OPTICALINSTRUMENTS

● IDENTIFICATION OF LENS● USES OF CONVEX SPHERICAL LENS● USES OF CONVEX CYLINDRICAL LENS● USES OF CONCAVE SPHERCIAL LENS● USES OF CONCAVE CYLINDRICAL LENS● OCCLUDER● PRISM IDENTIFICATION● USES OF PRISM● PRISM BAR COVER TEST● PINHOLE

● WORTH FOUR DOT TEST● DIPLOPIA CHARTING● MADDOX ROD● DIRECT AND INDIRECT

OPHTHALMOSCOPY● RETIONOSCOPY

● STENOPIC SLIT● RED AND GREEN GLASSES/GOGGLES

▶ Types of lens

spherical cylindricall

concave convexconcaveconvex

1.First hold the lens and close your one eye. Keep the lensclose to your other eye.

2.Now see at a distant object and move lens in bothvertical and horizontal plane and rotate the lens as well.

3.You have to observe 4 things.

▶ How to identify lens?

A. movement of the object-Whether it is in same direction or opposite direction?Whether movement is occurring in single or both planes?

B. Size of the object- whether it is magnified or minified?

C. Distance of the object- whether it is appearing fartheror closer?

D. On rotation- distortion present or absent?

ACCORDING TO POINT A,B,C OF PREVIOUS SLIDE, THERE ARE TWOCOMBINATIONS

❑ MOVEMENT- OPPOSITEDIRECTION

❑ OBJECT- MAGNIFIED❑ DISTANCE- FARTHER

❑ MOVEMENT- SAMEDIRECTION

❑ OBJECT- MINIFIED❑ DISTANCE- CLOSER

❑ MOVEMENT INBOTH PLANES

❑ NO DISTORTIONON ROTATION

❑ MOVEMENT INSINGLE PLANE

❑ DISTORTION ONROTATION

❑ MOVEMENT INBOTH PLANES

❑ NO DISTORTIONON ROTATION

❑ MOVEMENT INSINGLE PLANE

❑ DISTORTION ONROTATION

CONVEXSPHERICAL

LENS

CONCAVECYLINDRICAL

LENS

CONCAVESPHERICAL

LENS

CONVEXCYLINDRICAL

LENS

CONVEX CONCAVE

-In plane mirror, there is no movement at all.

-Spherical lens has a handle.

-Cylindrical lens has no handle but has an axismarked on rim.

-In cylindrical lens, movement only in one plane.While in spherical, both planes.

-Distortion is seen with cylindrical lens.

SOME EXTRA POINTS REGARDING LENS

NOTE- IN cylindrical lens, power ofcylindrical is perpendicular to the axisand to know whether power is inhorizontal or perpendicular plane, seethe movement of image. MOVEMENToccurs in the DIRECTION of the power.

Uses of convex spherical lens

HYPERMETROPIA- Simplehypermetropia

-Compond hypermetropicastigmatism-Mixed astigmatism

APHAKIA- power of +10to +11D is required.PRESBYOPIA

TRIAL FRAMESLIT LAMP BIMICROSCOPYOPERATING MICROSCOPEMAGNIFYING GLASS andLOOPDIRECT OPHTHALMOSOPEINDIRECT OPHTHALMOSCOPE-a condensing lens of +13/20Dis used.FUNDUS DIAGNOSTIC LENS-+78/90D is used.PLACIDO DISC- +6D is used.

Instruments and diagnostictherapeutic

Uses of convex cylindrical lens

Simplehypermetropic

astigmatism

Compoundhypermetropic

astigmatism

Mixedastigmatism

Uses of concave spherical lens

Simple myopiaHigh myopia(>-6D)CompoundmyopicastigmatismMixed astigmatism

Trial frameSlit lamp bimicroscopyDirect ophthalmoscopyOperating microscopeRHUBY LENS (-55to58D)used to mask corneapower in order tovisualise fundus

therapeutic Instruments and diagnostic

Uses of concave cylindrical lens

Simple myopicastigmatism

Compoundmyopic

astigmatism

Mixedastigmatism

OCCLUDERtherapeutic Instruments and diagnostic

Treatment ofAMBYLOPIA inchildren- basis ofuse is that weocclude the normaleye to stimulate thedevelopment ofabnormal eye.

To cover one eyein-• Trial frame• Specs correction• Squint testing-

cover uncovertest and covertest

▶ No movement on horizontal or vertical planes.▶ Movement only on rotation(i.e distortion present).▶ The image formed by prism is shifted to apex.▶ When we keep the prism on straight line, the line

appears to be broken.▶ On touching, we can appreciate the variable

thickness. Thicker part is the base and thinner isthe apex.

