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.

Inheritance of a novel COL8A2 mutation defines a distinct early-onset subtype of fuchs corneal dystrophy

PURPOSE

To characterize the genetic basis and phenotype of inherited Fuchs corneal dystrophy (FCD).

METHODS

DNA from blood was used for genome-wide linkage scans with tandem repeat polymorphisms. Mutation detection involved sequencing PCR-amplified exons. Families with FCD were clinically evaluated and graded on the Krachmer severity scale. Confocal specular microscopy visualized the morphology of endothelial guttae, small protrusions of Descemet's membrane that are characteristic of FCD.

RESULTS

Linkage was obtained to 1p34.3-p32 for the autosomal dominant kindred originally reported by Magovern in 1979. All 21 cases with FCD and one with posterior polymorphous dystrophy were heterozygous for L450W, a novel point mutation in the COL8A2 gene. Of 62 independent cases of familial FCD, none had the previously reported mutations in COL8A2. Corneal guttae in COL8A2 patients were small, rounded, and associated with the endothelial cell center. This contrasts with common FCD, in which guttae were larger, sharply peaked, and initially positioned at edges of endothelial cells. The profile of age and disease severity for the L450W FCD kindred suggested that disease onset occurred in infancy, compared with an average age of onset of 50 years estimated for 201 familial FCD patients in 62 other families.

CONCLUSIONS

A novel pathogenic L450W COL8A2 mutation was identified and its highly distinctive pathology characterized. This indicates that COL8A2 mutations give rise to a rare subtype of FCD. This study also provides the first direct evidence that COL8A2-FCD progresses from early to late stages in 25 years, a rate similar to that estimated for late-onset FCD.

Epithelial Innervation of Human Cornea

PURPOSE

Evaluation of a new method to visualize distribution and morphology of human corneal nerves (Adelta- and C-fibers) by means of fluorescence staining, confocal laser scanning microscopy, and 3-dimensional (3D) reconstruction.

METHODS

Trephinates of corneas with a diagnosis of Fuchs corneal dystrophy were sliced into layers of 200 microm thickness using a Draeger microkeratome (Storz, Germany). The anterior lamella was stained with the Life/Dead-Kit (Molecular Probes Inc.), examined by the confocal laser scanning microscope "Odyssey XL," step size between 0.5 and 1 microm, and optical sections were digitally 3D-reconstructed.

RESULTS

Immediate staining of explanted corneas by the Life/Dead-Kit gave a complete picture of the nerves in the central human cornea. Thin nerves running parallel to the Bowman layer in the subepithelial plexus perforate the Bowman layer orthogonally through tube-like structures. Passing the Bowman layer, Adelta- and C-fibers can be clearly distinguished by fiber diameter, and, while running in the basal epithelial plexus, by their spatial arrangement. Adelta-fibers run straight and parallel to the Bowman layer underneath the basal cell layer. C-fibers, after a short run parallel to the Bowman layer, send off multiple branches penetrating epithelial cell layers orthogonally, ending blindly in invaginations of the superficial cells. In contrast to C-fibers, Adelta-fibers show characteristic bulbous formations when kinking into the basal epithelial plexus.

CONCLUSIONS

Ex-vivo fluorescence staining of the cornea and 3D reconstructions of confocal scans provide a fast and easily reproducible tool to visualize nerves of the anterior living cornea at high resolution. This may help to clarify gross variations of nerve fiber patterns under various clinical and experimental conditions.

Epithelial cell, keratocyte, and endothelial cell apoptosis in Fuchs' dystrophy and in pseudophakic bullous keratopathy

PURPOSE

To elucidate the pathomechanism of Fuchs' dystrophy and pseudophakic bullous keratopathy (PBK) by examining cell apoptosis in different corneal layers.

METHODS

The authors studied corneal buttons obtained from 21 eyes following central penetrating keratoplasty: 14 corneal buttons (13 patients, age 70.8+/-10.0 years) with Fuchs' dystrophy, and 7 buttons (7 patients, age 69.6+/-10.2 years) with PBK. Four buttons from enucleated eyes with choroidal melanoma served as controls. Histologic changes were examined using light microscopy with hematoxylin-eosin (HE) staining. The average numbers of apoptotic cells per field of view (125x magnification) in separate samples of the epithelial, stromal, and endothelial layers were determined using the TUNEL (terminal deoxyribonucleotidyl transferase-mediated dUTP-digoxigenin nick-end labeling) assay.

