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Examination of strabismus

Dr. Sunita Kumawat, Deptt. Of ophthalmology, spmc bikaner.

Definition Derived from greek word strabismos, to suint, to look obliquely. Strabismus : It is the condition where visual axes of two eyes do not meet at point of regard.whether it is caused by abnormalities in binocular vision or by anomalies of neuromuscular control of ocular motility. crooked eyes/misaligned eyes/ crossed eyes

Orthophoria is an ideal condition of normal ocular alignment under binocular condition.Some perfer the term orthotropia.Heterophoria is a condition of ocular deviation kept latent by fusional mechanism (latent strabismus)Heterotropia is condition of ocular deviation that is manifest and not kept under control by fusional mechanism (manifest strabismus)

Classification of strabismus Heterophoria Heterotropia (manifest squint) (latent suint) Eso (convergent) Exo (divergent) Hyper (sursumvergent) Hypo (deorsumvergent) Cyclo (torsional)

Full description of the squint involves the use of many different terms, although in practice it is customary to apply any few of these to any particular squint. These are usually: first the eye which is affected, Rt. , Lt. or alternating.Secondly the presence of comitance or incomitanceThirdly the direction of deviation- convergent, divergent. Example: Rt. Comitant convergent strabismus Alternating comitant divergent strabismus

Additional terms which may be used in connection with the classification of strabismus:

Pseudostrabismus (apparent squint): false appearance of squint in absence of any deviation (broad epicanthal fold, flat bridge of nose, euryblepharon = false impression of convergent squint),

(Marked narrowing of lateral canthi , hypertelorism = false impression of divergent squint)

2.Fleeting squint3.Purposive squint

Angle kappa;The visual axis(line joining the fovea and the target object) is not the same as the optical or geometric axis(line passing through the centre of pupil and cornea)They differ normally by about +5 degrees out (exotropic), known as angle kappa.

Negative angle kappa (myopia) pseudo-esotropia.Large positive angle kappa (hypermetropia) leads to pseudo-exotropia

Preliminary examination:Presenting coplaints &History Visual acuity assessmentRefraction Examination of anterior and posterior segment

During history taking examinar should inspect the patient for:

-Size of both eyeballs and their position in the orbits, -Width of lid slits, lids motility and presence of the pathological synkineses, -Ocular movements and presence or absence of nystagmus, -Head posture, facial torsion, and chin position should also be inspected:

Visual acuity

Distance NearIn adults and children more >5yrs snellens chart, log MARcharts.Visual acuity can be measured in children:

1 Observation. 2 Optokinetic nystagmus. 3 Visual evoked potentials. 4 Forced choice preferential looking. 5 Graded optotypes of special construction. 6 Monocular fixation.

Visual acuity:

Detection Acuity test: assess the ability to detect the smallest stimulus eg: catford drum, STYCAR graded balls test,Boeck candy beads, Dot visual acuity.Recognition acuity tests: sjogrens hand test landdolts C, snellens E, Arrows, beal collins picture chart,allen picture chart, cardiff acuity cards, OKNOVIS.Resolution acuity test: Optokinetic nystagmus,Visual evoked potentials,Forced choice preferential looking,Graded optotypes of special construction.

Visual acuity in preverbal children: 1.Observation technique: Child in the first month of life reacts to the faces being near and his pupillary light reactions are normal. 2 to 5months of age child blinks in response to the visual threat and fixation are well developed. If the visual acuity of one eye is poorer than that of other eye, child will not allow to cover better-sighted eye.

2. Optokinetic nystagmusshowing the child white-and-black strips moved on the special cylinder.the higher density of strips is producing nystagmus in the child, better the visual acuity of the examined eye.

3. Visual evoked potentialsThey are useful in giving an objective record of underlying visual pathway and do exclude organic pathology.

4. forced choice preferential lookingThis technique is based on the childs eye reaction. child prefers to look to the pattern stimulus rather than homogenous field.Using calibrated square-wave gratings, teller and keeler acuity cards and cardiff acuity cards for the test, visual acuity can be assessed.

Visual acuity in children at 1 to 2 yrs of age can be tested by boeck candy test, worth ivory ball test & sheridans ball test.2 to 3yrs: crowded Kay picture, and keeler logMAR crowded test.

3 to 5 yrs: picture chart and single picture cards, Lea symbols, Tumbling E test, Snellen test. Child recognizes by naming or matching the picture or letter.

Monocular fixation Fixation of each eye separately is evaluated with visuscope in every child. Star of the device is clearly seen by the examined child & by the physician in the fundus of eyeThe child is asked to look straight into the star. fixing fovea on the mid-star, indicates central fixation. Visual acuity is good in such a case. If the patient does not fix with fovea, it indicates decreased visual acuity

Refraction:Grade of vision abnormality is determined in each child with the aid of automatic keratorefractometer. In newborns and young children hand-held autokeratorefractometer (Retinomax) is used. (after proper cycloplegia)

Anterior and posterior segment Examination

Examination of a case of squint

1.Motor status 2. Sensory status

Examination of motor status 1. Looking for head posture 2. Ocular deviation 3. Limitation of movements 4. Fusional vergence

Head posture:

Chin elevation or depressionFace turn to right or left sideHead tilt to right or left shoulder Patient chooses a head posture such that ocular deviation the least and image can be fused.

Cover uncover tests For distant fixation figure/ letter of 6/9 of snellen, from 6 mt. distance.Near fixation at 33 cm.

Cover-Uncover test:

Alternate cover testCovering both eyes alternately one and then the other eye,Each eye should be covered atleast for 2 seconds. fusion is broken, alternate cover test brings out the total deviation- heterophoria and heterotropia.

