05 November 2004
I. The use of the ophthalmoscope
Direct vs Indirect
II. The Normal Disc
Diameter of the optic nerve is 1.62mm.
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.
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.
A cilioretinal artery is present in 32% of eyes. It often looks like a hook.
25% of normal eyes have an optic crescent usually located temporally.
Most are associated with myopia.
Surface layer is nerve fibers from all over the retina
Pre-laminar retinal nerve is made of axonal fibers in fascicles separated by
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.
The retrolaminar nerve is behind the lamina cribosa and is where the myelin
typically starts being formed by oliodendrocytes.
The vascular supply of the optic nerve disc
The prelaminar disc is from the choroidal vessels and the very superficial
vessels from the Central Retinal Artery
Lamina cribosa supply is the short ciliary arteries
Posteriorly, there are branches from the ophthalmic artery, and pial vessels.
Venous drainage from the disc is through the central retinal vein and choroid
via the vortex veins.
The disc may appear larger partly due to refractive error.
There are frequently crescents associated with the disc when the pigment
epithelium does not reach the edge of the disc.
The disc may appear smaller, partly due to refractive error.
The cup is usually small or non-existent
These discs can be confused with disc swelling
Myelinated nerve fibers
Usually not associated with visual impairment. Myelinated nerve fibers can
May be unilateral or bilateral
May appear to be a nerve fiber layer infarct (soft exudate)
III. DISC ELEVATION
Papilledema is disc swelling due to increased intracranial pressure
of Papilledema--Classification according to Lars Frisen
0 = normal disc with blurring of nasal and temporal disc; no obscuration of the
vessel and the cup is maintained.
1 = C shaped blurring of the nasal, superior and inferior borders. Usually the
temporal margin is normal
2 = Elevation of the temporal margin
3 = Elevation of the entire disc with obscuration of the retinal vessels at the
4 = Complete obliteration of the cup and obscuration of the vessels on the
surface of the disc.
5 = Dome shaped appearance with all vessels being obscured.
Pseudopapilledema (anomalous optic discs, drusen, tilted optic disc, hypoplasia
of the disc)
IV. Differentiating Papilledema from Pseudopapilledema