Eye Examination Flashcards
What is the first step of any eye consultation?
Ascertain signalment (several ocular disease more predisposed in certain breeds/inherited) + history (both general and eye focused)
What is the second step of an eye consultation - describe how it is performed and what you would be looking for.
Examination under ambient lighting
Distance exam - blink rate, blepharospasm, redness, symmetry, discharge, exophthalmos (observed from above), entropion (observe different head positions)
Close exam - symmetry, protrusion of globe, strabismus, retropulsion, vestibulo-ocular reflex, inspection of eyelid margins, conjunctival fornices and third eyelid.
What is the 3rd step of the eye consultation. What does it assess and what would be a normal reading?
Schirmer Tear Test - quantitative assessment of tear film
Perform before local anaesthesia or other topical drops applied
STT 1 - basal + reflex tear production
STT 2 - (if local anaesthesia etc applied) - basal tear production
Normal value >15mm/min
10mm/min-15mm/min = borderline KCS
<10mm/min - confirmed KCS
(Cats range 3-32mm/min, average 17 - can read 0 with stress)
When should sample collection be performed and why?
What collection methods are there?
Prior to application of topical agents to eye - can have negative impact on microbial growth.
If eye very painful proxymetacaine can be used as will not affect bacteriology.
Bacteriology collection - sterile cotton tip swab
Cytology collection - cytobrushes or blunt end of scalpel
PCR collection - sterile swab or cytobrush with plain tube.
What neuro-ophthalmic reflexes/responses can be tested in an eye examination?
Pupillary Light Response - direct and consensual
Swinging flashlight test - for detection of pre-chiasmal lesions
Dazzle reflex - subcortical reflex, tests visual pathway to level of midbrain
Menace response - (not a reflex as learned response), assess visual pathway up to cortical level
How should the PLR be assessed and which nerves does it involve as the afferent and efferent arms? Which muscle is involved in the PLR?
Assess in darkened room
Afferent arm - optic nerve (CN II)
Efferent arm - parasympathetic fibres of occulomotor nerve (CNIII)
Constriction of iris sphincter muscle and relaxation of iris dilator muscle
Why do we see a consensual response when performing a PLR?
Due to decussation of nerve fibres at the optic chiasm and pretectal area.
What factors may affect the PLR and is the PLR a test for vision?
Factors that may affect the PLR - excitement (adrenergic state), iridial disease (iris atrophy, uveitis, synechiae, neoplasia), increased IOP, optic nerve or higher centre function.
NOT a test for vision - cerebrum is not involved in the PLR pathway. Pupillomotor fibres branch from optic tract before the visual fibres.
PLR can be intact if cortical blindness
PLR being absent does not always indicate blindness e.g iris atrophy
What is the swinging flashlight test and what response should we expect?
Used to detect pre-chiasmal deficits
Penlight used to illuminate one pupil then immediately swing to opposite pupil
If pupil of second eye dilates as it its illuminated indicated a blinding lesion in that eye (up to chiasm)
Very small amount of dilatation following constriction can be normal - pupillary escape.
How does the dazzle reflex work and what are the afferent and efferent arms of this reflex?
Bright light shone into each eye - should elicit blink.
Afferent - optic nerve (CN II)
Efferent - facial nerve (CN VII)
Visual pathway tested to level of midbrain.
Complete cataracts would still be expected to dazzle if stimulated with bright enough light source.
What are the afferent and efferent arms of the menace response? What extraocular muscles are involved?
What would you expect in a patient with facial paralysis?
Learned response - 8-12 weeks, may be absent in excited/nervous patients.
Afferent arm = optic nerve (CN II)
Efferent arm = facial nerve (CN VII) + abducens (CNVI)
Flat hand/finger towards eye - should illicit blink and subtle globe retraction.
Extraocular muscles = orbicularis oculi (for blink), retractor bulbi (globe retraction)
Facial paralysis - absent blink but may see slight globe retraction and transient TEL protrusion.
What are some behavioural tests we can use for vision?
Visual tracking - cotton wool dropped in front of patient (subjective)
Visual placing - lift up to exam table slowly, should start to extend one or both legs. Cover individual eyes to assess.
Maze testing - assess navigated obstacles in different lighting conditions
What are the afferent and efferent arms of the palpebral reflex?
Afferent arm = ophthalmic and maxillary branches of trigeminal nerve (CNV)
Efferent arm = facial nerve (CN VII) + abducens (CN VI)
Centre of upper lid - supraorbital nerve (ophthalmic branch)
Lateral canthus = lacrimal nerve (ophthalmic branch)
Medial canthus = trochlear nerve (ophthalmic branch)
Centre of lower lid = zygomatic nerve (maxillary branch)
What does the corneal reflex test? What are afferent and efferent arms?
Corneal reflex = wisp of cotton wool onto cornea, should elicit blink response
Afferent = ophthalmic branch of trigeminal nerve (CNV)
Efferent = facial nerve (CN VII) + abducens (CN VI)
Blink via orbicularis oculi and retraction by retractor bulbi.
What areas are we examining with focal illumination +/- magnification?
Adnexa + ocular surface + anterior segment
What are the principles of parallax when observing cataracts? What shape are anterior vs posterior cataracts?
Anterior capsular/cortical cataracts - move away from examiner
Posterior cataracts - move with examiner
Anterior = upright Y
Posterior = inverted Y
What is lentodonesis/phacodonesis vs iridodonesis?
Lentodonesis/phacodonesis = wobble of lens during movement of globe
Iridodonesis = wobble of iris with movement of globe
Why do we do both indirect ophthalmoscopy and direct ophthalmoscopy?
Indirect - wide overview of fundus (locate lesions)
Direct - magnified view of fundus, examine areas of interest in more detail.