Prism -alternate cover test To measure the angle of strabismus, the prism bar is moved before one eye. Then cover test performed with increasing strength of prism. Strength of the prism at which fixation movement stops is the value of the angle of strabismus.

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Prism base is always directed opposite the eye deviation. The test is performed for both distant vision of 6 m and near vision of 30 cm. Esotropia: prism base- out. Exotropia: prism base- in. Hypertropia: prism base- down.-Hypotropia: prism base-up-The results are expressed in prism diopter (PD).

The value of angle of strabismus can also be assessed with Krimsky test or examining eye fundus through the prism.

Angle of strabismus by fundus examinationThe patient asked to views distant point with normal eye.stronger prisms are placed before the deviating eye.examining fundus through the prism with the visuscope straight ahead (Baranowska-George).The prism corresponding with the angle of strabismus is the one through which the examiner sees fovea in line with the visuscope star

Light reflex testsHirschberg methodKrimsky methodBruckners test

Hirschberg methodAmount of deviation: note location of corneal light reflex 1 mm = 7 or 15Reflex at border of pupil = 15

Reflex at limbus = 45

Used as an initial screen for strabismus.

Krimsky methodThis test is used to centralize the corneal reflection in squinting eye as compared to the reflex in fixing eye.

Results are expressed in prism diopter (PD).angle of strabismus = prism required for centralize the corneal reflex. It is Convenient test for quick evaluation of the angle of strabismus, especially in the abnormal fixation of the squint eye and ambylopia.

Bruckner TestPerformed by using direct ophthalmoscope to obtain a red reflex simultaneously in both eyes.Deviated eye will have a lighter and brighter reflex than the fixing eye.

Eye movement and extent of versions: Observation of ocular ductions, which are the actual monocular movements of the eyeObservation of binocular alignment(in all gazes).

Monocular eye movementsA- elevation B- depression C- adbuction d- adduction Eextortion F- intortion

Motility testsTests versions and ductionsGrades under/overaction Left inferior oblique overactionLeft lateral rectus underaction

Forced duction test

A topical anesthetic eyedrops are given to the conjunctival sac of the patients eye. Then, the conjunctiva in the limbus is grasped with forceps and an attempt to abduct the eyeball toward weakened muscle. Limitation or block of eyeball rotation means the mechanical restriction of movement

Hess screening: is a gray screen covered with the net of tangent lines. In the semi dark room the patient wearing red-green spectacles projects green light to super impose red points lit on the screen by the examiner. All the points are plotted in turn.Result should be mapped in all gaze positions.

In orthophoria two lights are super imposed in all nine position of gaze.Goggle then reversed and procedure is repeated.The relative positions are marked by examinar on hess chart and connected with straight lines.

Two chart of both eyes are comparedSmaller chart indicates the eye with paretic muscle (Rt.)Larger chart indicates eye with Over acting yolk muscle(Lt. eye).Greatest restriction is in main direction of action of muscle (Rt. Lateral rectus).Greatest expansion in the main direction of action of the yolk muscle(Lt. medial rectus).

Showing changes with rt. Superior rectus palsy

Lees screen

Sensory status: Test for stereopsisTest for binocularity & Diplopia

Qualitative tests for Stereopsis: Langs 2 pencil test Synoptophore Quantitative tests for Stereopsis: Random Dot testTitmus Fly Test TNO Test Frisby stereo testLangs Stereo TestStereoscope (holmes, key stone, asher law)

Stereopsis:Can be detected by Using targets which lie in two planes, but are so constructed that they stimulate disparate retinal elements and give a three dimensional effect, for example:

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Synoptophore It is a versatile instrument & has special sets of slides for testing : simultaneous perception, fusion, stereopsis.Presence of stereopsis indicates good binocular single vision.Can measure: objective angle subjective angle of deviation & angle of anomaly.

Test for diplopia: Maddox rod: Test is performed 5 m before Maddox cross. One eye covered with maddox rod, Fellow eye fixes the white light on the scale. Patient with ortophoria sees the red line running through the light point. If the red line is on another side of the light (crossed position), there is exophoria.

If the red line is on the same side (uncrossed position), esophoria is present. The red line may rotate downward (hyperphoria), upward (hypophoria), outside (incyclophoria) , inside (excyclophoria). Deviation of the eye is read on the Maddox scale in prism diopters

Cannot differentiate tropia from phoria

White spot converted into red streak

Double maddox rod:

Maddox wingDissociates eyes for near fixation (1/3 m)

Measures heterophoria

Rt. Eye sees only a white vertical & red horizontal arrow.Lt. eye sees only horizontal and vertical rows of numbers the no. where white arrow points= Hz. Deviationthe no. where red arrow points= Vt. Deviation.Cyclophoria measured by asking the pt. to move the red arrow to put it parallel with Hz. Row of numbers

Red green goggle:Image will be farthest in the direction of paralysed muscle

Worth four dot test

Bagolini lensEach lens has fine striation which convert a point sorce of light in into line.Two lenses are placed 45 & 135 degree in front of each eye.

normal person perceives Two streaks intersect at their centres, form an oblique cross.If Pt. sees two line but they do not form a cross.If Only one streak is seen.If Pt. sees a small gap in one of the streak.

Ocular deviation:

References: Practical orthoptics in the treatment of squint; T.Keith Lyle.Strabismus simplified; Pradeep sharm.Paediatric ophthalmology & strabismus; AAOParsons diseases of eye.Kanski Brad Bowling; clinical ophthalmology.Internet resources.

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