RESULTS

In 11 of the Fuchs' dystrophy corneas and 2 of the PBK corneas, apoptotic activity was detected. In the control corneas no apoptotic activity was found. Compared to the controls there was a statistically significant difference in the mean (normalized) apoptotic cell numbers for all three layers (p=0.01 in each case) in the Fuchs' dystrophy corneas, and for the stromal layer (p<0.01) in PBK corneas. The apoptotic cell numbers for the epithelial and endothelial layers of the latter were higher, but the difference was not statistically significant (p=0.07, 0.07).

CONCLUSIONS

Apoptosis may play a role in the pathomechanism of Fuchs' dystrophy and in keratocyte death in corneas with PBK.

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.

The effect of corneal thickness on intraocular pressure measurement in patients with corneal pathology

BACKGROUND/AIM

To compare intraocular pressure (IOP) measurements taken by the Goldmann applanation tonometer, the Tono-Pen and the ocular blood flow pneumotonometer in eyes with varying central corneal thickness (CCT) due to penetrating keratoplasty (PK), keratoconus (KC), and Fuchs' endothelial dystrophy (FED).

METHODS

IOP was measured with the Goldmann applanation tonometer, Tono-Pen XL, and OBF pneumotonometer in 127 eyes with the following corneal abnormalities. There were 56 eyes that had undergone PK, 37 eyes with KC, and 34 eyes with FED. CCT was measured using an ultrasound pachymeter after IOP determinations had been made.

RESULTS

Mean IOP measurements in all three patient groups were significantly higher when measured by OBF pneumotonometer. Linear regression analysis showed that patients with FED had a significant increase in IOP with increasing CCT of 0.18 mm Hg/10 microm using the Goldmann tonometer, 0.15 mm Hg/10 microm with the Tono-Pen, and 0.26 mm Hg/10 microm with the OBF pneumotonometer. In patients with KC and after PK, linear regression analysis did not show a significant effect of CCT on IOP. A multivariate linear regression model controlling for age, sex, graft size, and patient group, showed that the effect of CCT on IOP for Tono-Pen (0.13 mm Hg/10 microm CCT) and Goldmann (0.14 mm Hg/10 microm CCT) were significantly lower than for the OBF pneumotonometer (0.26 mm Hg/10 microm CCT).

CONCLUSIONS

This study found that mean IOP measurements using the OBF pneumotonometer were significantly higher than those made using the Goldmann applanation tonometer or Tono-Pen in eyes with a variety of cornel pathologies. The OBF pneumotonometer was found to be most affected by variation in CCT. For all three instruments, the relation between IOP and CCT depended on the corneal pathology and was greatest for FED.

Altered expression of aquaporins in bullous keratopathy and Fuchs' dystrophy corneas

Corneas with edema-related diseases lose transparency, which causes significant vision loss. This study analyzed seven aquaporins (AQPs) in normal corneas, pseudophakic/aphakic bullous keratopathy (PBK/ABK) corneas, Fuchs' dystrophy corneas, keratoconus corneas, post-cataract surgery (PCS) corneas, and normal organ-cultured corneas. RNA levels for AQP1, AQP4, and beta2-microglobulin were measured by RT-PCR. AQP1 antibody localized to stromal cells of all corneas. PBK/ABK and Fuchs' dystrophy corneas had decreased endothelial cell staining compared with normal. AQP1 mRNA was found in whole corneas and cultured stromal fibroblasts but not in isolated epithelial cells. AQP3 staining was found in basal epithelial cells of the normal, Fuchs' dystrophy, and keratoconus corneas but throughout the entire epithelium of PBK/ABK corneas. AQP4 antibody localized to endothelial cells of all corneas and in stromal cells of PBK/ABK corneas. AQP4 mRNA was identified in whole human corneas. AQP5 was found in epithelial cells of all corneas. AQP0, AQP2, and AQP9 were not found in any corneas. Normal AQP distributions were found in PCS and organ-cultured corneas, although they showed signs of swelling. Our study demonstrates that AQP abnormalities are found in PBK/ABK corneas (decreased AQP1, increased AQP3 and AQP4) and Fuchs' dystrophy corneas (decreased AQP1). Although both have vision-disrupting corneal edema, the mechanisms of fluid accumulation may be different in each disease.

[Morphologic characteristics of cornea in Fuchs endothelial dystrophy observed by confocal microscopy]

OBJECTIVE

To analyze the image of corneas with Fuchs endothelial dystrophy using confocal microscopy in vivo.

METHODS

Central corneas of 38 eyes (19 patients aged 33 approximately 76 years) were examined using scanning slit confocal microscopy in vivo after being diagnosed with Fuchs endothelial dystrophy. They were divided into two groups namely symptomatic (19 eyes) and asymptomatic (19 eyes). The control group comprised of 30 normal eyes. The images were analyzed visually for morphology of corneas and the densities of cells, as well as the diameter of the guttae and the corneal nerves were counted by NAVIS software.

