Light scattering after acute UV-B injury rises continuously to a
maximum, after which increasing opacification results in decreasing
forward light scattering.
23 Therefore, the measurement of
forward light scattering in this system is most sensitive when the lens
is not densely opaque. Pilot exposures based on the Pitts et al. rabbit
study estimated the minimum dose (D) to produce significant light
scattering at each wavelength.
24 The initial part of the
dose–response curve was determined by using small, regular increments
between doses (0, 0.25 D, 0.5 D, D, and twice D). The initial part of
the dose–response curve is well described by a quadratic polynomial:
y =
m 1 +
m 2 x 2 (where
y is light scattering, in tEDC units, and
x is
dose, in kilojoules per square meter). Variance increases with dose, so
estimates of the parameters and confidence intervals were calculated
with weighted curvilinear regression (Origin 6.0; Microcal,
Northampton, MA). Because a clear lens scatters some light, the minimum
forward light scattering with no UV-B dose is not zero. When
m 2 is zero, the function reduces to
y =
m 1, and
m 1 thus defines the forward light
scattering, in tEDC units, of the clear lenses in each wavelength
group. The 95% confidence intervals were calculated to show the
reliability of
m 1 and
m 2.
25