Optic disc

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Optic disc
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Ophthalmoscopy photograph showing the optic disc as a bright area on the right where blood vessels converge.
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The terminal portion of the optic nerve and its entrance into the eyeball, in horizontal section.
Details
SynonymsOptic disk, optic disc, optic nerve head, blind spot, Mariotte blind spot, Mariotte's blind spot, optic papilla, discus nervi optici [TA], papilla nervi optici, porus opticus)
Identifiers
Latin discus nervi optici
MeSH D009898
TA98 A15.2.04.019
TA2 6788
FMA 58634
Anatomical terminology

The optic disc or optic nerve head is the point of exit for ganglion cell axons leaving the eye. Because there are no rods or cones overlying the optic disc, it corresponds to a small blind spot in each eye.

Contents

The ganglion cell axons form the optic nerve 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 in a normal human eye carries 1–1.2 million afferent nerve fibers from the eye toward the brain. The optic disc is also the entry point for the major arteries that supply the retina with blood, and the exit point for the veins from the retina. [1]

Structure

The optic disc is placed 3 to 4 mm to the nasal side of the fovea. It is a vertical oval, with average dimensions of 1.76mm horizontally by 1.92mm vertically. [2] 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 diseases.

Function

The optic disc or optic nerve head is the point of exit for ganglion cell axons leaving the eye. Because there are no rods or cones overlying the optic disc, it corresponds to a small blind spot in each eye.

Clinical significance

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

Schematic diagram of the human eye, with the optic disc, or blind spot, at the lower left. Shown is a horizontal cross section of the right eye, viewed from above. Schematic diagram of the human eye en.svg
Schematic diagram of the human eye, 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. [3] 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.[ citation needed ]

Imaging

Optic disc cross-sections imaged by an SD-OCT. SD-OCT Optic Disc Cross-Sections.png
Optic disc cross-sections imaged by an SD-OCT.

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. [4] 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. [5] 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. [6]

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. [7] 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. [7]

Abnormalities

See also

Related Research Articles

<span class="mw-page-title-main">Retina</span> Part of the eye

The retina 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 processes that image within the retina and sends nerve impulses along the optic nerve to the visual cortex to create visual perception. The retina serves a function which is in many ways analogous to that of the film or image sensor in a camera.

<span class="mw-page-title-main">Glaucoma</span> Group of eye diseases

Glaucoma is a group of eye diseases that lead to damage of the optic nerve, which transmits visual information from the eye to the brain. Glaucoma may cause vision loss if left untreated. It has been called the "silent thief of sight" because the loss of vision usually occurs slowly over a long period of time. A major risk factor for glaucoma is increased pressure within the eye, known as intraocular pressure (IOP). It is associated with old age, a family history of glaucoma, and certain medical conditions or medications. The word glaucoma comes from the Ancient Greek word γλαυκóς, meaning 'gleaming, blue-green, gray'.

<span class="mw-page-title-main">Optic nerve</span> Second cranial nerve, which connects the eyes to the brain

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 from optic stalks during the seventh week of development and is composed of retinal ganglion cell axons and glial cells; it extends from the optic disc to the optic chiasma and continues as the optic tract to the lateral geniculate nucleus, pretectal nuclei, and superior colliculus.

<span class="mw-page-title-main">Hypertensive retinopathy</span> Medical condition

Hypertensive retinopathy is damage to the retina and retinal circulation due to high blood pressure.

<span class="mw-page-title-main">Choroid</span> Vascular layer of the eye, containing connective tissue, and lying between the retina and the sclera

The choroid, also known as the choroidea or choroid coat, is a part of the uvea, the vascular layer of the eye. It contains connective tissues, and lies between the retina and the sclera. The human choroid is thickest at the far extreme rear of the eye, while in the outlying areas it narrows to 0.1 mm. The choroid provides oxygen and nourishment to the outer layers of the retina. Along with the ciliary body and iris, the choroid forms the uveal tract.

<span class="mw-page-title-main">Ophthalmoscopy</span> Part of an eye examination

Ophthalmoscopy, also called funduscopy, is a test that allows a health professional to see inside the fundus of the eye and other structures using an ophthalmoscope. It is done as part of an eye examination and may be done as part of a routine physical examination. It is crucial in determining the health of the retina, optic disc, and vitreous humor.

