How We See Flashcards
What is refraction?
Bending of light when it passes from one optical medium to another
What is accommodation?
Changes occurring in both eyes as it changes focus from a distant to a close object
What is refractive errors?
When there is a mismatch between how much we bend light rays
How does a sharp image form on the retina?
Light waves from an object bend at the cornea
Then bend more at the lens to form a clear image on the retina = refraction
What happens when an object moves closer?
Eye needs more bending power to focus = lens becomes thicker = more powerful = clear image
What 3 things happen simultaneously and make up accommodation?
- Lens changes shape (thicker + more spherical)
- Pupil constricts
- Eyes converge
What is the process of the lens thickening in accommodation?
Ciliary muscle contracts = makes ciliary body bulge Space in middle decreases Suspensory ligaments become lax Lens is no longer under stretch Lens = thicker
What is the pupillary constrictor?
(sphincter pupillae)
Concentric muscle around border of pupil
Parasympathetic innervation (CN III)
What muscles are used in convergence of the eyes?
Medial rectus muscles of both eyes
What is myopia?
Short-sightedness
What is hyperopia?
Long-sightedness
What is astigmatism?
Non-spherical curvature of cornea (or lens)
What is presbyopia?
Long-sightedness of old age
What does it mean if someone is an emmetrope?
They have perfect vision
What causes myopia?
Eyeball too long
When cornea + lens bend light rays they form the image in front on the retina
What are symptoms of myopia?
Headaches
Not being able to see distant objects
Infants/preverbal children - divergent squint
Toddlers - loss of interest in sports/people and more interest in books/pictures
How is myopia corrected?
Bending power needs to be decreased Biconcave lenses (glasses, contact lenses or laser eye surgery)
What causes hyperopia?
Eyeball too short or cornea + lens too flat
Image is formed behind retina
Using all power to see things far away
What are the symptoms of hyperopia?
Eyestrain after reading/working on a computer Convergent squint (children/toddlers) Squint must be corrected quickly to prevent lazy eye
How is hyperopia corrected?
Biconvex glasses (able to rest accommodative power)
Contact lenses
Laser eye surgery
What causes astigmatism?
Surface has different curvatures in different meridians
Bending of light different on opposite axis
Image formed is hazy
How is astigmatism corrected?
Special glasses = cylindrical glasses
Curved only in 1 axis
Laser eye surgery
Special contact lenses (toric lenses)
What causes presbyopia?
Lens get less mobile/elastic with age
When ciliary muscle contracts, it isn’t as capable as before to change shape
Usually in 5th decade of life
How is presbyopia corrected?
Biconvex “reading” glasses
