session 2. visual acuity (pptminimizer)
DESCRIPTION
visualTRANSCRIPT
Tasmanian Eye Clinics G.P. Seminar
Tasmanian Eye Clinics G.P. Seminar
Session 2. Visual Acuity
VISUAL ACUITY
(20 mins)
VISUAL ACUITY
(20 mins)
RETINAL ARCHITECTURE
RETINA
• ROD AND CONES
BIPOLAR CELLS
GANGLION CELLS
NERVE FIBRE LAYER
•RETINAL FUNCTION
• Outer segments of Cones and Rods contain visual pigments,which absorb photons & generate an electrical current. _
Bipolar cells amacrine cells
Ganglion cells
Ganglion cell axone OPTIC NERVE
Central vs Peripheral Vision
Central vs Peripheral Vision
• Macula function.• Detailed with high
definition.• Reading and
colour vision.• Reliance on cones.• Parvocellular
pathway.
• Macula function.• Detailed with high
definition.• Reading and
colour vision.• Reliance on cones.• Parvocellular
pathway.
• Discerns movement and action.
• Relies on rods.• Dark adaptation
function.• Magnocellular
pathway
• Discerns movement and action.
• Relies on rods.• Dark adaptation
function.• Magnocellular
pathway
maculamacula
foveafovea
Recording Visual Acuity is not complex and
measures the most essential function of the eye.
Form acuity is only one way of assessing visual function.
Other functions are contrast sensitivity and dark adaptation.
Recording Visual Acuity is not complex and
measures the most essential function of the eye.
Form acuity is only one way of assessing visual function.
Other functions are contrast sensitivity and dark adaptation.
VISUAL ACUITYVISUAL ACUITY
• RECORD• RECORD• RECORD• You are not defendable if there is
no recorded acuity.
• RECORD• RECORD• RECORD• You are not defendable if there is
no recorded acuity.
RecordingRecording
• Record the result in the following manner.
• Remember no record = no defence
• Record the result in the following manner.
• Remember no record = no defence
Visual Acuity Visual Acuity
• Va’s Recorded at 6metres or 3metres.• The Numerator represents the distance used
and the denominator the line read.• Ie 6/6 represents reading the line at 6 metres
that should be read at 6 metres.• The Americans use 20/20 ( ie 6 metres ) as
the convention.• Young people can read better than
6/6 ,usually 6/5 or 6/4.• The chart used is actually based on a fallacy
but become imbedded in law
• Va’s Recorded at 6metres or 3metres.• The Numerator represents the distance used
and the denominator the line read.• Ie 6/6 represents reading the line at 6 metres
that should be read at 6 metres.• The Americans use 20/20 ( ie 6 metres ) as
the convention.• Young people can read better than
6/6 ,usually 6/5 or 6/4.• The chart used is actually based on a fallacy
but become imbedded in law
A fallacy but imbedded in LAWA fallcy but imbedded in LAW
Snellens E chart Landolts Rings
SHERIDAN GARDNER for Children,SHERIDAN GARDNER for Children,
“One thing like other thing”“One thing like other thing”
Recording Visual Acuity.Recording Visual Acuity.
• V.r (V.r (uncorrected) at distance.
• corrected ie with glasses)
• No glasses with Pin Hole.
• V.r. for near.
• V.r (V.r (uncorrected) at distance.
• corrected ie with glasses)
• No glasses with Pin Hole.
• V.r. for near.
• V.l.( uncorrected) at distance.
• V.l.(corrected ie with glasses).
• No glasses with Pin Hole.
• V.l. for near.
• V.l.( uncorrected) at distance.
• V.l.(corrected ie with glasses).
• No glasses with Pin Hole.
• V.l. for near.
PIN HOLE PIN HOLE
• A pinhole or stenopaeic device converts the eye into a pinhole camera and neutralises refractive error.
• A pinhole is used to create a shorthand refraction.
• If Visual Acuity is depressed it may be due to a simple refractive error .
• The pinhole test allows a non optical person to assess the visual potential of the eye.
• A pinhole or stenopaeic device converts the eye into a pinhole camera and neutralises refractive error.
• A pinhole is used to create a shorthand refraction.
• If Visual Acuity is depressed it may be due to a simple refractive error .
• The pinhole test allows a non optical person to assess the visual potential of the eye.
DEVICE PIN HOLE DEVICE PIN HOLE
Near VisionNear Vision
• Recorded in point print form.(remember the readers!)
• N8 is approximately the size of newsprint.
• N6 the phone book.• N10 most magazines.• Record with reading glasses if used.
• Recorded in point print form.(remember the readers!)
