Wednesday, January 18, 2006

INTERNAL (GROSS) EXAMINATION OF THE EYE


Eyes may be incised for internal examination in other ways (see figure to the left) Usually this involves a posteroanterior incision in different meridians. For example, eyes that have had cataract extractions may be incised in a vertical plane nasal to the optic nerve in order to study the corneal wound and its complications. Surgical eyes with intraocular tumors must be incised in a plane to slightly intersect the tumor to facilitate study. The mechanics of the operation remain the same, the only difference being the degree of rotation of the incision from the horizontal meridian. All surgically aphakic and pseudophakic eyes will be opened with an incision at the equator in a coronal plane.

The "grossing in" or internal examination is carried out with a stereomicroscope and a deep Petri dish containing 50% ethanol; submersion of calottes in ethanol eliminates most reflections from the vitreous body and permits detailed examination of the inner surfaces of the eye. However, the eye must have been equilibrated in ethanol in the steps prior to the examination. The concentration of the alcohol in which the eye is examined must be precisely that in which the eye has been stored, otherwise the vitreous becomes "refractive" and examination of deeper structures is virtually impossible. Alternatively, the calottes may be stored overnight in the new alcohol (to achieve equilibration). Some important observations concerning the vitreous body (posterior vitreous detachment and the degree of synchysis), however, is best studied while suspending the calottes in air.

When manipulating the calottes in the Petri dish, care must be taken to grasp only episcleral tissue, extraocular muscles, or the like, since artifactual changes in the retina and uvea will occur readily with direct application of forceps. The inner aspects of the calottes are now studied systematically using low power (7x) and, if indicated high magnification. A variety of lighting techniques must be used, including: diffuse vs. focused, direct vs. oblique, direct vs. transillumination, etc...In effect the light is always moving, since many lesions can only be characterized completely with combinations of lighting and magnification.

Transillumination of the calottes can also be accomplished readily with the table light, during the internal examination. Subtle conditions of the vitreous can often be seen best with oblique Illumination that casts a shadow under the lesion. Subtle epiretinal or preretinal conditions deep in the calotte may only be seen by focusing the light on the adjacent retina as a secondary (indirect) light source. With proper examination techniques, gross examination of the optic nerve will yield almost as much information as time-consuming (and delayed) examination of microscopic tissue sections, even when special stains are employed. This is especially true of lesions causing demyelinization axon bundles. The light must be focused and oblique while examining the nerve on the submerged large calotte.

Findings from stereomicroscopic examination of the opened globe are drawn to scale on the gross sheet and labeled outside the drawings of the eye. (The semi-diagrammatic drawings of the opened globe on the sheet show the small (superior) calotte on the right and the large (inferior) calotte on the left. These drawings are three (3) times the normal size and all findings should be drawn to scale in their relative topographical location. The large calotte has been drawn as if it is slightly tipped upward in the front so that one can see the optic disc and the macula. One should record in the lower one-third of sheet only the important gross findings: if some categories are negative, indicate so. The bottom also constitutes a check-list for the examiner.

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