FUNDOSCOPIC EXAMINATION

05 November 2004

I. The use of the ophthalmoscope

Ophthalmoscopy: Direct vs Indirect
Slides on technique

II. The Normal Disc

1. Diameter of the optic nerve is 1.62mm.

2. The cup is formed embryologically by invagination of the optic vesicle at 34 weeks gestation. The inner wall of the cup at this stage will become the retina and the outer wall will be the retinal pigment epithelium. The cup is an apparent space centrally. The physiologic cup size varies from less that 0.1 to 0.9 of the total disc diameter.

3. The central retinal artery enters the eye at the optic nerve head-- usually nasal to the exit of the central retinal vein. It divides into superior and inferior branches. It further branches to supply 4 quadrants of the retina.

4. A cilioretinal artery is present in 32% of eyes. It often looks like a hook.

5. 25% of normal eyes have an optic crescent usually located temporally. Most are associated with myopia.

6. Histologic appearance of the optic nerve

a. Surface layer is nerve fibers from all over the retina

b. Pre-laminar retinal nerve is made of axonal fibers in fascicles separated by glial elements.

c. Lamina cribosa is a connective tissue "sieve" consisting of holes which bundle the million axons as they cross into the optic nerve, The lamina is deeper in hyperopic eyes and more shallow in myopic eyes. The lamina cribosa can bee seen in about 1/3 of eyes.

d. The retrolaminar nerve is behind the lamina cribosa and is where the myelin typically starts being formed by oliodendrocytes.

7. The vascular supply of the optic nerve disc

a. The prelaminar disc is from the choroidal vessels and the very superficial vessels from the     Central Retinal Artery

b. Lamina cribosa supply is the short ciliary arteries

c. Posteriorly, there are branches from the ophthalmic artery, and pial vessels.

d. Venous drainage from the disc is through the central retinal vein and choroid via the vortex veins.

8. Myopia

a. The disc may appear larger partly due to refractive error.

b. There are frequently crescents associated with the disc when the pigment epithelium does not reach the edge of the disc.

9. Hyperopia

a. The disc may appear smaller, partly due to refractive error.

b. The cup is usually small or non-existent

c. These discs can be confused with disc swelling

10. Myelinated nerve fibers

a. A developmental anomaly where myelination continues past the lamina cribosa along nerve fibers of the disc and retina. It typically has "feathered" edges which follow the nerve fiber layer.

b. Usually not associated with visual impairment. Myelinated nerve fibers can simulate papilledema.

c. May be unilateral or bilateral

d. May appear to be a nerve fiber layer infarct (soft exudate)

III. DISC ELEVATION

1. Papilledema is disc swelling due to increased intracranial pressure

Grades of Papilledema--Classification according to Lars Frisen

Stage 0 = normal disc with blurring of nasal and temporal disc; no obscuration of the vessel and the cup is maintained.

Stage 1 = C shaped blurring of the nasal, superior and inferior borders. Usually the temporal margin is normal

Stage 2 = Elevation of the temporal margin

Stage 3 = Elevation of the entire disc with obscuration of the retinal vessels at the disc margin

Stage 4 = Complete obliteration of the cup and obscuration of the vessels on the surface of the disc.

Stage 5 = Dome shaped appearance with all vessels being obscured.

2. Pseudopapilledema (anomalous optic discs, drusen, tilted optic disc, hypoplasia of the disc)

IV. Differentiating Papilledema from Pseudopapilledema