Eye Physiology Flashcards
Which nerves control the pupillary reflex?
Cranial nerves II and III.
Autonomic nervous systems
Stimulation of the parasympathetic nerves ________ the pupillary sphincter muscle, thereby ________ the pupillary ________.
Stimulation of the parasympathetic nerves excites the pupillary sphincter muscle, thereby decreasing the pupillary aperture (miosis)
Sympathetic stimulation _______ the pupil.
Dilates (mydriasis)
Direct Response
Pupil constricts when being illuminated.
Consensual Response
Pupil constricts when contralateral pupil is illuminated.
Accomodation
- Response to looking at something moving toward the eye.
- The ability to adjust the refractive power of the lens.
Afferent pupillary defect
Decreased direct response caused by decreased visual function in one eye. The affected pupil will DILATE in response to light.
Why do we have eyelashes?
Primarily to keep sweat out of the eye.
3 things that can block pupillary reflex.
Alcoholism, Encephalitis, CNS Syphilis
Which muscles does CN III (occulomotor) innervate?
Medial rectus: Turns medially
Superior rectus: Elevates eye and rolls upward.
Inferior rectus: Depresses eye and rolls down
Inferior oblique: Elevates eye and turns lateral
Which muscle does CN IV (trochlear) innervate?
Superior oblique: Turns the eye down and out.
Which muscle does CN VI (Abducens) innervate?
Lateral rectus: Moves eye laterally
Conjugate Gaze
Refers to the use of both eyes to look steadily on one direction.
Saccadic Eye Movements
Consists of small jumping movements that represent rapid shift in conjugate gaze orientation.
Hippus
A reflex response of the pupil to light that is completely normal. Do not confuse with afferent pupillary defect.
Nystagmus
The sequence of slow ocular rotation, a saccade, and slow rotation.
T of F: The lens of the eye is extremely vascular.
False, the lens is Avascular
The lens is ______ for distance vision.
Flattened. Sympathetic input relaxes the ciliary muscle, tightening the ciliary zonule and flattening the lens.
The lens _______ for close vision.
Bulges. Parasympathetic input contracts ciliary muscle, loosening the ciliary zonule, allowing the lens to bulge.
When light rays strike an interface that is perpendicular to the beam, rays ______ deviate from the course.
Do not.
Which CN in in control of accommodation of the lens?
Parasympathetic division of CN III is in control.
Suspension of the lens.
Occurs via 70 suspensory ligaments that attach radially around the lens. The hold constant tension of the lens, and if they were not there, the lens would assume a spherical shape.
Meridional and circular fibers make up the?
Ciliary muscle
What happens to the lens when the ciliary body contracts?
The ligaments relax, and the lens becomes more spherical, which is good for close vision.
What controls the ciliary muscle?
Parasympathetic nerve signals from CN III.
T of F. Sympathetic stimulation plays a large role in accommodation.
False, sympathetic fibers play almost no role in accommodation.
Emmetropia
Normal vision.
Presbyopia
Old Eyes. As a person grows older: -The lens grows larger and thicker -Lens becomes less elastic -Ability of lens to change shape decreases. -Less power for accommodation
Hyperopia
Far-Sightedness (distant objects are seen clearly)
-Eyeball is too short so focal point is behind the retina.
Myopia
Near-sightedness (Can see close objects)
- Eyeball is too long so focal point is in front of retina.
- The ciliary muscle can’t relax enough to extend the focal point any further.
Which type of lens will correct myopia?
Concave (bowtie)
Which type of lens will correct hyperopia?
Convex (oval)
Astigmatism
This is an abnormally shaped lens. Should be a golfball, but is an egg. No degree of accommodation can correct the error.
Rods
Black and white vision
Cones
Color vision.
There are blue, green and red cones that are specific for each of those colors.
Disease of peripheral retina affects _____ cones.
Blue
Diseases of the more central retina affect _____ and _____ cones because?
Red and Green because blue cones are not present in the central fovea.
Males are more frequently affected with which color blindness?
Red, Green and Red/Green
Moving Parallax
Relative distance of an object can be determined by the extent to which they move when the person moves their head back and forth. The farther it is, the less it moves across the retina.
Stereopsis
Binocular vision. The distance of an object will determine the relative locations on the retina for each eye.
-The closer, the further separated on the retina.
Aqueous Humor
Intraocular fluid that is in front of the lens.
-freely flowing fluid.
Vitreous Humor
Intraocular fluid that lies between the posterior surface of the lens and the retina.
-Gelatinous mass, slow diffusion and very little fluid flow.
Role of the intraocular fluid
Maintains sufficient pressure to keep eyeball distended.
What forms the aqueous humor?
The ciliary body, at 2-3 microliters/minute.
Average Intraocular Pressure
12-20mm Hg
Glaucoma
One of the most common causes of blindness.
-Intraocular pressure becomes pathologically high (as high as 60-70 mmHg)
-Generally results from an increase in outflow resistance.
Tx: Decrease production or increase absorption
