Flashcards in Vision 1 Deck (34):
what is refraction?
Bending of light when it passes from one optical medium to another
how does a sharp image form on the retina?
Light waves from an object bend at the cornea, bend some more at the lens to form a clear image on the retina.
what is the bending of light waves is called ?
what occurs to the lens when an object comes closer?
lens becomes thicker & hence more powerful
The changes occurring in both eyes as it changes focus from a distant to a close object is called what?
what 3 things happen simultaneously & comprise accommodation?
Lens changes shape (becomes thicker & more spherical)
how does the lens become thicker?
Ciliary body contraction (parasympathetic)
Suspensory ligaments become lax
Lens is no longer under stretch
how do we sharpen our focus?
the pupil constricts to allow only a few rays (those from the object) to pass through
what is the muscle that allows pupil to constrict?
Pupillary constrictor (sphincter pupillae)
what is convergence?
our eyes have to turn in to look at the object up close
what muscle do we use to converge?
medial rectus muscles of both eyes (IIIn of both sides)
what is the medical term for short-sightedness?
what is the medical term for long-sightedness?
what is Astigmatism?
non-spherical curvature of cornea (or lens)
what is Presbyopia?
long-sightedness of old age
what is emmetropia?
Close objects look clear, distant objects appear hazy
light focuses in front of retina
what is the most common cause of myopia?
eyeball too long
So the cornea + lens, when they bend rays of light, make the image to form IN FRONT OF the retina. So far off objects not seen clearly.
(Basically “bending power” is too much for eyeball)
why can people with myopia still see clearly when objects are close?
“bending power” actually comes into use. The image is formed on the retina without needing to increase curvature of lens.
what are symptoms of myopia?
Headaches, Complain of not being able to see blackboard/ distant objects.
Infants & preverbal children- divergent squint
child losing interest in class
how do you correct myopia?
Bending power needs to be decreased via biconcave lenses:
Laser eye surgery
Close objects look hazy, distant objects appear clear
light focuses behind retina
what is the most common cause of hyperopia?
Eyeball too short or cornea + lens too flat
distant object formed behind retina-accommodative power used to make lens thicker. allowing image to form on retina.
When seeing closer objects, more and more power used until ultimately, lens power is all used up!
what are symptoms of hyperopia?
Symptoms of eyestrain after reading etc
Convergent squint in children/ toddlers
how do you correct hyperopia?
Biconvex glasses alleviates use of glasses for focussing distant objects and ‘rests’ the accomodative power
Laser Eye surgery
(correction with glasses/lenses to preserve vision in both eyes and prevent a “lazy eye”)
Close and distant objects appear hazy
cornea surface has different curvatures in different meridians
how does the variance in the two axises affect how the image formed on the retina
bend the light in two different ways so get more than one image
how do you correct Astigmatism?
special glasses – called cylindrical glasses (which are curved in only one axis).
Laser eye surgery can also be used to correct the defect.
special contact lenses called toric lenses.
With age the lens gets less mobile/elastic.
So when the ciliary muscle contracts, it is not as capable as before to change shape.
So seeing near objects starts to become difficult needs glasses to read.
what is integrated into cell membrane of rods and cones?
visual pigment rhodopsin in rods and cone opsins S, M and L in cones
How does bleaching of the visual pigment result in phototransduction?
What role does Vitamin A play in the visual pigment?
visual pigment regeneration
vitamin A deficiency can cause what problem with vision?
Vitamin A is also essential for all healthy epithelium. So conjunctiva and corneal epithelium are also abnormal.