U14C2 Vision Loss

Question 1

What are horizontal and amacrine cells?

Answer 1

Horizontal cells- enable lateral interactions between photoreceptors and bipolar cells that maintain the visual system’s sensitivity to contrast over a wide range of light intensities or luminance – GABAergic neurons by turning off surrounding rods
Amacrine cells- are thought to make various contributions to visual function - for example, one amacrine cell type transmits information from rod photoreceptors to retinal ganglion cells
Both of these inhibitory systems cause neighbouring circuits to inhibit one another, emphasizing differences in the visual field

Question 2

What is the visual response to dark vs light?

Answer 2

Question 3

How does an action potential get to V1?

Answer 3

Question 4

What are the differential diagnoses for vision loss?

Answer 4

Question 5

How are retinal abnormalities graded?

Answer 5

Question 6

What is the RAPD reflex?

Answer 6

Question 7

What is the accommodation reflex?

Answer 7

Question 8

Visual vs horizontal gaze centre?

Answer 8

Question 9

What are the signs and symptoms of MS leading to vision loss?

Answer 9

• Peri-orbital/retro-ocular pain(exacerbated by eye movements)- Due to Inflammation
• Double vision- Due to Optic Neuritis & weakening of the eyemuscles (as nerves that control the eye muscles develop plaques/undergodemyelination) which causes misalignment of the eyes&raquo_space; double vision
• Loss of visual acuity with scotoma(scotoma- visual field abnormality where you have blind spots present in yourvision)-Due to optic disc swelling, damage to optic nerve, improper transduction of vision
• Reducedcolourperception-Optic neuritis&raquo_space; disruption of visual signalsalong optic nerve pathway&raquo_space; can cause blurred, grey and dim vision
• Relative afferent papillary defect (RAPD)-Damage to optic nerve/asymmetricaldisease of optic nerve
• Reduced movement of the eye-Nerves that control the eye musclesdevelopplaques/undergo demyelination&raquo_space; weakening of the extraocular muscles
• Optic disc swelling (papillitis)- Due to damage of most distal, intrabulbar portion of the opticnerve&raquo_space; inflammation & swelling
• Phosphenes(Images of light orcolourthat you can see while your eyes are closed)- Due to damage to optic nerve
• Uhthoff’s phenomenon(Worsening of visual/neurological symptoms w/ increase in body temperature)-related to demyelinating disorders such as MS
• Pulfrich’sphenomenon(Altered perception of moving objects- two-dimensionalobjectsare perceived tobe three-dimensional)- Due to discrepancies in signal transmission time between each eye and thevisual cortex
• Peri-venous sheathing- A collection of exudation containing inflammatory cells which surrounds theaffected vessels&raquo_space; Indicates retinal vascular inflammation

Question 10

What are the diagnostic methods for vision?

Answer 10

CNII (sensory)-

• Function: Transmits sensory visual information from the retina to the brain
• Foramen: Optic canal
• Assessments of the optic nerve: Inspecting the pupils, visual acuity using Snellen chart, pupil reflexes, accommodation reflex, colour vision using Ishihara plates, visual inattention, visual field assessment, blind spot assessment, fundoscopy

CNIII, IV and VI (motor)-

• Foramen: Superior orbital fissure
• Function: transmit motor information to extraocular muscles to control eye movement and eyelid function
• CNIII carries PS fibres responsible for pupillary constriction
• Assessment: eyelid inspection, eye movements (H-test), strabismus (light reflex test and cover test)

Question 11

What is the certificate of visual impairment?

Answer 11