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Frances E. Jones, Barbara P. Palka, Jeremy A. Guggenheim, Robert D. Young, James R. Ralphs, Andrew J. Quantock; The Dynamics of Corneal Compaction in the Developing Chick. Invest. Ophthalmol. Vis. Sci. 2011;52(14):2535.
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© ARVO (1962-2015); The Authors (2016-present)
To determine how the thickness of the embryonic chick cornea changes in the embryonic day 9 to 18 (E9-E18) developmental period, and the potential involvement of the corneal endothelium.
A-scan ultrasonography was used to measure corneal thickness in the left eyes of 123 embryonic chicks aged between E9 and E18 (n=9-13 at each timepoint; data presented as mean ± SD). The system consisted of a Panametrics model 5073PR pulser-receiver and a 20 MHz transducer fitted with a 15 mm saline stand-off perfused at 0.05 ml/min. Ultrasound velocities were assumed to be 1.534 mm/µs in the cornea. Immunohistochemical examination of the corneal endothelium was performed on 10µm cryosections from embryonic corneas using a rabbit anti Na+/HCO³ co-transporter polyclonal primary antibody and Alexa Fluor 488 secondary antibody.
Corneal thickness, which measured 170µm (±19.8; n=13) at E9, progressively increased to 199µm (±13.8; n=13) at E10, 217µm (±13.5; n=13) at E11, and 263µm (±26.2; n=9) at E12. All changes, from day-to-day, were significant at <0.001. After E12, the corneal thickness reached a plateau, with no significant differences between consecutive days at E13 (270µm ±16.1; n=12; E12-E13 P = 0.655), E14 (279µm (±22.8; n=12; E13-E14 P = 0.177) and E15 (270µm (±13.0; n=13; E14-E15 P =0.202). From E15 onwards the cornea became increasingly thinner, measuring 235µm (±12.4; n=13) at E16, 213µm (±13.3; n=13) at E17, and 201µm (±14.0; n=12) at E18. All changes, from day-to-day, were significant at <0.001 apart from E17-E18 at P=0.007. Immunohistochemistry highlighted the presence of a Na+/HCO³ co-transporter in the endothelial layer at E15.
Corneal thickness in the embryonic chick attains its maximum value of between 260-280µm in the E12 and E15 developmental period. Thinning to 200µm by E18 is undoubtedly associated with matrix compaction, probably with the involvement of the Na+/HCO³ co-transporter in the corneal endothelium driving stromal dehydration.
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