M4 Flashcards
4 Types of Visual Acuity
Detection (minimum visible)
Resolution(minimum resolvable)
Recognition (minimum recognizable)
Hyperacuity (minimum discriminable)
Detection
(minimum visible)
Resolution
(minimum resolvable)
Recognition
(minimum recognizable)
Hyperacuity
(minimum discriminable)
refers to the smallest test object that can be detected
Detection (minimum visible)
Stycar Balls and ‘Hundreds and Thousands’
Examples of Detection (minimum visible)
- Detection tasks are often less affected by visual impairment than complex acuity tasks
Detection (minimum visible)
- may grossly overestimate VA in visually impaired children
Detection (minimum visible)
- Motor problem reducing control of fine hand movements rather than the inability to detect the targets could cause failure to the test.
Detection (minimum visible)
measures the smallest angular separation between adjacent targets than can be resolved
Resolution (minimum resolvable)
PL tests and VEP
Examples of Resolution (minimum resolvable)
- more useful and sensitive measure of VA than detection tests.
Resolution (minimum resolvable)
- can be succesful in estimating acuity in infants from birth
Resolution (minimum resolvable)
- refers to the ability to identify a form or its orientation
Recognition (minimum recognisable)
Snellen chart, acuity tests that use both letters or other optotypes
Examples of Recognition (minimum recognisable)
- children from about 2.5 years of age can be tested successfully
Recognition (minimum recognisable)
*larger target size
*less degraded in peripheral retina, stimulates parafoveal area
*not affected by contour interaction
RESOLUTION
*smaller target size
*more degraded in peripheral retina, does not stimulate parafoveal areas
*affected by contour interaction - crowding phenomenon
RECOGNITION
ability to determine differences between two stimuli (size, orientation and position)
Hyperacuity (minimum discriminable)
limited less by optical and retinal factors
Hyperacuity (minimum discriminable)
believed to reflect cortical processing
Hyperacuity (minimum discriminable)
vernier acuity and stereoacuity
Examples of Hyperacuity (minimum discriminable)
- monitor visual development in children
- we can detect children with reduced binocular acuity * detect interocular acuity difference
- need to test VA monocularly otherwise amblyopia will not be detected
- a VA test with both eyes open only represents the VA in the good eye
- to monitor the treatment efficacy (change in acuity resulting in spectacle Rx)
- disease progression
Why is VA test necessary?
Screening Test for Young Children and Retardates
STYCAR GRADED BALL TEST
- Age: 3 months to 2 years
- Test target: white balls with diameter ranging from 3mm - 6.16cm
STYCAR GRADED BALL TEST
- The child watches as the balls are presented (rolled or mounted on stick) against a black screen by the hidden examiner.
- The examiner observes the child’s responses to successively smaller balls. The smallest ball fixed is recorded as estimate of child’s acuity
STYCAR GRADED BALL TEST
sprinkles are held in the palm of the hand are used to gain attention for infants over 6 months old
Hundreds and Thousands
- At 9 months: baby may prod the decorations
- at 1 year old: baby may attempt to pick them up
Hundreds and Thousands
principle: a child will prefer to look at an object with visual interest (grating) rather than a plain field of the same luminance
Preferential Looking
- used from birth and most appropriate acuity test for children under 2.5 years
Preferential Looking
- when the grating is too narrow to be differentiated, the child will gaze randomly at one side or the other
Preferential Looking
alternating black and white lines of equal thickness and length
Square-wave gratings
use pictures constructed of black and white lines
Vanishing optotypes
Keeler Acuity System (UK)
Teller acuity cards (US)
Lea paddles
Square-wave gratings
Cardiff acuity test
Vanishing optotypes
*Test Distance: 40 cm
* Cardiff: 1m or 50cm
Preferential Looking
Procedure:
* A gross target is presented first
* Cards are presented (unseen by the optom)
* Optom watches the infant through the peephole
* A judgement must be made by the optom if child is fixating to
right or left/up or down (force-choice)
* VA is estimated as the highest spatial frequency (finest grating)
the child was able to see.
Preferential Looking
- examiner should be unaware of the position of the stimulus when presenting to avoid bias
- judgements must be based on eye movements rather than pointing/verbal response
- cards are presented atleast twice for a definite response.
