vision Flashcards
the iris - amount of light
donut shaped band of tissue which regulates the amount of light that reaches the retina by adjusting the size of the pupil
Pupil dilation/ constriction
Dilation - the iris relaxes - sensitivity is improved, acuity is poor
Constriction - iris contracts , acuity is improved
the cornea- focusing the image
covers the front of the eye and works with the lens to focus incoming light
the lens - focusing
held in place nu suspensory ligaments called zonules.
Changes shape by a process of accommodation
Accommodation - the lens
A rounder thicker lens - bends light more (near objects)
A flatter lens- bends light less (far objects)
The retina - transduction
Thin sensitive tissue at the back of the eye, contains a layer of photoreceptor cells.
The macula - transduction
the centre of the retina is the macula
- VERY high concentration of photoreceptor cells
The fovea
The centre of the macula- sharpest vision.
- no rods only cones
- blood vessels and other cells are displaced to the sides
Rods
best in dim light
Very few around the fovea - why stars disappear when you look directly at them.
The optic disc - the blind spot
Where GANGLION cell axons leave the retina
there are no photoreceptors
the brain uses completion to fill in the gap.
the sclera
white of the eye - protective layer
the choroid
a layer of tisse between the retina and sclera
contains many blood vessels and is critical for providing o2 and glucose to the retinal cells
tapetum lucidum
animals have a reflective tusse
What are the three layers of the retina
- photoreceptors
- bipolar cells
- retinal ganglion cells
photoreceptors
Rods and cones.
Rods: Rhodopsin inactive, sodium channels are kep open by cyclic GMP , cell is depolarised. Rods release glutamate
Cones: Rhodopsin activates, cyclic GMP is broken down, sodium channels close, cell is hyperpolarised, glutamate reduced.
what is scotopic vision
dim light (Rods)
do rods have high or low convergence
rods have high convergence: Many to 1 = results in poor acuity but good sensitivity
do cones have high or low convergence
Cones have low convergence: 1 to 1= results in good acuity but poor sensitivity.
deuteranomoly
form of colour blindness where the sensitivity of the green cones is shifter towards the red.
saccades
the eye continually scans the visual field so information can be integrated
bipolar cells
process input from the photoreceptors and output to retinal ganglion cells
allow some low level signal processing (aided by interneurons: horizontal and amacrine cells)
photoreceptors converge via bipolar cells to retinal ganglion cells (few to 1 for cones, many to 1 for rods)
retinal ganglion cells
Facilitate the detection of edges.
Either on centre off surround or off centre on surround= This means that edges can be detected.
Horizontal cells
mediate the detection of mach bands.
when activated they inhibit other cells which creates a bigger difference between areas of high and low illumination
