Visual System Flashcards
What type of vision loss results from damage to the optic chiasm?
Loss of peripheral vision (bitemporal hemianopia).
What happens with damage posterior to the optic chiasm?
Loss of the same side of the visual field in both eyes (homonymous hemianopia).
What are the three layers of the eye?
Fibrous (cornea, sclera)
Vascular (iris, ciliary body, choroid)
Neural (retina)
What is the function of the fovea?
It provides the highest resolution vision by focusing the visual target.
What are conjugate eye movements?
Movements where both eyes move in the same direction (e.g. vestibulo-ocular, optokinetic).
What are disconjugate eye movements?
Movements where the eyes move in opposite directions (e.g. saccade, smooth pursuit, vergence).
Name the six extraocular muscles.
Superior rectus, inferior rectus, medial rectus, lateral rectus, superior oblique, inferior oblique.
What cranial nerve innervates most of the extraocular muscles?
CN III – Oculomotor nerve.
What muscle does CN IV (Trochlear) innervate?
Superior oblique.
What muscle does CN VI (Abducens) innervate?
Lateral rectus.
What is miosis?
Pupil constriction (parasympathetic control).
What is mydriasis?
Pupil dilation (sympathetic control).
What parasympathetic nerve controls pupil constriction?
CN III – Oculomotor nerve.
What is the purpose of lens accommodation?
To focus on near objects.
What are the three components of accommodation?
Pupil constriction
Lens thickening
Convergence of eyes
What is the most common cause of blindness worldwide?
Cataract.
What causes cataracts?
Lens clouding from protein deposition and aging.
What are risk factors for cataracts?
Aging, diabetes, trauma, UV light, smoking.
What is a major risk factor for glaucoma?
Raised intraocular pressure.
Name two tests used in glaucoma diagnosis
Tonometry and visual field testing (perimetry).
Name one drug class used to treat glaucoma.
Beta-blockers (also: prostaglandin analogues, miotics, CA inhibitors).
What is the main function of rods?
Night (scotopic) vision; highly light-sensitive.
What is the main function of cones?
Day (photopic) vision; colour and detail detection.
Where is visual acuity highest in the retina?
Fovea (central part of macula).
What cone types do humans normally have?
L (red), M (green), S (blue).
What is red-green colour blindness called?
Protanopia = no red cones
Deuteranopia = no green cones
What is the inheritance pattern of red-green colour blindness?
X-linked recessive (more common in males).
What thalamic structure relays visual input?
Lateral geniculate nucleus (LGN).
What type of cells send greyscale/light-dark info to LGN?
Parasol ganglion cells (magnocellular layers).
What cells send colour-opponent signals to LGN?
Midget ganglion cells (parvocellular layers).
What is the function of the primary visual cortex (V1)?
Processes visual information; located in occipital lobe.
How is V1 organized?
Retinotopically – central vision at posterior end, peripheral vision more anterior.
What is the role of the Fusiform Face Area (FFA)?
Specialised for face recognition.
What does the Parahippocampal Place Area (PPA) process?
Visual scenes and places.
What is the Lateral Occipital Cortex (LOC) involved in?
Object recognition.
What is optic ataxia?
Impairment in using vision to guide movements (e.g. grabbing objects).
What is visual form agnosia?
Inability to recognise objects by sight, despite intact vision.
glaucoma treatment drugs? 5
- Beta blockers
- Alpha2-adrenoceptor agonists
- Carbonic anhydrase inhibitors
- Prostaglandin analogues
- Miotics (muscarinic agonists)
What is the order of structures in the visual pathway from retina to cortex?
Retina → Optic nerve → Optic chiasm → Optic tract → Lateral geniculate nucleus → Optic radiations → Primary visual cortex (V1).
Where does the optic tract carry visual information from?
The contralateral visual field (e.g., left optic tract = right visual field).
What is the pupillary light reflex?
Constriction of both pupils in response to light.
What is the afferent limb of the pupillary reflex?
Optic nerve (CN II).
What is the efferent limb of the pupillary reflex?
Oculomotor nerve (CN III) → ciliary ganglion → sphincter pupillae.
What is an Argyll Robertson pupil?
Pupil that accommodates but doesn’t react to light (classically seen in neurosyphilis).
What is an afferent pupillary defect (Marcus Gunn pupil)?
Pupil constricts less when light is shone in the affected eye (seen on swinging light test).
A lesion in the right optic tract would cause…?
Left homonymous hemianopia.
What eye movement deficit would you see with a CN III lesion?
“Down and out” eye + ptosis + dilated pupil.
What is the classic sign of a CN IV (Trochlear) palsy?
Vertical diplopia, worsened when looking down (e.g., reading stairs).
What deficit occurs with CN VI (Abducens) palsy?
Inability to abduct the affected eye (horizontal diplopia).
What are vergence movements?
Disconjugate movements that adjust the eyes for viewing objects at different distances (e.g., convergence when viewing something close).
Which reflex includes convergence, accommodation, and pupil constriction?
The near (accommodation) reflex.
Which cone is responsible for detecting long-wavelength (red) light?
L-cone.
What causes red-green colour blindness?
Absence or dysfunction of L or M cones (X-linked recessive).
Where is the primary visual cortex located?
Calcarine sulcus of the occipital lobe.
What type of information does the magnocellular pathway process?
Motion and broad outlines (greyscale, luminance contrast).
What does the parvocellular pathway specialise in?
Fine detail and colour.
What vision loss is associated with a lesion at the optic chiasm?
Bitemporal hemianopia.
What does damage to Meyer’s loop (temporal lobe) cause?
“Pie in the sky” – contralateral superior quadrantanopia.
What about damage to the optic radiation in the parietal lobe?
“Pie on the floor” – contralateral inferior quadrantanopia.
Which drug class increases aqueous humour outflow and treats glaucoma?
Prostaglandin analogues (e.g., latanoprost).
What do beta-blockers (e.g., timolol) do in glaucoma?
Reduce aqueous humour production.
What does the sympathetic nervous system do to the pupil?
Dilates it (mydriasis).
Which ganglion is involved in parasympathetic innervation to the eye?
Ciliary ganglion.
What is the main cause of painless progressive vision loss in elderly?
Cataract.
What is the primary cause of blindness in diabetic patients?
Diabetic retinopathy.
What is age-related macular degeneration (AMD)?
Degeneration of the central retina (macula), leading to central vision loss.
What is prosopagnosia?
Inability to recognize faces (often due to damage in the fusiform face area).