RESULTS

(1) In the symptomatic groups, confocal microscopy revealed guttae in 19 eyes. The diameter of the guttae ranged from 20 to 60 micro m. The density of endothelial cells was statistically significant compared with the control group (t = 18.74, P < 0.01). Descemet's membrane was thickened in 9 eyes. Dark bands 6.0 approximately 10.8 micro m in diameter were detected in 14 eyes. All eyes showed a diffuse increased light reflection in the stroma.17 eyes exhibited an abnormal Bowman's layer: multiple focal bright reflection. 10 eyes revealed normal corneal nerves. The differences between posterior and anterior keratocyte densities in the control and study groups were not statistically significantly different (t = 0.854, 1.173; P = 0.38, 0.24 respectively). (2) In the asymptomatic groups, less number of guttae could be seen in the endothelial layer. The diameter of the guttae was 15 approximately 40 micro m. The densities of endothelial cells were not significantly different compared with control group (t = 1.998, P = 0.053). Other layers of the cornea exhibited no other abnormal phenomenon. The densities of endothelial cells between symptomatic and asymptomatic groups were statistically significantly different (t = 8.352, P < 0.01).

CONCLUSIONS

Morphologic characteristics of cornea are observed by confocal microscopy in Chinese patients with Fuchs endothelial dystrophy. Preliminary results demonstrate that there is no significant difference between Chinese and western patients. Confocal microscopy allows to diagnose Fuchs dystrophy and visualize endothelial cells within the swollen cornea. And it is especially useful for patients whose endothelial cells can not be seen with non-contact specular microscopy.

Distribution of TFF peptides in corneal disease and pterygium

The central cornea of 10 cadavers and 33 patients suffering from keratoconus, herpetic keratitis, Fuchs' dystrophy and pterygium were analysed focusing on the expression of TFF peptides by means of reverse transcription polymerase chain reaction and immunohistochemistry. TFF1 and TFF3 transcripts were detected in healthy corneae as well as in pterygia. Only TFF3 mRNA was transcribed in keratoconus, Fuchs' dystrophy and herpetic keratitis. Immunohistochemistry revealed absence of all three TFF peptides in healthy corneae but production of TFF3 in each of the diseased corneae. In pterygia both TFF1 and TFF3 synthesis was detectable in goblet cells. The absence of TFF peptide production in the healthy cornea indicates that TFF3 secretion is induced in different corneal diseases by yet unknown stimuli. Here TFF3 synthesis can be interpreted as a protection mechanism, because all corneal diseases analysed are characterized by progressive tissue destruction. TFF1 and TFF3 production by goblet cells in pterygia is comparable to the healthy conjunctiva suggesting that TFF peptides do not play a significant role in the pathogenesis of pterygia.

Aquaporin-1 expression is decreased in human and mouse corneal endothelial dysfunction

PURPOSE

To determine if aquaporin-1 expression is decreased in human and mouse corneal endothelial dysfunction.

METHODS

Immunohistochemistry with anti-aquaporin 1 antibody and confocal microscopy were used to study a case series of human corneal specimens, and a mouse model of corneal endothelial injury was created with injection of sterile hot water into the anterior chamber with a 33 gauge needle. Western blotting of mouse and human corneas was used to provide confirmatory evidence.

RESULTS

Aquaporin-1 was found to be expressed in normal human cornea and decreased in human corneas with endothelial disease but not in human corneas with non-endothelial corneal disease. Aquaporin-1 was also found to be reduced in mouse corneas subjected to corneal endothelial injury. Both results were confirmed by western blot analysis.

CONCLUSIONS

Corneal endothelial injury is associated with decreased aquaporin-1 expression.

Comparison of confocal biomicroscopy and noncontact specular microscopy for evaluation of the corneal endothelium

PURPOSE

To compare the clinical efficacy of confocal biomicroscopy with that of noncontact specular microscopy for the evaluation of the corneal endothelium.

METHODS

The corneal endothelium was examined in 14 normal subjects (28 eyes) and in 6 patients (11 eyes) with Fuchs corneal endothelial dystrophy using a noncontact specular microscope (SP-2000P, Topcon, Japan) and a confocal biomicroscope (ConfoScan, Tomey, Japan). The images and the calculated densities of corneal endothelial cells obtained by the 2 techniques were compared.

