Visual acuity is the resolving power of the eye. Ability to see the separate objects as separate.

1. VISUAL ACUITY
Aynul karim
B.Optom 10th batch

2. Visualacuity
• Is the resolvingpowerof theeye.
• Abilityto seeaseparateobject asseparate.
• Visualacuitydependent on:-
-The refractiveerror of the eye
-The health and the integrity of the eye
-The test target used
-The test condition
- The proper room illumination

3. Typesof VisualAcuity
• MinimumDetectable(visible)
• MinimumSeparable (resolution)
• Minimumcognizable (recognition)
• MinimumDiscriminable (hyperacuity)

4. ACUITYTASKS
MINIMUMDETECTABLE:
• Ability to determine whetheror not anobjectis presentin avisualfield.The limit for this kind of
acuityis1 arc second.
MINIMUMSEPARABLE:
• Discriminationof 2 spatially separatedtargets.
• Normal angularthreshold of discrimination for resolution 30-60 seconds of anarc.(minimum
angleof resolution)
MINIMUMCOGNIZIABLE:
• Not onlydiscrimination of the spatial characteristics of the test pattern but also the pattern with
which he has previous experience (Identification of faces, letters, symbols, pictures etc.)
MinimumDiscriminable:
• Ability to determine whetheror not two parallel and straight lines arealigned in the frontal
plane.

5. What do you
mean by 6/60?
6/6 isthe visualacuityof anormal person. If visualacuityis6/60, this means the
person is only able to read the top letter of chart from a distance of 6m/20feet.

6. Theoriesof visualacuity
1.Receptortheory
 If the imagesfallon twoconesseparatedbyanunilluminatedone,then the points
of light wouldbeperceivedastwodistinct sources.
 Twoadjacentpoint canberecognizedasseparatewhentheysubtendanangleof 1
min arch.
2. RayleighCriterionfor resolution
 Twopoint sourcesareresolvedfrom eachother whenseparatedbyat least the
radius of the airy disc.
 The centraldisk issurrounded bylessintenseconcentric rings.

7. DistanceAcuity Chart
• Snellen's distance acuity chart
• Bailey-Loviechart •
• Feinbloom DistanceTestchart
• • Chronister PocketAcuity Chart
NearAcuity chart
 SingleLetterchart
• ReducedSnellen'schart
• LightHouse near visual acuity test
• Designs for vision number chart
• ReducedFerris-Bailey ETDRS chart
 WordandContinuousTextCharts
• Jaeger's chart
• Roman test tyoes
• Lighthouse continuous text card for adults
• MNREAD card

8. Basics of snellen acuity chart
 Snellen Fraction is the most common notation of acuity.
 The distant acuity is usually tested by snellen chart.
 Consist of a series of black capital letters on a white board, arranged in lines, each
progressively diminishing in size.
 Each letters fits in a square.
 Assume 5x5 grid for letters with detail separation of 1/5 of letter size.

9. Characteristics
 The traditional Snellen chart is printed with eleven lines of block letters.
 Ten Sloan letters C, D, E, F, L, N, O, P, T, Z are used in the traditional Snellen chart.
 The first line consists of one very large letter, which may be one of several letters, for
example E, H, or N.
 Subsequent rows have increasing numbers of letters that decrease in size.
 The symbols on an acuity chart are formally known as "optotypes"
 Each letter is perfectly placed in a square which is divided into 25
small squares
 Each letter subtends an angle of 5 minute the nodal point of the eye.
 Each component part of the letter subtends an angle of 1 minute at
the nodal point from a given distance in metres.
 End point consist of recognition of letter.

12. PROCEDURE
 • Patient is kept at 6 meter distance (divergence of rays entering the pupil is so slight
that it can be considered as parallel & accommodation is relaxed)
 • Each eye has to be tested separately
 • Patient is asked to close the eye not being tested with the cup of the palm
 • Illumination should be adequate ( 100 foot candles)
 • Patient is asked to read from the top letter Vision are taken as 6/60, 6/36, 6/24....
 • If one cannot see the top line from 6 meter patient is slowly asked to move towards
the chart till one can read the top line. Vision is recorded as 5/60, 4/60, 3/60, 2/60 &
1/60
 • Or he is asked to count fingers of examiner and his vision is recorded as CF3FT, CF 2FT,
CF1FT OR CF close to face

13. • If patient cannot count fingers close to face then examiner moves his hand close to
the patients face .If patient can appreciate the hand movements (HM), VA is
recorded as HM.
• If patient cannot appreciate HM he is then taken to a dark room and asked to close
one eye firmly with palm and look straight
• Light is thrown on the open eye from all directions i.e up, down, nasal &temporal. If
patient can recognize the light and indicate its direction then visual acuity is
recorded as PL + & PR + is all 4 quadrants.
• if patient is not able to perceive light from a particular quadrant then negative sign
is put against that quadrant and is said to have faulty PR.
• If patient can see the glow of light but cannot indicate the side of projected rays
then vision is recorded as only PL with no PR.
• If pt cannot percieve any glow vision is recorded as no PL.

