optic atrophy


Optic Atrophy

 

Definition

Optic atrophy can be defined as damage to the optic nerve resulting in a degeneration or destruction of the optic nerve. Optic atrophy may also be referred to as optic nerve head pallor because of the pale appearance of the optic nerve head as seen at the back of the eye. Possible causes of optic atrophy include: optic neuritis, Leber's hereditary optic atrophy, toxic or nutritional optic neuropathy, glaucoma, vascular disorders, trauma, and other systemic disorders.

Description

The process of vision involves light entering the eye and triggering chemical changes in the retina, a pigmented layer lining the back of the eye. Nerve impulses created by this process travel to the brain via the optic nerve. Using a hand-held instrument called an ophthalmoscope, the doctor can see the optic nerve head (optic disc) which is the part of the optic nerve that enters at the back of the eyeball. In optic atrophy, the disc is pale and has fewer blood vessels than normal.

Causes and symptoms

Symptoms of optic atrophy are a change in the optic disc and a decrease in visual function. This change in visual function can be a decrease in sharpness and clarity of vision (visual acuity) or decreases in side (peripheral) vision. Color vision and contrast sensitivity can also be affected.There are many possible causes of optic atrophy. The causes can range from trauma to systemic disorders. Some possible causes of optic atrophy include:
  • Optic neuritis. Optic neuritis is an inflammation of the optic nerve. It may be associated with eye pain worsened by eye movement. It is more common in young to middle-aged women. Some patients with optic neuritis may develop multiple sclerosis later on in life.
  • Leber's hereditary optic neuropathy. This is a disease of young men (late teens, early 20s), characterized by an onset over a few weeks of painless, severe, central visual loss in one eye, followed weeks or months later by the same process in the other eye. At first the optic disc may be slightly swollen, but eventually there is optic atrophy. The visual loss is generally permanent. This condition is hereditary. If a patient knows that Leber's runs in the family, genetic counseling should be considered.
  • Toxic optic neuropathy. Nutritional deficiencies and poisons can be associated with gradual vision loss and optic atrophy, or with sudden vision loss and optic disc swelling. Toxic and nutritional optic neuropathies are uncommon in the United States, but took on epidemic proportions in Cuba in 1992–1993. The most common toxic optic neuropathy is known as tobacco-alcohol amblyopia, thought to be caused by exposure to cyanide from tobacco smoking, and by low levels of vitamin B12 because of poor nutrition and poor absorption associated with drinking alcohol. Other possible toxins included ethambutol, methyl alcohol (moonshine), ethylene glycol (antifreeze), cyanide, lead, and carbon monoxide. Certain medications have also been implicated. Nutritional optic neuropathy may be caused by deficiencies of protein, or of the B vitamins and folate, associated with starvation, malabsorption, or alcoholism.
  • Glaucoma. Glaucoma may be caused by an increase of pressure inside the eye. This increased pressure may eventually affect the optic nerve if left untreated.
  • Compressive optic neuropathy. This is the result of a tumor or other lesion putting pressure on the optic nerve. Another possible cause is enlargement of muscles involved in eye movement seen in hyperthyroidism (Graves' disease).
  • Retinitis pigmentosa. This is a hereditary ocular disorder.
  • Syphilis. Left untreated, this disease may result in optic atrophy.

Diagnosis

Diagnosis involves recognizing the characteristic changes in the optic disc with an ophthalmoscope, and measuring visual acuity, usually with an eye chart. Visual field testing can test peripheral vision. Color vision and contrast sensitivity can also be tested. Family history is important in the diagnosis of inherited conditions. Exposure to poisons, drugs, and even medications should be determined. Suspected poisoning can be confirmed through blood and urine analysis, as can vitamin deficiency.Brain magnetic resonance imaging (MRI) may show a tumor or other structure putting pressure on the optic nerve, or may show plaques characteristic of multiple sclerosis, which is frequently associated with optic neuritis. However, similar MRI lesions may appear in Leber's hereditary optic neuropathy. Mitochondrial DNA testing can be done on a blood sample, and can identify the mutation responsible for Leber's.Visual evoked potentials (VEP), which measure speed of conduction over the nerve pathways involved in sight, may detect abnormalities in the clinically unaffected eye in early cases of Leber's. Fluorescein angiography gives more detail about blood vessels in the retina.

Treatment

Treatment of optic neuritis with steroids is controversial. As of mid-1998, there is no known treatment for Leber's hereditary optic neuropathy. Treatment of other causes of optic atrophy varies depending upon the underlying disease.

