Ординатура / Офтальмология / Английские материалы / Oxford American Handbook of Ophthalmology_Tsai, Denniston, Murray_2011

26 CHAPTER 1 Clinical skills

Table 1.12 Optical properties of commonly used lenses

When using lenses with the slit lamp, the overall magnification seen = lens magnification (listed above) xslit lamp magnification (varies from 10 to 25x).

For an approach to diagnosing anisocoria, see p. 659.

Anatomy and physiology

Parasympathetic pathway (Light response)

CN II JPretectalJE-W nuclei JCN III J ciliary J short JCONSTRICT nucleus (bilateral) (inf) ganglion ciliary n

Known synapses are marked in bold.

Parasympathetic pathway (Near response)

rectus

Light-near dissociation is where dorsal midbrain pathology selectively reduces the response to light while preserving the response to near, and is thought to be due to the near pathway being placed ventral to the more dorsal pretectal nucleus serving the light pathway.

Sympathetic pathway

28 CHAPTER 1 Clinical skills

Pharmacological testing

The diagnosis of anisocoria (p. 659) may in some cases be assisted by pharmacological testing. These tests depend on comparing the response of the abnormal and the normal pupils, thus the agent should be instilled in both eyes and the response measured.

Diagnostic agents for an abnormally large pupil (e.g., for diagnosing Adie’s pupil)

Pharmacology

Pilocarpine is a direct muscarinic agonist. A normal pupil will constrict in response to 1% pilocarpine. A response to 0.125% indicates denervation hypersensitivity, as occurs in an Adie’s pupil.

Method

Administer a drop of 0.125% pilocarpine to both eyes. At 0 and 30 min measure pupil size when fixing on a distant target in identical dim lighting conditions. In Adie’s pupil the affected eye shows a significantly greater response.

Diagnostic agents for an abnormally small pupil (e.g., for diagnosing Horner’s pupil)

Pharmacology

Cocaine inhibits norepinephrine reuptake at the neuromuscular junction of the dilator pupillae, thus increasing sympathetic tone. In the presence of a normal sympathetic pathway, cocaine results in dilation. In a Horner’s syndrome, the abnormal pupil does not dilate.

Hydroxyamphetamine stimulates release of preformed norepinephrine. In a first or second order Horner’s, the post-ganglionic neuron is intact and thus the pupil will dilate in response to hydroxyamphetamine. In a third order Horner’s, the pupil will not dilate. This test should not be performed within 48 hours of the cocaine test.

Method

•Diagnose Horner’s pupil: Administer 4% cocaine to both eyes. Repeat at 1 min. At 0 and 60 min, measure pupil sizes when fixing on a distant target in identical ambient lighting conditions. The test is positive for Horner’s if there is no/poor dilation to cocaine.

•Identify level: Administer 1% hydroxyamphetamine to both eyes. Measure pupil sizes to distinguish between a firstor second-order neuron lesion (normal dilation) and a third-order neuron lesion (no/ poor dilation). This test is not reliable if performed within 48 hours of cocaine test.

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Corneal reflection tests

Hirschberg test

This test is used to detect or estimate the size of a manifest deviation. Ask the patient to fix his/her gaze on a penlight at 1 foot, and note the corneal reflections. The normal position is just nasal to the center of the cornea. Every 1 mm deviation represents 7° or 15 . If the reflection is deflected nasally, the eye is divergent (i.e., exotropic); if deflected temporally, the eye is convergent (i.e., esotropic).

Krimsky test

In the Krimsky test, this deviation is measured by placing a prism bar in front of the deviating eye and finding the prism strength at which the corneal reflexes are symmetrical. The prism should be orientated to “point” in the direction of deviation, i.e., base-out for an esotropia, base-in for an exotropia.

Cover tests

Cover–uncover test

The cover test reveals a manifest deviation. Ask the patient to fix his/ her gaze on a target (near, distance, non-accommodative, and sometimes far distance). Occlude each eye in turn (starting with the fixing eye) and observe any movement of the uncovered eye. For example, inward movement indicates that the eye was previously divergent (i.e., exotropic), and downward movement that it was previously elevated (i.e., hypertropic).

The uncover test may reveal a latent deviation. Occlude the first eye again for a few seconds. Look for any movement of the covered eye as the occluder is removed. Repeat for the other eye. For example, inward movement indicates that the occluded eye has drifted out (i.e., exophoric).

Perform the cover test in the nine positions of gaze to (1) identify the direction of maximum separation (indicates the direction of paretic muscle’s action/maximum restriction) and (2) compare ductions and versions.

OCULAR MOTILITY EXAMINATION (2) 31

Ocular motility examination (2)

Cover tests (cont.)

Alternate cover test

This detects the total deviation (latent + manifest) by causing dissociation of binocular single vision (BSV). Ask the patient to fix on a target (near, distance, non-accommodative). Repeatedly cover each eye in turn for 2–3 sec, so that one eye is always covered. Note the direction and amplitude of any deviation elicited. Once BSV is broken down, remove the occluder and note the speed of recovery of each eye in turn. Also look for dissociated vertical deviation (DVD) and manifest latent nystagmus (MLN), which are common in infantile esotropia.