RESULTS

For normal subjects, the images of corneal endothelial cells obtained by the 2 techniques were almost identical, although the density of these cells determined by confocal biomicroscopy (2916 +/- 334 cells/mm2) was slightly higher than that determined by noncontact specular microscopy (2765 +/- 323 cells/mm2). In contrast, whereas clear images of corneal endothelial cells, allowing the determination of cell density, were obtained for all 11 eyes of the patient group by confocal biomicroscopy, clear images were obtained for only 4 of these 11 eyes (36.4%) by noncontact specular microscopy.

CONCLUSION

Both noncontact specular microscopy and confocal biomicroscopy revealed the shapes and number of endothelial cells in the normal cornea. However, for corneas with Fuchs dystrophy, clear images were obtained only by confocal biomicroscopy. Confocal biomicroscopy is thus an effective tool for evaluation of the diseased corneal endothelium.

Corneal decompensation after laser in situ keratomileusis in fuchs' endothelial dystrophy

PURPOSE

To report corneal decompensation after laser in situ keratomileusis (LASIK) in a patient with Fuchs' endothelial dystrophy.

METHODS

Observational case report.

RESULTS

A 47-year-old woman with cornea guttata without symptoms or findings of corneal edema had uneventful LASIK for -5.50 -0.50 x 150 in the right eye and -4.00 -1.25 x 170 in the left eye. Postoperatively, she developed corneal edema, with significant loss of best-corrected visual acuity in both eyes. Preoperative corneal thickness was 587 microm in the right eye and 549 microm in the left eye, measured by ultrasound pachymetry. These readings were 550 and 560 microm on day 67 postoperatively. Endothelial cell counts showed means of 1209 and 1661 cells/mm2 in the right and left eyes, respectively.

CONCLUSION

Caution is suggested when considering LASIK in eyes with severe cornea guttata.

Wavelet analysis for corneal topographic surface characterization

PURPOSE

To demonstrate a mathematical method for multiscalar decomposition of discrete corneal topography height data into a space-scale space using wavelet analysis techniques, and to demonstrate the clinical applicability of these computations in the postkeratoplasty cornea.

METHODS

Fifty patients with either Fuchs' dystrophy (n = 20) or keratoconus (n = 30) were seen preoperatively, at 3 months, at 1 year (before suture removal) and again at 19 +/- 3 months (after suture removal) following nonmechanical trephination with an excimer laser for penetrating keratoplasty. Patients were assessed using corneal topography analysis (TMS-1), subjective refraction, and best-corrected visual acuity (VA) at each interval. Two-dimensional biorthogonal wavelets with the order 6.8 at the scales j = 1-4 revealed the following parameters: root-mean square (RMSDEV) and mean absolute (MEANDEV) deviation and maximum absolute height of the peaks or pitches (MAXPEAK) relative to the reference surface specified with the approximation component of scale j = 4. RMSDEV was correlated with the VA at various follow-up intervals. The multiscalar basis components: roughness, waviness and form were separated and recovered from the wavelet soft thresholding techniques. Peaks and pits within the three-dimensional corneal surface topography were detected and localized using the wavelet hard thresholding techniques.

RESULTS

In patients with keratoconus, the RMSDEV and the MEANDEV increased from 4.31 +/- 1.25/5.98 +/- 1.88 microm preoperatively to the 3 months follow-up (4.98 +/- 1.41/6.92 +/- 2.16 microm) and thereafter decreased continuously to the end of the follow-up (1.87 +/- 0.63/2.63 +/- 1.07 microm), whereas in Fuchs' dystrophy the respective values started at a higher preoperative level (6.36 +/- 1.24/7.20 +/- 2.64 microm) and decreased continuously over time (2.73 +/- 1.10/3.71 +/- 1.05 microm after suture removal). In the keratoconus group, the MAXPEAK was increased at the 3 month postoperative exam (8.78 +/- 2.29 microm) when compared to the preoperative value (6.55 +/- 2.56 microm); however, it decreased again and returned to the preoperative level after one year (6.34 +/- 2.12 microm after suture removal). In Fuchs' dystrophy, the MAXPEAK was unchanged preoperatively (8.26 +/- 2.83 microm) to the 3 months follow-up, but decreased continuously to the end of the follow-up period (4.57 +/- 1.36 microm). The RMSDEV was significantly lower in keratoconus than in Fuchs' dystrophy preoperatively (P = 0.01) and after suture removal (P = 0.005) and correlated inversely with VA preoperatively (R = -0.53, P = 0.04/R = -0.69, P = 0.02), at the 1 year exam (R = -0.61, P = 0.02/R = -0.52, P = 0.05) and after suture removal (R = -0.73, P = 0.01/R = -0.66, P = 0.025) in keratoconus/Fuchs' dystrophy.