▶ There is arrow mark on the rim.

PRISMHow to identify?

Uses of prismtherapeutic Instruments and diagnostic

❖ For squint-cosmeticpurpose(whensurgery isn’tindicated)

❖ For relievingdiplopia

❖ For post surgicalresidual squint.

❖ Slit lamp.❖ Direct and indirect

ophthalmoscope❖ Applanation tonometer❖ Synoptophore❖ Prism bar- prism bar

cover test and prism barreflex test.

❖ Prism vergence- prismvergence test.

❖ Maddox double prismtest- for cyclophoria

• It is best test to measure degree of deviation in tropia(squint)• Therefore, this test is done before squint surgery.

• Steps• 1. place the prism bar in front of deviating eye with apex

towards the deviation.• 2. move the prism bar down till you get a normal corneal

reflection.• 3. quantify the prism power.

Prism bar cover test

esotropia

Normal cornealreflection(light

reflection isseen at the

centre of pupil) Corneal reflection in squint

❑ IT HAS A CENTRE HOLE OF DIAMETER 1.2MM.

PRINCIPLE- PERIPHERAL RAYS COMING TO EYES ARE BLOCKEDAND ONLY CENTRAL RAYS FALLS ON RETINA.

Pinhole TEST

PATIENT WITHDIMINITIONOF VISION(DECREASED

VISUALACUITY VA)

DOPINHOLE

TEST

VA IMPROVES

VA DOESNOTIMPROVE

VA DECREASE

REFRACTIVEERROR

OCULARPATHOLOGY

MACULARPATHOLOGY

IN CASE OF REFRACTIVE ERRORS

❑ The diameter of slit is 1mm.Uses1. To determine axis of cylinder.2. To know axis of optical iridectomy.3. FIMCHAM TEST- used to differentiate coloredhalos of cataract and glaucoma.

STENOPIC SLIT

we rotate the stenopic slit

Intermittentcolored halos

Acute congestiveglaucoma

cataract

Colored halos inall quadrants

Red green glasses/goggles❖ red glass in front of right eye.green glass in front of left eye.

❖ Principle- dissociation of two eyes.i.e normally with red glass person is able to see redcolor but not green and vise versa with green glass.

❖ uses- worth four dot test. diplopia charting

hess screen test

▶ patient is asked to wear goggles andlook at the screen having 4 dots(2 green, 1 red, 1white).

▶ if patient is having diplopia, the white dot is perceivedas red by right eye and green by left eye. Hence 5dots are seen.

▶ If patient is having right eye suppression, he will notsee green dot and perceive white dot as red.

▶ If patient is having left eye suppression, he will notsee red dot and perceive white dot as green.

normal

left eyesuppression

right eyesuppression

diplopia

▶ patient is made to wear goggles and look at thepoint source of light which is moved in allcardinal direction of movement of eye.

▶ patient has to tell-1. area of single vision and diplopia2. distance beteen two images in case of diplopia.3. the level of two images with respect to each

other.4. crossed or uncrossed diplopia

▶ it is a red plano convex cylindricallens which converts point sourceof light into a streak of light.

▶ it is used to diagnose latentsquint(phorias)

▶ principle- dissociation of binocularsingle vision (BSV)

▶ a horizontally place maddox rodproduces vertical streak and viceversa

BSV consists of -● simulataneous

macular perception● fusion● depth perception

how to test?▶ keep both the eyes of the patient open and make him wear

trial frame▶ put maddox rod (horizontally for horizontal deviation and

vertically for vertical deviation) in front of one eye.▶ ask the patient to look at a point source of light.▶ patient sees one spot of light(from eye without maddox rod)

and one RED streak of light(from eye with maddox rod.▶ ask the patient relative position of spot and streak.▶ in a normal person, because of BSV, both spot and streak

coincide each other.

