Corneal endothelial injury thresholds for exposures to 1.54 micro m radiation.

The endothelial injury threshold was determined in rabbit for an 11-s exposure to 1.54 micro m radiation from an Erbium fiber laser. The beam was Gaussian with a 1/e diameter of 7 mm. Cell damage was detected with a wet staining technique. The threshold dose for these conditions is 4.4 x 10(5) J m(-2) (44 J cm) and is only 9% greater than the threshold for epithelial damage for the same exposure conditions. Exposures just above the threshold caused substantial endothelial damage, including loss of cells. The calculated endothelial temperature increase at the threshold is similar to that calculated for the epithelium at its injury threshold for the same exposure conditions. The results suggest that endothelial damage can be correlated with a critical temperature damage model with a critical temperature increase near 40 degrees C. The results also suggest that if a person were to receive an exposure only slightly above the epithelial injury threshold from a beam having a diameter of 7 mm (which is the diameter of the exit pupil of 7 x 50 binoculars) he or she would risk sustaining substantial endothelial damage.

Light-scattering and ultrastructure of healed penetrating corneal wounds.

PURPOSE: To investigate quantitatively for the first time the relationship between light-scattering and ultrastructure of semitransparent scars resulting from penetrating wounds in rabbit cornea. METHODS: Penetrating wounds, 2 mm in diameter, were made in the central cornea and allowed to heal for 3.6 to 4.5 years at which time the rabbits were killed. The scar and cornea thickness outside the scar were measured using ultrasonic pachymetry. Corneas were excised immediately and their transmissivity was measured from 400 to 700 nm. The tissue was then prepared for transmission electron microscopy. Transmission electron micrographs (TEMs) were analyzed to determine fibril positions and radii. Scattering was calculated using the direct summation of fields (DSF) METHOD: RESULTS: Scar thickness averaged 0.26 +/- 0.04 mm, and the scars were flat. Thickness outside the scars averaged 0.40 +/- 0.04 mm. Three scars were moderately transparent, five were less transparent, and one was much less transparent. The wavelength dependence of the measured total scattering cross- section was indicative of the presence of voids (lakes) in the collagen fibril distribution, and lakes were evident in the TEMs. The images showed enlarged fibrils and some showed bimodal distributions of fibril diameters. Calculated scattering was characteristic of that expected from regions containing lakes-a finding consistent with the scattering measurements. CONCLUSIONS: Despite the long healing time, these scars remained highly scattering. A combination of lakes, disordered fibril distributions, and a significant population of enlarged fibrils can explain the scattering. A possible cellular contribution cannot be ruled out.

Role of electron microscopy in the diagnosis of ocular mucous membrane pemphigoid.

PURPOSE: To evaluate the role of electron microscopy (EM) for the diagnosis of ocular mucous membrane pemphigoid (MMP) among patients with cicatrizing conjunctivitis. DESIGN: Retrospective case series. PARTICIPANTS: One hundred twenty-eight patients with cicatrizing conjunctivitis referred for the evaluation of possible ocular MMP between January 1985 and February 2002 who underwent conjunctival biopsy and evaluation with EM and direct immunofluorescent (DIF) techniques. METHODS: The diagnosis of each patient was based on DIF techniques. The reproducibility of EM readings was measured by assessing intraobserver and interobserver variability. The diagnosis from EM was compared to the DIF diagnosis from the same patient to evaluate the validity of the EM diagnosis. MAIN OUTCOME MEASURES: Sensitivity, specificity, positive predictive value, and negative predictive value of EM for diagnosing ocular MMP. RESULTS: One hundred twenty-six of 128 conjunctival biopsies were available for evaluation of EM findings. The percent agreement between 2 readings from the same observer was 92%, and the percent agreement between 2 independent observers was 78%. The sensitivity and specificity of EM for the diagnosis of ocular MMP were 51% and 72%, respectively. The positive predictive value of EM for the diagnosis of ocular MMP was 49%. CONCLUSIONS: The reproducibility of EM findings was good as indicated by high percent agreement for both intraobserver and interobserver measurements. However, the sensitivity, specificity, and positive predictive value of EM for the diagnosis of ocular MMP was low. It seems that EM has limited usefulness in the diagnosis of ocular MMP.

Immunohistochemistry and electron microscopy of early-onset fuchs corneal dystrophy in three cases with the same L450W COL8A2 mutation.

