Squint assessment

ASSESSMENT OF ASSESSMENT OF A SQUINT A SQUINT PATIENTPATIENT

Siraj SafiSiraj SafiLecturer in OptometryLecturer in OptometryPICO, HMC , PeshawarPICO, HMC , Peshawar

Assessment StepsAssessment Steps1.1. History History 2.2. Visual AcuityVisual Acuity3.3. Ocular DeviationOcular Deviation4.4. Ocular MovementOcular Movement5.5. Binocular FunctionBinocular Function6.6. RefractionRefraction

1.History1.History

1.History1.History Patient with ocular motility Patient with ocular motility

disorder present for one or more disorder present for one or more of the following reason:of the following reason:

Manifest strabismusManifest strabismus Defective ocular movementDefective ocular movement NystagmusNystagmus AHPAHP Defective visionDefective vision Subjective symptomsSubjective symptoms

1.History continue….1.History continue…. The reason for attendance must first The reason for attendance must first

be established.be established. In children greater emphasis is In children greater emphasis is

placed on obstetric history and placed on obstetric history and developmental miles stone.developmental miles stone.

Where as the medical history can be Where as the medical history can be of paramount importance in adult.of paramount importance in adult.

1.History continue….1.History continue….a. Medical history:a. Medical history: The child general developmentThe child general development Recent illness and treatmentRecent illness and treatment Any trauma to the head and faceAny trauma to the head and face Any systemic disease Any systemic disease

b. Obstetric historyb. Obstetric history The mothers health during pregnancyThe mothers health during pregnancy Delivery Delivery The child birth weightThe child birth weight

c. Family historyc. Family history Parental consanguinityParental consanguinity StrabismusStrabismus Refractive errorRefractive error

1.History continue….1.History continue….e. Strabismus in children:e. Strabismus in children: The Direction of strabismusThe Direction of strabismus The age at which it was first noticedThe age at which it was first noticed Who noticed itWho noticed it Whether the onset was gradual or suddenWhether the onset was gradual or sudden Frequency of deviation (constant or intermittent) Previous treatment, if any, and the type and

results of such treatment

f. Strabismus in Adults:f. Strabismus in Adults: CosmeticCosmetic Subjective symptomsSubjective symptoms

2.Visual 2.Visual AcuityAcuity

2.Visual Acuity2.Visual Acuity Easy in adults or older children Easy in adults or older children Very difficult in infants. Very difficult in infants. But even than can be assessed by But even than can be assessed by

various techniques various techniques

Normal visual Normal visual developmentdevelopment

From Alec. M Ansons and Helen From Alec. M Ansons and Helen Davis Davis

The development of VA from birth to age The development of VA from birth to age three year three year Age Visual Acuity

New Born

I months

4 - 6 months

3 years

6/240

6/18 - 6/6

6/6 with single optotypes

6/180 - 6/90

Normal visual developmentNormal visual development

Age related VA estimated by test Age related VA estimated by test methodmethod

Technique

OKN

FPL

VEP

Birth 2 months

4 months

6 months

1 year Age for 20/20

20/40020/400

20/800

20/800

20/800

20/150

20/200

20/200

20/60

20/100

20/150

20/40

20/60

20/50

20/20

20-30 months

18-24 months

6-12 months

From Kenneth W. Wright

Age Indication For VA Age Indication For VA TestsTests Age 0-6/12:Age 0-6/12:

VEPVEP , ,FCPL, OKN, CSM, Objection to FCPL, OKN, CSM, Objection to occlusion, Catford Drum etc.occlusion, Catford Drum etc.

6/12 to 2 years: 6/12 to 2 years: 100s & 1000s, Stycar balls, FCPL, Cardiff 100s & 1000s, Stycar balls, FCPL, Cardiff cards…cards…

2 to 3 years:2 to 3 years: Kay pictures, Illiterate E, Lea Kay pictures, Illiterate E, Lea

Symbol.........Symbol......... 3+ years:3+ years: Sheridan Gardener, Landolt C, Snellen , Sheridan Gardener, Landolt C, Snellen ,

LogMar……. LogMar…….

CSMCSM The ability of each eye to fixate The ability of each eye to fixate

Centrally, steadily, and Maintain Centrally, steadily, and Maintain fixation.fixation.

