L3: Young doctors guide to eye

Question 1

What are the 7 bones that make up the orbit (where the eyes sit).
Why is it good to have so many small bones

Answer 1

Frontal, lacrimal, Ethmoid, Maximillary, Palatine, Sphenoid, Zygomatic

Small bones can move and therefore facilitate growth more easily.
It allows for fissures/holes for vessels

Question 2

Where do the extraocular muscles come from and attach to - not too important

Answer 2

All the muscles come from behind the orbit where they attach to a sheath around the optic nerve before attaching to the sclera around the circumference of the globe.

Question 3

What are the 6 extraocular muscles, their movements and innervation. How does this movement work

Answer 3

Rectii muscles

• Lat+ Med: abduct and adduct
• Sup+ Inf: Up and down

Oblique muscles

• Sup : Down, abduct, intort.
• Inf: Up,abduct, extort

Innervation by CN3, except Sup ob (4) and Lat rectis (6)

The paired muscles work by increasing innervation to one and relaxing the other to bring about movement

Question 4

What are the muscles of eyelid needed to close and open + innervation

Answer 4

1. To close the eyelid: Orbicularis oculi - CN7

2. Open/lifting the eye lid: Levator palpebrae - CN3

Question 5

What lines the globe and the eyelid

Answer 5

Conjunctiva

Question 6

What is the 3 layers of the Tear film, producers and the function (for tear reflex)

Answer 6

A 3 layers of liquid:
(10 uL) from outside to inside,

Oil: Tarsal gland - slows down evaporation of tear film
Aqueous: lacrimal gland
Mucin: Goblet cells of the conjunctivis

Allows the eyelids to move smoothly over the cornea without injuring it.

Question 7

Explain where tears start and go in the lacrimal system for tear reflex: foreign dirt)

Answer 7

1. Lacrimal gland +accessory lacrimal glands produces tears on the upper lateral side, flows across the eye (helped by blinking reflex)
2. to inner corner, draining through Punta which then drain into the lacrimal sac, then nasolacrimal duct

Question 8

What is subconjunctival hemorrhage triggered by

- Common

Answer 8

Typically idiopathic or after severe coughing, sneezing or vomit.
Rarely associated with anticoagulants or high bp

Question 9

How are eyelid injuries, lacerations treated

Answer 9

The eyelid has to be closed in layers to retain its function and minimise scarring

Question 10

What does ptosis and 2 neurogenic causes

can also be caused by Congenital, involutional, myogenic, mechanical, traumatic,

Answer 10

Dysfunction of levator palpebrae superiorus: drooping lid. Have to treat it if its obstructing the pupil: 3mm-4mm

Causes:
Neurogenic cause: 1.CN3 palsy: upper lid ptosis, also most extraocular muscles not working so eye is down and out and big open pupil.

2. Horner’s syndrome: damage to sympathetic innervation: small pupil (subtle miosis), Subtle ptosis (muller’s muscle)

Question 11

What bones are broken in an Orbital blow out fracture,

how does it show on imaging and what are the signs

Answer 11

The floor of the orbit is thin (nasal, lacrimal and ethmoid).
It is broken with force which pushes eye and its contents back.

Shows a tear drop of muscle and fat- inf rectus getting trapped below on imaging.

Signs

• Can’t look up or down bc of inf rec trapped
• Black eye (haematoma)
• Infra-orbital nerve anaesthesia
• Double vision

Question 12

What is Thyroid eye disease: signs, CT scan features and complications

Answer 12

Signs:

• Lid changes: lag (slow to close), retraction (see sclera), lagophthalmos- dry eye
• Ocular surface inflammation
• Proptosis of the globe: Maximum diameter of globe extends beyond the lat orbital rim on CT

Complication: corneal exposure treated with lubricants /taping eyelid shut

-Myopathy: can get double vision,
extra ocular muscle > rice size on CT: can lead to optic nerve compression leading to surgical intervention

-Optic neuropathy: Tenting of optic nerve on right side on CT

Question 13

What are refractive errors and their correction of 3 Ametropia: hypermetropia, myopia, astigmatism

Answer 13

RE: The image of a distant target cannot be bough to focus by the lens system at the foveola leaving a blur circle

Hypermetropia: (Long sight) parallel light rays focus behind the retina. Corrected by convex lens

Myopia (short sight) : parallel light rays focus in front of the retina. Corrected by concave lens

Astigmatism: Two different focal planes of light

Question 14

What are the cellular layers of the cornea from outside to in. What are the two jobs of cornea

Answer 14

1. Epithelium
2. Bowmans membrane
3. Stroma: collagen, keratocytes
4. Descemet’s layer
5. Endothelium

Highly innervated to get dirt immediately out due to risk of scarring, infection,

Curvature does 2/3 of light focusing, maintained by the lamellar tension + intraocular pressure

Question 15

How does the structure of the cornea’s layers help to keep it clear, right thickness

Answer 15

1. Collagen lamellae arranged parallel to the eye with adjacent layers provides strength.
2. Stroma also has hyaluronic acid = attracts water, altering distance of passage to light. This is compensated by
   Endothelial pump pumps water out of the cornea to ant chamber retain the spacing of lamellae.
3. No blood vessels in the cornea

Question 16

What is the most common condition for corneal transplant,

Answer 16

Keratoconus:
Shape of cornea becomes cone pointing out.

multifactorial or final common pathway for a variety of pathological processes.

