Superior Cornea Research Articles

Viscosity-dependent fluid dynamics of eyedrops on the ocular surface

To determine whether the viscosity of eyedrops affects the distribution of the precorneal tear film. Using a differential pachymetry map, we obtained tear film thickness in healthy volunteers before and after the instillation of nonviscous, aqueous artificial tears and a 0.3% sodium hyaluronate solution. The instillation of aqueous artificial tears disclosed a significant (P < .05) thickening of the superior corneal tear film compared with the inferior corneal tear film. The increase in thickness by 0.3% sodium hyaluronate solution was uniform, with no differences between the superior and inferior cornea. Aqueous artificial tears caused an uneven thickening of the precorneal tear film, with most of the thickening observed at the superior cornea. Lower sections of the cornea may benefit less from the instillation of nonviscous solutions.

Pellucid Marginal Degeneration with Superior Corneal Thinning

Pellucid marginal degeneration is a noninflammatory thinning disorder typically involving the inferior cornea. We describe a patient with superior corneal thinning similar to classic pellucid marginal degeneration. An 80-year-old man was evaluated for high astigmatism. The right superior cornea had a prominent band of thinning with ectasia. Both inferior corneas had characteristic zones of thinning without inflammation. Superior pellucid marginal corneal degeneration should be considered in the differential diagnosis of superior corneal ectatic disorders.

Clinical and specular micrographic findings in corneal guttata and Fuchs' corneal endothelial dystrophy

Focal excrescenses of altered basement membrane material, known as corneal guttata, are a common occurrence in the elderly. A small proportion of those who develop this condition exhibit signs of corneal endothelial dysfunction and progress to Fuchs' corneal endothelial dystrophy. The relationship between the distribution and relative density of guttata and the morphological appearance of the corneal endothelium is as yet poorly understood.In this study, 40 eyes of 20 caucasian patients (5 male and 15 female) identified as having central corneal endothelial guttata were examined (mean age 76 years). Ten eyes noted as having a previous history of ocular trauma, surgery or anterior segment inflammation were excluded from the study. Clinical and specular micrographic findings are compared.Clinical examination confirmed that guttata were most densely distributed in the central cornea. Examination of all four mid‐peripheral quadrants identified the superior cornea as being least severely affected in the majority of cases. In 26 of the 30 eyes examined there was evidence of pigmentary dusting of the corneal endothelium. The severity of guttata did not appear to correlate with the density or distribution of the pigment. In cases of moderate to advanced disease, where guttata had become confluent and thus obscured the view of the corneal endothelium, the clinical differentiation of pigment, guttata and diffuse scarring became difficult. Specular microscopy confirmed the accuracy of the clinical five‐point scale used to quantify the distribution and density of guttata in the study. Quantitative analysis of corneal endothelial cells from the mid‐peripheral cornea indicated that the severity of guttata did not necessarily correlate with a reduced cell count. Central cell counts proved elusive as reflections from the irregular surface created by confluent guttata failed to produce specular images of the underlying endothelium.The authors conclude that the specular microscope is a useful diagnostic tool in the differentiation of guttata from other abnormalities of the endothelium and Descemet's membrane. Specular micrographic imaging also enables the examiner to quantify the distribution and density of guttata. The relationship between the severity of corneal guttata, endothelial cell counts and pigmentation is not well defined and further study of the progression of the disease process is required.

The Effect of Poor Fixation on Computer-assisted Topographic Corneal Analysis: Pseudokeratoconus

The effect of changing the alignment of the corneal surface in relation to the plane of the videokeratoscope mires in computer-assisted topographic corneal analysis was evaluated. The corneas of five subjects were analyzed with the visual axis at 0 degrees, 2.5 degrees, 5 degrees, and 10 degrees below the central axis of the videokeratoscope. The relative steepness of the inferior and superior cornea was compared using inferior-superior (I-S) values at each deviation from the central axis. A similar analysis was performed on three aspheric test surfaces with different central curvatures. The difference in the relative steepness of the inferior and superior cornea was found to increase in proportion to the deviation from alignment with the central axis in both the test subjects and the aspheric test surfaces. This change in relative steepness produces a pattern that mimics keratoconus and can be seen at deviations of less than 5 degrees in some patients. The increase in the I-S value was significant at 5 degrees of deviation (P < 0.05). It also was found that this effect increased as the central curvature of the aspheric surfaces increased.