CONCLUSIONS

The use of wavelet analysis can provide significant clinical information by separating the raw data into the parameters: "roughness", "waviness", "form" and various multiscalar peaks and pits. The RMSDEV, a quantitative measure for corneal irregularity, can be used as a new approach for the prediction of potential visual acuity after penetrating keratoplasty. The decomposition of the surface elevation into fundamental components is crucial for a subsequent mathematically based extraction of clinical parameters or for topography-based flying-spot ablation of irregular corneal astigmatism.

Three-axis ellipsoidal fitting of videokeratoscopic height data after penetrating keratoplasty

PURPOSE

After penetrating keratoplasty corneal topography tends to be irregular and the fitting of spectacle glasses or contact lenses may be difficult. The purpose of this study was to demonstrate a mathematical method for approximation of discrete corneal topography height data with an ellipsoid for better appreciation of the clinical outcome after PK.

PATIENTS AND METHODS

In 50 eyes (30 keratoconus, 20 Fuchs' dystrophy) penetrating keratoplasty was performed using nonmechanical trephination with the excimer laser 193 nm. Main outcome measures were objective corneal astigmatism (regular keratometry, corneal topography (TMS-1)), subjective refraction and best-corrected visual acuity (VA) in a fixed postoperative gate 3 and 12 month postoperatively and after suture removal. An approximation algorithm was applied for fitting a general ellipsoidal surface (not rotationally symmetric) to raw corneal topography height data. A set of parameters (meridional power, axis and asphericity) were calculated. The root mean square error (RMS) was determined between raw topography power data and the ellipsoidal model surface within an apical distance of 3 mm. The cylinder of subjective refraction was correlated with the keratometric readings, the Simulated Keratometry (SimK) of the topography system and the respective parameters of the model surface.

RESULTS

The amount of the SimK cylinder yielded higher values than keratometry and the ellipsoidal fit; subjective refraction yielded the lowest value at each follow-up interval. The ellipsoidal fit showed the best correlation to the refractive cylinder at all follow-up stages (p = 0.04 at 3, p = 0.01 at 12 months and p = 0.002 after suture removal). The axis of the best ellipsoidal fit showed a significant correlation with the axis of the refractive cylinder at all follow-up intervals (p = 0.02 at 3 months, p = 0.01 before suture removal and p = 0.002 after suture removal). The axis of the keratometric cylinder showed a mild correlation at all follow-up examinations (p = 0.05 at 3 months, p = 0.02 before suture removal and p = 0.04 after suture). The cylinder of the topographic modeling system, however, showed a significant correlation with the refractive cylinder axis only after suture removal (p = 0.04). The paracentral corneal power of SimK (45.9D at 3 months, 44.4D at 12 months and 43.0D after suture removal) exceeded the respective values of conventional keratometry (43.1D at 3 months, 42.9D at 12 months and 41.7D after suture removal) and the ellipsoidal fit (43.3D at 3 months, 43.0D at 12 months and 41.8D after suture removal). The corneal asphericity from the ellipsoidal fit reached an approximately spherical shape in radial direction (A = 1.0) in the initial time period after penetrating keratoplasty, remained stable before suture removal and decreased significantly (p = 0.02) to a final value of A = 0.86 indicating a (normal) prolate shape of the cornea. The approximation error between the raw corneal topography height data and the best ellipsoidal fit model surface was nearly unchanged before suture removal (1.8 +/- 0.7 microm at 3 months and 1.9 +/- 1.1 microm at 12 months, p = 0.30) and decreased significantly to the examination after suture removal (0.9 +/- 0.5 microm, p = 0.01).

CONCLUSIONS

The approximation of corneal topography height data with an ellipsoidal model surface renders reconstruction of clinically relevant corneal topography parameters including corneal asphericity. Even in markedly irregular corneal surfaces, such as after PK, the correlation of amount/axis of refractive cylinder with the model surface parameters is more accurate than with respective SimK values of corneal topography analysis.

VSX1: a gene for posterior polymorphous dystrophy and keratoconus

We identified mutations in the VSX1 homeobox gene for two distinct inherited corneal dystrophies; posterior polymorphous dystrophy (PPD) and keratoconus. One of the mutation (R166W) responsible for keratoconus altered the homeodomain and impaired DNA binding. Two other sequence changes (L159M and G160D) were associated with keratoconus and PPD, respectively, and involved a region adjacent to the homeodomain. The G160D substitution, and a fourth defect affecting the highly conserved CVC domain (P247R), occurred in a child with very severe PPD who required a corneal transplant at 3 months of age. In this family, relatives with the G160D change alone had mild to moderate PPD, while P247R alone caused no corneal abnormalities. However, with either the G160D or P247R mutation, electroretinography detected abnormal function of the inner retina, where VSX1 is expressed. These data define the molecular basis of two important corneal dystrophies and reveal the importance of the CVC domain in the human retina.

