(7.2) Vision Flashcards
Briefly describe the layers that light have to travel through before being detected by photoreceptors. Each briefly describe its function.
1) Cornea - a refractive medium
2) Aqueous Humerus - controls intraocular pressure
3) Lens - contractions to allow accommodation by refracting light onto retina
4) Vitreous Humerus - holds retina in place
Briefly describe the process of accommodation to adjust near vision.
1) Afferent info via Retinal Ganglion -> Optic Nerve -> Optic Chiasma -> Optic Tract -> Lateral Geniculate Ganglion -> Radiation -> medial Occipital Lobe
2) synapse BILATERALLY at Edinger-Westphal Nucleus with PNS pre-ganglionic fibres
3) PNS preganglionic fibres travel with Optic N (CN III)
4) synapse at Ciliary Ganglion with PNS post-ganglionic fibres, stimulating:
- Medial Rectus -> convergence of both eyes
- Constrictor Pupillae -> constricted pupils
- Ciliary Muscles -> fatten lens
What components are involved in accommodation to adjust close vision.
REMOVAL of PNS stimulation, removing:
- convergence of eyes
- pupil constriction
- fat pupils
What allows the consensual response in the contralateral eye in a light reflex & accommodation.
bilateral synapse at Edinger-Westphal nucleus
What is Hypermetropia? What are the possible causes?
Far sighted due to image focuses BEHIND retina, possible causes:
- weak lens -> impaired dioptric strength
- eyeballs too small
What is Myopia? What are the possible causes?
Short sighted due to image focuses IN FRONT of retina, possible causes:
- eyeballs too long causing normal dioptric strength too high
What is Presbyopia?
Old sighted due to lens losing its elasticity, impairing dioptric strength , becoming far sighted
e.g. those who are short sighted in young life will improve over age
What visions do Rods responsible for? How do they relay their stimuli to postsynamptic fibres?
- Light sensitive -> night vision
- Convergence of several rod cells to one bipolar neurone
What visions do Cones responsible for? How do they relay their stimuli to postsynamptic fibres?
- Colour sensitive, day vision
- One to one synapase with bipolar cell
What is Fovea? In terms of vision, how can you describe its quality, explain.
- The area where Cones concentrated at
- Takes up the biggest area in Lateral geniculate nucleus
- Maximal acuity
Which structures detect the left visual field?
- Nasal hemiretina of left eye
- Temporal hemiretina of right eye
What is the most common cause of Non-homonymous Bilateral Hemianopia? Explain why
Pituitary gland pathology e.g. Pituitary Adenoma
- Optic Chiasma located anterior to Pituitary Gland
- Damage axons from Nasal Hemiretinae from both eyes cross here
What visual impairment may a lesion at Optic Chiasma cause? Explain why
- Tunnel Vision = Non-homonymous Bilateral Hemianopia
- Damage axons from Nasal Hemiretinae from both eyes, which cross at Optic Chiasma
What do you call it when there’s a visual field defect that is surrounded by normal visual fields? What may be the possible causes?
Scotoma
- Non-pathological: Optic disc, where no photoreceptors located, retinal axons compose into Optic N exits
- Pathological: Retina/Optic N pathologies e.g. Vascular blockage, Multiple Sclerosis
What structure do most of retinal ganglionic axons terminate? Where is it found?
Lateral Geniculate Nucleus found in Thalamus
What are the two pathways in Optic Radiation? What types of vision does each responsible of?
- Magnocellular: detecting fast moving stimuli
- Parvocellular: detecting colour and acute vision
What visual defect may result from a lesion at Right Optic Tract?
Homonymous Left Hemianopia
What visual defect may result from a lesion at Left Geniculocalcarine Tract?
Homonymous Right Hemianopia
Describe the pathway of Geniculocalcarine tract that carries fibres from the Superior retina.
1) arise from Dorsomedial area
1) through Parietal Lobe
2) directly via Internal Capsule
3) enters Visual cortex in Medial Occipital Lobe
Describe the pathway of Geniculocalcarine tract that carries fibres from the Inferior retina.
1) arise from Ventrolateral area
2) through Temporal Lobe
3) loops around Meyer’s Loop of Lateral Ventricles
4) via Internal Capsule
5) enters Visual cortex in Medial Occipital Lobe
What visual defect may result from a lesion at Right Meyer’s Loop of Lateral Ventricles?
Superior Left Homonymous Quadratanopia
What visual defect may result from a lesion of Geniculocalcarine Tract at Left Parietal Lobe?
Inferior Right Homonymous Quadratanopia
What visual defect may result from a lesion at Visual Cortex receiving Left Geniculocalcarine Tract from superior retina?
Inferior Right Homonymous Quadratanopia + Macular sparing
Suggest 3 ways causing complete right side vision.
Pathologies in Left Eye or Left Optic Nerve:
- Enucleation (eyeball removal) of the left eye
- Left Optic Neuritis
- Trauma
Describe the role of Superior Colliculus in vision.
- Receives inputs from Optic tracts -> orientate eyes towards stimuli
- Where Tectospinal tract arise -> allows head responds to visual stimuli by neck muscle movements
What is located at the centre of retina?
Macula, with Fovea at its centre
