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 indicate 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), and
optic disc drusen. Women in an advanced stage of pregnancy with
pre-eclampsia should be screened by an ophthalmoscopic examination of the optic disc for early evidence of a rise in
intracranial pressure.
Pale disc , with the optic disc, or blind spot, at the lower left. Shown is a horizontal cross section of the right eye, viewed from above. A normal optic disc is orange to pink in colour and 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 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 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 the 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 by an eye care physician. Ophthalmologists and optometrists are able to provide this service. Blood flow in the
retina and
choroid in the optic disc region can be revealed non invasively by near-infrared
laser Doppler imaging.
Laser Doppler imaging 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. 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 1,000 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==