Objective measurement of backscattered light from the anterior and posterior cornea in vivo.
OBJECTIVE
To develop an objective and repeatable method of measuring corneal backscattered light from different depths of the cornea in vivo.


METHODS
A modified slit lamp ("scatterometer"), with a video camera and synchronous white strobe light, was used to capture images of a 0.1-mm-wide slit beam through the cornea. Image analysis software was developed to measure backscatter from digitized high-magnification images of 82 normal corneas of 41 subjects. Forty eyes of 20 of the same subjects were examined again after 1 month. Mean backscatter from the anterior, middle, and posterior thirds of the cornea was compared between repeated measurements, and expressed in arbitrary scatter units (SU).


RESULTS
Backscatter in the anterior third of the cornea was 451 +/- 42 SU (mean +/- SD, n = 82), from the middle third was 274 +/- 29 SU (n = 82), and from the posterior third was 242 +/- 28 SU (n = 82). The difference in backscatter measured a month apart was 5 +/- 27 SU (P = 0.34), 2 +/- 17 SU (P = 0.42), and 0 +/- 15 SU (P = 0.95) in the anterior, middle, and posterior thirds of the cornea, respectively. Minimum detectable differences between measurements were 12, 8, and 7 SU in the anterior, middle and posterior thirds, respectively (alpha = 0.05, beta = 0.20, n = 40).


CONCLUSIONS
Backscatter can be measured at different depths of the cornea from high-magnification digitized images of a narrow slit beam through the cornea. The method is objective and repeatable and can be applied in prospective studies of deep and posterior lamellar keratoplasty.
Patel
Sanjay V
SV
Department of Ophthalmology, Mayo Clinic College of Medicine, Rochester, Minnesota 55905, USA. patel.sanjay@mayo.edu
Winter
Eric J
EJ
McLaren
Jay W
JW
Bourne
William M
WM
D000328:Adult; D003315:Cornea / Q000033:anatomy & histology / Q000528:radiation effects*; D003941:Diagnostic Techniques, Ophthalmological; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008027:Light; D008875:Middle Aged; D012542:Scattering, Radiation