neuro tests Flashcards
GVF
The GVF displayed is a classic example of overlapping or crossing isopters indicative of functional vision loss. In patients with organic disease resulting in a small central island of vision such as severe glaucoma or severe papilledema, there would be no crossing of the various isopters. The fact that isopters cross indicates variability in testing results that is not compatible with real disease.
For instance, the purple lines in this GVF outline where the patient can see the V4E stimulus and the light brown lines outline where the patient can see the III4E stimulus. The V4E stimulus is larger than the III4E stimulus and should ALWAYS have a larger field than the III4E. When the purple lines pass inside of the light brown lines (see arrows in image below), that would mean that the patient was able to see the larger stimulus in an area where he/she could not see the smaller stimulus with the same intensity. No real pathology would ever cause crossing of the isopters such as in this GVF.
FA differentiating optic nerve swelling and NVD
Just as in NAION or CRVO, you would see some mild leakage of fluorescein into the swollen substance of the nerve head from optic disc telangectasias; in contrast, with frank NVD, you would see leakage of fluorescein which appears much more hyperfluorescent, is visibly above the plane of the retina, and diffuses into the vitreous in the later stages of the FA.
There is fluorescein leakage around the optic nerve with any cause of optic disc edema AND with NVD. The difference is that NVD often grows anteriorly into the vitreous scaffolding so the leakage in that case can be seen extending into the vitreous.
VEP
Diagnose optic neuropathy on VEP: Prolonged latency more specific than decreased amplitude
Performed by presenting a visual stimulus to one eye (e.g. a flash, alternating patterns, etc) and measuring electrical brain waves over the occipital cortex.Rough estimate of the function of the entire afferent visual pathway. VEP is an electrical signal extracted from simultaneously generated EEG.
An abnormal VEP does not aide in localizing pathology to any particular portion of the visual Pathway; VEPs have very poor specificity.
Useful to prove good vision in a patient suspected of functional vision loss, but the test does require good cooperation (especially a pattern-reversal VEP which provides the best assessment of visual acuity). An uncooperative patient will likely blink or defocus purposefully which will falsely reduce the pattern waveform and underestimate the function of the visual pathway. (Pt can produce false reading by using accommodation to fog their vision).
VEP’s are an excellent tool for estimating visual function in patients unable to communicate such as young pre-verbal children or cognitively challenged patients. Again, however, pattern-reversal VEP’s are the best test for estimating an actual visual acuity and require decent cooperation.
VEP cannot distinguish b/t ON vs. retinal disorders. Two critical parameters used for functional evaluation = height of first positive or upwards wave (amplitude) and the amount of time between stimulus presentation and the appearance of this wave (latency).
MRI
T1 weighted images provide the best visualization of anatomy. In T1 images, bone and fat is bright while CSF, vitreous, and air is dark.
T2 images optimize the difference in water content between tissues and therefore is excellent for demonstrating pathology. In T2 images, bone is bright, fat is dark, and CSF / aqueous is very bright.
FLAIR (or fluid attenuated inversion recovery) is a subset of T2 sequencing that attenuates the bright signal of CSF allowing for better visualization in the periventricular regions adjacent to the CSF.
DWI (or diffusion weighted imaging) is a sequence which highlights recent vascular perfusion abnormalities. Thus, DWI is ideal for evaluation of cerebral infarctions. DWI can show a cerebrovascular accident (CVA) minutes after onset and will stay abnormal up to 3 weeks following a CVA.
Multifocal erg vs full field erg
full field ERG is best at evaluating rod function although the stimulus frequency can be altered to evaluate gross cone function. For assessing focal retinal dysfunction within the macula, go to multifocal erg
amsler grid degrees (also HVF and Goldman)
The Amsler grid tests the central 20 degrees (i.e. 10 degrees on either side of fixation) and is often used at home by patients with macular degeneration to assess for any acute changes in vision in between office visits.
Humphrey visual field testing can test the central 10 degrees, 24 degrees, or 30 degrees depending on the setting chosen.
Goldman visual fields are used to evaluate the entire visual field (the machine can test up to 180 degrees horizontally which far outreaches the potential monocular visual field in humans).
