Sensory evaluation of strabismus

Review of BSVSENSORY EVALUATION OF

STRABISMUS

Gauri S. Shrestha, M.optom,Lecturer

Deepa Dhungel, B.Optom II year

Normal Binocular Vision

• Monocular: 160°(w)X175°(h)• Binocular: 200° (w)X175°(h)• Region of binocular overlap: 120° (w)X135°(h)

visual field

Prerequisite for BSV• Separate fields of vision must

overlap in all direction of gazes.

• Separate fields of fixation must overlap with coordinated movements of the two eyes.

• Neural transmission from the two eyes must reach the same area of brain.

• Perceptual co-ordination must take place.

Corresponding retinal points• Every retinal point or

area has a partner in the fellow retina with which it shares relative subjective visual direction

Horopter • “Locus of all the object points that are imaged

in corresponding retinal elements at a given fixation point”

Panum’s fusional area

• The region around the horopter that’s allows single vision.

• Object stimulates slightly non- corresponding points

• Objects are not only seen single, but are seen stereoscopically.

Physiological diplopia

• The diplopia elicited by an object off the Panum’s fusional area

• Types– Crossed (heteronymous) diplopia– Uncrossed (homonymous) diplopia

Grades of BSV

• 1 – simultaneous perception

• 2 - superimposition

• 3 – flat fusion

• 4 - Stereopsis

Simultaneous perception

• Is the most elementary type of binocularity

• Occurs when the visual cortex perceives separate stimuli to the two eyes at the same time and concerns itself essentially with the absence of suppression.

• The two different pictures are seen simultaneously in the same direction

• Differing targets are the superimposed into one

2 - superimposition

• Cortical unification of visual stimuli into a single percept after simultaneous stimulation of corresponding retinal areas.

• The objects must be similar in shape and size

3 – flat fusion

4 - Stereopsis

• It is the ability to fuse images that stimulate horizontally disparate retinal elements within Panum’s fusional area resulting in binocular appreciation of visual object in depth i.e. in the third dimension

• Stereopsis occurs when – Retinal disparity is large enough for simple fusion

but small enough not to cause diplopia

Abnormal binocular vision

• Sensory adaptation– Confusion– Diplopia– Supression– Ecccentric fixation– Anomalous retinal correspondence (ARC)– Amblyopia

Diplopia /Confusion

Introduction - Suppression

• Cortical inhibition of visual sensation that originates from spatially abnormal eye to eliminate the problem of visual confusion and diplopia.

• Pathologic suppression results from strabismic misalignment of the visual axes

• Physiologic suppression occur in eyes with BSV

Patient without suppression

Classification of suppression

• Physiologic v/s Pathologic• Central v/s peripheral• Monocular v/s alternating• Facultative v/s obligatory

3. ARC• Sensory anomaly where the fovea of the

fixating eye and a non-foveal site of the deviating eye have a common visual direction

• Objective angle(<H)–

• Subjective angle(<S)–

• Angle of anomaly (<A)

Types

A= H-S

• No anomaly• Harmonic ARC• Unharmonic ARC• Paradoxical ARC I & II

4/6/2007 27

Types of ARC

• Harmonious ARC;– Angle of anomaly(A)=

objective angle (D)– (S)=0

4/6/2007 28

• Unharmonious ARC– Subjective angle(S) is

less than Obj angle but greater than zero.

– Angle of anomaly not equal to the obj angle

Eccentric fixation

• The fovea has lost its principal visual direction• Px reports that they are looking straight at an

object stimulating non foveolar retinal area• Types– Foveal off-center ---1 degree or less (> 0 degrees)– Parafoveal---3 degrees or less (> 1 degree)– Paramacular---5 degrees or less (> 3 degrees)– Peripheral---Greater than 5 degrees

Tests for Sensory Anomalies

Worth Four-Dot Test• a gross test which provides

information only about the status of peripheral binocular cooperation

• Harmonious ARC= 4 lights (Deviation)

• 2 lights (Left suppression)• 3 lights (right suppression• 5 lights (Diplopia)

Bagolini striated glasses

• The Bagolini lenses have fine barely visible striations, oriented at 135 degrees before the right eye and 45 degrees before the left eye

4/6/2007 33

Bagolini striated glasses test

NRC/ HAC UAC, Esotrope,

UAC, Exotrope

Vertical ARC

4 prism base out test

• Usually determines whether a patient has bifoveal fixation or a small suppression scotoma.