<span class="mw-page-title-main">Coloboma</span> Hole in one of the structures of the eye

A coloboma is a hole in one of the structures of the eye, such as the iris, retina, choroid, or optic disc. The hole is present from birth and can be caused when a gap called the choroid fissure, which is present during early stages of prenatal development, fails to close up completely before a child is born. Ocular coloboma is relatively uncommon, affecting less than one in every 10,000 births.

<span class="mw-page-title-main">Central retinal artery</span>

The central retinal artery branches off the ophthalmic artery, running inferior to the optic nerve within its dural sheath to the eyeball.

<span class="mw-page-title-main">Coats' disease</span> Human eye disease causing full or partial blindness

Coats' disease is a rare congenital, nonhereditary eye disorder, causing full or partial blindness, characterized by abnormal development of blood vessels behind the retina. Coats' disease can also fall under glaucoma.

Holographic interferometry (HI) is a technique which enables the measurements of static and dynamic displacements of objects with optically rough surfaces at optical interferometric precision. These measurements can be applied to stress, strain and vibration analysis, as well as to non-destructive testing and radiation dosimetry. It can also be used to detect optical path length variations in transparent media, which enables, for example, fluid flow to be visualised and analyzed. It can also be used to generate contours representing the form of the surface.

<span class="mw-page-title-main">Dilated fundus examination</span>

Dilated fundus examination (DFE) is a diagnostic procedure that uses mydriatic eye drops to dilate or enlarge the pupil in order to obtain a better view of the fundus of the eye. Once the pupil is dilated, examiners use ophthalmoscopy to view the eye's interior, which makes it easier to assess the retina, optic nerve head, blood vessels, and other important features. DFE has been found to be a more effective method for evaluating eye health when compared to non-dilated examination, and is the best method of evaluating structures behind the iris. It is frequently performed by ophthalmologists and optometrists as part of an eye examination.

Optic neuropathy is damage to the optic nerve from any cause. The optic nerve is a bundle of millions of fibers in the retina that sends visual signals to the brain. [1].

<span class="mw-page-title-main">Optic disc drusen</span> Medical condition

Optic disc drusen (ODD) are globules of mucoproteins and mucopolysaccharides that progressively calcify in the optic disc. They are thought to be the remnants of the axonal transport system of degenerated retinal ganglion cells. ODD have also been referred to as congenitally elevated or anomalous discs, pseudopapilledema, pseudoneuritis, buried disc drusen, and disc hyaline bodies.

<span class="mw-page-title-main">Optic pit</span> Medical condition

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 10,000 people with no predilection for either gender. There is currently no known risk factors for their development. Optic pits are important because they are associated with posterior vitreous detachments (PVD) and even serous retinal detachments.

<span class="mw-page-title-main">Fundus photography</span> Medical imaging of the eyes

Fundus photography involves photographing the rear of an eye, also known as the fundus. Specialized fundus cameras consisting of an intricate microscope attached to a flash enabled camera are used in fundus photography. The main structures that can be visualized on a fundus photo are the central and peripheral retina, optic disc and macula. Fundus photography can be performed with colored filters, or with specialized dyes including fluorescein and indocyanine green.

Microangiography is a type of angiography that consists of the radiography of small blood or lymphatic vessels of an organ. While most other types of angiography cannot produce images of vessels smaller than 200 µm in diameter, microangiography does just that. A microangiographic image is the result of injection of a contrast medium into either the blood or the lymphatic system and, then, enlargement of the resulting radiograph. Thus, an image is obtained in which there is contrast between vessel and surrounding tissue. It is often used in order to detect microvascular lesions in organs. But, it has been suggested that microangiography can also be used to detect tumors through visualization of tumor-induced small blood vessels. This is because tumor growths require vascularization before they can develop more rapidly. A few of the commonly used types are fluorescent, silicone rubber, and synchrotron radiation microangiography.

<span class="mw-page-title-main">Laser Doppler imaging</span>

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 back is detected using a photodiode that converts it into an electrical signal. Then the signal is processed to calculate a signal that is proportional to the tissue perfusion in the scanned area. When the process is completed, the signal is processed to generate an image that shows the perfusion on a screen.

