Flashcards in Visual defects Deck (75)
Why is the pupil black?
Pupil is the opening that allows light to enter the eye; appears dark because of the light absorbing pigment epithelium in the retina.
What does the iris contain and what is its function?
Iris is pigmented to give the “eye’s colour”; contains two muscles to vary the size of the pupil.
Does Cornea contained blood vessels and if not what supports it?
Cornea lacks blood vessels and is nourished by aqueous humour.
What is the Cornea continous with?
The sclera of the eye
What is Conjunctiva?
Conjunctiva is a membrane that folds back from the inside of the eyelids and attaches to the sclera
What controls the movement of the eyeball in the orbit of the skull?
What is the vitreous humour?
Vitreous humour is a viscous jellylike substance that lies between the lens and the retina; it keeps the eye spherical.
What is the fovea?
Is the point of highest visual acuity in the retina, where light can reach photoreceptors directly.
What is the lens attached to and how is it suspended?
Lens is a transparent structure suspended by ligaments (zonule fibres) attached to the ciliary muscles which control the shape of the lens.
What is refraction?
Refraction is the bending of light rays.
When does refraction occur?
Refraction occurs when light passes from one transparent medium (e.g. air) to another (e.g. cornea).
Refraction occurs when light is slowed down as it changes from one media to another.
What occurs when light passess through the cornea?
Light rays that strike the curved surface of the cornea bend so that they converge on the back of the eye.
Light rays that enter the centre of the eye pass straight to the retina
Why does lens also refract light?
The lens also refracts light rays passing through it to produce a sharp image.
How does lens bring close images into focus?
Close images are brough into focus by the lens changing shape (accommodation)
What is the outcome of rounding the lens?
increases the curvature of The lens surface and increases the refractive power.
What changes occur to the lengs with change in age?
The ability to accommodate the lens changes with age.
Accomodation occurs due to what structure?
Accommodation is due to contraction of the ciliary muscles which relieves the tension on the zonule fibres, allowing the lens to become rounder due to its natural elasticity.
How does the lens change its shape?
By the contraction of the ciliary muscles
What is the optic disc?
origin of blood vessels; where optic nerve axons exit eye (blind spot)
What is the route of light and how is it focued?
Light is focused by the cornea and the lens and then passes through the vitreous humour to the retina.
What does the pigmented epithelium contain?
Cells in the pigment epithelium are filled with the black pigment melanin which absorbs any light not absorbed by the retina.
What are the two types of photoreceptors in retina?
Cones – colour system – daylight.
Rods – no colour – low light levels
Absorption occurs in what part of the photoreceptors?
The outer segment contains a stack of membranous disks which contain light sensitive photopigments.
What is the function of photoreceptors?
Photoreceptors transduce light energy into changes in membrane potential.
In mesopic --> twilight what type of photoreceptor is active?
Both rods and cones
What is the pigment in rods called?
How many types of pigments are there in cones?
In each cone there is one of three types of opsins
What is another name for colour blindness?
What is hyperopia?
“farsightedness” – close-up objects = blurry