Conoidal Fitting of Corneal Topography Height Data After Excimer Laser Penetrating Keratoplasty

PURPOSE

To demonstrate a mathematical method for approximation of discrete corneal topography height data with a biconic model surface for better appreciation of the optical performance of the graft after penetrating keratoplasty.

METHODS

In this retrospective study we included 50 eyes of 50 patients (30 keratoconus; 20 Fuchs' dystrophy) undergoing nonmechanical excimer laser penetrating keratoplasty. Conventional keratometry, corneal topography (TMS-1), subjective refraction, and best spectacle-corrected visual acuity (BSCVA) were assessed preoperatively, 3 and 6 months postoperatively, and before/after suture removal. A biconic model surface was fitted to the topographic raw data (8.0-mm region of interest) minimizing the root mean square error and a set of parameters (meridional power, axis, conic constant, and approximation error) was determined. The refractive cylinder was correlated with keratometric power readings, the Simulated Keratometry (SimK) of the topography system, and the respective parameters of the model surface.

RESULTS

Keratometric/SimK astigmatism increased from preoperatively (3.40/4.30 D) to 3 months (4.30/4.80 D) and decreased to 3.40/3.90 D after suture removal. Refractive cylinder/cylinder of the biconic increased slightly from 2.10/2.60 D preoperatively to 3.20/3.30 D after suture removal. The topographic cylinder SimK yielded the highest and the refractive cylinder the lowest values at each follow-up examination. Central keratometric power readings were stable before suture removal and decreased (about 1 D) due to suture removal. The conic constants in both meridional cross-sections changed from a prolate to a spherical shape in the early time course after penetrating keratoplasty and reconverted to a prolate shape after suture removal. Regarding cylinder axis, there was a significant correlation of the model surface with the refractive cylinder at all examination (P < .05) but only a mild correlation of the keratometric and SimK cylinder axis to the refractive cylinder axis at some examination stages.

CONCLUSION

Approximation of corneal topography height data with a biconic model surface renders reconstruction of clinically relevant corneal topography parameters including corneal asphericity with marked data compression. The correlation of amount/axis of refractive cylinder was best represented with the model surface parameters.

[Postmortem evaluation of corneal astigmatism after astigmatism oriented penetrating keratoplasty]

BACKGROUND

Reduction of astigmatism following penetrating keratoplasty can be achieved if the graft is oriented according to astigmatism parameters in donor and host (AOPKP). Postmortem evaluation of these parameters is therefore essential. The aim of our investigation was to compare postmortem measurements using a hand-held keratometer with those of the living donor's astigmatism.

METHOD

The 72-year-old female patient had undergone AOPKP on her right eye. After death the astigmatism in the right eye was evaluated 4.5 h postmortem using a hand-held keratometer. After explantation, the eyeball was examined by computer-assisted topography (TMS-1).

RESULTS/CONCLUSION

We could show that hand keratometry in situ is reliable for evaluating astigmatism in donor eyes after death. As far as our AOPKP study is concerned, these results are of great interest. Reduction of postoperative astigmatism following penetrating keratoplasty is only possible if data on astigmatism of the donor and host corneas are available.

Missense mutations in COL8A2, the gene encoding the alpha2 chain of type VIII collagen, cause two forms of corneal endothelial dystrophy

Corneal clarity is maintained by its endothelium, which functions abnormally in the endothelial dystrophies, leading to corneal opacification. This group of conditions includes Fuchs' endothelial dystrophy of the cornea (FECD), one of the commonest indications for corneal transplantation performed in developed countries, posterior polymorphous dystrophy (PPCD) and the congenital hereditary endothelial dystrophies (CHED). A genome-wide search of a three-generation family with early-onset FECD demonstrated significant linkage with D1S2830 (Z(max) = 3.72, theta = 0.0). Refinement of the critical region defined a 6-7 cM interval of chromosome 1p34.3-p32 within which lies the COL8A2 gene. This encodes the 703 amino acid alpha2 chain of type VIII collagen, a short-chain collagen which is a component of endothelial basement membranes and which represented a strong candidate gene. Analysis of its coding sequence defined a missense mutation (gln455lys) within the triple helical domain of the protein in this family. Mutation analysis in patients with FECD and PPCD demonstrated further missense substitutions in familial and sporadic cases of FECD as well as in a single family with PPCD. This is the first description of the molecular basis of any of the corneal endothelial dystrophies or of mutations in type VIII collagen in association with human disease. This suggests that the underlying pathogenesis of FECD and PPCD may be related to disturbance of the role of type VIII collagen in influencing the terminal differentiation of the neural crest derived corneal endothelial cell.

