Biomedical Engineering Reference
In-Depth Information
Fig. 42 Histologic section of the anterior cornea of a Sprague-Dawley rat with
corneal dystrophy. The areas of basement membrane thickening, disorganiza-
tion, and mineralization are indicated by the arrows. H&E 100
common in mice, and varies in prevalence, appearance, and severity
by strain of rat/mouse, sex, age, and shipment and supplier. It is
more prevalent in males and increases in prevalence and in some
species severity with age [
23
]. The prevalence will vary from 5 to
100 % [
30
-
36
]. It has been variously termed corneal dystrophy,
calcific keratopathy, corneal opacity, corneal calcification, and spon-
taneous corneal degeneration. It has also been reproduced experi-
mentally in rats by corneal desiccation which can occur secondary
to dehydration, a decrease in blink rate, sedation, or anesthesia. As
it increases in severity with age it can be associated with secondary
keratitis (typically nasal), especially in the Fischer 344 rat (Fig.
43
).
In addition, keratitis can occur secondary to anesthesia, corneal
exposure, keratoconjunctivitis sicca, sialodacryoadenitis (SDA),
environment (dust, irritants), and conjunctivitis.
Cataracts may be seen during pretest screening and are most
often nuclear (Fig.
39
). They can be unilateral or bilateral and if
possible, these animals are eliminated from the study. Posterior
cortical cataracts are also seen, often associated with a PH with or
without hemorrhage. Cataracts may also be spontaneous, asso-
ciated with age, secondary to retinal degeneration, or associated
with trauma, anesthesia, or other external factors (Fig.
44
)[
29
,
54
-
56
]. Acquired cataracts may also be treatment related and the
result of a toxicologic effect. The examiner should always ascertain
if orbital bleeding was performed during the study in question,
especially if the cataracts are unilateral and typically in the same
eye within the study animals. Reversible lens opacities may be
