Eye Flashcards
Bones forming the equine bony orbit
- Frontal bone and is zygomatic process
- Zygomatic bone and its temporal process
- Temporal bone and its zygomatic process
- Lacrimal bone
Distichiasis, Trichiasis and ectopic cilia
Distichiasis - hairs arise from the Meibomian gland opening and contact cornea
Trichiasis - hairs in the correct position but point towards the cornea
Ectopic Cilium -hairs arise in the Meibomin Gland and exit the palpaebral conjunctiva
Which nerves are being blocked at A, B, C and D?
What structures should each desensitise?
A - supraorbital; branch of CNV.a. Rx in desensitisation of the middle 2/3 of the upper eyelid and skin fanning out from here towards dorsal midline of forehead.
B - lacrimal; branch of CNV.a. Rx in anesthesia of lateral canthus of eye, temporal angle of orbit and lateral aspect of upper eyelid.
C - infratrochlear; branch of CNV.a. Rx in anesthesia of medial canthus of eye, medial aspect of upper and lower eyelids and a small region of skin fanning out rostroventrally
D - zygomatofacial (zygomatic); branch of CNV.a. Rx in anesthesia of middle 2/3 of lower eyelid, and small region of skin fanning out ventrally. Needle is inserted at the most ventral aspect of the rim of the bony orbit
Which nerve is being blocked and what will be the effect?
Auriculopalpaebral block (palpaebral branch; from CV VII)
Rx in motor blockade of the upper eyelid. No sensory loss
Nerve usually palpable at the dorsal aspect of the zygomatic arch
Which nerves will be desensitised during a retrobulbar block?
Briefly describe 2 approaches
CN II, III, IV, V (opthalmic and maxillary branches) and VI
Rx in motor blockade of extra-ocular muscles and ciliary body (CN III, IV and VI) and sensory blockade of peri-orbital skin, fascia and the eyeball itself (CN V). CN II is also desensitized
- 19g spinal needle enters at the supra-orbital fossa just caudal to the caudal rim of the supra-orbital process. The needle is advanced ventrally caudal to the globe until it reaches the retrobulbar space at which time the eye will rotate dorsally as the needle penetrates the dorsal fascia of the retrobulbar orbital cone. Inject 10-20ml local and expect some exopthalmus
- 19g spinal needle pre-curved and inserted down axial aspect of the orbit adjacent to the globe
Describe extra-occular mm innervations
III (occulomotor) - medial, dorsal and ventral rectus plus ventral oblique mm. Also supplies the levator palpaebrae superioris and parasympathetic fibres to the ciliary body.
IV (trochlear) - dorsal oblique mm
VI (abducens) - Lateral rectus and retractor bulbi mm
Possible advantages of US guided maxillary nerve block (O’Neil 2014)
More accurate needle placement so lower local volumes can be used
Less risk of iatrogenic injury to nearby neurovascular structures incl. deep facial vein, infraorbital artery, descending palatine artery; thus avoidance of their potential sequalae incl. temporary blindness, haemorrhage and severe swelling
2 most common/prominent features/signs of retrobulbar disease
*Exopthalmus (Nb differentiate from bupthalmos (eg glaucoma) by comparison of the limbus to limbus horizontal corneal diameter between the 2 eyes in a horse with a normal contralateral globe.)
*Strabismus
Vision loss may also be seen
Ddx for exopthalmus/retrobulbar dz
Divided into 1ary or 2ary
1ary orbital dz - the tissue of origin is within the retrobulbar space
- neoplasia (neruoendocrine, SCC)
- cyst
- inflammation
- FB
2ary to sinonasal disease - arising outside of the orbit with extension via local invasion or metastasis
- neoplasia (sarcomas and carcinomas)
- sinus cyst
- infection (fungal usually - errosive)
What is the orbital fissure?
What nerves pass through here?
How does this differ in cattle?
Foramen in the sphenoial bone in the caudomedial orbit which separates brain from eye.
If represents the exit from the calvarium of CN III, IV & VI, plus Va (opthalmic)
Lies adjact to optic foramen (CN II), rostral alar foramen (maxillary aa/nn) & ethmoidal foramen (CNI).
The ox has a foramen orbitorotundum that represents a combination of the orbital fissure and round foramen found in other species. This structure conveys the oculomotor, trochlear, ophthalmic, maxillary, and abducent nerves.
4 major foramina in the apex of the equine globe.
Which nerves do each of these convey?
1) Ethmoidal - CNI aa/vv/nn
2) Rostral alar foramen - CNVb (maxillary); exits skull via round foramen, alar canal, then enters orbit via rostral alar canal)
3) Orbital fissure - CN III, IV, Va & VI
4) Optic foramen - CNII/opthalmic aa
Foramina of the globe