CentrallyCentrally means foveal fixation means foveal fixation Steady Steady means no nystagmoid movementmeans no nystagmoid movement MaintainMaintain mean the ability of one eye to mean the ability of one eye to

maintain fixation when viewing is maintain fixation when viewing is converted from a monocular condition converted from a monocular condition to a binocular condition.to a binocular condition.

3.Ocular 3.Ocular deviationdeviation

3.Ocular deviation3.Ocular deviation Detection of Strabismus can be Detection of Strabismus can be

made through:made through:

Observation of the patient Observation of the patient appearanceappearance

Observation of the corneal reflexObservation of the corneal reflex The cover testThe cover test

3.Ocular deviation cont…3.Ocular deviation cont… The cover testThe cover test

It is an objective test which is the It is an objective test which is the core stone of investigation of core stone of investigation of strabismus.strabismus.

Requires:Requires: Pin torchPin torch OccluderOccluder Target for 33cm and 6mTarget for 33cm and 6m

3.Ocular deviation cont…3.Ocular deviation cont… The cover test can be used in two The cover test can be used in two

ways:ways:1) The cover /uncover in which one eye 1) The cover /uncover in which one eye

is covered and the observer notes:is covered and the observer notes:a)a) The movement of the uncovered eye The movement of the uncovered eye

to take up fixation.to take up fixation.b)b) The position and movement of the The position and movement of the

covered eye as cover is removed.covered eye as cover is removed.

3.Ocular deviation cont…3.Ocular deviation cont…2) Alternate cover test in which both 2) Alternate cover test in which both

eyes are covers alternatively the eyes are covers alternatively the movement of the covered eye is movement of the covered eye is noted as the cover is changed from noted as the cover is changed from one eye to the other.one eye to the other.

It is more dissociative than It is more dissociative than cover/uncover test cover/uncover test

3.Ocular deviation cont…3.Ocular deviation cont… Information provided by the cover Information provided by the cover

test:test: Direction of deviationDirection of deviation The difference in angle from near to distance The difference in angle from near to distance The effect of accommodation The effect of accommodation Comitance and incometanceComitance and incometance Estimation of VAEstimation of VA The speed of recovery in latent strabismusThe speed of recovery in latent strabismus Constant ,intermittent, unilateral or alternatingConstant ,intermittent, unilateral or alternating Latent nystagmus or latent component in Latent nystagmus or latent component in

manifest nystagmusmanifest nystagmus DVD DVD A/V PatternA/V Pattern

3.Ocular deviation cont…3.Ocular deviation cont…Confirmation and measurement of Confirmation and measurement of

strabismus:strabismus:1.1. HirschbergHirschberg2.2. Krimsky Krimsky 3.3. Prism cover testPrism cover test4.4. Simultaneous PCTSimultaneous PCT5.5. Maddox rod Maddox rod 6.6. Double Maddox rodDouble Maddox rod7.7. Maddox wingMaddox wing8.8. Major amblyoscopeMajor amblyoscope9.9. Diagnostic occlusionDiagnostic occlusion

1.Hirschberg1.Hirschberg Used as an initial screen for Used as an initial screen for strabismusstrabismusHow it works:How it works:

At 33cm front of child with penlight At 33cm front of child with penlight shining at eyesshining at eyesLight reflection will be at the same point Light reflection will be at the same point in each eyein each eye

Normal Exotropia Esotropia

3.Ocular deviation cont…3.Ocular deviation cont…1.1. HirschbergHirschberg

2.Krimsky2.Krimsky TestTest

This test is used to centralize This test is used to centralize the corneal reflection in the the corneal reflection in the squinting eye with compared to squinting eye with compared to the fixing eye.the fixing eye.

3.Prism Cover Test3.Prism Cover Test Measure squint/misalignment Measure squint/misalignment Single prism/prism bar Single prism/prism bar Primary position or in all positions of Primary position or in all positions of

gaze gaze For near and distanceFor near and distance

4. SIULTANEOUS PCT4. SIULTANEOUS PCT

The prism is placed in front of the The prism is placed in front of the deviating eye and a cover simultaneously deviating eye and a cover simultaneously introduced in front of the fixing eye.introduced in front of the fixing eye.

The aim is to neutralize the movement of The aim is to neutralize the movement of the squinting eye as the fixing eye is the squinting eye as the fixing eye is covered. covered.

