8. Eye globe anatomy and pathology

Question 1

name 3 structures which maintain position of eyeball

Answer 1

1. suspensory ligament (sits underneath like sling)
2. rectus muscles
3. orbital fat

Question 2

label this image

Answer 2

Question 3

describe the structure and function of the 3 layers of the eyeball

Answer 3

• outer layer: tough fibrous SCLERA continuous anteriorly with transparent CORNEA and posteriorly with dura mater covering optic n

(provides attachment for extra-ocular muscles and gives shape to eyeball)

• middle layer: vascular layer consisting of CHOROID which continuous anteriorly as CILIARY BODY and IRIS
• inner layer: RETINA composed of inner photosensitive layer and outer pigmented layer containing melanin

Question 4

describe the components of the iris and its innervation

Answer 4

• thin contractile diaphragm with a central aperture - the PUPIL - for light transmission
• formed of SPHINCTER PUPILLAE (PNS via occulomotor n.) and DILATOR PUPILLAE (SNS via ophthalmic a.)

Question 5

describe how the shape of the lens can be changed

Answer 5

• edges of lens are attached to ciliary bodies by circular suspensory ligaments
• contraction of ciliary muscle, stimulated by PNS (EWN… CN III… ciliary ganglion… CN Va), alters tension in suspensory ligaments… change in shape of lens (wider) and in refractive power

Question 6

name the 3 chambers of the eyeball - what does each contain

Answer 6

1. anterior chamber: between cornea and iris - filled with aqueous humour
2. posterior chamber: between iris and lens - contain ciliary body and processes which secrete the aqueous humour
3. vitreous chamber: posterior to lens - filled with vitreous humour

Question 7

what is the function of aqueous humour and describe its production

Answer 7

• functions:
  1. support shape of eyeball by exerting pressure (along with vitreous humour)
  2. provide nourishment to lens and cornea (as have no blood supply)
• production:
  i. secreted by CILIARY PROCESSES within ciliary body…
  ii. flows from posterior chamber to anterior chamber via PUPIL…
  iii. drains through IRIDOCORNEAL ANGLE (between ant. iris and post. cornea)…
  iv. drains via TRABECULAR NETWORK into CANAL OF SCHLEMM which joins venous circulation

Question 8

describe how action potentials are generated in response to light

Answer 8

1. light is refracted as it passes between different transparent media: cornea, lens and aqueous/vitreous humours…
2. brings light to focal point on retina…
3. neurosensory layer of retina senses light via phoroRs:
   - CONES (mainly concentrated at macula/fovea) - responsible for high visual acuity and colour vision
   - RODS (20x more than cones) - responsible for vision in low intensity light
4. photoRs convert light energy to electrical impulses that ultimately reach otpic disc (devoid of photoRs - blindspot)

Question 9

why is the accomodation reflex required and what are its 3 main components

Answer 9

• with very near objects, light rays are more divergent and greater refraction is required:
  1. automatic pupillary contraction - ensures light from near objects passes through centre of lens
  2. convergence of eyes - ensures image is focused on fovea of both retina
  3. thickening of lens - ciliary muscle contraction… ciliary body moves closer to lens… loosens pull on circular suspensory ligaments… lens more biconcave

Question 10

what is uveitis and when does it commonly occur

Answer 10

• inflammation of choroid layer presenting with red, painful eye often made worse when when trying to focus or looking at bright lights
• Rare but typically associated with autoimmune conditions such as ankylosing spondylitis and inflammatory bowel disease
• Must refer urgently to ophthalmology for treatment with corticosteroids.

Question 11

what is colour blindness

Answer 11

inherited absence/dysfunction in 1 of 3 types of cone cells (red-, green- or blue-sensitive)

Question 12

what causes cataracts

Answer 12

• gradual age-related degradation of proteins in lens causing it to become clouded and less transparent - significant visual impairment
• can be successfully treated with surgery

Question 13

what is presbyopia

Answer 13

• age-related visual impairment due to lens become denser and less elastic… decreases ability to accomodate and focus on near objects
• can be corrected with glasses

Question 14

name this condition - which signs suggest this and what symptoms would the P report

Answer 14

signs:

1. red eye
2. fixed or sluggish, semi-dilated often irregular oval-shaped pupil
3. eye feels hard and tender to palpate through upper eyelid

symptoms:

1. sudden onset pain
2. blurred vision or halos around objects (due to corneal oedema)
3. nausea and vomiting

Question 15

what causes glaucoma and what are the 2 main types

Answer 15

i. obstruction of aqueous humour drainage from anterior chamber…
ii. increased intra-occular pressure….
iii. irreversible damage and death of optic n. (optic disc cupping)…
iv. impaired vision and blindness (if untreated)
1. open-angle glaucoma (most common): chronic agre-related deterioration of trabecular meshwork - develops painlessly and insidiously over time
2. closed-angle glaucoma: acute narrowing of iridiocorneal angle blocking off access to trabecular meshwork

Question 16

describe the management of glaucoma

Answer 16

1. pilocarpine muscarinic eye drops - cause contraction of ciliary muscle, opening the trabecular meshwork
2. strong analgesia
3. surgery

Question 17

suggest how visual acuity could be tested

Answer 17

1. Snellen Chart
2. reading test closer to eye

Question 18

suggest how visual fields can be tested

Answer 18

confrontation