The Concept of Vision Flashcards
Describe the rays of light which hit the eye when looking at far away objects?
Only parallel rays hit the cornea. No light bending is required and field of vision is infinite
What happens when looking at objects up close?
Divergent rays hit the cornea and the lens needs to bend the rays to form an image
Explain Accommodation?
The ability to focus far away as well as up close
What occurs when the ciliary muscle contracts?
The lens bulges and the space in the middle decreases
What happens when the suspensory ligament relaxes?
Pressure on the lens decreases and it becomes more spherical which allows for focusing close up
Lens thickening allows for what action?
Focusing on objects up close
Parasympathetic action on the lens by which nerve permits the action of lens thickening?
The occularmotor nerve (CNIII)
Name the three steps of accommodation?
1 Lens thickens 2. Pupil Constricts 3. Eyes converge
What role does the pupil play in accommodation?
It constricts to allow only a few rays through, allowing for sharper focus
What occurs in the convergence step of accommodation?
The eyes turn to look at the object by using the medial rectus
What is myopia?
farsightedness. Occurs because eyeball is slightly longer so the image will form slightly in front of the retina. Far away = hazy
What is hyperopia?
nearsightedness. Occurs because eyeball is too short or the cornea and lens is too flat. Near = hazy
What is astigmatism?
Close and distant objects = hazy as surface has different curvatures in different meridians
What causes presbyopia?
Lens is less stretchy
What happens when the right optic nerve is damaged?
Blindness in one eye,
What happens when the optic chiasma is disrupted in the middle?
bitemporal hemianopia
What is refraction?
The bending of light to form a clear image on the retina
When does the lens thicken?
As objects become closer to increase refraction
How does the lens thicken?
Ciliary muscle contracts to make ciliary body bulge, space in middle decreases, suspensory ligaments relax and lens is no longer under stretch so lens can thicken
What muscle is used for convergence?
Medial rectus
Which rectus muscle is thicker in the eyes of humans?
The medial rectus
Define presbyopia
Long sightedness of old age
What is perfect vision also known as?
Emmetropia
What are symptoms of myopia?
Headaches, unable to see distant objects, divergent squint
How is myopia corrected?
Biconcave lenses
What are symptoms of hyperopia?
Symptoms of eyestrain, convergent squint
How is hyperopia corrected?
Biconvex lenses
How is an astigmatism corrected?
Toric lenses or laser eye surgery
What is phototransduction?
The conversion of light energy to an electrochemical response by rods and cones
What do rods and cones activate?
Optic nerve neurones
How does bleaching of the visual pigment result in phototransduction?
Phototransduction cascadde
What role does Vit A play in visual pigment?
Visual pigment regeneration
What does a vitamin A deficiency lead to?
night blindness and abnormal corneal epithelium or conjunctiva
Where do medial fibres of the optic nerve cross over to the opposite side?
The optic chiasm
Where do fibres of the optic tract synapse?
Lateral Geniculate Body of the Thalamus
What happens if the right optic tract is damaged?
Contralateral Homonymous Hemianopia
What happens if the optic radiation is damaged?
Contralateral homonymous hemianopia
What do intrinsic muscles of the eye control?
Pupil diameter and lens curvature
What do extrinsic muscles of the eye control?
Eye movement
Where do the recti muscles arise from?
The apex of the orbit
Where does the sup. oblique muscle arise from?
The roof of the orbit posteriorly
Where does the inf. oblique arise from?
The roof of orbit anteriorly
What is the function of the LPS?
to ELEVATE THE UPPER EYELID
What do the obliques do when the eye is adducted?
Elevate/Depress the eye
What do the recti do when the eye is abducted?
Elevate/Depress the eye
What is the action of the MR?
Primary - ADDUCTION
What is the action of the LR?
Primary - Abduction
What is the action of the SR?
Primary - Elevation
Secondary - Adduction
Tertiary - Intorsion
What is the action of the IR?
Primary - Depression
Secondary - Adduction
Tertiary - Extorsion
What is the action of the SO?
Primary - Intorsion
Secondary - Depression
Tertiary - Abduction
What is the action of the IO?
Primary - Extorsion
Secondary - Elevation
Tertiary - Abduction
What is esotropia?
Convergent Squint
What is extropia?
Divergent squint
What are the consequences of having a squint?
Amblyopia - lazy eye
Diploplia
What are the ciliaris and constrictor pupillae innervated by?
Parasympathetically innervated by the CNIII
Where is the ciliaris located?
Ciliary body
Where is constrictor pupillae located?
in iris at pupillary border
Where is dilator pupillae located?
Iris
What occurs at times of increased illumiation?
Parasympathetic innervation causes pupils to constrict
What occurs at times of decreased illumination?
Sympathetic innervation causes pupils to dilate
Where do impulses of light travel once they fall on the retina?
Optic nerve -> optic chiasm -> optic tract –> midbrain
Where do signals from light transduction go when the reach the EWN?
EWN –> preganglionic system in orbit –> ciliary ganglion –> constrictor pupillae