The test is performed with the same way by The test is performed with the same way by increasing the strength of the prism until increasing the strength of the prism until the squinting eye did not move under the the squinting eye did not move under the prism. prism.

It grieves the estimation of tropia only.It grieves the estimation of tropia only.

5.MADDOX ROD5.MADDOX ROD Use of the Maddox rod Use of the Maddox rod

provides entirely provides entirely subjective method of subjective method of measuring horizontal, measuring horizontal, vertical and torsional vertical and torsional deviation . (Phoria)deviation . (Phoria)

Dissociation of the eye is Dissociation of the eye is achieved by presenting achieved by presenting a spot light to one eye a spot light to one eye and a line image to the and a line image to the other eye.other eye.

6.Double MADDOX ROD6.Double MADDOX ROD Torsional deviations:Torsional deviations: Torsional deviation can be measured with Torsional deviation can be measured with

double Maddox rod.double Maddox rod. The Maddox rod can be placed parallel in The Maddox rod can be placed parallel in

front of both eyes better if have different front of both eyes better if have different color.color.

The patient is asked wither the both lines The patient is asked wither the both lines are exactly align when placed parallel are exactly align when placed parallel Maddox rod in front of both eyes or Maddox rod in front of both eyes or vertical prism can be introduced to vertical prism can be introduced to separate the lines and than ask separate the lines and than ask

7.MADDOX WING7.MADDOX WING

The Maddox wing dissociates the The Maddox wing dissociates the eyes by means of two septa, so eyes by means of two septa, so that the horizontal and vertical that the horizontal and vertical measurement scales are visible to measurement scales are visible to the left eye and the right eye sees the left eye and the right eye sees the two arrows , one vertical to the two arrows , one vertical to indicate the horizontal indicate the horizontal measurement and the other measurement and the other horizontal indicating the vertical horizontal indicating the vertical measurement for 33cm with measurement for 33cm with correction.correction.

Measurements are recorded in Measurements are recorded in prism dioptres prism dioptres

8. Synoptophore8. Synoptophore Uses:Uses: Angle of deviationAngle of deviation Assessment of Assessment of

retinal retinal correspondencecorrespondence

Fusional amplitudeFusional amplitude StereopsisStereopsis

9.DIAGNOSTIC 9.DIAGNOSTIC OCCLUSSIONOCCLUSSION

Diagnostic occlusion can be used to induce Diagnostic occlusion can be used to induce full dissociation when it is thought that the full dissociation when it is thought that the maximum angle of deviation has not been maximum angle of deviation has not been revealed. revealed.

Used in:Used in: Intermittent exotropia.Intermittent exotropia. To diagnose whether symptoms are due to To diagnose whether symptoms are due to

hetrophoria.hetrophoria. To differentiate between real or apparent To differentiate between real or apparent

limitation of abduction in children.limitation of abduction in children.

4.Ocular 4.Ocular MovementMovement

4.Ocular Movement4.Ocular Movement

A.A. Clinical assessment and recording Clinical assessment and recording of ocular movementsof ocular movements

B.B. 3- step test3- step testC.C. Hess testHess testD.D. FDTFDTE.E. FGTFGT

MuscleMuscle Length Length of active of active musclemuscle(mm)(mm)

OriginOrigin Anatomic Anatomic insetioninsetion

DirectiDirection of on of pullpull

innervatioinnervationn

MedialMedialRectusRectus

4040 AnnulusAnnulusOf zinnOf zinn

5.5 mm from5.5 mm fromMedical Medical limbuslimbus

9090oo Lower Lower CN IIICN III

LateralLateralRectusRectus

4040 AnnulusAnnulusOf ainnOf ainn

6.9 mm from6.9 mm fromLateral Lateral limbus limbus

9090oo CN VICN VI

SuperiSuperiororRectusRectus


7.7 mm from7.7 mm fromSuperior Superior limbuslimbus

2323oo Upper Upper CN IIICN III

InferioInferiorrRectusRectus


6.5 mm from6.5 mm fromInferior Inferior limbuslimbus


SuperiSuperiororObliquObliquee

3232 Orbital Orbital apex apex above above annulus annulus of zinnof zinn

Posterior toPosterior toEquator inEquator inSuperotempoSuperotemporalralQuadrantQuadrant

