Optics: Retinal Image Foramtion Flashcards
Where is retinal image formed?
In the paraxial domain
2 applications for predicting retinal image size:
- The type of optical correction can affect the retinal image size
- Calculation of risks from radiation damage in the eye
If the difference in magnification between the two images is significant than more than 10%…
The brain may have difficulty fusing the two images into one for binocular vision
Term for when the brain has difficulty fusing the two images into one:
Aniseikonia
VA examination tests only a ______ wide patch of retina at the fovea center
25 micron
Two equations to find h’:
h’ = h(l’/l)
h’ = x tan(theta)
How to convert 5 mins of arc into degrees?
Take the number of mins given and divide that number by 60
Ex:
5/60 =0.0833
4/60 =0.0667
Etc..
Objects angular subtense is the…
Size of the object and its distance from primary nodal point (N)
An object that subtends 1 degree at the primary nodal point will have a retinal image size of:
Tan (1 degree) x 16.7 = about .3mm
20/20 snellen letter E subtends ___ min of arc
5
Retinal magnification factor
0.3mm/deg
Distortion =
Variation in magnification as a function of field angle
Assume that the retinal magnification is constant for all…
Retinal eccentricities
In an actual eye magnification _______ with field angle
Decreases
Impact of distortion on our vision
-image on retina is minefield more in periphery
-our peripheral vision doesn’t seem to notice the distortion intrinsic to the eye
Impact of distortion of retinal imaging:
-image if retina magnified more in periphery
-how much distortion is in clinical fundus photos?
For 22.5 degree retinal photo, there is distortion in theperiphery making the image __% larger compared to center of the image
3% larger