Neutral density filter
Many clinicians do not quantify the severity of an APD in practice preferring instead to only document its presence. Some clinicians will comment on whether an APD is questionable, subtle, or brisk. Some clinicians will measure the severity of an APD by using neutral density filters.
In a patient with a right APD, neutral density filters are held over the left eye starting with the least dense filter (usually 0.3 log units). The swinging flashlight test is then performed with the filter covering the left eye. If the right pupil still dilates immediately when the flashlight is swung from the left eye to the right eye then the APD is still present.
The density of the filter over the left eye is increased to 0.6 log units and the swinging flashlight test is repeated. This continues until the APD has been “neutralized.” If too strong of a filter is placed over the better eye then the APD will actually reverse. The density of the filter required to neutralize the APD defines the severity of the APD.
The advantage of grading an APD is that it allows an additional objective means (along with visual acuity, color vision, and visual fields) to follow a patient for possible progression of optic nerve pathology. If only the presence of an APD is documented then it is impossible to know if the APD gets worse over time.
GVF
Smallest target size = 0 = 1/16 mm^2
every following test has an area 4x prior target size
I (least intense stimulus)= 1/4 mm^2, and II =1 mm^2, III = 4, IV = 16, V (most intense stimulus)= 64
Absolute scotoma on GVF
Absolute scotoma = confirm by testing with brightest and largest target size (V4e)
Photostress recovery time
Differentiate ON from macular disease:
Optic nerve dx: normal recovery time
Macular dx: prolonged recovery
“poor man’s ERG” - start by measuring BCVA, then shine bright light in patient’s eye for ~ 30 seconds. After removing light, patient asked to read BCVA line (or one line larger). Time required for patient to read this is photostress recovery time. Normal: 45-60s.
Recovery time > 90s indicates significant maculopathy. (Walsh and Hoyt says shine the light 10 seconds, and > 99% normals will be < 50s)
LP for IIH
Should not have any pleocytosis (increased WBC suggests infection, malignancy, inflammation)
Opening pressure needs to be > 25 cm H2O to be considered elevated. Measuring in CM or MM reflects CSF fluid column height in manometer, and NOT mm Hg as in barometric pressure.
Drugs that cause drug induced ICP
Vitamin A and derivatives (isotretinoin), tetracycline family of Abx, OCP, prednisone (both in use and sudden withdrawal), synthetic GH, CYCLOSPORINE.
Paradoxical OKN
slow phase of eye movement in OPPOSITE direction that of rotating OKN drum (ex: congenital motor nystagmus)
Extinction
- a form of neglect involving the visual field
- extinction describes the inability to see a stimulus in one hemifield of an eye only when a target is simultaneously presented in both hemifields of that eye. When a stimulus is tested by itself in the hemifield exhibiting extinction, the stimulus is seen. Extinction is usually associated with parietal lobe lesions and the phenomena would be exhibited in the contralateral hemifield of both eyes. Gaze preference is the tendency to look with both eyes in a certain direction although the patient retains the ability to look in other directions if they choose (distinguishing gaze preference from gaze palsy).
Double Maddox Rod
The double Maddox rod is performed by placing two differently colored Maddox rods in front of each eye using a trial frame. While testing procedures may vary, generally a red Maadox rod lens with ridges oriented vertically is placed over the right eye and a clear Maadox rod lens with ridges oriented vertically is placed over the left eye. When both eyes are open and a light stimulus provided, the patient will see two horizontal lines extending from left to right. An eye with no torsional deviation will see the its respective line as parallel to the floor while any torsional deviation results in a slanted line.
To measure the exact amount of torsional deviation, the patient is directed to rotate the trial frame knob responsible for clockwise/counter clockwise rotation of the lens until the tilted line is parallel to the other horizontal line in the unaffected eye (and parallel to the floor). The examiner can then read on the trial frame how many degrees of rotation were required to normalize the slanted line. While it is more difficult to measure precise degrees of rotation, assessing fundus torsion on indirect ophthalmoscopy is another acceptable means to diagnose ocular torsion.
