Visual acuity refers to the ability to see details clearly. It depends on factors like refractive error, eye health, test targets, lighting conditions. There are different types of visual acuity tasks like minimum detectable, minimum separable, minimum cognizable, minimum discriminable. The Snellen chart is commonly used to measure distance visual acuity, with results written as fractions like 6/6 or 6/60. Near acuity can be measured with charts like Jaeger or single letter charts. Visual acuity is important to properly examine in children using techniques tailored to their age and development to obtain cooperation.

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.