Biomedical Engineering Reference
In-Depth Information
tracts in the cornea, sclera or uvea, orbital lesions following orbital
venipuncture, and light-induced photoreceptor degeneration
[
13
,
28
-
37
]. Albino rodents housed on the top shelf of racks may
be exposed to an excessive amount of light, even though the
illumination in the room may be within acceptable limits [
38
] and
consequently develop light-induced outer retinal (photoreceptor)
degeneration.
Spontaneous background findings involving the globe are findings
that occur as a result of a congenital defect, trauma, inherited
condition, or aging change and are well described in the literature
[
13
,
35
,
39
-
52
]. Some spontaneous ocular findings are reversible,
such as cold cataracts in anesthetized mice [
53
,
54
], and others may
be a background finding or may be a toxicologic finding, such as
corneal calcification in rodents [
55
-
59
]. Spontaneous changes may
also involve the optic nerve, such as idiopathic bilateral optic neu-
ropathy in monkeys [
60
].
2.4 Spontaneous
Background Findings
Preclinical toxicologic findings are findings that occur as a result of
the administration of a test article and are well described in the
literature [
13
,
14
,
22
,
35
,
40
,
47
,
61
-
68
]. Any of the ocular
structures may be affected, including some findings that occur in
ocular structures not present in the human eye, such as tapetum
lucidum in dogs and the harderian gland in rodents [
69
,
70
].
2.5 Toxicologic
Findings
With the different types of ocular tissues and the various methods
of identifying specific findings in the structures of the eye, the use of
descriptive terms is necessary. Findings need to be identified as to
their location. The following terms may be used: superior, inferior,
nasal, temporal, inner (internal), outer (external), anterior, poste-
rior, central, or peripheral. The anterior central aspect of the globe
(or lens) is the anterior pole and the posterior central aspect of
the globe (or lens) is the posterior pole. A vertical plane through
these poles is the median or midsagittal plane and planes parallel
with the midsagittal plane are sagittal planes. A plane that divides a
globe into an anterior and posterior portion is a coronal (frontal)
plane, such as a plane through the equator of the globe (or lens).
Some terms indicate that a finding is adjacent to another structure
(e.g., peripapillary, meaning close to the optic nerve).
If specific cells or areas of the eye are involved, then those terms
should be used. For example, minimal diffuse retinal degeneration
is nonspecific and implies a change in some part of the retina. Since
any change in the retina is important, even minimal ones, the
portion of the retina or retinal cells involved should be indicated.
Another example is displaced photoreceptor cell nuclei (PDN).
These PDN may be observed in retinas with photoreceptor degen-
eration or they may be observed in retinas with no evidence of
photoreceptor degeneration [
71
,
72
]. Since the presence of PDN
2.6 Ocular
Terminology