• Two hit gene + environment hypothesis .
• generally commences late puberty

Question 17

What structures does light pass through to get to the retina

Answer 17

1. Cornea (40 diopters of focus)
2. pupil
3. lens (20 diopters of focus)

Question 18

Describe the structure of the lens

Answer 18

Lens has epithelium on front surface. The body is made of fibre cells having laid in an annular pattern over time with nucleus having in utero cells.

The lens is connected to the ciliary body and held in place by suspensory ligaments of the lens (zonules). It is just behind the iris

Question 19

The ciliary body contains ciliary muscle which surrounds the circumference of the lens. What is its job and how does it change with old age

Answer 19

Accommodation: the ciliary muscle contracts to increase curvature of the lens which refracts more light, this helps with near work. So better allows close focus.

Older age cannot accommodate as well as used to because of stiffer lens

Question 20

Ciliary body produces aqueous humour. what is its purpose, What is the flow

Answer 20

Nourishes the lens and the cornea (avascular). The flow helps to maintain the shape of the anterior chamber and the pressure in the eye.

1. Ciliary epithelium
2. up in between lens and iris
3. out the pupil
4. away towards the angle of the anterior chamber.
5. It drains through the trabecular meshwork
6. Schlemm’s canal to veinous system.

Question 21

How is cataract diagnosed and treated

Answer 21

• Using opthalmoscope + slit lamp microscope
• There will reduced visual acuity and significant lens opacity

Surgical:

• Intracapsular (developing)
• Phacoemulsification: most popular- removal of the cateract via a small incision, foldable and injectable intraocular lens
• Femtolaser assisted, - Extracapsular (sometimes developing)

Question 22

What are the causes of cataract

• region cortical or nucleus

Answer 22

Majority: Aging: over time, the nucleus of fibre cells in the lens dissolves, therefore they cannot form new proteins, so break down and forming opacity within the lens.

Metabolic- diabetes
Toxic- oral corticosteroids
Traumatic- irradiation
Secondary - uveitis

Question 23

What cellular layers does nerve signal generated by light hitting photoreceptor rods and cones go through

(Light first travels the opposite way)

Answer 23

0. Retinal pigment epithelium
1. Photoreceptor r&c
2. Outer synaptic layer
3. Connecting and processing cells (bipolar cells)
4. Inner synaptic layer
5. Ganglion cells.
6. Retinal nerve fibre layers -> to the optic nerve

Question 24

What is the function of Retinal pigment epithelium.

- why are photoreceptors at the back of the eye?

Answer 24

Retinal pigment epithelium (external to retina) helps 1.formation of photo pigments,

2. renewal of photo receptors,
3. transport of water and nutrients, 4.reduction of damage due to scattered light -

Question 25

What is the function of Xanthophyll caratenoids in the Macula lutea

Answer 25

Zeaxanthin
Lutein
are protective pigments against UV light damage of photoreceptor cells in those areas (mostly cones)

Question 26

What other vessels pass through the optic nerve

Answer 26

Central opthalamic artery and vein

Question 27

How do we see colour ?

Answer 27

3 types of cone cells which absorb most light at Red, green and blue frequencies and then some other in a bell curve.

To see other colours than the peaks, there needs to be a simultaneous excitation of cone cells of the ones whos ranges overlap (eg. red and green for orange)

Question 28

How is X-linked red-green colour blindness ranked - mild, moderate or severe

Answer 28

Normal: at least one green and red, can have multiple

Moderately: mutation in some of the gene for one, other is ok: not full spectrum

Mild: Has mutated version but also a good copy + other good copy.

Severe: Only one copy of red or green- cannot tell difference between them

Question 29

What is Glaucoma
- most common cause of progressive loss of vision,

What are the two types

Answer 29

An optic neuropathy with specific pattern of axonal loss (and visual field loss) often associated with elevated intra-ocular pressure

1. Open angle:
   - 1’presumed angle predisposition, (trabecular meshwork) 2’cells + inflammation
2. Closed angle
   1’ narrow anterior chamber angle, 2’ tumours, synechiae

Question 30

What is the normal intraocular pressure

Answer 30

11-22 mmHg. Thicker cornea will make the pressure higher.

Question 31

What is optic nerve cupping: a symptom of glaucoma

Answer 31

The optic nerve sits inside a disc, with a central cup. In normal patients the cup diameter should be 0.5 disc.

A cup 0.5 < is When optic nerve axons for peripheral vision are lost, affecting central vision last.

Question 32

What are 3 Retinal diseases:

Answer 32

Age related macular degeneration: haemorrhage, end stage- scarring

Diabetic retinopathy:
- infarctions in small blood vessels, haemorrhages

Retinal detachment