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Testing sensory visual Testing sensory visual functionfunction

22 types:types:1) psychophysical tests1) psychophysical tests2) electrophysical tests2) electrophysical tests

Psycho-physical tests:Psycho-physical tests:

1- visual acuity1- visual acuity

2-contrast sesitivity2-contrast sesitivity

3-amsler grid3-amsler grid

4-light brightness comparison test4-light brightness comparison test

5-photostress test5-photostress test

6- Dark adaptation6- Dark adaptation

7-color vision test7-color vision test

Electro-physical testsElectro-physical tests

• ElectroretinographyElectroretinography

• ElectrooculographyElectrooculography

• Visual evoked potentialVisual evoked potential

Visual acuityVisual acuity

• the most common clinical measurement of the most common clinical measurement of visual function visual function

• is the ability to resolve a spatial pattern is the ability to resolve a spatial pattern separated by a visual angle of one minute separated by a visual angle of one minute of arc of arc

• VA is a VA is a quantitativequantitative measure of the ability measure of the ability to identify black symbols on a white to identify black symbols on a white background at a standardized distance as background at a standardized distance as the size of the symbols is varied the size of the symbols is varied

• 6/6 vision6/6 vision" the " the numeratornumerator refers to the refers to the distance in meter from which a person can distance in meter from which a person can reliably distinguish a pair of objects. The reliably distinguish a pair of objects. The denominatordenominator is the distance from which an is the distance from which an 'average' person would be able to 'average' person would be able to distinguish —the distance at which their distinguish —the distance at which their separation angle is 1 separation angle is 1 arc minutearc minute. .

• Visual acuity is often measured Visual acuity is often measured according to the size of letters according to the size of letters viewed on a viewed on a SnellenSnellen chart chart or the size or the size of other symbols, such as of other symbols, such as LandoltLandolt Cs Cs or or Tumbling ETumbling E. .

ContrastContrast sensitivitysensitivity

..

• ContrastContrast is the difference in visual is the difference in visual properties that makes an object properties that makes an object distinguishable from other objects and distinguishable from other objects and the background .the background .

• determined by the difference in the determined by the difference in the colorcolor and and brightnessbrightness of the object and of the object and other objects within the same other objects within the same field of viewfield of view. .

• Can detect very eary visual dysfunction, Can detect very eary visual dysfunction, even when snellen VA is normaleven when snellen VA is normal

• Example: Pelli-Robson chartExample: Pelli-Robson chart

Amsler gridAmsler grid

• a grid of horizontal and vertical lines used a grid of horizontal and vertical lines used to monitor a person's central 20 to monitor a person's central 20 visual fieldvisual field..

• Mainly for screening &monitoring macular Mainly for screening &monitoring macular disease. disease.

• The original Amsler grid was black and The original Amsler grid was black and whitewhite. . A color version with a blue and A color version with a blue and yellow grid is more sensitive and can be yellow grid is more sensitive and can be used to test for a wide variety of visual used to test for a wide variety of visual pathway abnormalities, including those pathway abnormalities, including those associated with the retina, the associated with the retina, the optic nerveoptic nerve, , and the and the pituitary glandpituitary gland..

• There are 7 charts ,each consisting of 10cm There are 7 charts ,each consisting of 10cm squar. squar.

An Amsler grid, as seen by a person An Amsler grid, as seen by a person with normal visionwith normal vision. .

• An Amsler grid, as it might be viewed An Amsler grid, as it might be viewed by a person with by a person with age related macular degenerationage related macular degeneration. .

• Macular disease = wavy linesMacular disease = wavy lines

• Optic nerve disease = missing or Optic nerve disease = missing or faint lines but not distortedfaint lines but not distorted

Dark adaptationDark adaptation

• the ability of the visual system to the ability of the visual system to adjust to various levels of darkness adjust to various levels of darkness and light.and light.

• Tested by dark adaptometry.Tested by dark adaptometry.

• Maily useful in patients with Maily useful in patients with nyctalopia.nyctalopia.

Photo-stress testPhoto-stress test

• Gross test of dark adaptation.Gross test of dark adaptation.

• Used to differentiate visual loss Used to differentiate visual loss caused by macular from that caused caused by macular from that caused by an optic nerve lesion.by an optic nerve lesion.

• Normal recovery time = 15-30 Normal recovery time = 15-30 secondsseconds

• Delay in visual recovery indicates Delay in visual recovery indicates macular pathology (e.g CME ,CSR)macular pathology (e.g CME ,CSR)

Light brightness testLight brightness test

• To test optic nerve function by To test optic nerve function by comparing light brightness in one comparing light brightness in one eye with the fellow.eye with the fellow.