PURPOSE: A rare, familial early-onset form of Fuchs corneal dystrophy (FCD) is caused by mutation in the COL8A2 gene. This study describes the aberrant pattern of distribution of collagen type VIII and basement membrane components in Descemet's membrane (DM) and endothelium of three individuals with the same L450W mutation that represent different stages of early-onset FCD. METHODS: Immunohistochemical studies with bright field, fluorescence, and confocal microscopy characterized the pathology of sectioned corneal buttons with antibodies against COL8A1, COL8A2, COL4, laminin, and fibronectin. A portion of each was processed for electron microscopy. RESULTS: Histologic examination of pathologic changes in case 1 demonstrated relative preservation of the endothelium, whereas in case 2 much of this layer was atrophic and in case 3 there was complete loss of the endothelium. DM also increased in thickness to 25 mum for case 1, to 31 mum for case 2, and to 38 mum for case 3. Case 1 was the only specimen to reveal shallow warts along the posterior surface of DM, whereas the most advanced specimen, case 3, showed evidence of earlier nodularity that had been buried by the accretion of further extracellular matrix material. The posterior aspect of DM in this specimen had the unusual property of lighter staining relative to the anterior region of DM, laid down earlier in life. Immunocytochemistry revealed increased expression and complex, sharply defined patterns of deposition of collagen VIII, collagen IV, laminin, and fibronectin. Ultrastructurally, the posterior nonbanded layer of DM was intermixed with banded collagen, and the posterior region of DM showed a high density of foci of spindle-shaped structures with intense-staining bands, spaced at approximately 120 nm. Finally, ultrastructural studies of the endothelium in case 1 revealed unusual accumulation of swelling mitochondria. The endothelial cells also had large amounts of abnormal prominent rough endoplasmic reticulum. Type VIII collagen alpha 2 immunogold signal was associated with the highly granular ribosomes of the rough endoplasmic reticulum of these patients. CONCLUSIONS: Microscopic and electron microscopic examination revealed pathological changes in DM of L450W COL8A2 mutants that were consistent with several-fold increased growth of the extracellular matrix and progressive deposition and synthesis of extracellular material by endothelial cells. As with late-onset FCD, this is accompanied by attenuation and eventual loss of the endothelium itself. Whether the abnormal deposition of collagen, laminin, and fibronectin contributes to the dysfunction and death of the endothelium remains to be determined.

A morphologic study of Fuchs dystrophy and bullous keratopathy.

PURPOSE: To describe the morphologic features of Fuchs corneal dystrophy and compare them with those of bullous keratopathy. METHODS: This was an observational case series. The study group consisted of 32 corneal buttons with a diagnosis of Fuchs dystrophy and the comparison group consisted of 22 corneal buttons with bullous keratopathy. Morphologic analysis was performed of corneal buttons from patients with the clinical diagnosis of Fuchs dystrophy or bullous keratopathy by light and electron microscopy. RESULTS: The main outcome measure was identification of degenerated keratocytes, granular material in and around keratocytes, and lipid keratopathy. The overall morphologic features of Fuchs dystrophy and bullous keratopathy are similar to those described in previous literature. A high proportion of keratocytes exhibited degenerative changes (78.9% in Fuchs dystrophy versus 50.5% in bullous keratopathy). Granular material was identified in and around variably degenerated keratocytes in all cases of Fuchs dystrophy and in 14 of 22 (64%) of the corneas with bullous keratopathy. The percentage of keratocytes with granular deposits was higher in Fuchs dystrophy corneas as compared with corneas with bullous keratopathy (51.7% versus 14.1%, P < 0.0005). Lipid keratopathy was a common occurrence in both Fuchs dystrophy and bullous keratopathy (23/32 [72%] versus 12/22 [55%]). CONCLUSIONS: Histopathologic changes in the corneal stroma and keratocytes occur in Fuchs dystrophy. Secondary lipid keratopathy ensues and may contribute to corneal haze. A higher proportion of keratocytes in Fuchs dystrophy have granular deposit than in bullous keratopathy. That a high proportion of keratocytes had degenerative changes in both Fuchs dystrophy and bullous keratopathy suggests that keratocytes may degenerate secondary to altered stromal microenvironment because of endothelial cell loss.

Immunotactoid keratopathy: a clinicopathologic case report and a review of reports of corneal involvement in systemic paraproteinemias.

Corneal deposits in association with paraproteinemias have been well described in the ophthalmic literature. Recent reports in the renal literature have described immunotactoid deposition associated with glomerulopathy-organized microtubular deposits of IgGkappa that measured 32-50 nm in diameter on renal biopsies. We present a case of corneal immunotactoid deposition in the setting of chronic lymphocytic leukemia and review previous reports of corneal deposition in the setting of systemic paraproteinemia, highlighting the etiology, differential diagnosis, prognosis, and treatment of corneal involvement. We propose the use of the term immunotactoid keratopathy to describe corneal IgGkappa deposits appearing as tubular, electron-dense, crystalloid deposits with a central lucent core on electron microscopy and suggest that these patients undergo directed systemic workup to evaluate for potential etiologies of their systemic paraproteinemia. To illustrate the spectrum of paraprotein deposition in the cornea, and to emphasize the importance of ophthalmic evaluation in the setting of systemic paraproteinemias, we include a case of a 44-year-old man with immunoprotein corneal deposition who was subsequently diagnosed with multiple myeloma.