5151oo CN IVCN IV

InferioInferiorrObliquObliquee

3737 Behind Behind lacrimal lacrimal fossafossa

Muscular Muscular area near area near MaculaMacula


A way to rememberA way to remember All obliques AbductAll obliques Abduct All vertical Recti AdductAll vertical Recti Adduct All superior muscles Intort All superior muscles Intort All inferior muscles ExtortAll inferior muscles Extort

ocular movementsocular movements The The ocular movementsocular movements are of four are of four

types: types: Ductions Ductions Versions Versions Vergences Vergences Supra nuclear movementsSupra nuclear movements

Ocular movements (terms)Ocular movements (terms) Agonist muscleAgonist muscle Antagonist muscleAntagonist muscle Yoke MusclesYoke Muscles SynergistSynergistLaws of ocular motilityLaws of ocular motility Sherrington law of reciprocal

innervations Hering Law of equal innervations

Full muscle sequelae will Full muscle sequelae will includeinclude

Primary paresis of the musclePrimary paresis of the muscle Over action of contralateral Over action of contralateral

synergistsynergist Contracture (O/A) of ipsilateral Contracture (O/A) of ipsilateral

antagonistantagonist Under action of contralateral Under action of contralateral

antagonist (2ndry inhibitional palsy)antagonist (2ndry inhibitional palsy)

Nine Position Of GazeNine Position Of Gaze

R LRLRLMR

RMRLLR

RSRLIO

RIOLSR

RIRLSO

RSOLIR

The Diagnostic Positions of Gaze

H-PATTERN TESTH-PATTERN TESTInstruction to the Px should be: “We are now going to assess how well yourInstruction to the Px should be: “We are now going to assess how well your

eye muscles work together. I would like you to follow the target with youreye muscles work together. I would like you to follow the target with your

eyes while keeping your head still. Let me know if you feel any pain oneyes while keeping your head still. Let me know if you feel any pain on

eye movement or if you detect double vision at any time in the test.”eye movement or if you detect double vision at any time in the test.”

RSR

LIO

RLR

LMR

RIR

LSO

LSR

RIO

LLR

RMR

LIR

RSO

Recording of Ocular Recording of Ocular MovementsMovementsGrid formGrid form

IOLTSRRT..

SOLTIRRT..

SRLTIORT..

IRLTSORT..

Rt. Gaze Lt. Gaze

Recording of Ocular Recording of Ocular MovementsMovementsGrid formGrid form

Rt. Gaze Lt. Gaze

E.g. RT SO Palsy

Rt+/ Lt-

Rt-- / Lt++

Recording of Ocular Recording of Ocular MovementsMovements

Diagrammatic formDiagrammatic form

Rt. eye Lt. Eye

Recording of Ocular Recording of Ocular MovementsMovements

Descriptive form:Descriptive form: e.g..e.g.. Rt. Medial rectus is under acting -2Rt. Medial rectus is under acting -2 oror Rt. MR u/a -2Rt. MR u/a -2 Rt. MR u/a --Rt. MR u/a --

Three – Step Test Three – Step Test

Three – Step TestThree – Step Test Superior oblique palsies are often Superior oblique palsies are often

diagnosed using the three-step test.diagnosed using the three-step test. There are eight cyclovertically There are eight cyclovertically

acting muscles; four work as acting muscles; four work as depressor of the eye and four work depressor of the eye and four work as elevators of the eye.as elevators of the eye.

Four in each eye. Four in each eye.

Step-1Step-1

Determine which eye is hypertropic by Determine which eye is hypertropic by using the cover test.using the cover test.

Step-1 narrows the number of possibly Step-1 narrows the number of possibly under acting muscles from eight to under acting muscles from eight to four four

e.g. Rt hypertropia:e.g. Rt hypertropia:This means that either the depressors of the Rt eye This means that either the depressors of the Rt eye

are weak (RIR,RSO) or the elevators of the Lt eye are weak (RIR,RSO) or the elevators of the Lt eye are weak (LIO,LIR).are weak (LIO,LIR). Draw an oval around themDraw an oval around them

R HypertropiaR Hypertropia

RSR RIO

LSOLIR

RSO

RIR RSO

LIO LSR

Depressors of R eye

Elevators of L eye

Step-2Step-2

Determine whether the vertical Determine whether the vertical deviation is greater in Rt gaze or in Lt deviation is greater in Rt gaze or in Lt gaze.gaze.

e.g. in Lt gaze. This implicates one of the four e.g. in Lt gaze. This implicates one of the four vertical acting muscles used in left gaze, the two vertical acting muscles used in left gaze, the two possible muscles at this point are either both possible muscles at this point are either both intortors or both extortors. Draw an oval around the intortors or both extortors. Draw an oval around the four vertically acting muscles that are used in Lt four vertically acting muscles that are used in Lt gaze. gaze.