Prognosis

Many patients with optic neuritis eventually develop multiple sclerosis. Most patients have a gradual recovery of vision after a single episode of optic neuritis, even without treatment. Prognosis for visual improvement in Leber's hereditary optic neuropathy is poor, with the specific rate highly dependent on which mitochondrial DNA mutation is present. If the cause of toxic or nutritional deficiency optic neuropathy can be found and treated early, such as stopping smoking and taking vitamins in tobacco-alcohol amblyopia, vision generally returns to near normal over several months' time. However, visual loss is often permanent in cases of long-standing toxic or nutritional deficiency optic neuropathy.

Prevention

People noticing a decrease in vision (central and/or side vision) should ask their eye care practitioner for a check up. Patients should also go for regular vision exams. Patients should ask their doctor how often that should be, as certain conditons may warrant more frequent exams. Early detection of inflammations or other problems lessens the chance of developing optic atrophy.

Key terms

Atrophy — A destruction or dying of cells, tissues, or organs.Cerebellar — Involving the part of the brain (cerebellum), which controls walking, balance, and coordination.Mitochondia — A structure in the cell responsible for producing energy. A defect in the DNA in the mitochondria is involved in Leber's optic neuropathy.Neuritis — An inflammation of the nerves.Neuropathy — A disturbance of the nerves, not caused by an inflammation. For example, the cause may be toxins, or unknown.As of mid 1998, there are no preventive measures that can definitely abort Leber's hereditary optic neuropathy in those genetically at risk, or in those at risk based on earlier involvement of one eye. However, some doctors recommend that their patients take vitamin C, vitamin E, coenzyme Q10, or other antioxidants, and that they avoid the use of tobacco or alcohol. Patients should ask their doctors about the use of vitamins. Avoiding toxin exposure and nutritional deficiency should prevent toxic or nutritional deficiency optic neuropathy.

Resources

Organizations

American Academy of Neurology. 1080 Montreal Ave., St. Paul, MN 55116. (612) 695-1940. http://www.aan.com.Prevent Blindness America. 500 East Remington Road, Schaumburg, IL 60173. (800) 331-2020. http://www.preventblindness.org.

optic atrophy

Permanent degeneration, with loss of the component nerve fibres, of the optic nerve. This causes variable degrees of permanent visual loss. Optic atrophy may be hereditary or due to many causes including injury, pressure from a growing pituitary tumour, methanol poisoning, MULTIPLE SCLEROSIS, GLAUCOMA or RETINITIS PIGMENTOSA.

canal 

A tubular channel which allows the passage of air, food, blood, excretions, secretions, or anatomical structures such as nerves or blood vessels.
Cloquet's canal See hyaloid canal.
Hannover's canal A space about the equator of the crystalline lens made up between the anterior and posterior parts of the zonule of Zinn and containing aqueous humour and zonular fibres (Fig. C1).
hyaloid canal A channel in the vitreous humour, running from the optic disc to the crystalline lens. In fetal life this canal contains the hyaloid artery, which nourishes the lens, but it usually disappears prior to birth. Syn. central canal; Cloquet's canal; Stilling's canal. See hyaloid remnant.
infraorbital canal A channel beginning at the infraorbital groove in the floor of the orbit and ending at the infraorbital foramen of the maxillary bone opening onto the face below the inferior orbital margin. It is a channel for the infraorbital artery and the infraorbital nerve.
nasolacrimal canal See Table O4.
optic canal A canal leading from the middle cranial fossa to the apex of the orbit in the small wing of the sphenoid bone through which pass the optic nerve and the ophthalmic artery. Syn. optic foramen. See Table O4.
canal of Petit A space between the posterior fibres of the zonule of Zinn and the anterior surface of the vitreous humour (Fig. C1).
Schlemm's canal A circular venous sinus located in the corneoscleral junction, anterior to the scleral spur and receiving aqueous humour from the anterior chamber and discharging into the aqueous and the anterior ciliary veins (Fig. C1). Syn. scleral sinus; sinus circularis iridis; sinus venosus sclerae; venous circle of Leber. See trabecular meshwork; scleral spur; aqueous vein.
Stilling's canal See hyaloid canal.enlarge picture" >Fig. C1 Section diagram through the anterior portion of the eyeenlarge pictureFig. C1 Section diagram through the anterior portion of the eye

