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Optic Atrophy
Optic atrophy is the final common morphologic endpoint of any disease process that causes axon
degeneration ...
2. Retrograde degeneration: In conditions with retrograde degeneration (optic nerve
compression by intracranial tumor), de...
C. Etiologic classification
Regardless of etiology, optic atrophy is associated with variable degrees of visual dysfunctio...
Visual acuity: It is measured using Snellen’s optotypes or using a Log MAR chart. Visual acuity
is reduced, occasionally t...
Peripapillary retinal nerve fiber layer
Early focal loss of axons produces dark wedge shaped defects (best seen with a red...
 Pupil is semi dilated and direct reflex is very sluggish or absent. Swinging Flash light test
depicts Marcus Gunn pupil....
Bold line paper, Black ink with felt tipped pen for writing.
When color perception is impacted, a person may have difficul...
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Optic atrophy and low vision

Optic atrophy-introduction, types, investigations and low vision management

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Optic atrophy and low vision

  1. 1. Optic Atrophy Optic atrophy is the final common morphologic endpoint of any disease process that causes axon degeneration in the retinogeniculate pathway. Clinically, optic atrophy manifests as changes in the color and the structure of the optic disc associated with variable degrees of visual dysfunction. Optic atrophy represents the permanent loss of retinal ganglion cell axons in conjunction with retinal ganglion cell death. The axons possess a myelin sheath provided by oligodendrocytes. Once damaged, the axons do not regenerate. Light incident from the ophthalmoscope undergoes total internal reflection through the axonal fibers, and subsequent reflection from the capillaries on the disc surface gives rise to the characteristic yellow-pink color of a healthy optic disc. Degenerated axons lose this optical property which explains the pallor in optic atrophy. Alternatively, the loss of pial capillaries which supply the optic disc may be the cause of disc pallor. The Kestenbaum index is the number of capillaries counted on the optic disc, which normally is around 10. Less than 6 capillaries indicates optic atrophy; more than 12 suggests disc hyperaemia. Histopathology changes in optic atrophy1  Shrinkage or loss of both myelin and axis cylinders  Gliosis  Deepening of the physiologic cup with barring of the lamina cribrosa  Widening of the subarachnoid space with redundant dura  Widening of the pial septa  Severed nerve leads to bulbous axonal swellings (Cajal end bulbs); may be observed at the anterior cut end of the fibers Classification Optic atrophy is classified as pathologic, ophthalmoscopic, or etiologic1 . A. Pathologic classification 1) Anterograde degeneration (Wallerian degeneration): In conditions with anterograde degeneration (e.g. toxic retinopathy, chronic simple glaucoma), deterioration begins in the retina and proceeds toward the lateral geniculate body (i.e., to the brain). Axon thickness determines the rate of degeneration. Larger axons disintegrate more rapidly than smaller axons. The essential feature is swelling and degeneration of the axon terminal in the lateral geniculate body (LGB), observed as early as 24 hours. Leukocytes rarely present in Wallerian degeneration.
  2. 2. 2. Retrograde degeneration: In conditions with retrograde degeneration (optic nerve compression by intracranial tumor), deterioration starts from the proximal portion of the axon and proceeds toward the optic disc (i.e., to the eye). The time course of this degeneration is apparently independent of the distance of the injury from the ganglion cell body. Thus, damage to the retrobulbar portion of the optic nerve, the optic chiasma, or the optic tract causes pathologic and visible degeneration of the ganglion cell body simultaneously. 3. Trans-synaptic degeneration: In trans-synaptic degeneration, a neuron on one side of a synapse degenerates as a consequence of the loss of a neuron on the other side. This type of degeneration is observed in patients with occipital damage incurred either in utero or during early infancy. B. Ophthalmoscopic classification 1. Primary optic atrophy: In conditions with primary optic atrophy (e.g. Pituitary tumor, optic nerve tumor, traumatic optic neuropathy, multiple sclerosis), optic nerve fibers degenerate in an orderly manner and are replaced by columns of glial cells without alteration in the architecture of the optic nerve head. The disc is chalky white and sharply demarcated, and the retinal vessels are normal. Lamina cribrosa is well defined. 2. Secondary optic atrophy: In conditions with secondary optic atrophy (e.g., papilledema, papillitis), the atrophy is secondary to papilledema. Optic nerve fibers exhibit marked degeneration, with excessive proliferation of glial tissue. The architecture is lost, resulting in indistinct margins. The disc is grey or dirty grey, the margins are poorly defined, and the lamina cribrosa is obscured due to proliferating fibro glial tissue. Hyaline bodies (corpora amylacea) or drusen may be observed. Peripapillary sheathing of arteries as well as tortuous veins may be observed. Progressive contraction of visual fields may be seen as well. Optic atrophy following papilledema (secondary). 3. Consecutive optic atrophy: In consecutive optic atrophy (e.g., retinitis pigmentosa, myopia, central retinal artery occlusion), the disc is waxy pale with a normal disc margin, marked attenuation of arteries, and a normal physiologic cup. Consecutive optic atrophy following pan retinal photocoagulation (PRP). 4. Glaucomatous optic atrophy: Also known as cavernous optic atrophy, marked cupping of the disc is observed in glaucomatous optic atrophy. Characteristics include vertical enlargement of cup, visibility of the laminar pores (laminar dot sign), backward bowing of the lamina cribrosa, bayoneting and nasal shifting of the retinal vessels, and Peripapillary halo and atrophy. Splinter hemorrhage at the disc margin may be observed 5. Temporal pallor: Temporal pallor may be observed in traumatic or nutritional optic neuropathy, and it is most commonly seen in patients with multiple sclerosis, particularly in those with a history of optic neuritis. The disc is pale with a clear, demarcated margin and normal vessels, and the physiologic pallor temporally is more distinctly pale.
  3. 3. C. Etiologic classification Regardless of etiology, optic atrophy is associated with variable degrees of visual dysfunction, which may be detected by one or all of the optic nerve function tests. 1. Hereditary: This is divided into congenital or infantile optic atrophy (recessive or dominant form), Behr hereditary optic atrophy (autosomal recessive), and Leber optic atrophy. 2. Consecutive atrophy: Consecutive atrophy is an ascending type of atrophy (e.g., chorioretinitis, pigmentary retinal dystrophy, cerebromacular degeneration) that usually follows diseases of the choroid or the retina. 3. Circulatory atrophy: Circulatory is an ischemic optic neuropathy observed when the perfusion pressure of the ciliary body falls below the intraocular pressure. Circulatory atrophy is observed in central retinal artery occlusion, carotid artery occlusion, and cranial arteritis. 4. Metabolic atrophy: Metabolic atrophy is observed in disorders such as thyroid ophthalmopathy, juvenile diabetes mellitus, nutritional amblyopia, toxic amblyopia, tobacco, methyl alcohol, and drugs (e.g., ethambutol, sulphonamides). 5. Demyelinating atrophy: Demyelinating atrophy is observed in diseases such as multiple sclerosis and Devic disease. 6. Pressure or traction atrophy: Pressure or traction atrophy is observed in diseases such as glaucoma and papilledema. 7. Postinflammatory atrophy: Postinflammatory atrophy is observed in diseases such as optic neuritis, perineuritis secondary to inflammation of the meninges, and sinus and orbital cellulites. 8. Traumatic optic neuropathy: The exact pathophysiology of traumatic optic neuropathy is poorly understood, although optic nerve avulsion and transection, optic nerve sheath hematoma, and optic nerve impingement from a penetrating foreign body or bony fragment all reflect traumatic forms of optic nerve dysfunction that can lead to optic atrophy. Epidemiology Optic atrophy can be seen in any age group. There is no sex predisposition noted. Differential diagnosis Non-pathologic disc pallor is seen in axial myopia, myelinated nerve fibers, optic disc pit, tilted disc, and disc drusen. Viewing the disc in a pseudophakic eye, or using a brighter ophthalmoscope than usual can cause the disc to look paler. Clinical Work-up
  4. 4. Visual acuity: It is measured using Snellen’s optotypes or using a Log MAR chart. Visual acuity is reduced, occasionally to no light perception. Color vision: Color vision is more decreased in patients with optic nerve disorders than in those with retinal disorders especially in patients with ischemic and compressive optic neuropathy. Color vision may be assessed with pseudo isochromatic tests (e.g., Ishihara color blindness test, Hardy-Rand-Rittler polychromatic plates, and Dvorine plates) or the Farnsworth-Munsell 100 Hues test or the Farnsworth panel D-15 test. Pupillary evaluation: Pupil size should be noted, as well as the magnitude and the latency of the direct and consensual responses to light and near stimulation. A relative afferent pupillary defect (RAPD) is a hallmark of unilateral or asymmetric afferent sensory abnormality. Occasionally it is the only objective sign elicited. RAPD can be quantitatively graded by balancing the defect using neutral density filters. Clinically, it is graded as follows:  Initial constriction, but greater escape to a larger intermediate size than when the light is swung back to normal eye (trace).  No changes in initial pupillary size, followed by dilation of the pupils (1-2+)  Immediate dilation of the pupil, instead of normal initial constriction (3-4+) Contrast sensitivity test: This test measures the ability to perceive slight changes in luminance between regions that are not separated by definite borders, and is a sensitive test for optic nerve function. It can be tested using Pelli-Robson contrast sensitivity chart, Cambridge low-contrast grating test or Arden gratings. Pulfrich phenomenon: In optic nerve damage, the transmission of impulses to the occipital cortex is delayed. In patients with unilateral or markedly asymmetric optic neuropathy, when an oscillating small target in a frontal plane is viewed binocularly, the target appears to move in an elliptic path rather than in a to-and-fro path. Extraocular movements: Restriction can be obtained in cases of compressive optic neuropathy due to either the mass effect or the involvement of the nerve supplying the muscle. Cranial nerve examination: All cranial nerves are examined to rule out associated nerve involvement to help determine the site of the lesion. Ophthalmoscopic features Optic disc Optic disc changes can present with temporal pallor, focal pallor or bow-tie pallor (as seen in compression of the optic chiasma), or cupping (glaucomatous damage). In the early stages of the atrophic process the optic disc loses its reddish hue. The substance of the disc slowly decreases, leaving a pale, shallow exposed lamina cribrosa. In the end stages of the atrophic process the retinal vessels of the normal caliber still emerge centrally through the otherwise avascular disc. Focal notching or diffuse obliteration of the neuroretinal rim with preservation of color of any remaining rim tissue is characteristic of glaucoma. Optic disc cupping also develops in patients in non-glaucomatous eyes due to ischemia, compression, inflammation, hereditary disorders or trauma.
  5. 5. Peripapillary retinal nerve fiber layer Early focal loss of axons produces dark wedge shaped defects (best seen with a red-free filter on slit-lamp bio-microscopy) in the peripapillary retinal nerve fiber layer. Retinal vessels In most cases of optic atrophy, the retinal arteries are narrowed or attenuated. In cases of non- arteritic anterior ischemic optic neuropathy, the vessels may be focally narrowed or completely obliterated. Investigations Visual field testing: In optic neuropathy, visual field changes can include enlargement of the blind spot, caecocentral scotoma, altitudinal defects (e.g. anterior ischemic optic neuropathy, optic neuritis), and bitemporal defects (e.g. compressive lesions, similar to optic chiasma tumors). Neuro-imaging: Neuro-imaging is indicated to find the cause of atrophy.  Ultrasonography is recommended when orbital tumor is suspected.  For post-traumatic optic neuropathy a noncontrast CT scan is preferred.  In optic neuritis or multiple sclerosis, a gadolinium-enhanced MRI/fluid-attenuated inversion recovery (FLAIR) sequence is useful to detect hyper intense areas of demyelination. Electroretinogram (ERG)  Abnormal electroretinogram (ERG) results that can be seen are as follows:  Subnormal: Potential less than 0.08 microvolts; seen in toxic neuropathy  Negative: a preserved a-wave but absent b-wave. It May be seen in arteritic AION or central retinal artery occlusion.  Extinguished ERG: seen in complete optic atrophy.  N95:P50 ratio in pattern ERG is low in optic neuropathy and normal in maculopathy. Visually evoked potential (VEP) In optic neuritis the VEP has an increased latency period as compared to the normal eye which persists even after visual recovery. Compressive optic lesions tend to reduce the amplitude and cause waveform changes of the VEP. Unexplained optic atrophy As optic atrophy is a sign of end-stage optic nerve damage, and not a diagnosis in itself, further investigation is required if the above tests do not reveal its cause. Clinical features of optic atrophy  Loss of vision: may be sudden or gradual onset (depending upon the cause of optic atrophy) and partial or total (depending upon the degree of atrophy).
  6. 6.  Pupil is semi dilated and direct reflex is very sluggish or absent. Swinging Flash light test depicts Marcus Gunn pupil.  Ophthalmoscopic appearance of the disc varies with type of optic atrophy.  Visual field loss varies with the distribution of the fibers that have been damaged. In general the field loss is peripheral in systemic infections, central in focal optic neuritis and eccentric when the nerve or tracts are compressed. Paracentral, caecocentral or central scotomas may be present. Treatment No proven treatment exists to reverse optic atrophy. At present, the best defense is early diagnosis. If specific treatment of the cause is initiated before the development of optic atrophy, useful vision may be salvaged. For example, early diagnosis and prompt treatment can help in compressive and toxic neuropathies. Neuro-protective agents like gingko biloba have been tried with anecdotal success. Research in stem cell therapy may provide answers in the not-too-distant future. Low-vision aids should be considered for occupational rehabilitation. Low Vision Management Magnification at both distance and near with the use of low vision devices must be considered for the patients with reduced visual acuity due to optic atrophy. For distance too, telescopes are very useful (Handheld versus spectacle mounted clip-on). Direct illumination along with magnification & Reading stand quite helpful for performing near tasks. Excessive lighting should be avoided for these patients. Sun lenses, tints and filters should be used to eliminate glare both outdoor and indoor. Non optical systems should be demonstrated and let them follow in their dailies. Orientation and mobility management techniques and devices can be demonstrated for the patients with low vision. Sighted guide technique, canes, dog guides and electronic travel aids can be given to the patients for mobility. Eccentric viewing if central vision is affected. Patients with central scotoma often have to use eccentric viewing to function more effectively. When a person has a large scotoma, being able to effectively use an eccentric point can be more difficult with optical magnification. Eccentric viewing may be easier with an assistive technology device.7 Additionally, as fixation moves further from the fovea, the impact of crowding increases. Using different types of text presentation can lessen the effects of visual crowding7 . For example, studies have reported that using text stretching to increase the spacing between letters and words can reduce crowding and may be beneficial for the person trying to read with a central scotoma Peak cap and Sunglasses prove to be helpful for outdoors to tackle photophobia. A patient with severe contrast sensitivity loss may functions better using reverse contrast, which can only be achieved with electronic magnification assistive technology7 .
  7. 7. Bold line paper, Black ink with felt tipped pen for writing. When color perception is impacted, a person may have difficulty with color contrasts, which may make text or objects on a colored background more difficult to see. Using electronic magnification, colors can be converted to black and white, and if necessary, contrast can also be enhanced. In addition, if a person has problems with color identification, assistive technology can offer solutions. Genetic counseling is must for the case of heredodegenerative forms of optic atrophy2 . References: 1. Optic Atrophy-A major review by Dr. Devendra V. Venkatramani, Dr. Gangaprasad Muthaiah Amula, Dr. Rashmin A. Gandhi 2. Richard L.Brilliant.Essentials of Low Vision Practice 3. The Lighthouse Ophthalmology Resident training manual by Eleanor, Benjamin Freed, Karen R. Seidman, Michael Fischer. 4. Wolff’s anatomy of eye and orbit Eighth edition. 5. Comprehensive Ophthalmology bu A K Khurana 6. lowvision.preventable 7. website of lighthouse international Raju Kaiti M. Optometry (Practioner) Amity University