It may be either the RSO or LSR. These are the only It may be either the RSO or LSR. These are the only muscles circles twice.muscles circles twice.

R HypertropiaR Hypertropia

RSR

LSO

RSO

RIR RSO

LIORIO

RSO

LSR

LIR

Left Gaze

Step-3Step-3 This step is also known as Bielschowsky This step is also known as Bielschowsky

head tilting test, it involves tilting the head tilting test, it involves tilting the head to the Right then to the Left.head to the Right then to the Left.

Head tilt to the Right stimulate intorsion Head tilt to the Right stimulate intorsion of the Rt eye (RSR,RSO) and extorsion 0f of the Rt eye (RSR,RSO) and extorsion 0f the L eye (LIR,LIO) and vice versa.the L eye (LIR,LIO) and vice versa.

e.g. in the same case suppose that the vertical e.g. in the same case suppose that the vertical deviation increases to the Rt tilt. This implicates deviation increases to the Rt tilt. This implicates the four muscles that act vertically in the R tilt the four muscles that act vertically in the R tilt position. Draw an oval around these muscles. position. Draw an oval around these muscles. Note that the RSO is the only muscles that is Note that the RSO is the only muscles that is surrounded by three ovals. surrounded by three ovals.

LSO

RSO

RIR RSO

LIORIO LSR

LIR

Left Gaze

RSO

RSRLIO

LIR

Tilt to R sideRt. SO Palsy

Hess testHess test

Principle of testPrinciple of test1. 1. Dissociation of the eyes by Dissociation of the eyes by

either:either: Red and Green goggles in case of Hess.Red and Green goggles in case of Hess. The mirror in case of Lees Screen.The mirror in case of Lees Screen.2. 2. Foveal projection in the presence of Foveal projection in the presence of

normal retinal correspondence. normal retinal correspondence. 3. Herring’s and Sherrington’s Law:3. Herring’s and Sherrington’s Law: Explain the development of Explain the development of muscle muscle

sequelae.sequelae.

Uses of Hess TestUses of Hess Test

1. 1. Diagnosis ofDiagnosis of Underaction or Overaction of EOM.Underaction or Overaction of EOM. Mechanical or Neurogenic palsy.Mechanical or Neurogenic palsy. A or V patternA or V pattern2. Planning of surgery and post-op 2. Planning of surgery and post-op

effects of surgeryeffects of surgery3. Monitoring of condition.3. Monitoring of condition.

How to interpretHow to interpret


FDT force duction test:FDT force duction test:The purpose of the force duction test The purpose of the force duction test is to assess passive movement of the is to assess passive movement of the globe in case in which active ocular globe in case in which active ocular movements are limited either movements are limited either neurologically or mechanically. neurologically or mechanically.


FGT force generation test:FGT force generation test:The force generation test assesses The force generation test assesses the active muscle force which the active muscle force which enables eye movement to take place.enables eye movement to take place.The aim of the test is to calculate the The aim of the test is to calculate the potential force in an apparently potential force in an apparently paralised muscle. paralised muscle.

5.Binocular 5.Binocular FunctionFunction

Investigation of BSVInvestigation of BSV It can be done through:It can be done through: Bagolini GlassesBagolini Glasses Worth 4 lights Worth 4 lights Prism reflex testPrism reflex test 4 4 ∆ Prism test∆ Prism test Stereo acuity testsStereo acuity tests

Bagolini glassesBagolini glasses

Apparatus consists of a pair of plano- Apparatus consists of a pair of plano- glasses marked with fine parallel glasses marked with fine parallel striation of 45striation of 45o o & 135& 135o o on the other.on the other.

Line image is formed at 90Line image is formed at 90oo of of striation.striation.

