Structural collagen alterations in macular corneal dystrophy occur mainly in the posterior stroma.
OBJECTIVE
Collagen fibrils in the corneal stroma in macular corneal dystrophy, on average, are more closely spaced than in the normal cornea. This study was conducted to investigate if this occurs uniformly across the stroma or is more prevalent at certain stromal depths.


METHODS
Microbeam synchrotron X-ray fiber diffraction patterns were obtained in 25 microm steps across the whole thickness of a thin strip of a macular corneal dystrophy cornea obtained at keratoplasty. Data were analyzed for mean collagen interfibrillar spacing at all positions. Serum was analyzed immunochemically to determine immunophenotype, and transmission electron microscopy was carried out to visualize stromal ultrastructure.


RESULTS
Keratan sulphate was not detectable in blood serum, classifying the disease as macular corneal dystrophy type I. Collagen interfibrillar spacing dropped linearly with stromal depth from the anterior to posterior cornea, measuring 5-10% less in the posterior 100 microm of the MCD stroma compared to the anterior 100 microm (p < 0.001). Isolated pockets of collagen fibrils with unusually large diameters were identified in the deep stroma.


CONCLUSIONS
Collagen fibril spacing is reduced and large-diameter collagen fibrils are seen in macular corneal dystrophy type I, with the deep stroma affected more. We speculate that the ultrastructural abnormalities are more prevalent in the posterior stroma because the structural influence of sulphated keratan sulphate glycosaminoglycans/proteoglycans is high in this region of the cornea.
Palka
Barbara P
BP
School of Optometry & Vision Sciences, Cardiff University, Cardiff, United Kingdom.
Sotozono
Chie
C
Tanioka
Hidetoshi
H
Akama
Tomoya O
TO
Yagi
Naoto
N
Boote
Craig
C
Young
Robert D
RD
Meek
Keith M
KM
Kinoshita
Shigeru
S
Quantock
Andrew J
AJ
D003317:Corneal Dystrophies, Hereditary / Q000097:blood / Q000473:pathology* / Q000601:surgery; D003319:Corneal Stroma / Q000648:ultrastructure*; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D024022:Fibrillar Collagens / Q000737:chemistry / Q000648:ultrastructure*; D006801:Humans; D016130:Immunophenotyping; D007632:Keratan Sulfate / Q000097:blood; D015948:Keratoplasty, Penetrating; D008875:Middle Aged; D014961:X-Ray Diffraction
D024022:Fibrillar Collagens; D007632:Keratan Sulfate