disc

1. A flat, circular, coin-shaped structure. 2. In anatomy, the intervertebral disc.
Airy's disc Owing to the wave nature of light, the image of a point source consists of a diffraction pattern. If light passes through a circular aperture, the diffraction pattern will appear as a bright central disc, called Airy's disc, surrounded by concentric light and dark rings. Airy's disc receives about 87% of the luminous flux, the next concentric ring about 8%, and the next 3%. The radius of Airy's disc equals1.22λ f/dwhere d is the radius of the entrance pupil of the optical system of focal length f and λ the wavelength of the light used. In the eye, with a pupil of 4 mm diameter and λ = 507 nm, the diameter of Airy's disc is about 5 mm, which corresponds to a visual angle of about one minute of arc (Fig. D5). Syn. diffraction disc. See Rayleigh criterion; point-spread function; limit of resolution.
choked d . See papilloedema.
cupped disc An enlarged and deepened excavation of the physiological cup. It may be physiological, or due to glaucoma (glaucomatous cup), or following atrophy of the optic nerve (as in papilloedema).
diffraction disc See Airy's disc.
Maxwell disc A rotating disc onto which differently coloured discs which are radially slit can be fitted together to overlap and divide the surface into sectors of different colours. It may be used to investigate colour mixture.
morning glory disc A congenital, usually unilateral, anomaly of the optic disc. It may be due to a failure of the embryonic fissure such that the optic disc and some peripapillary tissue prolapse posteriorly. The optic disc is abnormally large and a white-grey tuft of glial tissue covers its centre. The annular zone surrounding the disc has irregular areas of pigmentation and depigmentation. The optic disc thus resembles a morning glory flower. Patients present with reduced visual acuity and strabismus and, in about one-third of patients, retinal detachment.
optic disc Region of the fundus of the eye corresponding to the optic nerve head. It can be seen with the ophthalmoscope as a pinkish-yellow area with usually a whitish depression called the physiological cup. The optic disc has an area of about 2.7 mm2, a horizontal width of about 1.75 mm and a vertical height of about 1.9 mm. The optic disc is the anatomical correlate of the physiological blind spot. It is greatly affected in glaucoma, papillitis, Leber's hereditary optic atrophy. Syn. optic nerve head; optic papilla (this is not strictly correct because the disc is not elevated above the surrounding retina). See glaucomatous cup; optic disc drusen; neuroretinal rim; papilloedema; Swann's syndrome.
pinhole disc (ph) A blank disc with a small aperture (2 mm diameter or less) mounted in a trial lens rim. It is used to reduce the size of the blur circle in an ametropic eye. In this condition vision will improve giving an indication of the final visual acuity that will be obtained with corrective lenses. If no improvement occurs, the eye is amblyopic. This procedure is called the pinhole test.
Scheiner's disc  An opaque disc in which there are two pinholes separated by a distance less than the pupil diameter. It is used to measure the dioptric changes during accommodation or to detect the type of ametropia (Fig. D6). See Scheiner's experiment.
situs inversus of the disc A congenital, usually bilateral condition in which the retinal vessels course nasally from the disc instead of temporally. It is often associated with congenital scleral crescent and myopic astigmatism.
stenopaeic disc 1. A pinhole disc. 2. A blank disc with a slit used in detecting and measuring the astigmatism of the eye (Fig. D7). Syn. stenopaeic slit. Note: also spelt stenopeic or stenopaic. See kinescope; stenopaeic spectacles.
tilted disc A congenital, bilateral condition in which the optic nerves insert obliquely into the globe. It is often associated with congenital scleral crescent and myopic astigmatism. The only sign is a bitemporal visual field defect (often upper temporal).enlarge picture" >Fig. D5 Point spread function of the intensity of the diffraction pattern from a circular aperture. Airys disc is represented by the central disc (AA), the radius of which is equal to 1.22 λ f ′/ d , the radius of the next concentric light ring () is equal to 2.23 λ f ′/ d . The light intensity is maximum in the middle of Airys disc, it is equal to 1enlarge pictureFig. D5 Point spread function of the intensity of the diffraction pattern from a circular aperture. Airy's disc is represented by the central disc (AA), the radius of which is equal to 1.22 λf′/d, the radius of the next concentric light ring () is equal to 2.23 λf′/d. The light intensity is maximum in the middle of Airy's disc, it is equal to 1enlarge picture" >Fig. D6 Images of a distant object formed on the retina of an unaccommodated emmetrope (clear, single image), a hyperope and a myope (blurred, double images) looking through a Scheiners discenlarge pictureFig. D6 Images of a distant object formed on the retina of an unaccommodated emmetrope (clear, single image), a hyperope and a myope (blurred, double images) looking through a Scheiner's discenlarge picture" >Fig. D7 Stenopaeic slitenlarge pictureFig. D7 Stenopaeic slit