Neuro-ophthalmology Illustrated Chapter 1 – Examination 1

Questions:
1. What is the minimum visual acuity needed to correctly read the control plate on the color vision testing plates?
2. Which is the more sensitive color vision test, Hardy-Rand-Rittler or Ishihara for optic neuropathy?
3. What are the causes of acquired unilateral or bilateral reduced color vision?

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Questions with answers:
1. What is the minimum visual acuity needed to correctly read the control plate on the color vision testing plates?
The control plate can be read by patients with a visual acuity of at least 20/400.

2. Which is the more sensitive color vision test, Hardy-Rand-Rittler or Ishihara for optic neuropathy?
HRR plates are more likely than Ishihara plates to detect a color vision defect, particularly when the visual acuity is 20/25 or better. However, neither test is sensitive enough to be used as the sole criterion for the diagnosis of nonglaucomatous optic neuropathy. The results of comparing color perception (saturation) of the two eyes may be more useful than absolute color vision responses, particularly in patients with unilateral disease.  

3. What are the causes of acquired unilateral or bilateral reduced color vision?
Acquired unilateral or bilateral color loss occurs most commonly with maculopathies, optic neuropathies, chiasma disorders, and, more rarely, bilateral occipital lesions.

The information below is from Neuro-ophthalmology Illustrated-2nd Edition. Biousse V and Newman NJ. 2012. Thieme

1 The Neuro-ophthalmic Examination
A detailed neuro-ophthalmic examination is part of routine neurologic and ophthalmic examinations. It is a powerful means to detect and localize lesions that involve the visual system. Documentation of the extent of damage within the visual system is also an invaluable method to assess the effect of various therapies and often guides the management of numerous neurologic and neurosurgical disorders.

The extent of the neuro-ophthalmic examination varies depending on the patient’s complaints, but parts of it should always be performed in detail in selected neurologic disorders, and some parts of the neuro-ophthalmic examination should be systematically performed in most neurologic and systemic diseases. For example, in a patient with an occipital infarction, evaluations of visual acuity, color vision, and formal visual fields are the most important. A patient with known multiple sclerosis needs a thorough examination, because all functions involved in the visual system may be affected. In a patient complaining of diplopia or with anisocoria, formal visual field testing is usually not necessary, whereas all patients with raised intracranial pressure and papilledema should have formal visual field testing, even when they have no visual symptoms.

Most examination techniques detailed here are best performed with appropriate tools in a neuro-ophthalmologist’s or ophthalmologist’s office. However, a basic neuro-ophthalmic examination (including evaluation of the vision, pupillary function, ocular motility, and funduscopy) can be performed at the bedside, in the emergency room, or in a neurologist’s office with only very few tools (see ▶Table 1.1 for a list of required tools).

The examination usually follows a specific order, as given in the following discussion(e.g., you have to examine the visual acuity before flashing light into the eyes; the pupils need to be examined before drops are placed in the eyes; funduscopic examination is the last part of the examination).

1.1 Visual Acuity
In examining the patient’s visual acuity, each eye is tested separately (▶Fig. 1.1). Visual acuity is measured with the patient’s corrective lenses or a pinhole (▶Fig. 1.2). There are two types of visual acuity tests: distance and near.

Distance visual acuity is tested as follows (▶Fig. 1.1 and ▶Fig. 1.2):
1. Place a Snellen chart at 20 feet.
2. Record the smallest letters read by the patient with each eye (e.g., “20/20 right eye with correction; 20/25 left eye with pinhole”).
3. If the patient cannot read the largest letter, visual acuity is less than 20/400 and is recorded as “count fingers,” “hand motion,” “light perception,” or “no light perception.”

The pinhole is an opaque panel perforated with one or more holes 1.0 to 1.5mm in diameter. The holes restrict incoming light rays to a narrow path that bypasses refractive irregularities and presents a single, focused image to the fovea of the retina. Refractive errors and visual loss from cataracts improve with a pinhole. If visual acuity cannot be improved with a pinhole, then other media opacities, optic nerve disease, maculopathy, or amblyopia is likely the cause of visual loss. The test may be unreliable with young children, the elderly, and cognitively impaired individuals.     

