The form sense and visual acuity

Define visual acuity

the smallest visible detail that can be seen

Define spacial resolution

the ability of the visual system to resolve detail

what are the 4 types of visual acuity

1. detection

2. resolution

3. relative localisation

4. recognition

Define detection acuity

the ability to detect an object / angular size of the smallest visible target

what is the threshold if the chance is 50:50

75%

Define resolution acuity

the ability to resolve the details of an object

Define relative localisation acuity

ability to localise relative features of an object

Define recognition acuity

the ability to recognise an object

factors affecting spatial resolution

1. optics of the eye and the quality of the retinal image

2. the structure and function of the retina

3. capacity of neural pathways

Most clinical tests are based on which type of visual acuity

recognition acuity

Define E₂

the eccentricity at which the foveal threshold has doubled

what factors affect visual acuity

1. refractive error

2. retinal location

3. contrast

4. contour interactions

5. luminance

6. orientation

7. movement of the eyes/target

8. developmental aspects

9. crowding

emmetropia

perfect eye sight( 20/20, 6/6 )

optical quality is not diminished and the focus is conjugate with the retina

where in the eye is visual acuity the best

the fovea

define contrast

the ratio of the increment of light luminance and is referred to as the weber fraction

what is the formula for contrast

luminance of the object / luminance of the background