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J. V. Jester, M. Winkler, C. J. Nien-Shy, S. Massei, T. Juhasz, D. J. Brown; Superior-Inferior Distribution of Anterior, Transverse (Sutural) Lamellae in the Human Cornea. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4555.
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Recently, we have identified a population of anterior corneal lamellae that insert into the anterior limiting lamina (ALL, Bowman’s layer) and run transversely, deep into the human cornea. These "sutural" lamellae are noticeably lacking in corneas diagnosed with keratoconus suggesting that they serve an important biomechanical role in controlling corneal shape. The purpose of this study was to further characterize the organization and distribution of ‘sutural’ lamellae in the human cornea.
A normal 83 year old male cornea was obtained from the San Diego Eye Bank. The anterior chamber was perfused and then fixed under high pressure to thin the corneal stroma. The tissue was then embedded in agar, and 300 um thick 13 mm long slices from the superior-inferior (S-I) meridian including the limbus were obtained using a vibratome. Sections were then scanned by non-linear optical imaging of second harmonic generated signals (SHG) using a Zeiss 510 Meta and Chameleon femtosecond laser. A series of 504, 3D image stacks, 512x512 pixels by 81 planes with 0.91 um lateral and 2.0 um axial resolution covering an area of 15.6 mm x 5.9 mm was collected. Images stacks were then stitched together to generate a large scale, high resolution 3D image using Image J. The location and angle of all collagen lamellae inserting into the ALL and extending at least 50 um into the anterior stroma were then mapped using Metamorph Image Analysis software.
The total density of sutural lamellae averaged 27.6/mm and 28.2/mm in two contiguous S-I slices, however the density was significantly higher (p<0.01) in the superior region compared to the inferior region, averaging 18.4 + 2.8 vs 13.1 + 2.4. There was also a preferred orientation of sutural lamellae toward the limbus in both the superior and inferior region, with over 70% of lamellae showing this orientation, while in the central cornea there was an equal distribution. Interesting, at the corneal periphery, many sutural lamellae appear to have their origins in the scleral collagen with insertion into the ALL at various points along the cornea.
These results indicate that there are asymmetric distributions of ‘sutural’ lamellae over the corneal surface, with a higher density in the superior cornea and preferred orientations toward the limbus along the S-I meridian. These findings support the hypothesis that ‘sutural’ lamellae exert force on the ALL that controls the overall corneal shape and mechanical properties.
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