Ординатура / Офтальмология / Английские материалы / Practical Ophthalmology A Manual for the Beginning Ophthalmology Residents 4th edition_Wilson_1996
.pdf116 (Ihapicr (v. ()cular .Motility Examination
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The cover-uncover test is performed first to establish the presence of either a manifest deviation (heterotropia) or a latent deviation (heterophoria). The alternate cover test is then performed to measure the deviation.
Cover-uncover test
Clinical Protocol 6.5 describes how to perform the cover-uncover test. This test is usually done with the patient in an upright, seated position, but it can even be done with a bedridden patient who is prone or lying on one side. The only necessary condition is that the patient be able to maintain fixation on a target. As one eye is covered, observe the opposite, uncovered eye carefully for any movement. If there is movement oi the uncovered eye to pick up fixation, a (hetero)tropia is present. If the uncovered eye maintains fixation and if there is a refixation movement of the covered eye just after the occluder is removed, then a (heten>)phoria is present that becomes manifest only when binocularity is interrupted. If the patient has a phoria, the eyes will be straight both before and after the cover-uncover test; during the test, there will be a deviation caused by interruption of binocular vision. A patient with a heterotropia, however, starts with a deviating eye and ends with either the same eye or the opposite eye deviated. If the opposite eye is deviating at the conclusion of the test, the patient has alternating heterotropia. Some patients may start with straight eyes prior to the cover-uncover test but develop an overt deviation with or after testing, which indicates that their fusion is easily disrupted. Such a patient has an intermittent (hetero)tropia. The corresponding deviation should be denoted with parentheses, for example: X(T) or E(T), as appropriate.
Alternate cover test
The alternate cover test measures the total deviation, both latent and manifest. It does not specify how much of which type of deviation is present (ie, it does not distinguish a heterophoria from a heterotropia). The alternate cover test is a dissociative test, and it often results in a deviation appearing to be considerably larger than the amount initially noted with the cover-uncover test. Results of the alternate cover test are recorded as in the examples in Table 6.4. Clinical Protocol 6.6 explains how to perform the alternate cover test.
Simultaneous prism-cover test
The simultaneous prism-cover test (SPCT) is helpful in determining the actual heterotropia present when both eyes are uncovered. It is perlormed by covering the fixating eve at the same time that the prism is
Tests oi Alignment |
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placed in front of the deviating eye. The test is repeated using successively larger (or smaller) prism powers until the deviated eye no longer shifts when the fixating eye is covered. Record the results of this measurement by noting the total amount of the deviation found on alternate cover testing, with a bracketed reference to the amount found on SPCT.
Other Considerations With Alignment Tests
Parents of small children frequently voice concern about an infant's ocular alignment when no true deviation is present. What the parents have observed is known as pseiidostrabismus, an appearance of crossed eyes resulting from either prominent epicanthal folds or an angle kappa. With prominent epicanthal folds, the corneal light reflection will be centered when tested by Hirschberg's method. Angle kappa refers to the angle formed between the visual axis and the anatomic axis of the eye (Figure 6.8). The corneal light reflection will appear to be decentered if angle kappa is present, when in fact there is no true manifest strabismus; nasal decentration simulates an exotropia (positive angle kappa) and temporal decentration simulates an esotropia (negative angle kappa). Cover testing can demonstrate that the eyes are straight.
Frequently a patient will present with a head position that is caused bv ocular imbalance. Head tilts and face turns should be noted in the patients record. Many schemes have been devised for recording the findings of alignment testing. Two examples are illustrated in Figure 6.9. Notation can be made on such a schematic drawing, but the patient's head should be aligned before cover test measurements are taken. When measurements are taken with the patient assuming another head position, even if it is their habitual position, it should be noted.
Table 6.4 Sample Recording Results of Alternate Cover Testing
Example 1 |
Example 2 |
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XT 30A |
sc" |
RET'10A builds to 30A |
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X(T)' 20A |
cc" |
RE(T)'5A |
This example describes a patient wearing corrective lenses (cc") who has a constant exotropia of 30 prism diopters at distance and intermittent exotropia of 20 prism diopters
at near (near = '). Since no eye preference is stated, it is assumed that the patient alternates freely.
This example describes a patient who, when not wearing glasses (sc"), shows a constant right esotropia at near of 10 prism diopters that increases to 30 prism diopters. When this patient wears glasses, the right esotropia becomes intermittent and is reduced to 5 prism diopters.
118 Chapter 6: Ocular Motility Examination
Angle
kappa
Pupillary axis
Figure 6.8 Angle kappa is the angle formed between the visual and anatomic axes of the eye. ,. - .•' - .
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Figure 6.9 Two different schemes used to record the results < oar-tK ment and motility examinations.
