Biomedical Engineering Reference
In-Depth Information
does not always signify degeneration, PDN should be a separate
diagnosis.
Clinical observations should also be specific. Opacification of
the lens may be an indication of lenticular irreversible degeneration
(i.e., cataract) or it may be a reversible change [
73
]. Additionally,
microscopically, swelling of a few lenticular fibers with no other
lenticular changes may be a reversible finding. An accurate assess-
ment and management of the ocular finding can be obtained by use
of the correct term for the location and the diagnosis of a micro-
scopic finding.
2.7 Good Histologic
Sections of Globes
Getting pristine ocular sections for microscopic examination is
essential for detecting microscopic ocular findings. This begins
with enucleation [
10
-
13
,
25
,
74
]. Enucleation should be per-
formed on all experimental animals, including rodents, as soon as
possible after death of the animal [
74
]. A small portion (5 mm, if
possible) of retrobulbar optic nerve should remain with the globe.
These sections of optic nerve will be trimmed to obtain cross
sections for evaluation (especially of axons of retinal ganglion
cells). All extraocular tissue should be removed, unless there is a
need to keep the tissue attached (e.g., deposit in Tenon's capsule).
For rodents, the harderian gland should be removed. Removal of
extraocular tissue not only enhances fixation, but it also exposes
landmarks (e.g., long posterior ciliary body) that are used for
trimming. Any tissue removed should be saved in fixative and
labeled with the study number, animal number, and left (OS) or
right (OD) eye.
To perform an enucleation the medial and lateral commissures
of the eyelids may be cut to provide more exposure to the globe.
The eyelids and adjacent skin may be removed and the orbital bone
removed with rongeurs, if more exposure to the globe is needed.
Gentle tension may be applied to connective tissue attached to the
globe to aid in the removal of the globe from the orbit. Rough
handling of the globe may result in artifact (e.g., sensory retinal
separation). Excessive tugging on the globe results in artifactual
spaces or hyalinized deposits within the optic nerve [
75
,
76
].
Cutting the optic nerve too close to the globe may result in another
artifact, myelin within the subretinal space [
77
,
78
]. Once the
globe has been removed from the orbit and cleaned of extraocular
tissue, it should be put in a container for fixation. The identification
of the globe, including study number, animal number, and right or
left globe, should be maintained. If the orientation (i.e., superior,
inferior, nasal, and temporal) of the globe may be lost during
fixation (e.g., opaque albino rodent globe fixed in Davidson's
fixative), then the globe may be marked with tissue dye, tattoo
ink, or a fine suture (see Trimming for Light Microscopy below).
2.7.1
Enucleation
