Ординатура / Офтальмология / Английские материалы / Manual of Squint_Ahuja_2008
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monofixation is unable to appreciate all four dots at once. He may see only two red or three green dots depending upon the eye affected.
2.When the patient is brought closer to the panel bearing the dots, at one point he begins to appreciate all four dots. It happens at a critical distance, varying with the size of scotoma, as the angle subtended by the dots enlarges sufficiently enough to overcome the area of central suppression. The distance at which this happens allows the indirect estimation of the scotoma size. The latter being inversely proportional to be former.
3.2.4 PD base out prism test (Figs 10.17A to D). This rest is another method regulating used to reveal the scotoma in patients with monofixation syndrome. In this rest a 4 PD prism is placed base out over one eye, say right, while the patient fixates at a point 6 meters away. The prism displaces the image towards the base, in another words, from the fovea of the right eye to a point outs temporal retina (4 PD or 2° away from the fovea). Refixation movement of the right eye elicits a conjugate movement in the left (Levoversion). If the right eye has no foveal suppression. As consequences of this movement of the left eye the image the image in that eye has been shifted to an extrafoveal point. This eye thus makes a fusional movement back to its original position if foveal suppression is present in that eye, the
FIG. 10.16: Worth form dot test
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FIGS 10.17A TO D: 4 D prism test in microtropia
fusional movement is absent, however if central suppression is present in the eye which is not covered by the prism. The test is repeated with prism over the left eye. Interpretation of this test is as follows failure of eye with the prism to make a refixation movement or of the follow eye to a fusional movement, indicates the presence of foveal suppression and lack of bifoveal fusion.
Bagolini striated glases test (Figs 10.18A to C): A patient who has a central scotoma in his binocular visual field, will appreciate a break or gap in the streak around the light source. This break is usually ignored unless the patient is made aware of it. Transparency of the glasses has two advantages first, it allows a normal testing environment and second,
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A B
C
FIG. 10.18A TO C: Bagolini striated test
it allows the examiner to evaluate the alignment of the eyes and the patient’s sensorial response, simultaneously. Once the scotoma has been observed in one eye, the patient is encouraged to fixate with the other eye to see if the scotoma has been transferred to the other eye. Bagolini striated glasses test is the best test available for evaluating the status of retinal correspondence in monofixation syndrome.
Treatment of Microtropia
•Treat anisometropia
•Amblyopia is rare, if present, treat the amblyopia
•Iseikonic lens
•Contact lens
•Surgery is not needed.
11 Paralytic Squints
Paralytic squint is that type of squint in which the eyes move in an incoordinated manner so that angle of squint varies in different directions of gaze and on changing fixation from one eye to the other. This is caused by the motor imbalance of one or several extraocular muscles. The characteristic features of the paralytic squint are:
a.A motor deficiency in the field of action of the paretic muscle
b.Diplopia or double vision
c.Secondary deviation is greater than the primary deviation
d.Compensatory head postures
e.Absence of suppression and amblyopia.
ETIOLOGY
Paralysis can be due to:
a.Lesion of the nerve
b.Lesion of the muscles.
Lesion of the nerve can be at the level of nucleus, nerve roots, nerve
trunks or it can be a congenital absence or abnormalities of nerve nucleus. It may be due to:
a.Injury
b.Inflammation, e.g. Syphilis, disseminated sclerosis, etc.
c.Vascular diseases, e.g. Hemorrhage, thrombosis aneurysms, arteriosclerosis, etc.
d.Neoplasms, e.g. Brain tumor
e.Toxic, e.g. alcohol, lead, carbon monoxide
f.Degeneration, e.g. Chronic nuclear ophthalmoplegia
g.Other diseases like, thyroid ophthalmoplegia
h.Myasthenia gravis and ocular myopathies
i.Displacement of the visual axis of one eye so that parallelism with that of the other eye is lost. This may occur in:
1.Injuries like blow out fractures causing damage to the supports of the eyeball.
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2.Injuries causing loss of orbital fat such as may be produced by fracture of the floor of the orbit.
3.A space occupying lesion of orbit or adjacent to orbit, e.g. osteoma.
SYMPTOMS
1.Diplopia is the chief complaint. It occurs mainly in the field of action of the paralyzed muscle. This could be homonymous or heteronymous (Figs 11.1A and B). In cases of paralysis of long duration and congenital palsy diplopia will not be the chief complaint, since the patient either learns to ignore the false image or contracture of the antagonist increases the deviation so that the false image is thrown on to the less sensitive periphery of retina so that suppression is facilitated.
2.Vertigo and nausea is due to diplopia and false orientation. Vertigo occurs mainly when the paralyzed muscle is called into action and is
FIG. 11.1A: A Homonymous (uncrossed) diplopia
The image of object O falls on the fovea F1 of the non-deviating eye; and at a point NR nasal to the fovea F2 of the deviating (convergent) eye, the image of O being seen at O′
FIGS 11.1B: Heteronomous (crossed) diplopia
The image of object O falls on the fovea F1 of the non-deviating eye; and at a point TR temporal to the fovea F2 of the deviating (divergent) eye, the image of O being seen O′
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due to movement of the object with increasing velocity in the direction in which eye is moved.
3.False projection: This is a necessary accompaniment of binocular diplopia and depends on the same principle of increase in the secondary deviation, i.e. object is projected according to the amount of nervous energy exerted.