Bagolini glassesBagolini glassesTest distanceTest distance Can be used at 6m & 33cmCan be used at 6m & 33cm

Position of GazePosition of Gaze Can be used in any desired gazeCan be used in any desired gaze Upward and downward gaze Upward and downward gaze

especially in “A” &“V” patternespecially in “A” &“V” pattern

Worth 4 light testWorth 4 light test

It consists of four circular lightsIt consists of four circular lights Two green lightsTwo green lights One red lightOne red light One white light.One white light.

Worth 4 light testWorth 4 light testTest’s PhenomenonTest’s Phenomenon Red light is seen through red filter.Red light is seen through red filter. Green light is seen through green Green light is seen through green

filter.filter. White light is seen by both eyes.White light is seen by both eyes.

Worth 4 light testWorth 4 light test

ResultsResults1.1. 4 lights indicates BSV either normal 4 lights indicates BSV either normal

or less usually abnormal.or less usually abnormal.2.2. 2 lights are seen if left suppression is 2 lights are seen if left suppression is

present.present.3.3. 3lights are seen if there is right 3lights are seen if there is right

suppression.suppression.4.4. 5 lights are seen if diplopia is present.5 lights are seen if diplopia is present.

Prism reflex testPrism reflex test

The prism is used to assess the motor The prism is used to assess the motor system of the patient.system of the patient.

A 15A 15∆ to 20∆ is placed in front of one ∆ to 20∆ is placed in front of one eye and response of the other eye is eye and response of the other eye is seen.seen.

A response should be obtained in infants A response should be obtained in infants aged 6 months and up ward.aged 6 months and up ward.

Prism reflex testPrism reflex test

ResultsResults If all three movements are seen motor If all three movements are seen motor

fusion is present, however Asymmetry of fusion is present, however Asymmetry of movement should be noted.movement should be noted.

If the eye behind the prism fails to adduct If the eye behind the prism fails to adduct then there is a scotoma present in that eye.then there is a scotoma present in that eye.

If the other eye fails to recover then it If the other eye fails to recover then it indicates that suppression prevented the indicates that suppression prevented the recovery or lack of motor fusion.recovery or lack of motor fusion.

4 4 ∆ Prism test∆ Prism test The main aim of the test is to prove The main aim of the test is to prove

the presence of normal binocular the presence of normal binocular single vision. single vision.

44∆ Prism test∆ Prism test

A 4A 4∆∆ prism is placed in front of one eye prism is placed in front of one eye and the recovery is noted.and the recovery is noted.The strength of image moves the image The strength of image moves the image a little bit in the foveal area, if the a little bit in the foveal area, if the recovery and movement is seen then recovery and movement is seen then there is no scotoma present.there is no scotoma present.Prism can be used B.I, B.O, B.U & B.D.Prism can be used B.I, B.O, B.U & B.D.

Stereo acuityStereo acuity Include : Lang two pencil test Titmus Fly Test The Frisby Stereo-test TNO test The Lang Stereo-test

Tests for StereopsisTests for Stereopsis(Qualitative Tests)(Qualitative Tests)

1.1. Lang 2 pencil testLang 2 pencil testMethod:Method:

Pt places the pencils tip on the tip Pt places the pencils tip on the tip of the examiner’s pencil.of the examiner’s pencil.

Result:Result:It is a test mainly used for the It is a test mainly used for the detection of gross stereopsis.detection of gross stereopsis.

Titmus Fly Test – Polaroid Vectograph

Titmus Fly Test – Polaroid VectographThis test uses crossed Polaroid filters to present

slightly different aspects of the same object to each eye. The test comprises of three sections:

• The Housefly - which shows large disparities and should be seen in depth by most subjects.

• Circle Patterns – this section consists of patterns containing four circles. One of the circles in the pattern contains a graded disparity (crossed), so that when it is viewed binocularly it is seen to float in front of the others. The disparities of the circles range from 800 to 40 secs of arc.

• Animals – there are 3 rows of animals, one animal in each row having a crossed disparity which ranges from 400 – 100 secs of arc.

The Frisby Stereo-test

This is the only clinical test based on actual depth, where random shapes are printed on three clear plastic plates of different thickness. The test does not require any form of dissociation.

Each plate has 4 squares of curved random shapes, and one square contains a hidden circle that is printed on the opposite surface. Disparities range from 600 to 15 secs of arc.

Care should be taken that neither the plates nor the Px’s head move significantly during the testing procedure, as this may provide monocular cues.

If the first plate is recognised successfully then the thinner plates, which give smaller disparities, are presented in a similar fashion.

