1 Testing sensory visual function

2 types: 1) psychophysical tests 2) electrophysical tests

Psycho-physical tests: 1- visual acuity 2-contrast sesitivity 3-amsler grid 4-light brightness comparison test 5-photostress test 6- Dark adaptation 7-color vision test

Electro-physical tests Electroretinography Electroretinography Electrooculography Electrooculography Visual evoked potential Visual evoked potential

Visual acuity

the most common clinical measurement of visual function the most common clinical measurement of visual function is the ability to resolve a spatial pattern separated by a visual angle of one minute of arc is the ability to resolve a spatial pattern separated by a visual angle of one minute of arc VA is a quantitative measure of the ability to identify black symbols on a white background at a standardized distance as the size of the symbols is varied VA is a quantitative measure of the ability to identify black symbols on a white background at a standardized distance as the size of the symbols is variedquantitative 6/6 vision" the numerator refers to the distance in meter from which a person can reliably distinguish a pair of objects. The denominator is the distance from which an 'average' person would be able to distinguish — the distance at which their separation angle is 1 arc minute. 6/6 vision" the numerator refers to the distance in meter from which a person can reliably distinguish a pair of objects. The denominator is the distance from which an 'average' person would be able to distinguish — the distance at which their separation angle is 1 arc minute.numerator denominator arc minutenumerator denominator arc minute

Visual acuity is often measured according to the size of letters viewed on a Snellen chart or the size of other symbols, such as Landolt Cs or Tumbling E. Visual acuity is often measured according to the size of letters viewed on a Snellen chart or the size of other symbols, such as Landolt Cs or Tumbling E.Snellen chart Landolt CsTumbling ESnellen chart Landolt CsTumbling E

Contrast sensitivity.

Contrast is the difference in visual properties that makes an object distinguishable from other objects and the background. Contrast is the difference in visual properties that makes an object distinguishable from other objects and the background. determined by the difference in the color and brightness of the object and other objects within the same field of view. determined by the difference in the color and brightness of the object and other objects within the same field of view.colorbrightnessfield of viewcolorbrightnessfield of view Can detect very eary visual dysfunction, even when snellen VA is normal Can detect very eary visual dysfunction, even when snellen VA is normal Example: Pelli-Robson chart Example: Pelli-Robson chart

Amsler grid

a grid of horizontal and vertical lines used to monitor a person's central 20 visual field. a grid of horizontal and vertical lines used to monitor a person's central 20 visual field.visual fieldvisual field Mainly for screening &monitoring macular disease. Mainly for screening &monitoring macular disease. The original Amsler grid was black and white. A color version with a blue and yellow grid is more sensitive and can be used to test for a wide variety of visual pathway abnormalities, including those associated with the retina, the optic nerve, and the pituitary gland. The original Amsler grid was black and white. A color version with a blue and yellow grid is more sensitive and can be used to test for a wide variety of visual pathway abnormalities, including those associated with the retina, the optic nerve, and the pituitary gland. optic nervepituitary gland optic nervepituitary gland There are 7 charts,each consisting of 10cm squar. There are 7 charts,each consisting of 10cm squar.

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

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

Macular disease = wavy lines Macular disease = wavy lines Optic nerve disease = missing or faint lines but not distorted Optic nerve disease = missing or faint lines but not distorted

Dark adaptation the ability of the visual system to adjust to various levels of darkness and light. the ability of the visual system to adjust to various levels of darkness and light. Tested by dark adaptometry. Tested by dark adaptometry. Maily useful in patients with nyctalopia. Maily useful in patients with nyctalopia.

Photo-stress test Gross test of dark adaptation. Gross test of dark adaptation. Used to differentiate visual loss caused by macular from that caused by an optic nerve lesion. Used to differentiate visual loss caused by macular from that caused by an optic nerve lesion. Normal recovery time = seconds Normal recovery time = seconds Delay in visual recovery indicates macular pathology (e.g CME,CSR) Delay in visual recovery indicates macular pathology (e.g CME,CSR)

Light brightness test To test optic nerve function by comparing light brightness in one eye with the fellow. To test optic nerve function by comparing light brightness in one eye with the fellow. In optic neuropathy, light is less bright in the affected eye. In optic neuropathy, light is less bright in the affected eye.

