Optic disc

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Optic disc
Interior of posterior half of bulb of left eye. The veins are darker in appearance than the arteries.
The terminal portion of the optic nerve and its entrance into the eyeball, in horizontal section.
Gray's	subject #225 1015
MeSH	Optic+Disk

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The optic disc or optic nerve head is the location where ganglion cell axons exit the eye to form the optic nerve. There are no light sensitive rods or cones to respond to a light stimulus at this point thus it is also known as "the blind spot" or "anatomical blind spot"; the break in the visual field created by the optic disc is also called "the blind spot" or "physiological blind spot". The optic nerve head in a normal human eye carries from 1 to 1.2 million neurons from the eye towards the brain.

Clinical examination

The eye is unique due to the transparency of its optical medium. 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. Inspection of the optic disc by ophthalmoscopy or biomicroscopy 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 and other optic neuropathies, optic neuritis, anterior ischemic optic neuropathy or papilledema (i.e. optic disc swelling produced by raised intracranial pressure). 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.

Schematic diagram of the human eye, with the optical disc, or blind spot, at the bottom.

Imaging of the optic disc

Traditional colour-film camera images are the gold 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. However, since not everybody can be trained so well, automated techniques have been devised to supplant or replace the human expertise. Heidelberg Retinal Tomography (HRT-II), GDx-VCC and optical coherence tomography (Stratus-OCT 3) are the currently available computerised techniques for imaging various structures of the eyes, including the optic disc. They quantitate 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. It should be noted that imaging won't 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 by an eye care physician. Ophthalmologists and Optometrists are able to provide this service.

Retinography photograph showing the optic disc as a bright area on the right where blood vessels converge.

External links

• Diagram at Moorfields Eye Hospital
• Diagram at Ballard Optical

fr:Point aveugle nl:Blinde vlek ja:盲点 no:Den blinde flekksk:Slepá škvrna (oko) sv:Blinda fläcken

Acknowledgement and Attribution Regarding Sources of Content

Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .