Optic Atrophy Workup
- Author: Rashmin Gandhi, MBBS, FRCS(Edin), FRCS(Glasg); Chief Editor: Hampton Roy, Sr, MD more...
The type of neuroimaging study depends on the disease process.
For tumors located in the orbit, ultrasonography is recommended.
For papilledema, a B-scan ultrasound is recommended to look for optic sheath dilatation.
To find out whether a lesion is cystic or solid (eg, cysticercoids), CT or MRI is recommended. For solid lesions, MRI (with contrast or fat suppression) is preferred in areas in close proximity to the bony wall.
For fractures associated with trauma, a noncontrast CT scan is preferred.
For multiple sclerosis, a gadolinium-enhanced MRI/fluid-attenuated inversion recovery (FLAIR) sequence is useful to detect hyperechoic areas.
Optic nerve function tests
Visual acuity is a measure of overall function of the optics and neural components of the visual system. The test measures the visual angle subtended by the finest spatial detail that the observer can identify. In a Snellen visual acuity test, the angle subtended by the optotype at a given distance is 5 minutes.
The logMar chart, another type of visual acuity test, has the following advantages:
Each line has an equal number of letters.
Spacing is proportional to the letter size.
Change in visual acuity is in equal units.
Stimulus parameters affecting visual acuity include contrast of the chart, refractive error, pupil size, stimulus eccentricity, duration of stimulus presentation, type of optotype used, illumination, and crowding phenomenon.
In infants, the optokinetic nystagmus test and the preferential looking test provide information about the visual status of the child.
Visual acuity is assessed in preschool-aged children with the marble game test and the pictorial vision chart (Allen preschool card test). The illiterate Landolt C-ring test and arrow indicator test are also used.
Color vision is more decreased in patients with optic nerve disorders than in those with retinal disorders.
Prerequisites for color vision testing include proper lighting (both an adequate amount of light and the proper spectral distribution).
Color vision is profoundly decreased compared to visual acuity in patients with ischemic and compressive optic neuropathy. Color vision may be assessed with the following tests:
Pseudoisochromatic tests (eg, Ishihara color blindness test, Hardy-Rand-Rittler polychromatic plates, Dvorine plates) are most commonly used for screening. The tests are designed to identify the figure, number, or letter against the background of other dots. The test is quick and easy to perform. Disadvantages include a limited ability to classify acquired color vision deficits and to determine severity. In addition, the Ishihara test has little or no ability to screen for congenital or acquired blue-yellow color vision deficits.
The Farnsworth panel D-15 test consists of 15 color caps randomly placed in front of the patient with the reference cap. The patient is told to arrange the caps in an orderly transition of hue. On the back of the cap, the number sequence is given to assist in scoring the test. Limitation does not indicate the degree of color deficiency. This test helps in the diagnosis of moderate-to-severe color vision deficiency.
The Farnsworth-Munsell 100 Hues test consists of 85 colored caps in 4 boxes. The test subject has to arrange the transition hue one box at a time. Depending upon the type of color vision deficiency, the patient experiences arrangement confusion, leading to arrangement errors in that particular section. Thus, the type of color vision deficit can be classified.
In the Holmgren wool test, a color match from a selection of schemes of colored wools is performed.
In the city university color vision test, a center colored plate is matched with the closest hue from surrounding color plates.
In the lantern test, the patient has to name the color shown.
Contrast sensitivity test
This test measures the ability to perceive slight changes in luminance between regions that are not separated by definite borders. This is just as important as the ability to perceive sharp outlines of relatively small objects.
Tests used to measure contrast sensitivity include the following:
Cambridge low-contrast grating test
Pelli-Robson contrast sensitivity chart. Each letter subtends an angle of 3 degrees at a distance of 1 meter. Letters are organized in triplets with two triplets in each line. The contrast decreases from one triplet to the next. The log contrast sensitivity varies from 0.00-2.25.
Refractive errors and duration of stimulus presentation affect the contrast sensitivity measurement.
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 afferent sensory abnormality or bilateral asymmetric visual loss. Occasionally, RAPD is the only objective sign of anterior visual pathway dysfunction. It is a sensitive optic nerve function test.
RAPD can be quantitatively graded by balancing the defect; successive neutral density filters are added in 0.3 logarithmic steps over the normal eye while performing the swinging flashlight test until the defect disappears. The most useful neutral density filters are from 80% (0.1 log unit) to 1% (2.0 log units).
Clinically, it is graded as follows:
Immediate dilation of the pupil, instead of normal initial constriction (3-4+)
No changes in initial pupillary size, followed by dilation of the pupils (1-2+)
Initial constriction, but greater escape to a larger intermediate size than when the light is swung back to normal eye (trace)
Edge-light pupil cycle time
A thin beam of light is shown horizontally across the inferior aspect of the pupillary margin. The light induces pupillary constriction that moves the light out of the pupil. The pupil then redilates until the beam is once again at the edge of the pupillary margin, whereupon it constricts again, creating another cycle.
The time is calculated in milliseconds per cycle. Alternatively, the number of cycles in 1 minute is measured. The rate is normally 900 milliseconds per cycle.