[Changes in corneal structure observed with confocal microscopy during Fuchs endothelial dystrophy]

PURPOSE

The study aimed to in vivo evaluate corneal structure in Fuchs' dystrophy.

MATERIAL AND METHODS

Forty-two eyes of 21 patients (11 women and 10 men) aged 34-80 (mean 60.8) were studied. Sixteen patients presented clinical symptoms. The cornea was examined using a Confoscan P4 scanning slit confocal microscope (Tomey). Before examination, the cornea was anesthetized with 0.5% propacaine (Alcaine, Alcon) in order to inhibit the corneopalpebral reflex. A 40x microscope objective was covered with a drop of polyarylic acid gel (Vidisic, Mann Pharma) and then it was moved horizontally close to the patient's cornea and the examination was carried out.

RESULTS

In the early stage of Fuchs dystrophy, slit biomicroscopy revealed fine dark spots within the corneal endothelium, while in the advanced stage the cornea had the appearance of beaten metal. On confocal microscopy, there were diffused hyporeflective areas in the early-stage disease. The endothelial cells located beyond these areas were pleomorphic and polymegathic. In the late stage we observed diffused hyporeflective areas surrounded by hyperreflective endothelial cells, which could not be analyzed separately. Within the corneal stroma, the collagen fibers were blurred and the background illumination was increased. In the posterior part of the stroma, dark bands were seen. The epithelium contained cystic structures (blisters). The membranes of the basal cells were thickened and the background illumination was increased.

CONCLUSIONS

Confocal microscopy allows to diagnose Fuchs dystrophy and visualize endothelial cells within the swollen cornea.

Screening human donor corneas during organ culture for the presence of guttae

AIMS

To detect the presence of guttae by means of light microscopy during organ culture and to evaluate the influence of the presence of guttae in the donor tissue on transplantation outcome.

METHODS

Donor corneas were investigated for the presence of guttae by means of light microscopy at the end of organ culture. Recipient corneal buttons from patients with severe Fuchs' dystrophy and donor corneas with advanced guttae were first studied by light microscopy and subsequently by transmission electron microscopy. Lastly, 168 consecutive donor corneas were evaluated for the presence of guttae and issued for transplantation.

RESULTS

Corneal specimens with Fuchs' dystrophy displayed numerous round highly reflecting guttae at the level of the corneal endothelium. Donor corneas with advanced guttae showed less numerous guttae. Among 168 organ cultured donor corneas issued for transplantation, low density guttae were found in 43 (25.6%) corneas. The endothelial cell density and figure coefficient were significantly lower and organ culture time was significantly higher in the cornea guttata group than in the control group. The presence of grouped guttae significantly decreased the adjusted graft survival. The incidence of postoperative stage 3 cornea guttata was significantly higher when grouped guttae were found (5/6) than when no guttae or scattered guttae were found (8/101).

CONCLUSION

Cornea guttata can be detected during organ culture by means of light microscopy. It is associated with a decrease in endothelial cell figure coefficient and cell density. The presence of grouped guttae is associated with poorer graft survival and more frequent stage 3 cornea guttata in the graft after transplantation.

Preliminary clinical results of posterior lamellar keratoplasty through a sclerocorneal pocket incision

PURPOSE

To report the preliminary results of a surgical technique for transplantation of posterior corneal tissue through a sclerocorneal pocket incision for corneal endothelial disorders.

DESIGN

Retrospective, noncomparative, interventional cases series.

PARTICIPANTS AND INTERVENTION

In seven sighted human eyes, a deep stromal pocket was created across the cornea through a 9.0-mm superior scleral incision. A 7.0- or 7.5-mm diameter, posterior lamellar disc was excised and replaced by a 'same size' donor posterior disc, without suture fixation. The scleral incision was sutured.

MAIN OUTCOME MEASURES

Intra- and postoperative complications, best spectacle-corrected visual acuity, keratometry, topography, biomicroscopy, pachymetry, and endothelial cell density were evaluated.