Reminders for PL
Optotype-matching and naming tests
Recognition
- letters or picture-matching or naming tests
- Optotypes: isolated (uncrowded) or linear (crowded)
Test distance: 3m or 6m
Matching and naming
Procedure:
* Examiner presents the letter or picture targets * Child chooses a match from the key card
* Older children can name the picture or letter
Matching and naming
- 2-3 years of age
- single picture - Snellen format
⚬ 3/3 (6/6) - 3/30 (6/60) - Crowded version - LogMAR
⚬ 1.0-0.1
Kay Picture Test
- Lea shapes: square, circle, house and apple (heart)
- single and crowded format
- 2-3 years
- unlike Kay, symbols are
uniform in detail, line width and size
Lea Symbols
- 2.5-3yearsofage
- optotype: single letters
- no crowded version
- disadvantage: may overestimate acuity in amblyopia
Sheridan-Gardiner Test
Sonksen-Silver Acuity System
- 3.5 years of age
- uses Sheridan-Gardiner letters but presents letters in linear format
- contains contour interaction to elicit crowding phenomenon
- also uses Sheridan Gardiner letters
- the child has to identify the letter surrounded by four others
Cambridge Crowding Cards
- previously known as Glasgow Acuity Cards
- applies the Bailey-Lovie test
- letter size decreases in logarithmic
fashion - scoring system: each letter is scored
0.025
Versions: - uncrowded (2.5 - 3 years)
- crowded version (3.5 - 4 years)
LogMAR Acuity Test
- children have ample accommodation and few near vision problems when distance EOR is corrected
- those with neurological impairment or LV may have reduced acc
Near Vision Testing
- PL tests tend to overestimate VA (amblyopic eyes)
- It is important that the testing environment be quiet and free from distraction
- Young children tire quickly and lose motivation
- A lot of information about a child’s acuity can be gathered by simply observing them interacting with their environment
- Always end on a good note
Clinical pearls
-crucial for children with visual impairment / defects
Contrast Sensitivity
Hiding Heidi
Cardiff Contrast Test
Contrast Sensitivity
- important for career related decisions
- school related activities
Color Vision
- most commonly used
- red-green color deficiency screening test
- do not screen for blue-yellow defects
Ishihara Test
- 75cm
- 1st plate is visible to all regardless of CV status
- 14 plate edition: px must get 10 correct to pass
- 24 plate edition: plates 1-17 are administered to children who can recognize numbers
⚬ 13 out of 17 is required to pass
⚬ 18-24- if px cannot identify numbers-traceable curving lines
Ishihara Test
- CV test that does not classify type or severity
- only normal vs abnormal CV
- 12-14 plate pseudoisochromatic test
- 3-5 years
- 75cm
Color Vision Testing Made Esay
- Part 1: circle, square and star targets
- Part 2: boat, house, dog
- 1st plate is test plate and visible to all
Color Vision Testing Made Esay
- can detect and classify R-G defects & B-Y defects
- helpful in identifying congenital and acquired CV defects
- child friendly shapes and mini paint brush
Hardy-Rand-Rittler (HRR)
- first 4 plates are demonstration plates to confirm child’s understanding of the test
- the next 6 plates are used to separate normal from those with defective CV
- if the child fails demo plates –>px may be malingering or not cooperating, stop the test
Hardy-Rand-Rittler (HRR)
- if px completes demo plates, continue with remaining
- if child fails the 6 screening plates, there are 14 subsequent plates to diagnose extent and type of defect
⚬ if plates 5-6 are missed: B-Y defect is suspected
⚬ show plates 21-24
■ if error in 5-6 but no error in 21-24: mild defect
■ 21-22, no error in 23-24: moderate defect
■ 23-24 error: severe defect
Hardy-Rand-Rittler (HRR)
- 7-10 error: R-G defect suspect
■ only plates 11-20 are shown to concentrate on R-G defects
■ 11-15: defect is mild
■ 16-18:defect is moderate
■ 19-20: defect is severe
Hardy-Rand-Rittler (HRR)
px is asked to arrange 15 colored discs in order of hue and intensity
Farnsworth D-15
- It is important to identify children with CV defect as early as possible
- if child fails an initial CV screening test, it is beneficial to repeat testing in order to confirm deficiency
- it is equally important to educate pxs, teachers and parents regarding potential limitations in school or in future career paths
Clinical pearls
- directed towards cc (for px with short attention)
- older child: slit lamp
- younger / uncooperative child: hand held slit lamp
⚬ indirect ophthalmoscope with 20D or 28D lens
Ocular Health External
- Lids and Lashes
- Bulbar Conjunctiva
- Palpebral Conjunctiva
- Cornea
- Ant. Chamber Angle
- Iris
- Lens
Evaluation of ocular anterior segment/adnexa
- Cup/Disc Ratio
- A/V Ratio
- Vessel
- Venous Pulse
- Foveal Reflex
- Macula
- Vitreous
- Peripheral fundus
Evaluation of ocular posterior segment
