Differential swelling in compartments of the corneal stroma

When a hypotonic solution is applied to the corneal surface the stroma swells. This well-known osmotic response masks a surprising hydration change in the posterior stroma. This was studied by measuring thickness changes in the anterior, middle, and posterior stroma of the rabbit cornea. Measurements were made continuously for 1 hour following osmotic perturbation of the epithelial surface. The data revealed that following a hypotonic shift on the epithelial surface, the posterior stroma thinned briefly. This unexpected effect is predicted satisfactorily by Klyce and Russell's mathematical model. The method of measuring fluid flow between stromal compartments will allow further development of the model in describing the dynamics of stromal hydration.     

Effects of solutes on the swelling pressure of the corneal stroma.

The chemical environment of bare, excised rabbit corneal stroma was varied to determine the effects of solutes on the swelling pressure. Measurements of changes in the thickness of the stroma are converted to hydration units which are in turn converted to a change in swelling pressure at the initial hydration. The order of effects on swelling pressure are compared to the Hofmeister series for polyelectrolyte gels and the results are analyzed in the context of a structural theory of the swelling pressure of corneal stroma proposed by Hart and Farrell and based on the gel properties of the stroma.     

Circinate corneal scarring

A 56year‐old man presented with symptoms of monocular diplopia and reduced vision in his left eye. Visual acuities were R6/6, L6/12. At his previous visit left visual acuity was 6/6. An irregular area of anterior corneal stromal scarring was evident, encroaching on the visual axis of the left eye. Rigid lens fitting improved left visual acuity to 6/6, however, lens wear caused a corneal abrasion over the lesion after one to two hours of wear. Several other contact lens and surgical strategies were employed to successfully address the visual requirements of the patient.     

Deep corneal scarring in pellucid marginal corneal degeneration.

Crescent-shaped, deep corneal scars were observed in seven (39%) of 18 patients with pellucid marginal corneal degeneration. The scars most likely represent a degenerative change related to the precipitous alteration in curvature of the cornea in that area.     

Diffusion of fluorescein in the corneal stroma

Movement of fluorescein in the eye was simulated on the basis of a multiple-compartment model, in which the cornea was divided into a series of cylindrical sleeves to allow 3-dimensional diffusion of fluorescein with rapid exchange at the limbus. If the dye was administered into the central 5 mm of the cornea, the loss at the limbus was found to be negligible in the early period but it became considerable later. The effect of fluorescein exchange at the limbus on the calculations of the dye transfer coefficients was estimated. Systematic errors in the fluorophotometric measurement of aqueous humor flow are discussed.Supported by NIH Grant EYOO634 and the Mayo FoundationResearch to Prevent Blindness International Research Scholar     

Improvement in corneal scarring following bacterial keratitis

Aim

Bacterial keratitis results in corneal scarring and subsequent visual impairment. The long-term evolution of corneal scars has not been well described. In this case series, we identified patients who had improvement in corneal scarring and visual acuity from a clinical trial for bacterial keratitis.

Methods

We searched the records of the Steroids for Corneal Ulcers Trial (SCUT) for patients who had improvement in vision between the 3-month and 12-month visits and reviewed their clinical photographs.

Results

Of the 500 patients enrolled in SCUT, five patients with large central corneal scars due to bacterial keratitis are presented. All experienced improvement in rigid contact lens–corrected visual acuity from months 3 to 12. All patients also had marked improvement in corneal opacity during the same time period. None of the patients opted to have penetrating keratoplasty.

Conclusions

Corneal scars may continue to improve even many months after a bacterial corneal ulcer has healed. The corneal remodeling can be accompanied by considerable improvement in visual acuity, such that corneal transplantation may not be necessary.     

The organization of collagen in the corneal stroma

The cornea has evolved to fulfil the dual functions of enclosing and protecting the inner contents of the eye, and focussing light onto the retina with minimum scatter and optical degradation. It does this by means of the arrangement of the constituent collagen fibrils, an arrangement that is unique in connective tissues. This article reviews our current knowledge about the detailed organization of collagen in the corneal stroma, and presents new data suggesting that a significant proportion of collagen fibrils running across the cornea, change direction near the limbus and fuse with the circumferential limbal collagen.     

Penetrating keratoplasty for trachomatous corneal scarring

PURPOSE: To evaluate graft survival and visual outcome after penetrating keratoplasty (PKP) for trachomatous corneal scarring. METHODS: A retrospective review was conducted on all cases of PKP performed at King Khaled Eye Specialist Hospital between January 1, 1997, and December 31, 2001, for trachomatous corneal scarring. RESULTS: This study included 127 eyes. The mean age at the time of surgery was 64.7 years (range, 40-90 years). The mean follow-up was 1266 days (range, 91-3423 days). At the most recent visit, 102 (80.2%) grafts were clear, and 25 (19.7%) had failed. Kaplan-Meier graft survival was 98.3% at 1 year, 85.9% at 2 years, 83.2% at 3 years, 80.2% at 4 years, and 76.6% at 5 years. Major postoperative complications included worsening of glaucoma (27.6%), endothelial rejection (17.3%), and bacterial keratitis (8.7%). Visual acuity improved in 107 (84.3%) eyes, remained the same in 12 (9.5%) eyes, and worsened in 8 (6.3%) eyes. Final visual acuity of 20/160 or better was obtained in 67 (56.7%) eyes. CONCLUSIONS: Treating trachomatous corneal scarring with PKP can be associated with a good prognosis for graft survival and improved vision in carefully selected cases with mild or well-controlled ocular surface disease and absent or previously surgically corrected eyelid abnormalities.