8.4. Physiology of vision. Flashcards
I. Structure of the eye
3A. Where can you find aqueous humor?
The anterior and posterior chambers of the eye maintain a circulation of aqueous humor fluid that is produced by the ciliary body and drained
through Schlemm’s canal at the corneo-scleral junction
I. Structure of the eye
3B. What is the role of aqueous humor?
Aqueous humor is necessary to give nutrients to the lens and cornea, as well as to create refractive power for the eye
I. Structure of the eye
3C. What happen if there is a problem in the draining of the aqueous humor
Any problem that occur in the draining of the aqueous humor can result in glaucoma
-> in which the intraocular pressure increases and eventually presses on the optic nerve, causing blindness
I. Structure of the eye
4A. What does the middle vascular layer include?
The vascular coat of the eye includes the ciliary body, choroid and iris
I. Structure of the eye
4B. What are the features of the choroid (Middle vascular layer)?
The choroid is the most vascular part of the body, and proportionally has a higher
blood + oxygen supply than even the kidneys
I. Structure of the eye
4C. Describe the oxygen saturation of the vascular coat?
The oxygen saturation of the vascular coat is 90%, while the retinal artery is only 45%
-> but even then, the eye is always on the verge of partial hypoxia (as indicated by the amount of lactate found in the aqueous humor)
II. Image formation of the eyes
1. What is the image formation based on?
The image formation is based on the combined refractive power of the cornea, aqueous humor, lens and vitreous body (refractive power – D = 1/focal length)
II. Image formation of the eyes
2. Where does refractive power come from?
The majority of the refractive power comes from the cornea, but the lens provides a refractive power that can be adjusted
II. Image formation of the eyes
3. Explain the properties of convex lens
The refractive power of all these layers combined acts as a convex lens that produces an inverted image on the retina for visualization
II. Image formation of the eyes
4. What is the role of lens and ciliary muscles in image formation?
- Since the majority of the refractive power of the eye is given by the cornea, the lens is meant to tune the eye so that ideally, the inverted image is projected perfectly on the retina.
- The ciliary muscles contract or relax to adjust the lens according to what the eye is looking at and how far away it is => accommodation (compensation for the distance of the object).
II. Image formation of the eyes - Accommodation
5A. Describe the accommodation when viewing at a distant object
When viewing at a distant object => lens must be flat (↑ focal length)
- The ciliary muscles are relaxed
- Zonular fibers are tightened
- Lens is flattened
II. Image formation of the eyes
5B. Describe the accommodation when viewing at a close object
When viewing at a close object -> lens must be more round (↓ focal length = ↑D)
- Ciliary muscles are contracted
- Zonular fibers are relaxed
- Lens is contracted -> reduced focal length -> clear view of close object
III. The retina
1. What is retina?
The retina is a multi-cellular layered part of the eye that detects light and sends this message through the optic nerve to the CNS to process these signals into the actual image that you are looking at.
III. The retina
2. What is retina made up?
The retina is made up of multiple neurons in a circuit as well as glial cells and a pigmented epithelium.
III. The retina
3A. What are Müller cells?
Long glial cells that stretch almost the entire length of the retina
III. The retina
3B. What are the 6 functions of Müller cells?
- Function to maintain the EC environment by regulating K+-levels
- Uptake of neurotransmitters
- Remove debris
- Store glycogen for energy
- Form an electrical insulation
- Provide protection of the neurons