RESULTS

Six to 12 months after surgery, all transplants were clear and in position. Best spectacle-corrected visual acuity was limited by preexisting maculopathies in two eyes and varied from 20/80 to 20/20. Postoperative astigmatism averaged 1. 54 diopters (D; standard deviation [SD] +/- 0.81 D), pachymetry averaged 0.49 mm (SD +/- 0.09 mm), and postoperative endothelial cell density averaged 2520 cells/mm(2) (SD +/- 340 cells/mm(2)). In one eye, a microperforation occurred during stromal pocket dissection so that the procedure was converted into a penetrating keratoplasty.

CONCLUSIONS

Posterior lamellar keratoplasty through a sclerocorneal pocket incision is a feasible surgical approach to manage corneal endothelial disorders.

Corneal endothelial cell apoptosis in patients with Fuchs' dystrophy

PURPOSE

To investigate whether apoptosis plays a notable role in degeneration of corneal endothelial cells in patients with Fuchs' dystrophy.

METHODS

Forty-seven corneal buttons from 41 patients with Fuchs' dystrophy were studied. Nucleus labeling, transmission electron microscopy (TEM), and TdT-dUTP terminal nick-end labeling (TUNEL) were used to detect apoptosis. TEM and TUNEL were performed on sections of all 47 corneal buttons, and nucleus labeling was performed on the last 10 corneas. Seven human donor corneas, two corneal buttons from two patients with keratoconus, and one corneal button from a patient with interstitial keratitis were used as negative controls for detection of apoptotic endothelial cells. Negative controls were studied by means of nucleus labeling, TUNEL, and TEM.

RESULTS

In the nucleus labeling assay, the average percentage of apoptotic endothelial cells was 2.65% in the Fuchs' dystrophy group (n = 10) and 0.23% in the control group (n = 10; P = 0.0003). In the TUNEL assay, labeling of some endothelial cells was observed on 42 of 47 corneas in the Fuchs' dystrophy group, whereas it was absent on most specimens of the control group. In TEM, most endothelial cell nuclei had a normal appearance, and apoptotic endothelial cells featuring condensed nucleus and decreased cell size could be observed exceptionally. Some apoptotic cells were found in the basal epithelial cell layer by means of nucleus labeling, TUNEL, and TEM in the Fuchs' dystrophy group but not in the control group.

CONCLUSIONS

This study suggests that apoptosis plays an important role in endothelial cell degeneration in Fuchs' dystrophy. Because of a lack of conclusive evidence of increased endothelial apoptosis by TEM, further studies are needed to ascertain this finding.

[Twenty-three cases of primary cornea guttata]

PURPOSE

To evaluate the clinical aspects of patients with primary cornea guttata and the morphology of their corneal endothelial cells.

METHODS

Twenty-three patients who visited Kanazawa Medical University Hospital or related hospitals in Ishikawa or Fukui prefectures and were diagnosed as having primary cornea guttata by slit lamp microscopy and contact specular microscopy underwent an analysis of corneal endothelial cells as well as their clinical status.

RESULTS

In 23 cases, the number of men and young people under 30 years of age was low, with 4 and 2 cases respectively. There was no visual impairment due to cornea guttata. In the specular microscopic findings, the size and density of dark areas varied according to each case and there was asymmetry in some cases. The parameters of the endothelial cells, comprising mean cell area, hexagonality, and the coefficient of variation, were almost within normal limits except for 1 eye of a 79-year-old man who was speculated to be at an early stage of Fuchs' endothelial corneal dystrophy. Three cases had received cataract surgery, but showed no statistical changes in endothelial morphology before or after the surgery.

CONCLUSION

Cornea guttata is thought to be a disease which is not uncommon in Japanese people and which does not bring about visual impairment or abnormalities in corneal endothelial cell parameters except for a small number of patients. Such cases with remarkably decreased cell densities should be considered to be at an early stage of Fuchs' dystrophy.

Denovo development of corneal guttae and Fuchs' dystrophy in corneal grafts

PURPOSE

To describe two cases of de novo development of corneal guttae and Fuchs' dystrophy in donor tissue following penetrating keratoplasty (PK) for unrelated conditions.

METHODS

Two patients underwent PK for keratoconus and a disciform scar secondary to herpes simplex virus. They were followed clinically for a period of 16 and 11 years, respectively. Specular microscopy was used in one patient.

RESULTS

Corneal guttae were first noted 10 years and 4 years following transplantation in the first and second patient, respectively. In both cases, the corneal guttae gradually increased in number, involving the central and temporal portions of the corneal graft There were no corneal guttae present in the host corneal rim or contralateral cornea of either patient.

CONCLUSIONS

These cases provide evidence to suggest that some corneas may be genetically predetermined to develop corneal guttae and Fuchs' dystrophy many years before any changes can be clinically detected.