Near visual acuity is tested as follows (▶Fig. 1.3 and ▶Fig. 1.4)

1. Hold a near card at 14 inches from the patient. The patient should be tested with reading glasses (or a+2.00 or+3.00 lens) if he or she is older than age 50 (because of presbyopia).
2. Record the smallest letters or numbers read by the patient with each eye (e.g., “J1+right eye with correction; J1 left eye with correction”).

1.2 Color Vision, Color Saturation
Color vision can be assessed by several methods, and each eye is tested separately. The purpose of color vision testing is to detect acquired unilateral or bilateral color loss, which occurs most commonly with maculopathies, optic neuropathies, chiasma disorders, and, more rarely, bilateral occipital lesions.
The Ishihara pseudo isochromatic and the Hardy-Rand-Rittler (HRR) color plates are routinely used (▶Fig. 1.5).

The number of plates correctly identified with each eye is recorded (e.g., “14/14 Ishihara color plates right eye; control only left eye”). The control plate can be read by patients with a visual acuity of at least 20/400. Some patients with dementia and simultagnosia may have difficulty using these plates.
When color plates are unavailable, the difference in color perception between the two eyes may be identified using a red object (e.g., the top from a bottle of dilating drops) (▶Fig. 1.6).

Even with normal color plate testing, the patient may recognize a color difference in a red bottle top alternately presented to each eye. The patient should be asked to quantify the red desaturation (percentage of normal).

1.3 Contrast Sensitivity
Contrast sensitivity is another measure of visual function and is often abnormal in patients with optic neuropathies. Patients with maculopathies and cataracts also often have decreased contrast sensitivity. It is not tested in all patients but is useful in patients with visual complaints and an otherwise normal examination. It is also used as a measure of visual function in numerous clinical trials, especially multiple sclerosis trials. The test uses a chart with letters or stripes represented in various shades of gray.


Comparison between Hardy-Rand-Rittler 4th edition and Ishihara color plate tests for detection of dyschromatopsia in optic neuropathy.
Huna-Baron R1, Glovinsky Y, Habot-Wilner Z.Graefes Arch Clin Exp Ophthalmol. 2013;251(2):585-9.
BACKGROUND:
The aim of this work was to compare the specificity-sensitivity balance of the Hardy-Rand-Rittler (HRR) 4th edition with the Ishihara color plate tests for color-vision defects in patients with optic neuropathy.
METHODS:
This is a prospective case-control study. The study group included 43 patients (48 eyes) with newly diagnosed optic neuropathy, and the control group included 33 patients (33 right eyes) who were referred to the eye clinic for conditions other than optic nerve or retinal macular disorders. Individuals with visual acuity of less than 20/70 (0.54 Log MAR) were excluded. All patients underwent comprehensive eye examination and color-vision evaluation with both tests in a random order under standardized lighting conditions. The scores of the Ishihara and HRR tests were set as the number of plates identified out of 12 and six respectively.
RESULTS:
The receiver operating characteristics (ROC) curve was statistically significantly better when using the HRR test (area under curve [AUC] = 0.93 ± 0.03) than for the Ishihara test (AUC = 0.77 ± 0.05) (P = 0.0006). The best specificity-sensitivity balance for the HRR was 100 % and 79 % respectively, and for the Ishihara test 100 % and 48 % respectively.
CONCLUSIONS:
The HRR 4th edition test proved to be superior to the Ishihara test in detecting acquired dyschromatopsia due to optic neuropathy. We recommend using the HRR 4th edition test as a screening method for detection of color-vision defects in patients with optic neuropathy.

References:
1. Neuro-ophthalmology Illustrated-2nd Edition. Biousse V and Newman NJ. 2012. Thieme
2. Comparison between Hardy-Rand-Rittler 4th edition and Ishihara color plate tests for detection of dyschromatopsia in optic neuropathy. Huna-Baron R1, Glovinsky Y, Habot-Wilner Z.Graefes Arch Clin Exp Ophthalmol. 2013;251(2):585-9.

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