PURPOSE; Techniques employing polarized light propagation and scattering ar
e useful in examining the cornea's lamellar structure, Recent advances in t
heoretical methods have significantly increased the ability to relate featu
res of lamellar arrangements to measurements of transmitted polarized light
, The chick cornea, because of its hypothesized structure of a gradual heli
cal rotation of lamellar pairs, presents an interesting model for further d
evelopment of this methodology,
METHODS: Small-angle light scattering (SALS) and polarized transmission mea
surements were made on 7 week-old chick corneas under conditions that close
ly approximate the physiological state. Birefringence properties were deter
mined from the transmission measurements and compared to the results of mod
el calculations of polarized light propagating through lamellae organized a
ccording to the hypothesized structure for chick cornea,
RESULTS: The I+ small-angle light scattering pattern had 4 cloverleaf lobes
aligned with the crossed polarizer and analyzer axes, The lobes disappeare
d when the transcorneal pressure was increased from zero to 18 mmHg, Retard
ation measured at 18 mmHg was very small (similar to 0.01 mu m)
CONCLUSION: The disappearance of the I+ small-angle Light scattering patter
n when IOP is increased suggests that the lamellae undulate in their relaxe
d state and the undulations straighten when IOP is increased, Measured bire
fringence properties are consistent with the hypothesized lamellar structur
e.