Biomedical Engineering Reference
In-Depth Information
2 Microscopic Examination of the Eye
Light microscopic examination of the eye requires several factors
including (1) knowledge of the clinical ophthalmic findings, (2) an
understanding of comparative ocular anatomy and histology, (3) an
awareness of iatrogenic ocular findings and artifacts, (4) an aware-
ness of toxicologic changes that may occur in ocular tissues, (5)
accurate terminology, (6) good histologic sections of globes, and
(7) evaluation of extraocular tissues [
4
,
10
,
15
-
21
].
Basic and advanced techniques are used in the clinical examination
of the eye and are covered in previous chapters, as well in other
references [
10
,
18
,
20
,
22
-
24
]. The pathologist needs to be aware
of the test method (e.g., topical, oral gavage, etc.) and clinical
ophthalmic findings in order to provide an accurate microscopic
evaluation of the ocular structures, including microscopic corre-
lates [
10
]. This may be accomplished by reviewing ophthalmic
examination narrative reports or by the use of diagrams or images
[
25
]. To accomplish this goal, protocol and clinical information
needs to be available to the study pathologist at the time of enucle-
ation, trimming, and ocular section evaluation.
2.1 Awareness
of Clinical Ophthalmic
Findings and Type
of Test Article
Administration
The differences in ocular anatomy among laboratory animals have
been well documented in the scientific literature and reviewed in
Chapter
2
[
19
,
24
,
26
]. Extraocular tissue associated with the eye
includes the ocular adnexa, eyelids, and other contents within the
orbit. Ocular adnexa include extraocular muscles, ocular glands,
and the structures of the lacrimal drainage apparatus. The extrao-
cular muscles are generally not examined, but may be retained with
the globe. Examples of when they may be examined include sites of
injection into the subTenon's space or muscular issues. Ocular
glands vary among laboratory animal species. Many large labora-
tory animals have a main lacrimal gland located in the superior,
temporal, and anterior aspect of the orbit, but some species (e.g.,
the rabbit) have a large accessory lacrimal gland. Animals with third
eyelids have a lacrimal gland associated with that structure and
other modified lacrimal glands are present in some laboratory
animals. Rabbits have a Harder's gland with two distinct lobes,
the white lobe and the pink lobe [
27
]. Rodents have a harderian
gland that fills much of the posterior aspect of the orbit. Secretion
of the lacrimal gland contributes to the precorneal tear film and
drains away through the puncta that open up to canaliculli which
eventually form the nasolacrimal duct.
2.2 Awareness
of Comparative Ocular
Anatomy
Iatrogenic findings are those that are caused by the human involve-
ment or environmental exposure that are independent of the effect
of the test article. Examples of iatrogenic findings include needle
2.3 Iatrogenic
Findings