4.Defective ocular motility: Limitation of movement in the direction of action of paralyzed muscle is an important feature. The amount of limitation depends on the degree of paralysis.
5.Complementary head postures: The purpose of adopting an abnormal head posture is to turn the eyes as far away as possible from the field of action of the paralyzed muscle. This is an attempt to lessen diplopia and associated unpleasant consequences.
—In dextrorotators (RLR and LMR) palsy the head is turned to right.
—In SR and IO palsies the chin is elevated.
—In IR and SO palsies the chin is lowered.
Head tilt—A head tilt to either shoulder, around an anteroposterior axis) may occur to counter act torsional diplopia in paralysis of oblique and vertical muscles. Head tilt is often combined with a head turn and chin elevation or depression and is more common with anomalies of the oblique muscle than the vertical rectus muscles. In short, we can say that head is placed in such a way to avoid action of the affected muscle.
In LSR palsy the head is turned to the left in order to spare the action of the Laevoelevators.
In divergent squints chin is elevated and in convergent squint chin is depressed.
SEQUELAE OF EXTRAOCULAR MUSCLE PALSY (FIG. 11.2)
The paralytic deviation undergoes several stages. The first stage is characterized by weakness of the paretic muscle. Followed by over action of contralateral synergist muscle. Next stages is inhibitory palsy of contralateral antagonist. Occasionally for reasons unknown, the antagonist of the paretic muscle does not over act and the deviation remains limited to the field of action of paretic muscle. For example, (1) In case of RLR palsy. There will be weakness of RLR followed by over action of LMR and there will be contracture of the RMR and secondary inhibitional palsy in LLR. (2) In LSO palsy, there will be weakness of LSO (primary paresin), followed by over action of RIR. Then there will be contracture of LIO and secondary inhibitional palsy of RSR.
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FIG. 11.2: Sequelae of extrinsic ocular muscle palsy
CLINICAL EVALUATION OF THE PATIENT
History
History is most important, from the history we make out the following:
a.Onset is sudden or insidious
b.Presence of diplopia
c.Direction of diplopia
d.History of any other diseases like diabetes, hypertension, multiple sclerosis or malignant diseases especially bronchial carcinoma.
Record of Visual Acuity
If vision is very poor in the affected eye patient may not have diplopia.
Ocular Motility
Record the ocular motility in all the nine positions of gaze. This could be done using a perimeter. Both uniocular and binocular motility should be recorded.
Inspect from Distance
Compensatory Head Postures
The following are the characteristics of head postures:
i.The head is turned into the direction of field of action of the weak muscle so that the eyes are automatically turned into the opposit direction.
ii.Head tilt is to make up for the torsional deviation and is characteristic for the paralysis of oblique.
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FIG. 11.3: Diplopia charting
Cover Test
In paralytic squint cover test is employed to differentiate primary and secondary deviation. Here secondary deviation is always greater than the primary deviation.
Diplopia Charting (Fig. 11.3)
Diplopia is the most prominent symptoms and very much useful in diagnosis. Carry out the test in a darkroom. Make patient wear Armstrong’s glasses. Hold the light at one meter distance from the patient. Hold the light, direct infront of the patient, than move up and down then to right to left, right up, right down, left up an left down, and the positions of the images are accurately recorded on a chart. The following data are derived from the test.
a.The areas of single vision and diplopia
b.Distance between the two images in different areas of diplopia
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c.Whether the images are at the same level or not
d.Whether both are erect or one is inclined
e.Whether diplopia is crossed or uncrossed.
N.B. False image belongs to the paralyze eye and distance between the images are maximum in the direction of action of paralyzed muscle.
Hess Charting
This is of both diagnostic and prognostic value.
Advantages
1.Colors of fixation target and indicator are complementary to the goggles.
2.The method is independent of external illumination.
3.It is simple and there cannot be any misinterpretation on the part of the patient or examiner because only one of the red fixation spot light is presented at a time.
4.Less difficulty is encountered in testing patients with gross retinal inhibition as the light source from both fixation object and indicator produce adequate stimulus.
Interpretation
Compare the charts. The smaller chart indicate the paralyzed side and the larger the overacting side. In smaller chart, the greatest restriction indicates the direction of action of paralyzed muscle. In torsional deviations the fields have slopping sides.
Fields of Fixation (Uniocular and Binocular) (Figs 11.4 and 11.5)
a.Field of uniocular fixation in that area within which foveal fixation of a small test object can occur. Its extend corresponds to the limits of movements of the eyeball in different direction. This could be measured by means of a perimeter. The extend of field in the average normal eye is about 45o–50o except in the inner and downwards where it is limited to some extent by nose.
b.The fields of binocular fixation is that area within which bifoveal fixation of a small test object can occur. Its extent is limited partly by the limits of ocular movements and partly by nose. For the test to be of value the patients cooperation must be good and his binocular vision is strong. The test objects usually employed is 3-5 mm size and color is white.
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FIG. 11.4: Field of uniocular fixation
FIG. 11.5: Field of binocular fixation
Bielschowky’s Head Tilt Test
Bielschowky’s head tilt test is of great value in diagnosing paresis of the oblique muscle than that of rectus muscle because the vertical effect of obliques, provoked by tilting the head to either shoulder in patients with paralysis of vertical rectus muscle is less than that of rectus muscle.
Routine Ophthalmoscopic Examination
Routine ophthalmoscopic examination especially to study the disk for papilledema or papillitis.