Case 21- Eye and questions

Question 1

Projections of the retinal ganglion cells (RGC)

Answer 1

The retinal ganglion cell (RGC) axons project via the optic nerve, chiasm and tract to terminate in the lateral geniculate nucleus of the thalamus. They are functionally classed as either parvocellular or magnocellular. The parvocellular RGC’s give information regarding the specific detail of vision e.g. colour. The magnocellular RGC’s have information about shape and movement.

Question 2

Parvocellular or Magnocellular pathway

Answer 2

This is important when the information reaches the primary visual cortex which is located in the occipital lobe. It sits on either side of the calcarine sulcus and is known as V1. Within the cortex, there are cortical columns that receive information from either the parvocellular or magnocellular pathways.

Question 3

The where pathway

Answer 3

Neurones from V1 project to V2, V3 and V5.
Dorsal pathway, to the parietal region
This is an extension of the magnocellular pathway processing shape, movement and motion.

Question 4

The what pathway

Answer 4

Neurones from V1 project to V2 and V4.
The ventral stream, to the temporal region
This is an extension of the parvocellular pathway for the analysis of details.

Question 5

Akinetopsia

Answer 5

Caused by a lesion of the V5 area
Akinetopsia causes a patient to experience an impaired perception of motion. An object may jump from one position to another.
This could cause many difficulties, one example being that it may be hard to know when to cross the road as a car may appear to be a long way in the distance and then jump to its actual position close by.

Question 6

Prosopagnosia

Answer 6

The inability to recognise faces.
The medial temporal lobes have a record of faces (it is right-side dominant).
Damage to the temporal lobe or ventral stream from the visual cortex can cause this condition.

Question 7

Blindsight

Answer 7

This is an extremely rare phenomenon.
It can occur after damage to the occipital lobe e.g via a stroke.
A patient becomes cortically blind- i.e. there is no conscious awareness of sight as the primary visual cortex is damaged.
The rest of the visual pathway is still intact and the information processing can be taken over by other areas of the brain.
This means patients with blindsight cannot see but can walk down a corridor avoiding objects.

Question 8

Lesions in the L optic nerve

Answer 8

Monocular visual loss

Question 9

Lesions in the optic chiasm

Answer 9

Bitemporal hemianopia- no sight on the temporal side of each eye

Question 10

Lesions in the left optic tract

Answer 10

Homonymous hemianopia- no sight on the right side of both eyes

Question 11

Lesions in the left optic radiation- lateral fibres

Answer 11

Superior quadrantopia- no sight in the upper right

Question 12

Lesions in the left optic radiation- medial fibres

Answer 12

Inferior quadrantopia- no sight in the lower right

Question 13

Occipital visual cortex lesions

Answer 13

Homonymous hemianopia with or without macula sparing.

Question 14

Pupil- afferent and efferent connections

Answer 14

Afferent= Light entering the eye-> pre-tectal area

Efferent=Pre-tectal area->sphincter pupillae

Question 15

Sphincter pupillae

Answer 15

Circular muscle
Parasympathetic
Constriction/miosis

Question 16

Dilator pupillae

Answer 16

Radial muscle
Sympathetic
Dilation/mydriasis

Question 17

A patient has a lesion of CN II on the right side- what is the response of both pupils when light is shone into the right eye?

Answer 17

Right eye- no response

Left eye- no response

Question 18

A patient has a lesion of CN II on the right side- what is the response of both pupils when light is shone into the left eye?

Answer 18

Right eye- constriction

Left eye- constriction

Question 19

A patient has a lesion of CN III on the left side- what is the response of both pupils when light is shone into the left eye?

Answer 19

Right eye- constriction

Left eye- no response

Question 20

A patient has a lesion of CN III on the left side- what is the response of both pupils when light is shone into the right eye?

Answer 20

Right eye- constriction

Left eye- no response

Question 21

What other symptoms would you see with a CN III lesions

Answer 21

Dilated pupil- loss of parasympathetic supply to sphincter pupillae.
Full ptosis- loss of levator palpebrae superioris function.
Eye looks down and out- only lateral rectus and superior oblique can function.
Failure to accommodate- loss of function of sphincter pupillae, ciliary muscle and medial rectus

Question 22

Range our visual system is sensitive to

Answer 22

The visible light range of the electromagnetic wave spectrum ranges from 380nm (purple) to 740nm (red). Most electromagnetic energy emitted by the sun is within the visible range. We have blue, red and green cones which then combine to form other colors. Our perception of the world is filtered

Question 23

Importance of the fovea

Answer 23

Contains most of the cones (no rods)- where you have eye acuity and colour vision. The further out you go its most rods where you have night vision and movement. The photoreceptors have been pushed apart to create the foveal pit

Question 24

Optic disc

Answer 24

Where the optic nerve and blood vessels enter the eye. Is a blindspot with no rods or cones. Closest to the nose

Question 25

Macula

Answer 25

Surrounds the fovea. Has some rods but the majority is cones, important in color vision. Surrounded but the superior and inferior branch of the retinal vein or the radius from the fovea to the optic nerve. Location of central vision. The macula layer is composed of two or more ganglion cells on top of each other

Question 26

Organisation of the retina

Answer 26

Has pigmented epithelium at the back, reduces the light scatter and feeds the photoreceptors Phtoreceptors- cell bodies are in the outer nuclear layer. The outer nuclear layer is towards the back of the eye and the inner nuclear layer is near the front. In the outer plexiform layer the photoreceptors synapse onto the bipolar cells. The photoreceptor and bipolar cell are in parallel to each other. Horizontal cells are between them in outer plexiform layer The cell bodies of the bipolar cells are in the inner nuclear layer The bipolar cells project to the inner plexiform layer and synapse with the inner plexiform layer. The axons from the ganglion cells become the optic nerve