• A 4 prism dioptre base out prism is placed infront of one eye & a biphasic movement of the fellow eye is noted.

Vectographic tests

• Polarised charts seen with polarising lenses• One eye sees half of the chart and the other

sees the other half• Polamirror

• Looking into the mirror while wearing polarising glasses• No suppression both eyes seen• With suppression only one eye seen

• an instrument for the assessment of strabismus and the grade of binocular vision

Synoptophore

4/6/2007 39

Vectographic slide

• Subjective angle calculated and compared with objective angle

Binocular Perimetry and Haploscopy

• use of one form of color differentiation, such as red-green spectacles

• If left eye, provided with a green filter, fixates a green spot and right eye is provided with a red filter, a projected red light will be seen every where by the right eye except in the region of the scotomas.

Filter Bar Method

• Patient fixates a spot of light

• A filter bar (palest filter) is placed before the non-suppressing eye

• the density of the filter is increased until two lights are seen

• This filter is a measure of depth

Fig: Red filter bar

After-Image method (Hering-Beilschowsky test)

• In clinical practice the test is performed by using a battery-powered camera flash to produce a vertical afterimage in one eye and a horizontal afterimage in the other eye

• Resulting afterimage is that of a line with a break in its middle, which represents the fovea

4/6/2007 43

Hering-Beilschowsky After Image Test

• The patient fixates steadily the central mark, first with one eye while the slit is horizontal and then with the other eye while the slit is vertical

• In a darkened room or with the eyes closed, the patient sees the two successively imprinted as positive afterimages (bright lines)

• In a lighted room or with the eyes open, negative afterimages (dark lines) will be seen

• Then open eyes and look at a plain surface and see if lines cross

• In NRC the after images will coincide• In ARC the after images will be separated

4. Red Filter/Diplopia Method

• A spotlight is taken into account with both eyes open

• A red filter before the strabismic eye and a vertical prism (6-15∆) before one eye to move the image out of the suppression area

• The patient should see one red and one white light

• If vertically aligned but a strabismus is present = HRC

• If separated, either NRC or UNRC

5. Foveo-Foveal Test of Cu¨ppers

• An asterisk is placed on the fovea of the deviated eye while the other eye fixates the light on a Maddox cross or tangent screen

• If the fixation target appears to be superimposed on the central fixation light of the Maddox cross → normal retinal correspondence

• In the presence of anomalous correspondence foveae have different visual directions– The asterisk will be superimposed on one of the

numbers on the horizontal bar of the Maddox scale

– This number indicates the angle of anomaly in degrees

A,Schematic representation of the testing arrangement. B,Patient sees the asterisksuperimposed on the central fixation light of the Maddox scale(NRC, normal retinal correspondence). C, The asterisk appears over the number 4 on the horizontal bar of the Maddox scale

4/6/2007 53

Visuoscopy

Test of eccentric fixationAvailable in ophthalmoscope

4/6/2007 54

Tests for stereopsis1. Titmus stereotest

• is a vectograph and uses Polaroid dissociation glasses

2. TNO random dots stereotest

• An anaglyph, dissociation is by color instead of Polaroid filters

• TNO Random Dot Test:– consists of seven plates,

each of which contains various shapes

Tests For Stereopsis:…

3. Lang Stereotest• Consists of card, approx.

the size of a average post card in which random dots are incorporated in paragraph

• Cylindrical lenses laminated onto the surface of the card are used for dissociation of the eyes

Lang test