Pupillary Optics Flashcards
What is the optical system that has no power?
Iris
Iris forms the ______ of the eye to block undesirable light
Aperture stop
The opening of the aperture stop is known as the _____
Pupil
What are the two muscles that control the pupil
- sphincter pupillae
- dilator pupillae
What muscle constricts the pupil
Sphincter pupillae
What muscle dilates the pupil
Dilator pupillae
What division of the nervous system controls the pupilillary muscles
ANS
What is the pupil designed to do
- prevent undesirable light from getting to the lens/retina
- absorb light
- have melanin granules in stroma and epithelium (brown)
- has a unique biometrics ID system
What is the most reliable biometric ID systme?
Iris
Where are the melanin granules in people with brown eyes
Stroma and epithelium
Where are the melanin granules in people with blue eyes?
Only in the epithelium
Job description of the iris
- Stops undesirable light (pigmented tissue)
- Regulates retinal illuminance (pupil size and retinal layers)
- Controls DoF (smaller pupil)
- Helps in controlling retinal blur (diffraction and aberrations)
- Help design optical instruments (entrance and exit pupil)
Image of the aperture stop formed in object space (image formed by the cornea)
Entrance pupil (E)
Image of the aperture stop formed in the image space (image formed by the lens)
Exit pupil (E’)
___________ is an erect, virtual Aimee formed 0.5mm in front of the real pupil
Entrance pupil
Calculate the entrance pupil location where F=43D, n=1.336; n’=1, I=-3.6mm (anterior chamber depth)
L=nl
1.336/-.0036=-371.11D
L’=L+F
-371.11D+43D=-328.11D
I’=1/L’
1/-328.11D=-0.00304
Mag
L/L’
-371.11D/-328.11D=1.13
Entrance pupil appears larger than it really is, and is 13% larger than real pupil
Entrance pupil is erect, virtual image that is located 0.5mm in front of the actual pupil
Exit pupil is 0.07mm behind the real pupil and 3.1% larger than th real aperture
What is the most important factor affecting pupil size?
The level of illumination
What is the range of hte pupil diameters
2-8mm
How does the pupil respond to increase in illumination?
Decrease in pupil size
What is the latency of the pupil with low illumination
0.5 secs before dilation
Latency of pupil with increase illumination
Decrease to 0.2 or 0.3secs for constriction
Pupil centration
Decentered by 0.5mm nasally relative to the optical axis
Pupillary response and field of view
- more response, if light distribution in the cenrealt visual field
- less response, if light distribution in the peripheral visual field
Pupil response to changed in light level is mediated by what
Both rod and cone photoreceptors
-pupil doesn’t directly respond to light, the retina reacts and sends a signal