Question 27

Layers of the retina

Answer 27

1) Nerve fibre layer 2) Ganglion cell layer 3) Inner plexiform layer 4) Inner nuclear layer 5) Outer plexiform layer 6) Outer nuclear layer 7) Photoreceptors outer segments 8) Pigmented epithelium

Question 28

Hormone photoreceptors produce

Answer 28

Costantly produces Glutamate which goes down to the bipolar cells in the dark which the brain interprets as there being no signal. When light hits the photoreceptors the Na+ channels close down stopping the Glutamate from being released. In low light levels some Glutamate, in high levels less. GABA, Glycine, Acetylcholine and Dopamine can be released from amacrine cells and inhibit Glutamate production. Ganglion cells fire action potentials based on how much glutamate is produced

Question 29

Columns in the retina

Answer 29

Photoreceptors, Ganglion, Muller and Bipolar cells form columns The Horizontal and Amacrine cells form layers Ganglion cells go along in layers Muller cells form the innermost layer, the feet of glial cells are support cells The synaptic

Question 30

Effects of raised intra ocular pressure on the optic disc

Answer 30

There will be a cupped optic disc with a high cup to disc ratio, cup will appear bigger Can be due to Glaucoma

Question 31

Visual acuity and driving

Answer 31

The minimum eyesight standard for driving is 6/12 | You must- have an adequate field of vision and be able to read a car number plate made after 1/09/2001 from 20m

Question 32

Visual acuity and occupation

Answer 32

Lorry and bus drivers- must have a visual acuity at least 6/7.5 in their best eye and at least 6/60 in the other eye Other restriction- Armed forces, Air traffic control and Electrical engineers

Question 33

What nerve supplies the lateral rectus muscle

Answer 33

Abducens

Question 34

Result of right CN IV (trochlear) palsy

Answer 34

Superior oblique-normally helps pull eye down and out. On looking forwards: elevation and extorsion of the eye. On looking left: the eye elevates as it moves medially

Question 35

Oculomotor CNIII palsy

Answer 35

1. ‘Down and out’ palsy 2. Ptosis (innervates levator palpebrae superioris) 3. Mydriasis (large pupil)– carries parasympathetic fibres

Question 36

What are the afferent and efferent branches of the corneal reflex

Answer 36

Afferent- Trigeminal (V1) | Efferent- facial nerves

Question 37

What does the greater petrosal nerve supply

Answer 37

The greater petrosal nerve (a branch of the facial nerve – CNVII) gives parasympathetic supply to the lacrimal gland. If the cornea is dry then the greater petrosal nerve may be injured

Question 38

Where does the nerves for the lacrimal gland have their cell bodies

Answer 38

Superior salivatory nucleus

Question 39

Symptoms of cataracts

Answer 39

1) Change in refractive error 2) Blurred vision 3) Glare

Question 40

Most common complication after a cataract operation

Answer 40

Endophthalamitis

Question 41

Why does Presbyopia lead to reduced accomodation

Answer 41

There is reduced lens flexibility with age

Question 42

What structure in the eye is responsible for the most refractive power

Answer 42

The cornea

Question 43

What are the visual acuity standards for lorry and bus drivers

Answer 43

visual acuity at least 0.8 (6/7.5) in your best eye and at least 0.1 (6/60) in the other eye glasses can't be more than +8 (legally blind) uninterrupted horizontal visual field of at least 160 degrees - with an extension of at least 70 degrees left and right - and 30 degrees up and down

Question 44

What neurotransmitter is the cause of excitotoxicity

Answer 44

Glutamate

Question 44

What neurotransmitter is the cause of excitotoxicity

Answer 44

Glutamate

Question 45

Description of phototransduction

Answer 45

Light hitting photoreceptors hyperpolarise the photoreceptors by closing Na+/Ca+2 channels thus membrane potential hyperpolarises due to K+ effluc

Question 46

What neurotransmitter is recycled by monoamine oxidase (MAO) only

Answer 46

Serotonin

Question 47

Nerve supply to the cornea

Answer 47

It has a dense nerve supply derived from the long ciliary branches of the ophthalmic division of the trigeminal

Question 48

What structure of the temporal lobe is indicated in schizophrenia and epilepsy

Answer 48

The Hippocampus

Question 49

Where is a flame haemorrhage located

Answer 49

The Nerve fibre layer

Question 50

When do you get tardive dyskinesia

Answer 50

Following chronic use of antipsychotic drugs. There is proliferation of dopamine receptors and hypersensitivity of the nigrostriatal pathway. The effects are often irreversible

Question 51

What part of the eye is affected by cataracts

Answer 51

The Lens

Question 52

Occupations where a higher standard of visual acuity is required in the Uk

Answer 52

Bus and lorry driver

Question 53

The Pharmacokinetic property of typical antipsychotics

Answer 53

High plasma protein bound

Question 54

Cause of positive symptoms in schizophrenia

Answer 54

Dysregulation of dopaminergic pathways to the subcortical and limbic systems through hyperactivity acting on dopamine D2 receptors. The pathways to the prefrontal cortex are hypoactivated, are D1 receptor mediated and lead to negative symptoms of schizophrenia.

Question 54

Cause of positive symptoms in schizophrenia

Answer 54

Dysregulation of dopaminergic pathways to the subcortical and limbic systems through hyperactivity acting on dopamine D2 receptors. The pathways to the prefrontal cortex are hypoactivated, are D1 receptor mediated and lead to negative symptoms of schizophrenia.