At times the examiner will intentionally tilt the patients head to obtain measurements, most often as part of evaluating cycle vertically acting muscles. It is particularly useful to diagnose superior oblique palsies as part of the three-step test, in which the alignment of the eyes in primary position is compared to the alignment in far right and tar left gaze and then compared to the alignment when the head is tilted to the right and to the left. The first step of this test determines which eye is hypertropic by using cover-uncover testing. Four possible muscles will be responsible for a hyperdeviation noted in primary position (see Table 6.3). By asking the patient to look to either side and then by utilizing the utricular reflex, which realigns the eyes when the head is tilted, die number of underacting muscles is sequentially narrowed until the single underacting muscle is identified. Refer to the resources at the end of this chapter for a more detailed discussion of the three-step test.
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Diagnostic Use of Prisms
Plastic and glass prisms are used for quantitative measurement of the angle of deviation for all types of strabismus. Prisms are available singly or as bars of small horizontally or vertically oriented prisms attached to each other in increasing strength. Rotary prisms (Risiey's prisms) produce a continuum of prismatic power. A rotary prism may be handheld but can also be found mounted on the front of most refractors. Rotary prisms consist of two prisms of equal power that are counterrotated with respect to each another. The prismatic power produced varies from zero to the sum of the two powers. Rotary prisms are particularly useful in measuring phorias and fusional vergence amplitudes. Descriptions of the methods of measuring fusional vergences are beyond the scope of this text but can be found in any strabismus text, such as those listed at the end of this chapter.
The prism adaptation test (PAT) is used in the preoperative assessment ol a patient. Fresnel (plastic press-on) prisms are placed over the patients distance correction or, if necessary, on piano lenses. The patient wears this amount of prism for 30 minutes and is then remeasured by alternate cover testing. Additional amounts of prism may be necessary to achie\e an orthophoric position. Once orthophoria is maintained, the patient wears the prisms for a more extended period, ranging Irom several hours to a lew days, and is remeasured at the end of this rime. This test gives the examiner information concerning the mechanical realignment of the eves and the sensory response to this position.
In the 4X prism base-out test, a -P prism is placed base-out in Ironr of one eve while the patient fixes on a target. It the examiner notes a relixation movement in the eye that is behind the prism, no fovea I suppression is present. II no relixation movement is noted, loveal suppression is present in that eye. This rest is described in greater detail in the resources listed at the end of this chapter.
Pitfalls and Pointers
\ very small-angle deviation may be difficult to detect with the corneal lisdit reflection test and cover tests.
120 Chapter 6: Ocular Motility Examination
•Visual acuity testing is critical in all cases of suspected strabismus for detection of amblyopia.
; u; • The examiner must use ingenuity to keep a very young patient fixating. Such ploys as brightly colored toys, pictures, and storytelling about the objects are essential. A good general rule to set is "one toy, one look." A well-prepared resident will have several interesting toys or pictures always at hand.
•About 15% of children with pseudostrabismus develop manifest strabismus or amblyopia and, therefore, need more frequent followup than children whose eyes have always appeared straight.
•When testing binocularity with the Titmus test, make sure that the stereophotograph is clean (no scratches or fingerprints) and that the polarization of the viewing eyeglasses is effective.
Suggested Resources
Amblyopia [Preferred Practice Pattern]. San Francisco: American Academy of Ophthalmology; 1992.
Esotropia [Preferred Practice Pattern]. San Francisco: American Academy of Ophthalmology; 1992.
Helveston EM. Surgical Management of Strabismus: An, Atlas of
Strabismus Surgery. 4th ed. St Louis: CV Mosby Co; 1993.
Pediatric Ophthalmology and Strabismus. Basic and Clinical Science Course, Section 6. San Francisco: American Academy ot Ophthalmology; updated annually.
Tasman W, ed. Duane's Ophthalmology. Philadelphia: LippincottRaven; updated annually.
\on Xoonlen CK. Von \oordeii-.\'Iau///ci/ccs Atlas of Strabismus.
4lh ed. Si Louis: CV Mosby Co; 1983.
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Clinical Protocol 6.1 |
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Assessing the Ocular Movements |
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Sit facing the patient. Hold your finger or a small fixation target at eye |
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level about 10 to |
14 inches in front of the patient, with the patient look- |
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ing in primary position (straight ahead). |
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Ask the patient to follow the target as you move it into the six cardinal |
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fields and up and down along the midline. Elevate the upper eyelid with |
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a finger on your free hand to observe down gaze. |
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Note whether the amplitude of eye movements is normal or abnormal in |
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,. .. both eyes. Rate the amplitude for all fields of gaze by considering nor- |
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mal amplitude to be 100%, and rate lesser amplitudes accordingly. To |
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record the relative underaction or overaction, designate the normal as 0, |
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that is, no overactions or underactions are present. Use the numeral 4 to |
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designate maximum underaction or overaction. Underactions thus are |
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rated from -1 to -4, while overactions are rated from +1 to +4. |
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Note any nystagmus that may be present, and record the nystagmus |
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according to its presence, direction, and amplitude in any field of gaze |
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\\ here applicable. |
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Clinical Protocol 6.2
Determining Accommodative
Convergence/Accommodation Ratio
Distance-Near Method
1. Measure deviation at distance fixation, with refractive correction in
place. :'••'.