FEATURES DIRECT OPHTHALMO INDIRECT OPHTHALMO

CONDENSING LENS NOT PRESENT PRESENT +20D MOSTCOMMONLY

MAGNIFICATION POWER OF EYE/4NORMAL POWER IS 60D,SO MAGNIFICATION IS25X

POWER OF EYE/POWER OFCONDENSING LENSMAGNIFICATION 3X

ILLUMINATION LESS BRIGHT.THEREFORE CAN’T BEUSED IN HAZY MEDIALIKE CATARACT,VITREOUSHEMORRHAGE

MORE BRIGHT.CAN BE USED TO VISUALISE INHAZY MEDIA

DISTANT DIRECT OPHTHALMOSCOPY IS DONE FROM ADISTANCE OF 25CM AND IS USED TO VISUALISE ANTERIORSEGMENT

FEATURES DIRECT OPHTHALMO INDIRECT OPHTHALMO

DEPTHPERCEPTION

ABSENT BECAUSEMONO OCULAR

PRESENT BECAUSE IT ISBINOCULAR

AREA OF FOCUS 2DD(DISC DIAMETER) I.ESMALLER FIELD OF VIEW

8DD (MORE BECAUSEMAGNIFICATION IS LESS

USE TO VISUALISE CENTRALFUNDUS

TO VISUALISE PERIPHERALRETINA

IMAGE VIRTUAL AND ERECT REAL AND INVERTED

▶ IT IS ALSO KNOWN AS SKIASCOPY/SHADOW TEST.▶ THIS IS USED FOR OBJECTIVE ASSESSMENT OF REFRACTIVE

STATUS.▶STEPS

1. CYCLOPLEGICS ARE GIVEN TO RELAX ACCOMODATION.2. PATIENT IS MADE TO SIT AT A DISTANCE OF 1M AND A

LIGHT STREAK IS THROWN INTO PUPIL AMD FUNDAL REDRELFEX IS OBSERVED.

3. RETINOSCOPE IS MOVED IN HORIZONTAL AND VERTICALPLANES AND MOVEMENT OF RED REFLEX IS OBSERVED

4. IF MOVEMENT OF REFLEX IS IN THE SAME DIRECTIONAS THE STREAK, IT IS NEUTRALISED BY CONVEX(+)LENSAND VICE VERSA.NEUTRALISATION IS DONE IN BOTH PLANESNEUTRALISATION IS ACHIEVED WHEN NO MOVEMENTOF REFLEX OCCURS.

CALCULATION3 STEPS

1. NEUTRALISATION2. DISTANCE CORRECTION- FOR 1M DISTANCE “-1D” 1 ARM DISTANCE “-1.5D”

1. CYCLOPLEGIC CORRECTION- FOR ATROPINE “-1D” FOR HOMATROPINE “-0.5D” FOR TROPICAMIDE “-0.25D”

EXAMPLE.ON PERFORMING RETINOSCOPY AT A DISTANCE OF OFONE ARM FROM PATIENT AND USING TROPICAMIDE ASCYCLOPLEGIC, FOLLOWING RETINOSCOPY FINDINGSARE SEEN

PATIENT HAS SIMPLEMYOPIA WITH -0.5DSPHERICAL LENS.

SOLUTION.SINCE BOTH THE PLANES HAVE EQUAL RETINOSCOPY VALUES,ONLY SPHERICAL ERROR IS PRESENT.CYCLOPLEGIC CORRECTION -1.5DDISTANCE CORRECTION -1.5D

IF BOTH THE PLANES HAVE DIFFERENT VALUES ONRETINOSCOPY, THAN CYLINDRICAL LENS IS REQUIRED.

IN THIS CASE, WE TAKE ONE PLANE AS SPHERE AND TAKETHE VALUE OF RETINOSCOPY AS THE VALUE OF SPHERCIALLENS REQUIRED.

TO CALCULATE THE POWER OF CYLINDER REQUIRED, WESUBTRACT SPHERE RETINOSCOPY VALUE FROM CYLINDERRETINOSCOPY VALUE (C-S)

EXAMPLEON PERFORMING RETINOSCOPY AT A DISTANCE OF OF1M FROM PATIENT AND USING HOMATROPINE ASCYCLOPLEGIC, FOLLOWING RETINOSCOPY FINDINGS ARESEEN.

SOLUTION

SIMPLEMYOPICASTIGMATISM

LET’S TAKE A OVERVIEW OF DIFFERENT REFRACTIVEERROR AND GLASSES PRESCRIBED FOR IT.

-DS MYOPIA

+DS HYPERMETROPIA

-DC SIMPLE MYOPIC ASTIGMATISM

+DC SIMPLE HYPERMETROPIC ASTIGMATISM

-DS AND -DC COMPOUND MYOPIC ASTIGMATISM

+DS AND +DC COMPOUND HYPERMETROPICASTIGMATISM

+DS AND -DC (DC>DS) MIXED ASTIGMATISM

SPECTACLEPRESCRIPTION

REFRACTIVE ERROR