The Frisby Stereo-test

The TNO Test

Each test plate consists of a stereogram in which the images presented to each eye have been superimposed and printed in complimentary colours.

The stereograms are viewed through a pair of red and green filters.

The random dot stereograms have the advantage that they completely eliminate monocular cues, the patient is required to describe the shape which can only be seen stereoscopically.

TNO

The TNO test has 7 plates.

The first four plates are for screening purposes, the disparities are large and ungraded.

Plate I 2 butterflies are present, one can be seen monocularly, the other is only seen in stereopsis.

Plate II 4 discs, 2 are seen monocularly two require stereopsis.

Plate III four hidden shapes (O, , , ) are arranged around a centrally placed cross

Plate IV This is a suppression test. There are 3 discs, one seen by the right eye, one by the left, and one is seen binocularly.

Plate V-VII Here the test items (Pac-man Shapes) are presented at 6 different disparities ranging from 15 – 480 secs of arc.

Plate V Plate VI Plate VII

480 120 30

240 60 15

The Lang Stereo-test

The test consists of vertical sections that are seen alternately by each eye as they are seen through in-built cylindrical lens elements.

Displacement of the random dots creates the disparity which ranges from 1200 to 550 secs of arc.

The cards are held at the subject’s reading distance and he or she is asked to name or point to the pictures.

Lang

6.Refraction6.Refraction

Cycloplegia and retinoscopyCycloplegia and retinoscopy

Accurate refraction in children usually Accurate refraction in children usually requires full cycloplegia. requires full cycloplegia.

Adequate cycloplegia for retinoscopy may Adequate cycloplegia for retinoscopy may be obtained in 60 minutes following the be obtained in 60 minutes following the instillation of cyclopentolate 1% eye instillation of cyclopentolate 1% eye drops. drops.

Below the age of three months mydriatics Below the age of three months mydriatics are used in lower concentration to reduce are used in lower concentration to reduce the risk of toxicity. the risk of toxicity.

RefractionRefraction The routine use of atropine for The routine use of atropine for

diagnostic cycloplegia or mydriasis is diagnostic cycloplegia or mydriasis is unnecessary and may cause harmful unnecessary and may cause harmful side-effects. side-effects.

However, in patients with darkly However, in patients with darkly pigmented irides cyclopentolate may pigmented irides cyclopentolate may prove insufficient for full cycloplegia prove insufficient for full cycloplegia and it may be necessary to use and it may be necessary to use atropine eye drops or ointment. atropine eye drops or ointment.

Correction of refractive Correction of refractive errorerror

Hypermetropia :Hypermetropia : In all forms of esotropia, full correction In all forms of esotropia, full correction

of hypermetropia is the treatment of of hypermetropia is the treatment of choice. choice.

In practice, a reasonable lower limit for In practice, a reasonable lower limit for spectacle correction is + 1.50 dioptres spectacle correction is + 1.50 dioptres (+ 3.00 ret. @ 2/3 metre). (+ 3.00 ret. @ 2/3 metre).

When prescribing, 'full correction' means When prescribing, 'full correction' means that only the working distance is allowed that only the working distance is allowed for with no subtraction for cycloplegia. for with no subtraction for cycloplegia.

RefractionRefractionHypermetropia :Hypermetropia : In esophoria full correctionIn esophoria full correction In exophoria or tropia under correctionIn exophoria or tropia under correction In children without strabismus the In children without strabismus the

precise indication for treatment of precise indication for treatment of spherical errors is ill defined and will spherical errors is ill defined and will depend on the age of the child depend on the age of the child symptoms and the magnitude of the symptoms and the magnitude of the error. error.

RefractionRefraction MyopiaMyopia In esophoria or tropia under correctionIn esophoria or tropia under correction In exophoria or tropia full correction or even In exophoria or tropia full correction or even

over correctionover correction High myopia (-6.00 D or more) may require High myopia (-6.00 D or more) may require

correction in infancy and moderate myopia (4.00 correction in infancy and moderate myopia (4.00 D or more) in two year olds and older children. D or more) in two year olds and older children.

Lesser degrees of myopia do not usually cause Lesser degrees of myopia do not usually cause problems in small children and prescription can problems in small children and prescription can be based on subjective refraction over the age of be based on subjective refraction over the age of six years. six years.

Squint assessment

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