The optic disc or optic nerve head is the point of exit for ganglion cell

axon An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see spelling differences), is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action ...

s leaving the

eye Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light and conv ...

. Because there are no rods or cones overlying the optic disc, it corresponds to a small blind spot in each eye. The ganglion cell axons form the

optic nerve In neuroanatomy, the optic nerve, also known as the second cranial nerve, cranial nerve II, or simply CN II, is a paired cranial nerve that transmits visual information from the retina to the brain. In humans, the optic nerve is derived fro ...

after they leave the eye. The optic disc represents the beginning of the optic nerve and is the point where the axons of retinal ganglion cells come together. The optic disc is also the entry point for the major blood vessels that supply the

retina The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which then ...

. The optic disc in a normal human eye carries 1–1.2 million

afferent nerve fiber Afferent nerve fibers are the axons (nerve fibers) carried by a sensory nerve that relay sensory information from sensory receptors to regions of the brain. Afferent projections ''arrive'' at a particular brain region. Efferent nerve fibers ...

s from the eye towards the brain.

Structure

The optic disc is placed 3 to 4 mm to the nasal side of the

fovea Fovea () (Latin for "pit"; plural foveae ) is a term in anatomy. It refers to a pit or depression in a structure. Human anatomy * Fovea centralis of the retina * Fovea buccalis or Dimple * Fovea of the femoral head *Trochlear fovea of the f ...

. It is a vertical oval, with average dimensions of 1.76mm horizontally by 1.92mm vertically. There is a central depression, of variable size, called the optic cup. This depression can be a variety of shapes from a shallow indentation to a bean pot—this shape can be significant for diagnosis of some retinal disease.

Function

The optic disc or optic nerve head is the point of exit for ganglion cell

axons An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see spelling differences), is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action po ...

leaving the

. Because there are no rods or cones overlying the optic disc, it corresponds to a small blind spot in each eye.

Clinical significance

The eye is unique because of the transparency of its optical media. Almost all eye structures can be examined with appropriate optical equipment and lenses. Using a modern direct ophthalmoscope gives a view of the optic disc using the principle of reversibility of light. A slit lamp biomicroscopic examination along with an appropriate aspheric focusing lens (+66D, +78D or +90D) is required for a detailed stereoscopic view of the optic disc and structures inside the eye. A biomicroscopic exam can give an indication of the health of the optic nerve. In particular, the eye care physician notes the colour, cupping size (as a cup-to-disc ratio), sharpness of edge, swelling, hemorrhages, notching in the optic disc and any other unusual anomalies. It is useful for finding evidence corroborating the diagnosis of

glaucoma Glaucoma is a group of eye diseases that result in damage to the optic nerve (or retina) and cause vision loss. The most common type is open-angle (wide angle, chronic simple) glaucoma, in which the drainage angle for fluid within the eye re ...

and other optic neuropathies,

optic neuritis Optic neuritis describes any condition that causes inflammation of the optic nerve; it may be associated with demyelinating diseases, or infectious or inflammatory processes. It is also known as optic papillitis (when the head of the optic nerv ...

, anterior ischemic optic neuropathy or papilledema (i.e. optic disc swelling produced by raised intracranial pressure), and optic disc drusen. Women in advanced stage of pregnancy with pre-eclampsia should be screened by an ophthalmoscopic examination of the optic disc for early evidence of rise in intracranial pressure.

Pale disc

A normal optic disc is orange to pink in colour may vary based on ethnicity. A pale disc is an optic disc which varies in colour from a pale pink or orange colour to white. A pale disc is an indication of a disease condition.

Imaging

Traditional colour-film camera images are the reference standard in imaging, requiring an expert ophthalmic photographer, ophthalmic technician, optometrist or an ophthalmologist for taking standardised pictures of the optic disc. Stereoscopic images offer an excellent investigative tool for serial follow-up of suspected changes in the hands of an expert optometrist or ophthalmologist. Automated techniques have also been developed to allow for more efficient and less expensive imaging. Heidelberg retinal tomography ( HRT),

scanning laser polarimetry Scanning laser polarimetry is the use of polarised light to measure the thickness of the retinal nerve fiber layer as part of a glaucoma workup. The GDx-VCC is one example. However a Dutch study found that while there is a correlation between sta ...