• In optic neuropathy , light is less In optic neuropathy , light is less bright in the affected eye. bright in the affected eye.

Color visionColor vision

• ability to perceive differences between ability to perceive differences between colors .colors .

• color blindnesscolor blindness, a color vision , a color vision deficiency, is the inability to perceive deficiency, is the inability to perceive differences between some of the colors differences between some of the colors that others can distinguish.that others can distinguish.

• TestsTests::Ishihara: most often used to diagnose Ishihara: most often used to diagnose

redred--green color deficienciesgreen color deficiencies. .

Hardy-rand-rittler: more sensitive Hardy-rand-rittler: more sensitive than ishihara , it detect all 3 than ishihara , it detect all 3 congenital defects.congenital defects.

Farnsworth-Munsell 100-hue : most Farnsworth-Munsell 100-hue : most sensitive. sensitive.

Example of an Ishihara color test Example of an Ishihara color test plateplate

Electro-retinographyElectro-retinography

•measures the electrical responses of measures the electrical responses of various cell types in the various cell types in the retinaretina..• ElectrodesElectrodes are usually placed on the are usually placed on the corneacornea and the skin near the and the skin near the eyeeye with a with a reference electrode on forehead.reference electrode on forehead.•Potential between 2 electrodes is amplified Potential between 2 electrodes is amplified & displayed. & displayed.•Normal ERG is biphasic ,an aNormal ERG is biphasic ,an a--wave wave ((initial initial negative deflectionnegative deflection) ) followed by a bfollowed by a b--wave wave ((positive deflectionpositive deflection). ). •The leading edge of the aThe leading edge of the a--wave is wave is produced by the photoreceptors, while the produced by the photoreceptors, while the remainder of the wave is produced by a remainder of the wave is produced by a mixture of cells including photoreceptors, mixture of cells including photoreceptors, bipolarbipolar, , amacrineamacrine, and Muller cells. , and Muller cells.

•If a flash ERG is performed on a darkIf a flash ERG is performed on a dark--adapted adapted eye, the response is primarily from the eye, the response is primarily from the rod systemrod system and if a flash ERGs performed on a light adapted and if a flash ERGs performed on a light adapted eye will reflect the activity of the eye will reflect the activity of the cone systemcone system . .•The The multifocalmultifocal ERG ERG is used to record separate is used to record separate responses for different retinal locations. responses for different retinal locations. •Clinically used mainly by Clinically used mainly by ophthalmologistsophthalmologists and and optometrists, the optometrists, the electroretinogram (ERG)electroretinogram (ERG) is is used for the diagnosis of various retinal used for the diagnosis of various retinal disease ,examples:disease ,examples:Retinitis Retinitis pigmentosapigmentosaLeber'sLeber's congenital congenital amaurosisamaurosisCone dystrophyCone dystrophy Diabetic retinopathyDiabetic retinopathyRetinal vain acclusion..etcRetinal vain acclusion..etc

ElectrooculographyElectrooculography

• a technique for measuring the a technique for measuring the resting potentialresting potential of the of the retinaretina..

• The main applications are in The main applications are in ophthalmologicalophthalmological diagnosis and in diagnosis and in recording eye movements. recording eye movements.

• Unlike the electroretinogram, the Unlike the electroretinogram, the EOG does not represent the response EOG does not represent the response to individual visual stimuli.to individual visual stimuli.

• The EOG is used to assess the The EOG is used to assess the function of the pigment epitheliumfunction of the pigment epithelium. .

•During dark adaptation, the resting During dark adaptation, the resting potential decreases slightly and reaches potential decreases slightly and reaches a minimum ("dark trough") after several a minimum ("dark trough") after several minutes. When the light is switched on, minutes. When the light is switched on, a substantial increase of the resting a substantial increase of the resting potential occurs ("light peak"), which potential occurs ("light peak"), which drops off after a few minutes when the drops off after a few minutes when the retina adapts to the light. The ratio of retina adapts to the light. The ratio of the (the (light peaklight peak divided by divided by dark troughdark trough) ) is known as the is known as the Arden ratioArden ratio. .

Evoked potentialEvoked potential

•VEP is a recording of electrical activity VEP is a recording of electrical activity of the visual cortex after retinal of the visual cortex after retinal stimulation.stimulation.

Main indications:Main indications:Monitoring visual function in babies.Monitoring visual function in babies.Optic neuropathyOptic neuropathyMonitor macular pathway functionMonitor macular pathway function