Visual Optics Flashcards
What is the focal length?
Distance behind a convex lens at which parallel light rays converge
How does distance of an object affect focal length?
If the light source is brought closer to the lens, the focal length increases
What is a diopter?
The refractive power of a lens
The inverse of the focal length
The bigger the number, the stronger the lens
What are the four refractive interfaces of the eye?
Cornea
Aqueous humor
Lens
Vitreous humor
What is the primary function of the lens in eye function?
Accommodation
Who has the full range of accommodation?
Only young children
What is presbyopia?
The decline in ability to accommodate.
The elasticity of the lens decreases with age
What does pupil diameter affect?
Depth of focus
What is depth of focus (field)?
The degree to which objects in front of, or behind, the point of visual fixation remain in focus
Greatest when pupil diameter is smallest
What is the near reflex?
A triad of reflexes that occur when the eyes are fixated on an object and that object is moved closer.
What are the three reflexes part of the near triad?
Convergence of eyes - centers object on fovea
Accommodation - focuses object
Miosis (Pupil constriction) - maximizes DoF
What is the Argyll Robertson pupil?
Refers to bilateral small pupils that constrict when a patient focuses on a near object, but do not constrict when exposed to bright light.
Strongly associated with neurosyphilis
How is pupil dilation and constriction controlled?
Parasympathetic regulation of the ciliary muscles
Increased parasympathetic firing to constrict the pupil, decreased firing to dilate
What is an emmetropic eye?
A normal eye
Considered to be normal when parallel rays of light from distant objects are in sharp focus on the retina when the ciliary muscle is completely relaxed
What is hyperopia?
Farsightedness
Caused by an eyeball that is too short, or occasionally a lens system that is too weak