2.Remeasure deviation at 1/3 m (33 cm).
3.Calculate AC/A - 1/3 (n^-d^) + interpupillar} distance (cm).
continued
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Minus-Lens Method
1. Measure deviation at distance fixation, with refractive correction in place.
2 Remeasure deviation at distance fixation after adding -1.00 D to the correction worn for step 1 above.
3. Calculate AC/A = (A_L 0 0 - Ad) /D, where D = 1.00.
Clinical Protocol 6.3
Performing the Corneal Light
Reflection Test, Hirschberg's Method
1.Have the patient seated facing you with head straight and eyes directed in primary gaze.
2.Hold a penlight in front of the patient's eyes at a distance of approximately 2 feet, directing the light at the midpoint between the two eyes
of the patient. Align yourself with the light source. Instruct the patient to look directly at the light.
3.Compare the position of the two corneal light reflections and record the estimated result as prism diopters or degrees of deviation. Make a notation in parentheses beside the measurement: (by Hirschberg).
Clinical Protocol 6.4
Performing the Corneal Light
Reflection Test, Krimsky's Method
t.Position the patient, the penlight, and yourself as for Hirschberg's method above.
2. Choose a prism of a power estimated by the Hirschberg's method ol estimatin" deviation.
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3. Place the trial prism in front of the fixating {not the deviated) eye, with the apex of the prism (narrower end) pointing in the direction of the deviation. If a prism bar is available, use it with the flat (back) surface toward the patient, and the apexes of the prisms pointed in the direction or the deviation, as with single prisms.
4. Increase or decrease the strength of the trial prism until the light is reflected from each cornea symmetrically- • . •
5.Record the strength of the prism used, noting (by Krimsky) in paren-
theses beside the measurement. For example, if it was necessary to use a 30A prism to center the corneal reflections for a patient with a left
exotropia, record the results as follows:
LXT 30A (by Krimsky)
Clinical Protocol 6.5
Performing the Cover-Uncover Test
1.I lave the patient look at a distance lixation target, and position yourself directly opposite the patient, within arm's reach.
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Swiftly cover the fixating eve with an occluder or your hand, and |
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observe the other eye for any movement. Carefully note its direction. |
3.Uncover the eye and allow about three seconds for both eyes to be uncovered.
4.Swiftly cover the other eye and observe its fellow for any movement
5.Ensure that the patient is maintaining fixation on the same point as established for step 1.
6.After an interval of about a second, uncover the eye and observe it for any movement.
7.Note results but do not record them until other cover testing is completed.
8.Repeat the test for near, using a near fixation point.
9.Repeat the distance and near tests using the patients habitual rcfradtive correction, if applicable.
Clinical Protocol 6.6
Performing the Alternate Cover Test
1. With the patient seated upright and looking at a distance fixation point, : rapidly shift the occluder from one eye to the other several times, not allowing any interval of binocularity. The examiner should be seated slightly to the side of midline, facing the patient and at arm's length to
the patient.
2. Place a trial prism over one eye (usually the patient's dominant eye),
( while continuing to shift the cover from one eye to the other. Remember to orient the prism with the apex toward the direction of deviation. Choose the strength of the initial trial prism to approximate the deviation estimated by the position of the corneal light reflections.
3.Continue to place prisms of progressively higher power in front of the eye until no movement is noted in either eye (neutralization). Additional
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prisms may be introduced until a reversal of movement is noted. The use |
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of both horizontally and vertically placed prisms is often necessary to |
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completely neutralize the shift. |
4.Record the results as noted in the examples in Table 6.4; in addition you may diagram the results in the various diagnostic positions of gaze (see examples in Figure 6.9).
5.Repeat the test for near.
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Pupillary Examination
• he pupil is the window to the inner eye, through which light passes to reach retinal photoreceptors. Because of its potential to reveal serious neurologic or other disease, examination of the pupil is an important element of a thorough ophthalmic evaluation, requiring meticulous attention to detail. Pathologic disorders can alter the size, shape, and location of the pupil, as well as the way the pupil reacts to light and near-focus stimulation. The patient who has a pupillary abnormality generally comes to the attention of the ophthalmologist as a result of either anisocoria (difference in size between the two pupils) or reduced pupillary light reaction.
This chapter provides a brief, basic background about pupillary pathway anatomy and supplies instructions tor the principal tests to evaluate pupillary responses, ft also gives a brief overview of the pupillary abnormalities that are most commonly encountered through pupillary evaluation and testing.
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