of the corneal topography of the myopic population demonstrates that the refractive change resulting from radial keratotomy is related to alterations in corneal topography. The use of similar modifications of the corneal surface may be effective for newer refractive surgical procedures.

Laser trabeculoplasty for glaucoma in aphakic and pseudophakic eyes after penetrating keratoplasty

We used argon laser trabeculoplasty to treat medically uncontrolled glaucoma after penetrating keratoplasty in ten eyes that were aphakic or pseudophakic. These patients were examined over an average of 22.8 months (range, 12 to 37 months) after treatment. We found an average decrease in intraocular pressure of 9.1 mm Hg (range, +8 to -19), from an average of 30.6 mm Hg before treatment to an average of 21.5 mm Hg after treatment. Eight of ten eyes had a reduction of greater than 5 mm Hg, and six of ten eyes had intraocular pressure of less than 20 mm Hg. Visual function remained stable, and complications were rare. We now prefer argon laser trabeculoplasty to cyclocryotherapy for the initial treatment of patients with medically uncontrolled glaucoma who have predominantly open angles and a clear penetrating keratoplasty.