Color vision ability to perceive differences between colors. ability to perceive differences between colors. colors color blindness, a color vision deficiency, is the inability to perceive differences between some of the colors that others can distinguish. color blindness, a color vision deficiency, is the inability to perceive differences between some of the colors that others can distinguish.color visioncolorscolor visioncolors Tests: Tests: Ishihara: most often used to diagnose red-green color deficiencies. Ishihara: most often used to diagnose red-green color deficiencies.

Hardy-rand-rittler: more sensitive than ishihara, it detect all 3 congenital defects. Hardy-rand-rittler: more sensitive than ishihara, it detect all 3 congenital defects. Farnsworth-Munsell 100-hue : most sensitive. Farnsworth-Munsell 100-hue : most sensitive. Example of an Ishihara color test plate

Electro-retinography

measures the electrical responses of various cell types in the retina. measures the electrical responses of various cell types in the retina.retina Electrodes are usually placed on the cornea and the skin near the eye with a reference electrode on forehead. Electrodes are usually placed on the cornea and the skin near the eye with a reference electrode on forehead.ElectrodescorneaeyeElectrodescorneaeye Potential between 2 electrodes is amplified & displayed. Potential between 2 electrodes is amplified & displayed. Normal ERG is biphasic,an a-wave (initial negative deflection) followed by a b-wave (positive deflection). Normal ERG is biphasic,an a-wave (initial negative deflection) followed by a b-wave (positive deflection). The leading edge of the a-wave is produced by the photoreceptors, while the remainder of the wave is produced by a mixture of cells including photoreceptors, bipolar, amacrine, and Muller cells. The leading edge of the a-wave is produced by the photoreceptors, while the remainder of the wave is produced by a mixture of cells including photoreceptors, bipolar, amacrine, and Muller cells.bipolaramacrinebipolaramacrine

If a flash ERG is performed on a dark-adapted eye, the response is primarily from the rod system and if a flash ERGs performed on a light adapted eye will reflect the activity of the cone system. If a flash ERG is performed on a dark-adapted eye, the response is primarily from the rod system and if a flash ERGs performed on a light adapted eye will reflect the activity of the cone system.rod systemcone systemrod systemcone system The multifocal ERG is used to record separate responses for different retinal locations. The multifocal ERG is used to record separate responses for different retinal locations.multifocal Clinically used mainly by ophthalmologists and optometrists, the electroretinogram (ERG) is used for the diagnosis of various retinal disease,examples: Clinically used mainly by ophthalmologists and optometrists, the electroretinogram (ERG) is used for the diagnosis of various retinal disease,examples:ophthalmologists Retinitis pigmentosa Retinitis pigmentosa Leber's congenital amaurosis Leber's congenital amaurosis Cone dystrophy Cone dystrophy Diabetic retinopathy Retinal vain acclusion..etc

Electrooculography

a technique for measuring the resting potential of the retina. a technique for measuring the resting potential of the retina.resting potentialretinaresting potentialretina The main applications are in ophthalmological diagnosis and in recording eye movements. The main applications are in ophthalmological diagnosis and in recording eye movements. ophthalmologicaldiagnosiseye movements ophthalmologicaldiagnosiseye movements Unlike the electroretinogram, the EOG does not represent the response to individual visual stimuli. Unlike the electroretinogram, the EOG does not represent the response to individual visual stimuli.electroretinogram The EOG is used to assess the function of the pigment epithelium. The EOG is used to assess the function of the pigment epithelium.

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

Evoked potential

VEP is a recording of electrical activity of the visual cortex after retinal stimulation. VEP is a recording of electrical activity of the visual cortex after retinal stimulation. Main indications: Monitoring visual function in babies. Monitoring visual function in babies. Optic neuropathy Optic neuropathy Monitor macular pathway function Monitor macular pathway function