A hypothesis for the aetiology of soft contact lens-induced superior arcuate keratopathy

This paper presents a hypothesis to explain the aetiology of the common complication of soft contact lens wear; superior arcuate keratopathy (SEAL, SLAK, epithelial splitting). We suggest mechanical trauma resulting from inadequate lens flexure as the prime cause of this complication. Where lenses are not flexible enough to align with the contours of the cornea and sclera, lenses are forced to adopt a compromise shape that does not perfectly align the eye. The point of greatest misalignment is located in the superior peripheral cornea where pressure from the lid forces the lens against the cornea and results in mechanical irritation. We provide photographic evidence in support of this hypothesis and suggest ways of refitting to overcome the problem.

Topographical corneal edema. An update.

Measurement of the topographical corneal edema response has been previously restricted by the use of optical pachometry and small sample sizes. This study uses ultrasound pachometry to measure changes in the corneal thickness of 23 subjects at 9 locations during 2 hours' wear of a thick soft contact lens. The data are analysed using both averaged and individual location data. The averaged location analysis supports the current paradigm that less edema occurs in the peripheral cornea than in the central cornea during contact lens wear. However, the individual location analysis reveals a more complex corneal edema response in which the greatest amount of edema following 2 hours' contact lens wear occurred in the central and mid-peripheral temporal cornea, in comparison with the peripheral nasal and peripheral inferior cornea which showed the least edema. The edema measured in the peripheral temporal and peripheral superior cornea following 2 hours' contact lens wear was not significantly different from that measured in the central cornea. The edema measured in the central cornea following 2 hours' contact lens wear was not significantly different from that found at any mid-peripheral location. This study demonstrates that the corneal edema response associated with 2 hours' wear of a thick soft contact lens is a complex dynamic topographical process and cannot be simply modelled using averaged data from small samples.

Intrinsic Stability of 'Self-Sealing' Unsutured Cataract Wounds

Many operative and postoperative factors can influence cataract wound stability and postoperative astigmatism. The final outcome is fundamentally dependent on the intrinsic biomechanical stability of the corneal dome in the presence of the wound. We determined the stability of the central and peripheral cornea with computer-assisted topographic analysis of six freshly enucleated human globes. Self-sealing, unsutured, scleral tunnel wounds 4.0 mm in length were dissected, with widths varying from 1.4 to 6.0 mm. Intraocular pressure was elevated in 5-mm increments from 15 to 40 mm Hg without measurable topographic change in the visual axis or superior cornea. We conclude that these long scleral tunnel wounds do not necessarily destabilize the cornea within the usual range of intraocular pressure. Postoperative-induced astigmatism is therefore due to other operative and postoperative factors. Some of these factors may be identifiable with this model and controlled or eliminated.

Morphology and movement of corneal surface cells in humans.

We examined the morphology of the corneal surface epithelial cells in 13 eyes of 13 subjects using specular microscopy. We determined cell area, perimeter, and shape comparing the central cornea with the inferior and superior periphery. We found surface epithelial cells are significantly smaller in the central cornea. The cells measured 560 +/- 93 square microns in the central cornea, 850 +/- 135 square microns in the superior cornea and 777 +/- 176 square microns in the inferior cornea (p less than .005). Newly emerged surface cells are smaller and are thought to enlarge with time. We postulate that lid shearing forces are greater in the central cornea and contribute to epithelial cell exfoliation. We further postulate that preferential shearing of central corneal surface cells is an important factor driving the centripetal movement of corneal epithelial cells.