<span class="mw-page-title-main">Branch retinal vein occlusion</span> Medical condition

Branch retinal vein occlusion is a common retinal vascular disease of the elderly. It is caused by the occlusion of one of the branches of central retinal vein.

Megalopapilla is a non-progressive human eye condition in which the optic nerve head has an enlarged diameter, exceeding 2.1 mm with no other morphological abnormalities.

<span class="mw-page-title-main">Heidelberg Retinal Tomography</span>

The Heidelberg Retinal Tomography is a diagnostic procedure used in ophthalmology. The Heidelberg Retina Tomograph (HRT) is an ophthalmological confocal point scanning laser ophthalmoscope for examining the cornea and certain areas of the retina using different diagnostic modules. However, the most widely used area of application for HRT is the inspection of the optic nerve head (papilla) for early detection and follow-up of glaucoma. The procedure has established itself as an integral part of routine glaucoma diagnostics alongside the visual field examination (perimetry), the chamber angle examination (gonioscopy) and the measurement of intraocular pressure (tonometry). The HRT is the most widely used application of confocal scanning laser ophthalmoscopy.

References

  1. ↑ "blind spot". Encyclopædia Britannica . 2011. Retrieved June 21, 2017.
  2. ↑ Tasman, William; Jaeger, Edward A (2006). "Chapter 4: Anatomy of the Visual Sensory System". Duane's Ophthalmology. Philadelphia: Lippincott Williams & Wilkins. ISBN   9780781768559. OCLC   318288606.
  3. ↑ Heidary, Fatemeh; Gharebaghi, Reza; Wan Hitam, Wan Hazabbah; Shatriah, Ismail (2010). "Nerve fiber layer thickness". Ophthalmology. 117 (9): 1861–1862. doi:10.1016/j.ophtha.2010.05.024. ISSN   1549-4713. PMID   20816254. S2CID   11122001.
  4. 1 2 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.
  5. ↑ Puyo, Léo, Michel Paques, Mathias Fink, José-Alain Sahel, and Michael Atlan. "Waveform analysis of human retinal and choroidal blood flow with laser Doppler holography." Biomedical Optics Express 10, no. 10 (2019): 4942-4963.
  6. 1 2 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
  7. 1 2 Michelessi M, Lucenteforte E, Oddone F, Brazzelli M, Parravano M, Franchi S, Ng SM, Virgili G (2015). "Optic nerve head and fibre layer imaging for diagnosing glaucoma". Cochrane Database Syst Rev. 2020 (11): CD008803. doi:10.1002/14651858.CD008803.pub2. PMC   4732281 . PMID   26618332.
  8. ↑ Amador-Patarroyo, Manuel J.; Pérez-Rueda, Mario A.; Tellez, Carlos H. (1 January 2015). "Congenital anomalies of the optic nerve". Saudi Journal of Ophthalmology. 29 (1): 32–38. doi:10.1016/j.sjopt.2014.09.011. ISSN   1319-4534. PMC   4314572 . PMID   25859137.
  9. ↑ Magrath, GN; Cheeseman EW; Sarrica RA (2013). "Morning Glory Disc Anomaly". Pediatric Neurology. 49 (6): 517. doi:10.1016/j.pediatrneurol.2013.05.015. PMID   24095648.
  10. ↑ Barnard, Simon. "An Introduction to Diseases of the Optic nerve" . Retrieved 30 May 2014.
  11. ↑ Kindler (1970). "Morning glory syndrome: unusual congenital optic disk anomaly". Am J Ophthalmol. 69 (3): 376–84. doi:10.1016/0002-9394(70)92269-5. PMID   5418855.
  12. ↑ Georgalas, Ilias; Ladas, Ioannis; Georgopoulos, Gerasimos; Petrou, Petros (August 2011). "Optic disc pit: a review". Graefe's Archive for Clinical and Experimental Ophthalmology = Albrecht von Graefes Archiv für Klinische und Experimentelle Ophthalmologie. 249 (8): 1113–1122. doi:10.1007/s00417-011-1698-5. ISSN   1435-702X. PMID   21638030. S2CID   25880534.
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