Photostress recovery test
Principle-visual pigments bleach when exposed to an intense light source, resulting in a transient state of sensitivity loss and reduced central visual acuity.
To perform the test, the examiner should note the patient’s best-corrected visual acuity, shield one eye, and then ask the patient to look directly at a bright focal light that is held 2-3 cm from the eye for about 10 seconds. The time needed to return to within one line of best-corrected visual acuity level is measured; this time is the photostress recovery time.
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.
Cranial nerve examination
All cranial nerves are examined to rule out associated nerve involvement to help determine the site of the lesion.
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.
Optic disc changes can present with temporal pallor (as seen in toxic neuropathy and nutritional deficiency), focal pallor or bow-tie pallor (as seen in compression of the optic chiasma), and cupping (as seen in glaucomatous optic atrophy).
In the early stages of the atrophic process, the optic disc loses its reddish hue, and the substance of the disc slowly disappears, leaving a pale, shallow concave meniscus, the 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 or diffuse obliteration of the neuroretinal rim with preservation of color of any remaining rim tissue is specific for glaucoma.
Thinning of the neuroretinal rim was more common in glaucomatous cupping than in nonglaucomatous cupping but not significantly.
Pathologic optic disc cupping also develops in patients with normal intraocular pressures and optic atrophy from various causes, including ischemia, compression, inflammation, hereditary disorders, and trauma.
Peripapillary retinal nerve fiber layer
Early focal loss of axons is represented by the development of dark slits or wedges in the peripapillary retinal nerve fiber layer. These slits or bands appear darker or redder than the adjacent healthy tissue. The slit defects are most easily identified in the superior and inferior arcuate regions, where the nerve fiber layer is particularly thick.
In most cases of optic atrophy, the retinal arteries are narrowed or attenuated. In cases of nonarteritic anterior ischemic optic neuropathy, the vessels may be focally narrowed or completely obliterated. Nonarteritic anterior ischemic optic neuropathy is shown in the images below.
Visual field testing
Field testing methods include kinetic and static. In the kinetic method, the contours of the island are mapped at different levels, resulting in one isopter for each level tested. In the static method, the vertical contours of the island are mapped along a selected meridian.
As per the areas tested, the visual field is divided into the central visual field, which has a 30-degree radius, and anything beyond 30 degrees is called peripheral visual testing. The central visual field can be tested using an Amsler grid, confrontation techniques, a tangent screen, and a bowl perimeter. Peripheral visual testing includes automated perimetry and manual perimetry. Automated perimetry tests the central 60 degrees of the visual field, whereas manual perimetry tests the entire visual field.
In optic neuropathy, visual field changes can include enlargement of the blind spot and paracentral scotoma (eg, optic neuropathy), altitudinal defects (eg, anterior ischemic optic neuropathy, optic neuritis), and bitemporal defects (eg, compressive lesions, similar to optic chiasma tumors).
Abnormal electroretinogram (ERG) results that can be seen are as follows:
Subnormal: Potential less than 0.08 microvolts; seen in toxic neuropathy
Negative: When a large a-wave is seen; may be due to giant cell arteritis, central retinal artery occlusion, or central retinal vein occlusion
Extinguished: Response seen in complete optic atrophy
Visually evoked response
In optic neuritis, the visually evoked response (VER) has an increased latency period and a decreased amplitude as compared to the normal eye.
Compressive optic lesions tend to reduce the amplitude of the VER, while producing a minimal shift in the latency.
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|Age||15-50 y||Approximately 70 y||Sixth decade||Varies based on cause|
|Sex||Multiple sclerosis F>M||F>M||F=M||Varies based on cause|
|Visual acuity||Varies from mild blurring (34%) and moderate loss of acuity (12%) to severe or total loss of light perception (complete blindness) in 54% of cases, to no light perception. The loss of vision is acute and progressive.--Vision usually recovers within 2 mo||< 20/200 (6/60)||>20/200 (6/60)||Varies from mild blurring to no light perception|
|Color vision||Color vision > vision loss||Color vision loss = vision loss||Color vision loss = vision loss||Color vision = vision loss|
|Motility||Painful movement in cases of retrobulbar neuritis||Normal||Normal||Depends on the site of compression|
|Nystagmus||In multiple sclerosis, vertical nystagmus (upbeating or downbeating) may be seen||No||No||See-saw nystagmus in optic chiasm compression|
|Optic disc||Temporal pallor||Pallid disc edema||Segmental disc edema||Bow-tie pallor seen in optic chiasm compression; varies in other instances|
|VEP-increased latency <†>||VEP-reduced amplitude||VEP-reduced amplitude||Reduced VEP amplitude|
|In multiple sclerosis, hyperechoic lesions are seen in the brain on MRI||-||-||For exact location of compression|
|Other associations||Headache, scalp tenderness, jaw claudication||
Hypertension and diabetes
|Headache, vomiting, and focal neurologic deficits|
|*RAPD - Relative afferent pupil defect
<†>VEP - Visual-evoked potential