The Response of the Corneal Endothelium to Intraocular Surgery

The corneal endothelium is affected by age, disease, and intraocular surgery. With age, the endothelial cell density decreases linearly, the hexagonal pattern is less common, and there is an increased variation in cell size and shape. There are primary and secondary endotheliopathies in elderly patients which further compromise the endothelial reserve. Intraocular surgery causes cell loss in the superior cornea which requires a transformation and migration of endothelial cells from the central and inferior cornea. Although a stable endothelial mosaic is reestablished in most corneas, some maintain a bizarre endothelial appearance which is correlated with continued cell loss. Intraocular surgery causes an acute cell loss as well as a chronic cell loss which is greater than the normal attrition due to aging. There are many variables in predicting future corneal edema; longitudinal observation of endothelial cell loss may be the best prognosticator.

The superior cornea: is there a price for “living high”?

The superior cornea: is there a price for “living high”?

Terrien's Marginal Degeneration: Corneal Topography

Computer-assisted corneal topographic analysis was used to evaluate the corneal contour of four patients with Terrien's marginal degeneration. The corneal topography in these patients was characterized by flattening over the areas of peripheral thinning produced by the disorder. When thinning was restricted to the superior and/or inferior areas of the peripheral cornea, there was a relative steepening of the corneal surface approximately 90 degrees away from the midpoint of the thinned area. This resulted in high against-the-rule or oblique astigmatism characteristic of the disorder. This common pattern is attributable to the frequency with which the superior and/or inferior peripheral cornea is preferentially involved in Terrien's marginal degeneration. In some patients, the central corneal topography may remain relatively spherical if the area of thinning is small or if the disorder extends around the entire circumference of the cornea.

Computer-Assisted Corneal Topography in Keratoconus

Using a computer-assisted video-keratoscope, we determined the topographic findings of 14 eyes of 10 patients with keratoconus. None of these patients had worn contact lenses for at least one year prior to examination and were thus free of contact lens-induced topographical alterations. Two patterns commonly seen included inferior steepening more prominent temporally, and central steepening with a superimposed asymmetric bowtie pattern. When compared with normal eyes three quantitative parameters were significantly different (p less than 0.001): central corneal power, difference in corneal power between fellow eyes in the same patients, and steepening of the inferior cornea compared with the superior cornea. Study of the topography in keratoconus using this technique may prove useful for documenting the pattern of involvement of the anterior corneal surface and providing new insights into the pathogenesis of this condition.

Epithelial splits of the superior cornea in hydrogel contact lens patients

Epithelial splits of the superior cornea are a contact lens complication found in hydrogel lens wearers. The purpose of this paper is to describe the appearance of this lesion and to analyze its association with patient profiles, lens type, and lens care regimens. Differential diagnosis and treatment are also discussed.

Human cornea: superior and central oxygen demands.

Corneal oxygen demands, expressed as ratios of uptake rate relative to baseline rates derived from unstressed corneas, were determined with a micropolarographic system for central (closed eye) and superior (open eye) locations of one cornea of each of seven human subjects. The closed-eye central corneal measurements were repeated during two additional experimental sessions. Intrasubject variability of the three mean closed-eye central corneal rate ratios ranged as high as 23%, possibly representing effects of homeostatic mechanisms on the palpebral conjunctival capillaries of some subjects. For the open-eye superior cornea, which was covered by the upper eyelid of every subject prior to measurement, oxygen demand was found to have a greater intersubject range, but was diminished in magnitude relative to the demand associated with the closed-eye central cornea. Superior corneal oxygen demand was not found to be predictable from closed-eye central corneal oxygen demand or extent of eyelid overlap onto the cornea and thus indicated localized open-eye superior corneal environments that were significantly different from those of the corresponding closed-eye central corneas. Such localized environments may be critically important when gauging the susceptibility of particular eyes to superior corneal pathology during contact lens wear.

Sectorial corneal infiltrates and pannus in herpes zoster ophthalmicus

We report four patients with herpes zoster ophthalmicus who developed a dense pannus limited to a sector of the superior cornea that advanced to the central region of the cornea. The pannus appeared to develop in response to peripheral infiltrates in a subepithelial or anterior stromal location and not in association with disciform corneal edema, interstitial keratitis, or scleritis. The corneal pannus developed insidiously as a late complication without associated ulceration and with little or no anterior uveitis or conjunctival reaction. Additionally, all four patients developed anterior and mid-stromal infiltrates in a punctate or incomplete ring configuration at the leading border of the pannus that threatened the visual axis. In the three patients that were treated with topical corticosteroids, the infiltrates resolved with preservation of visual acuity. The other patient developed central scarring with a permanent reduction in vision. Patients with infiltrates and pannus in a sector of the cornea should be followed carefully and treated with topical corticosteroids when infiltrates appear to prevent progression to the central cornea.

