the third eyelid (dictating membrane)

Question 1

how is the position of the third eyelid determined?

Answer 1

by sympathetic tone

Question 2

describe the musculature controlling the third eyelid?

Answer 2

mostly vestigial in domestic species (well developed in LA)

the membrane moves passively across the eye when the globe is retracted by the retractor bulb muscles

Question 3

innervation of the third eyelid?

Answer 3

N. abducens

Question 4

describe the T-shaped cartilage?

Answer 4

cartilaginous skeleton of the third eyelid

embedded in the gland at its base

Question 5

describe the gland of the third eyelid?

Answer 5

seromucoid

produces 30-50% of the PTF

Question 6

describe the gland in pigs?

Answer 6

Harder’s gland - deeper within the orbit (not found in cats and dogs)

Question 7

third eyelid?

Answer 7

Production of the water layer of the PTF
distribution of the PTF while blinking
protection of the cornea, especially in grazing animals

Question 8

describe the aetiology of protrusion of the gland of the third eyelid (cherry eye)?

Answer 8

A defect, laxity in the retinaculum that binds the gland and the nicitans to the periorbit or a result of lymphoid hyperplasia

the laxity will allow the spontaneous prolapse of the gland

could be congenital or hereditary

Question 9

clinical signs of cherry eye?

Answer 9

reddish follicular mass appearing
uni or bilateral
swelling, drying and inflammation of the gland -> chronic cherry eye
decreased lacrimation

Question 10

treatment of cherry eye?

Answer 10

surgical replacement of the prolapsed gland (DO NOT EXCISE THE GLAND)

Question 11

describe the treatment of cherry eye in its early phases?

Answer 11

prolapsed gland can be manipulated into position (spontaneous healing)
but reoccurs

Question 12

describe the surgery for cherry eye?

Answer 12

replacement of the prolapsed gland
Anchoring or pocket technique:
- Pocket (Morgan’s) technique

Question 13

describe the aetiology of the evisceration of the T-shaped cartilage (scrolled third eyelid)?

Answer 13

rolling out of the margin of the membrane due to abnormal curvature of vertical portion of the T-shaped cartilage

developmental abnormality

Question 14

which species can be affected by scrolled third eyelid?

Answer 14

horses and dogs

Question 15

clinical signs of scrolled third eyelid?

Answer 15

the deformed and everted part of the T-shaped cartilage is seen under the conjunctiva of the nicitans

may be combined with gland prolapse

Question 16

treatment of scrolled third eyelid?

Answer 16

more cosmetic issue rather than pathogenic

dissection of the excessive curved portion of the cartilage

• Bulbar approach using scissors
• no scissors required

Question 17

background of evisceration of the third eyelid?

Answer 17

systemic

Question 18

the third eyelid can be prolapsed during Horner’s syndrome, true/ false?

Answer 18

true

Question 19

in which species do you see myositis eosinophilia?

Answer 19

dogs

Question 20

clinical signs of myositis eosinophilia?

Answer 20

enophthalmos in chronic ME
exophthalmos in acute ME
together with a third eyelid prolapse

Question 21

what is microphthalmos?

Answer 21

eye is smaller than normal
developmental abnormality (bi- or unilateral)

Question 22

how does exophthalmos occur?

Answer 22

bulging of the eye
Acue ME
retrobulbar masses (tumour, abscess etc.)

Question 23

in what species does idiopathic evisceration of the third eyelid occur?

Answer 23

cats

Question 24

aetiology of tumours of the third eyelid?

Answer 24

Rare
Carcinomas (SCC)

lymphoma, haemangioma or haemangiosarcoma, and adenocarcinoma of the third eyelids are also common
amelanotic or poorly pigmented third eyelids appear more susceptible

Question 25

treatments of tumours of the third eyelid?

Answer 25

surgery (excision of the tumour or extirpation of the third eyelid)

Question 26

what are the indications for extirpation of the third eyelid?

Answer 26

an irreparable traumatic injury or a malignant tumour