14. Measurementof visualacuityin pre verbaland non verbal patients
Objective
• 10 prism Diopter fixation test
• Preferential looking test
• Optokinetic nystagmustest (OKN)
• CatfordDrumTest
• Visualevokedpotential (VEP)
• Central steady and maintainance(CSM)
• Galvanicskin response
10 PDFixationTest
• It is method of testing for amblyopia
Procedures:A10pd prism vertically placedbeforeoneof theeyes
• While the child fixatesanobjectsucha toy
• The prism isintroduced beforeoneeyeand the fixation pattern is observed
If the fixation alternates b/w the 2 eyes,it is unlikelythat amblyopiaexists.
• However,if thereis no alteration of fixation, it canbeconcluded that amblyopia present.

15. Subjective
• Ivory ball
• Heiding Heidi
• TumblingE-pad test.
• SheridanGardiner HOTV test
• STYCAR Graded balls test.
• Allen chart.
• Light house card
• Lea Symbol
• Constant acuitycards test
• Ffook’stest
LEASYMBOL CHART
• It is doneatadistanceof 3meter
• The chart is available insimple aswell asformspiral booklet
• The maincardconsist of 5 symbols with onesymbols incentre andthe rest 4arelocatedincircular
formaroundthe central symbol
• These arrangement is done in particularto develop both crowding and confusing phenomenon for
the child difficulty
• The patientis given akey cardto pointout the symbol.
• These symbols arefixed and arekept astandardlikeapple,house, circle, square etc.
• The size of pictures goes ondecreasing from3/9.5 to 3/2.4 andthere arefourcardsfor eachsize

16. LogMAR chart
• Log MARAcuity :MAR (Minimum Angleof Resolution Snellen fraction,in reciprocal of
Snellen fraction.
• Examples for , 6/6 MAR is I min of arc
6/12 MAR is 2 min of Arc
so, Log10 of the minimum angleof resolution is the result of
LogMAR. Examples for, 6/6, MAR is 1’of arc and logMAR
is 10
6/60,MAR is 10’of arc and logMAR is1
So,Log of the MAR is used to notate the acuity. Geometrical progression of size &
spacing byo.1 and the letter style of log MAR is "Sans serif“. It’saa‘v’shaped acuity chart.
Everyline has 5 letters. Everyletter that is correctly read deducts 0.02 from that line &letter
to letter scoring system.
Example of log MAR scoringsystem-
• If the patient reads all the letters of the log MAR 0.40 line (20/50 ) &two letters from
the 0.30 line (20/40) it is scored as o.36.
log MAR =Line value+ (0.02 xmissingletter)
• LogMAR used in research &lowvision, testing distances are typically 4 or 2 meters.The
log MAR chart is availablein landolt C,Tumbling E aswellasin numeric &alphabet
optotypes

17. • Recording:
o Each letter has a score valueof 0.02 log units. Since there are 5 letters per line the
total scorefor alineon the LogMARchart representsachangeof 0.1 log units.
o Every letter that is correctly add 0.02 per letter read with that upper line.
o Everyletter that ismissingadd 0.02 per letter missingfrom that line.
o For reducingeveryhalf of the distanceadd0.3.
o Canbedonealsoat 2m,1m.
• Advantage:
o It isusedto find minimumvisualacuity.
o It canbeusedfor lowvision patients.
o The rate of progressionisslow.Eachlineconsistsof 5letters.
o The patient can't read the side letters, this will givethe motivation levelto the patient.
o It ismeasuredat adistanceof 3m the chart workup canalsobedone at a distance
1/2 meter.

19. Preferentiallooking Test
• PreferentialLooking chart.
- Infant prefers to look a pattern stimul when presented in homogenous field of
visiondistance38 cm,cm,8 cm
- Gratingacuityisrecordedin cyclesdegreeor the no.of plate of dark and bright
strawswithin 1 degreeof visual angle
- The conversionfrom cycle/degreeto snellenvaluesisobtained bydividingthe
numberof cyclesby30.

20. Performing pediatric
examination
Objectives:
• Present general advise & tips onPediatric clinical examination/approach
• Present general advise onhow to provide informationto Pediatric patients
Taking history:
• Readreferral letter andnotesbeforeinterview,
• Observe the child at play,mayprovide clues,
• Know/ask for the patients namewhen you welcome the family andthepatient.
Ask how heprefersto be addressed,
• Determine the relationship betweenthe adult andchild,
• Infants are most secure in parents lap or arms
• Older children might needsometime to get to know you.
• Avoid having bedsanddesksbetweenyou andfamily
• Havetoys available.. Or aplayspecialist at hand.Observe how heplaysand
interacts,
• Don't forget to address questions to the patient when appropriate

21. Approach to examining children (Obtaining child's cooperation)
• Makefriendswith the child,
• Beconfidentandgentle, Avoiddominating,
• Short mockexaminations,e.g.Auscultating ateddy or mothershand,askhelp to play specialist
parentor nurse
• Start exam on non-threatening area(handor knee),
• Explain what you are about to do, and what you want the child to do,
• Examinationis essential Don't askhis permission!...LOL
• Smileand talk,
• Leave unpleasant procedures last,
Approach to examining children (Adopting to child's age)
• Babies in first months best examined on examination couch with parent next to them,
• A toddler is best initially examinedonmotherslapor over parents shoulder,
• Preschool children maybeexaminedwhile playing,
• Older childrenandteenagers, concernedabout privacy.
• Teenager girls inpresence of mother,nurseor chaperone. Beawareof sensitivities inethnic
group.
Approach to examining children (Developmental skill)
• Watchthe childplay to asses development,A fewsimpletoys andbricks,acar,pencilandpaperis
all that is required.
• If developmental assessment focusof examination asses this before physical examination...As
cooperationmaybelost.