An Unusual Corneal Complication of Soft Contact Lens

An unusual complication caused by hydrophilic soft contact lenses developed in 13 patients (ten women and three men, 16 to 39 years old), most of whom had tight eyelids. The lesion consisted of an arc-like opacity in the superior cornea. The opacity lay in the superficial cornea about 1 to 3 mm from the corneoscleral limbus and had fine spokes extending away from the main trunk. In some cases the problem was unilateral and in others bilateral.

Ocular Chrysiasis

Thirty-four patients who had received over 1 gram of gold compounds for rheumatoid arthritis were examined for ocular chrysiasis. Ninety-seven percent of the patients receiving continuous chrysotherapy at the time of their ocular examination exhibited corneal chrysiasis. With few exceptions, corneal gold deposits were limited to the posterior one-half of the corneal thickness. Deposits tended to concentrate inferiorly and to spare the superior and peripheral cornea. Duration of chrysotherapy correlated positively with the clinically graded density of deposits. In this series, 55% (16/29) of these patients receiving gold therapy for three years or more had lenticular chrysiasis, although this has previously been considered rare. Our data suggest that gold is deposited in the cornea and lens from the anterior chamber aqueous fluid.

Decreased Endothelial Permeability in the Iridocorneal Endothelial Syndrome

Five patients with the iridocorneal endothelial (ICE) syndrome were examined by fluorophotometry. All patients had typical abnormal corneal endothelium, peripheral anterior synechiae, and distortion of the iris (pupillary irregularity or anterior stromal traction tears) in one eye only. Fluorescein was deposited in the superior cornea of both eyes by iontophoresis, and the cornea and anterior chamber concentrations and total mass of fluorescein were measured hourly over the ensuing eight hours. In all five patients, the endothelial permeability to fluorescein was within normal limits in the normal eye. In four of the five abnormal eyes, endothelial permeability was markedly decreased. In these four patients, the permeability to fluorescein in the normal eye was approximately six times that in the abnormal eye. In the fifth patient, the endothelial permeability was normal in both eyes. The central corneal thicknesses were normal in both eyes of all five patients. These results indicate that in many eyes with the ICE syndrome, corneal endothelial permeability to solutes is markedly decreased. Decreased endothelial permeability to solutes has not been documented previously in any clinical corneal disorder and may be of importance in the pathophysiologic changes that accompany endothelial disease.

Superior Limbic Keratoconjunctivitis

Superior limbic keratoconjunctivitis is a new clinical entity in which severe ocular irritation and discomfort may persist for many years. There is marked injection of the superior bulbar conjunctiva and some involvement of the superior cornea with staining and/or filaments. Light and electron microscopy show hyaline changes, nuclear abnormalities, and degeneration of the conjunctival epithelial cells. There is keratinization of the epithelium with all of the features observed in skin, namely horny cells with thickened cell membranes, increased cytoplasmic filaments, reduced organelles, keratohyalin granules, and various membranous structures. The a etiology and treatment of the condition are discussed.

Endothelial Cell Counts with and without Phacoemulsification

Many criteria, such as overall visual acuity and complication rates, have been used to compare the two methods of cataract removal. Since the effect of both procedures on the corneal endothelium is important, we applied our vertical cell disparity photography of the endothelium to a series of eyes operated on by both procedures. A preliminary report of vertical cell disparity was published in January 1978.1 A more comprehensive follow-up report was presented at the American Intra-Ocular Implant Society's 1978 meeting.2 In both reports, a definite disparity was documented between the endothelial cell density of the superior cornea and that of the central and inferior cornea. These studies consisted of 84% lens implant cases and 16% without lens implant. Figure 1 is a graphic demonstration