Basic Structure of Human Eye - VORBV (Week 4)

radius of curvature of front corneal surface

r1= +7.7mm

radius of curvature of back corneal surface

r2= +6.8mm

corneal thickness

0.5mm

corneal diameter

12mm

refractive index of cornea

1.376

refractive index of aqueous

1.336

as light travels through the system, it is refracted by the back surface of the cornea into?

the anterior chamber

what is the anterior chamber made up of

aqueous humour

what is the depth of anterior chamber

3mm

power of front surface of cornea

1.376 take away 1

power of back surface cornea

1.336 take away 1.376

diameter of pupil can vary in sizes between

1-8mm

what is the purpose of the pupil

control the amount of brightness and the optical quality of light entering eye

pupil size in dark

5-8mmp

pupil size in light

2-5mm

consensual pupil response

shining a light in one eye causes the other eye to have a response

when is pupil size also reduced

looking at something close up

name 2 clinical conditions that may affect pupil size

ocular drugs (mydriatic and miotic eye drops) and emotions

what does the crystalline lens provide a mechanism for

focusing at different distances

presbyopia

lens no longer able to produce accommodation

diameter of crystalline lens

9mm

radius of anterior surface of crystalline lens

+10mm

radius of posterior surface of crystalline lens

-6mm

thickness of crystalline lens

3.6mm

refractive media of crystalline lens

1.416

definition of accomodation

increase in power of crystalline lens that occurs to allow focus of the eye to change

what age does accommodation become less flexible

40

what does accommodates mean

when the eye alters its power

what is an increase in power known as

positive accomodation

what is a decrease in power known as

negative accommodation

how many layers is the retina divided into

10

name the retina layers

1.Pigment epithelium

2.Receptors rod and cones

3.Outer limiting membrane

4.Outer nuclear layer

5.Outer Plexiform layer

6.Inner nuclear layer

7.Inner plexiform layer

8.Ganglion cell layer

9.Optic nerve fibres

10.Inner limiting membrane

what does the energy contained in light that is incident on the retina intitiate?

chemical reaction in the retinal receptors (rods and cones) generating a neural discharge which is then passed to the brain

name the 2 photoreceptors on the retina

rods and cones

are rods and cones evenly distributed

no

central retina (fovea)

high retinal resolution densely packed cones

surrounding retina

larger more spread out cones and rods; lower retina resolution

what pattern does the central retina have

honeycomb, hexagonal shape

what are cones responsible for

vision in high ranges of luminance and for colour vision

what is the fovea

centre of macula

describe the distribution of cones in the fovea

higher

does the fovea contain rods

no, rod free

the foveolar is entirely ?

rod free (blind spot)

what do rods provide

achromatic vision in low levels of illimitation (scotopic vision)

how many types of colour sensitive photopigments are there in cones

3

how do cones respond

respond with maximum sensitivities in the blue, green and red regions

what are cones most sensitive do

yellow to green (555nm)

what are rods most sensitive to

blue/green (500nm)

what is dark adaptation

coming from a brightly lit environment to a dark environment

describe pupils change when there is a small change of light levels in eye

adjust quickly

what adaptations occur gradually for larger changes in brightness

biochemical and neural

how long does it take for cones to adapt in dark adaptations

7-10 min

how long does it take for rods to adapt in dark adaptations

20-30 min

what is the photopigment that rods contain called

rhodopsin

describe the colour change that rhodopsin gives

purple, orange, yellow, colourlessa

absorption of light causes rhodopsin (purple) to become?

bleached (transparent)

a bleached molecule will spontaneously revert back to?

unbleached state

is cone or rods dark adaptation faster?

cone

what do cones have outer segments of

3 classes of photopigments that bleach when exposed to light (blue, red, green)

refractive index of cornea

1.376

power of reduced eye formula

(n’-n)/r