Prism cover test

This measures the angle of deviation. Repeat the alternate cover test but with a prism bar placed in front of one eye, adjusting the prism strength until first neutralization and then reversal of the corrective movement occurs. The prism should be orientated to point in the direction of deviation, i.e., base-out for an esotropia.

Maddox tests

In these dissociative tests, different images are presented to each eye. They are generally used for assessing symptomatic phorias—whether for distance (Maddox rod), for near (Maddox wing), or torsional (two Maddox rods).

Maddox rod

For distance, a single Maddox rod (series of red cylinders) is placed horizontally in front of the right eye and the patient (with distance correction) fixates on a distant spot of white light. The patient will see a vertical red line and a white spot. If there is no phoria, the line will pass straight through the spot. If the image is crossed (i.e., the line is to the left of the light), there is an exophoria; if the line is to the right, there is an esophoria.

The phoria is then quantified by finding the prism required to neutralize it. The Maddox rod is then orientated vertically and the procedure repeated to identify any vertical phoria. If the line appears below the light, there is a right hyperphoria; if above it, there is a left hyperphoria. This is again quantified by neutralizing with prisms.

Maddox wing

For near, a Maddox wing is used. The patient (wearing his/her usual reading correction) looks through the apertures to view a vertical and horizontal arrow (with the right eye) and corresponding vertical and horizontal scales (with the left eye). The numbers indicated by the arrows (as seen by the patient) indicate the direction and size of the near phoria.

Two Maddox rod test

For torsion, a horizontally orientated Maddox rod is placed in front of each eye (one red, one white). The color of the tilted line is identified by the patient. The corresponding Maddox rod is rotated until the patient reports that it is vertical. The rotation required indicates the size of torsion. The two lines will fuse if there is no residual nontorsional deviation.

32 CHAPTER 1 Clinical skills

Parks–Bielschewsky 3-step test

This is used to identify a single underacting muscle in vertical/torsional deviations. It is particularly useful in superior oblique palsies (see Fig. 1.11, Table 1.15).

1.Perform cover test in primary position: identify higher eye.

2.Perform cover test with gaze to right then left: identify where separation (and diplopia) is greatest. This stage is based on the eye position where greatest vertical action occurs: for the oblique, this is when the eye is adducted; for the vertical recti, this is when the eye is abducted.

3.Perform cover test with head tilting to right then left shoulder: identify where separation (and diplopia) is greatest. This stage is based on the fact that the superior muscles intort the eyes, whereas the inferior muscles extort.

Caloric tests

This tests the vestibular, nuclear, and infranuclear pathways and can be useful in patients with decreased consciousness. Ideally, position the patient with the head inclined backward at 60°. Water placed in either ear causes nystagmus with fast phase as follows: cold–opposite, warm–same (COWS).

Step 1.

Right eye is the higher eye in the primary position

Step 2.

Disparity is greatest on gaze to the left

Step 3.

Disparity is greatest on head tilt to the right

Figure 1.11 Parks–Bielschowksy 3-step test: example of right superior oblique underaction.

Table 1.15 Theoretical manifestations of single muscle underactions

•Check whether they can see the white pin. Map out right/left visual field with the white pin (coming from unseen to seen, asking

the patient to identify when they first see the pin).

Any visual field abnormality should be confirmed on formal perimetry (p. 51).

Consider simultaneous presentation of gross targets to elicit inattention (this may occur in the context of stroke syndromes); simultaneous presentation of red targets (e.g., present across the midline to elicit the temporal depression of red perception of early chiasmal disease).

Additional clinical examinations may include pupils, optic discs, ocular motility, cranial nerves, and peripheral nervous system.

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Lids/ptosis examination

Table 1.17 An approach to examining the lids

•Inhibit frontalis by placing a thumb on the brow.

Measure any lagophthalmos.

•Ask patient to close eyes, gently at first and then squeeze eyes shut.

Assess orbicularis function and Bell’s phenomenon.

•Ask patient to keep looking upward at a target held superiorly.

•Ask patient to look rapidly from downgaze to a target held in primary position.

Consider examination of fundus, systemic review (myopathy, fatiguability).

Special tests

Fatiguability

The ability to sustain lid elevation is assessed in upgaze. Hold a target superiorly and ask the patient to maintain fixation on it for a minute. Note if either lid drifts down over that time, and reassess palpebral aperture in the primary position at the end of this period. If fatiguability is demonstrated, examine for associated fatiguability of ocular motility and general musculature. This is usually a sign of myasthenia.

Cogan’s twitch

Cogan’s twitch is an overshoot of the eyelid that occurs on rapid elevation of the eyes from downgaze to the primary position. Ask the patient to look down and then to look at a target held directly in front of him/her. Cogan’s twitch may be seen in myasthenia.