• N8 is approximately the size of newsprint.
• N6 the phone book.• N10 most magazines.• Record with reading glasses if used.
Clues from the Visual Acuity
Clues from the Visual Acuity
• Reading one side of chart may indicate a hemianopia.
• “Searching” movements of the head when trying to read the letters may suggest macula changes.
• A poorer reading acuity compared to the distance acuity suggests macula dysfunction.
• Reading one side of chart may indicate a hemianopia.
• “Searching” movements of the head when trying to read the letters may suggest macula changes.
• A poorer reading acuity compared to the distance acuity suggests macula dysfunction.
Technique PointsTechnique Points
• Cover each eye for the patient carefully to avoid “peeping”.
• Record the best line the patient can see even if there are mistakes and record as eg 6/6-2
• Single letter vision charts are easier to read than multiple letters but mask “ crowding”.
• Beware the illiterate and the memorised chart.
• Cover each eye for the patient carefully to avoid “peeping”.
• Record the best line the patient can see even if there are mistakes and record as eg 6/6-2
• Single letter vision charts are easier to read than multiple letters but mask “ crowding”.
• Beware the illiterate and the memorised chart.
Standard OccluderStandard Occluder
ACUITY STANDARDSACUITY STANDARDS
• 6/12 (corrected or uncorrected ) in at least one eye is the driving standard for an ordinary licence. A visual field of 120 degrees (binocular ) is also required.
• 6/9 for public vehicle licences.• <6/60 for the blind pension or
<5degrees of field in the better eye.
• 6/12 (corrected or uncorrected ) in at least one eye is the driving standard for an ordinary licence. A visual field of 120 degrees (binocular ) is also required.
• 6/9 for public vehicle licences.• <6/60 for the blind pension or
<5degrees of field in the better eye.
•A little about optics and lenses
•A little about optics and lenses
OpticsOptics
• The power of an optical surface is at the interface between a less dense and more dense medium .
• This creates REFRACTION.• All optical devices depend on
refraction.• The following illustrate the main
types of lenses.
• The power of an optical surface is at the interface between a less dense and more dense medium .
• This creates REFRACTION.• All optical devices depend on
refraction.• The following illustrate the main
types of lenses.
OPTICAL POWER occurs at an optical surface ie between 2 materials of
different refractive index
Power = N2-N1/r
alpha
beta
Parallel rays of light
f
CONVEX LENS
CONCAVE LENS
CYLINDRICAL LENS
No power in this plane
Lenses.Lenses.
• Convex.• Image moves in
opposite direction.• Magnify.• Focal plane
concept• Identify.
• Convex.• Image moves in
opposite direction.• Magnify.• Focal plane
concept• Identify.
• - lenses.• Concave.• Image moves in
same direction.• Make object
smaller.• Focal plane
concept.• Identify.
• - lenses.• Concave.• Image moves in
same direction.• Make object
smaller.• Focal plane
concept.• Identify.
+ lenses+ lenses
Spectacles.Spectacles.
• Single vision.• Bifocals etc.• Multifocals.• High + and – and the problems.• Identify main types.
• Single vision.• Bifocals etc.• Multifocals.• High + and – and the problems.• Identify main types.
Single VisionSingle Vision
D Segment BifocalD Segment Bifocal
Executive BifocalExecutive Bifocal
Round Segment BifocalRound Segment Bifocal
MultifocalMultifocal
TrifocalTrifocal
Increasing power of lensIncreasing power of lens
No demarcation No demarcation
Spectacle MaterialsSpectacle Materials
• CR39 1.49
• High Index Plastics(1.67)
• CR39 1.49
• High Index Plastics(1.67)
Reducing Edge thicknessReducing Edge thickness
& weight& weight
Practical Training (20 mins)
• Visual Acuity Drills.• Pin Hole use.• Methods of recording.• Identification of basic optical lenses.• Identification of basic glasses types.• Chart types & advice re use.
Visual Acuity Multiple Choices 1. Visual Acuity is the only method of assessing visual function. T. F. 2. Pinholes correct ametropia only in young subjects. T. F.3. Patients with macula dysfunction perform better on distance acuity measurement than near acuity. T. F.4. “Crowding” occurs in partially corrected amblyopia. T. F.5. Visual acuity is classically recorded on the page as if the examiner was the patient. T. F.6. Snellens Acuity charts accurately reflect the resolving power of the eye. T. F.7. Recording the Acuity in the affected eye only is “good enough” to save consultation time. T. F.8. Sheridan Gardiner charts are used to assess Acuity in pre verbal children only. T. F.