and optical coherence tomography are computerised techniques for imaging various structures of the eyes, including the optic disc. They quantify the nerve fiber layer of disc and surrounding retina and statistically correlate the findings with a database of previously screened population of normals. They are useful for baseline and serial follow-up to monitor minute changes in optic disc morphology. Imaging will not provide conclusive evidence for clinical diagnosis however, and the evidence needs to be supplanted by serial physiological testing for functional changes. Such tests may include visual field charting and final clinical interpretation of the complete

eye examination An eye examination is a series of tests performed to assess vision and ability to focus on and discern objects. It also includes other tests and examinations pertaining to the eyes. Eye examinations are primarily performed by an optometrist, ...

by an eye care physician. Ophthalmologists and optometrists are able to provide this service. Blood flow in the

and choroid in the optic disc region can be revealed non invasively by near-infrared

laser Doppler imaging Laser Doppler imaging (LDI) is an imaging method that uses a laser beam to scan live tissue. When the laser light reaches the tissue, the moving blood cells generate doppler components in the reflected ( backscattered) light. The light that comes ...

.Puyo, L., M. Paques, M. Fink, J-A. Sahel, and M. Atlan. "In vivo laser Doppler holography of the human retina." Biomedical optics express 9, no. 9 (2018): 4113-4129.

Laser Doppler imaging Laser Doppler imaging (LDI) is an imaging method that uses a laser beam to scan live tissue. When the laser light reaches the tissue, the moving blood cells generate doppler components in the reflected ( backscattered) light. The light that comes ...

can enable mapping of the local arterial resistivity index, and the possibility to perform unambiguous identification of retinal arteries and veins on the basis of their systole- diastole variations, and reveal ocular hemodynamics in human eyes. Furthermore, the Doppler spectrum asymmetry reveals the local direction of blood flow with respect to the optical axis. This directional information is overlaid on standard grayscale blood flow images to depict flow in the central artery and vein.Puyo, L., M. Paques, and M. Atlan. "Retinal blood flow reversal in out-of-plane vessels imaged with laser Doppler holography" https://arxiv.org/abs/2008.09813 A systematic review of 106 studies and 16,260 eyes compared the performance of the imaging techniques, and found that all three imaging tests performed very similarly when detecting for glaucoma. The review found that in 1000 patients subjected to imaging tests, with 200 having manifest glaucoma, the best imaging tests would miss 60 cases out of the 200 patients with glaucoma, and incorrectly refer 50 out of 800 patients without glaucoma.

Abnormalities

Megalopapilla Megalopapilla is a non-progressive human eye condition in which the optic nerve head (optic disc) has an enlarged diameter, exceeding 2.1 mm with no other morphological abnormalities. Clinical features In megalopapilla the optic disc diamete ...

: a non-progressive condition in which the optic disc is enlarged (diameter exceeding 2.1 mm) with no other morphological abnormalities. *

Morning glory disc anomaly The morning glory disc anomaly (MGDA) is a congenital deformity resulting from failure of the optic nerve to completely form in utero. The term was coined in 1970 by Kindler, noting a resemblance of the malformed optic nerve to the morning glory flo ...

: a unilateral congenital deformity resulting from failure of the optic nerve to completely form in utero. The term was coined in 1970 by Kindler, noting a resemblance of the malformed optic nerve to the morning glory flower. *

Optic pit Optic pit, optic nerve pit, or optic disc pit (ODP) is rare a congenital excavation (or regional depression) of the optic disc (also optic nerve head), resulting from a malformation during development of the eye. The incidence of ODP is 1 in 10,0 ...

: congenital excavation of the optic disc resulting from a malformation during development of the eye.

Gallery

File:LDH_ONH_ED.gif, Blood flow in the optic disc revealed by holographic

. File:LaserDopplerHolographyRetinaSpectralAsymmetry.gif, Local direction of blood flow with respect to the optical axis revealed by the Doppler spectrum asymmetry in out-of-plane retinal vessels by holographic

. File:Optic_cup_and_macula_-_3D_motion_parallax.gif, Three dimensional image of a healthy optic disc in a 24-year-old female. File:Optic disc detail.png, alt=High detail picture of optic disc., Optic disc showing microvasculature. File:Tilted Disc Syndrome.jpg, Tilted optic disc in left eye of a 20-year-old male. File:Optic disc edema and haemorrhage.jpg, Optic disc edema and haemorrhage

References

External links

Diagram at Moorfields Eye HospitalDiagram at Ballard OpticalRetinal Vein Pulsation Is in Phase with Intracranial Pressure and Not Intraocular Pressure
{{Authority control Human eye anatomy