Lesson 124 - Eye Exam

What are the three tunics?

1. fibrous

2. vascular

3. neurosensory

What makes up the fibrous tunic?

1. sclera

2. cornea

3. limbus

What makes up the vascular tunic?

1. choroid

2. ciliary body

3. iris

What makes up the neurosensory tunic?

retina

What are the three chambers?

1. anterior chamber

2. posterior chamber

3. vitreal chamber

Which chambers contain aqueous humor?

anterior and posterior chamber

What is the most powerful refractory structure of the eye?

cornea

What is the function of the lens?

accommodates or changes shape to focus light onto the back of the eye

What is the pathway for an electrical signal originating from the retina?

cones and rods -> bipolar cells -> ganglion cells (optic nerve)

Where does the optic nerve exit the orbit?

optic foramen

Where is the first order neuron for vision?

bipolar cell which takes signal from rods and cones to the ganglion cells

Where is the second order neuron for vision?

1. ganglion cells which make up the optic nerve

2. take signal from bipolar cells to lateral geniculate nucleus in the thalamas

3. some fibers cross in the optic chiasm

Where is the third order neuron for vision?

optic radiation which takes signal from lateral geniculate nucleus to the visual cortex

What is part of the basic eye exam?

1. take a proper history

2. observe the animal in waiting/exam rooms

3. observe interactions with owner

4. be systematic (outside to inside, front to back)

What are basic instruments for an eye exam?

1. focused light beam-penlight

2. schirmer's tear test strips

3. fluorescein

4. magnification

5. opthalmoscope

What is the first part of the basic eye exam?

reflexes and basic neuro-ophthalmic exam with menace response and vision tests and external eye exam

What do you do after performing neuro-ophthalmic exam and external eye exam?

schirmer tear test

What do you do after schirmer tear test?

culture and sensivity if indicated

What do you perform after culture?

opthalmic stains and anterior segment exam

What do you perform after opthalmic stains and anterior segment exam?

tonometry then drug-induced mydriasis and opthalmoscopy

What subcortical reflexes do we perform?

1. pupillary light reflex

2. dazzle reflex

3. palpebral reflex

What assessments of vision do we use?

1. menace response

2. cotton ball test

3. obstacle course/maze

4. visual placing response

What type of reflex is the PLR?

subcortical parasympathetic autonomic reflex

What reflex can be affected in highly excited and aggressive dogs and cats and why?

1. Pupillary light reflex

2. endogenous epinephrine dilate pupils causing them to poorly respond to the light

What lesion locations does pupillary light reflex help to identify?

retinal and pre-chiasmal optic nerve disease

Which axons decussate at the optic chiasm?

medial (nasal) axons from the retina

What is the afferent pathway for the PLR?

optic nerve -> optic chiasm -> pretectal nucleus in midbrain -> Edinger Westphal nucleus

What is the efferent pathway for the PLR?

parasympathetic fibers from CN III

What is the afferent pathway for the dazzle reflex?

retina and CN II

What is the efferent nerve for the dazzle reflex?

CN VII

What is not a test of vision, but a test for potential vision?

dazzle reflex

What is the pathway for the palpebral reflex?

1. afferent CN V

2. efferent CN VII

What is the visual placing reaction?

hold small pet in the air and advance toward a table, extension of borth forelegs is expected

What is a good way to test vision in cats?

1. laser pointer

2. difficult due to cats being unreliable for responses such as menace

What is the pathway for the menace response?

1. afferent is retina and CN II

2. efferent is CN VII, VI

What is something to keep in consideration with menace response and age?

young animals may not respond due to menace response being a learned behavior

Where is the lesion if the patient is visual with absent PLRs?

efferent problem (CN III or iris sphincter)

3 multiple choice options

Where is the lesion if the patient is non-visual with normal PLRs?

something obscuring vision (cataract) and cortical disease

3 multiple choice options

Where is the lesion if the patient is non-visual with absent PLRs?

retine or optic nerve

3 multiple choice options

What symmetry can you asssess for when performing external examination?

1. orbit

2. globe position

3. eyelids/eyelashes

4. nicitans position

What can change eyelash position?

1. pain

2. ptosis (facial nerve damage or horners syndrome)

3. enopthalmos

4. exopthalmos

What are some changes to globe position/size?

1. enophthalmos

2. exophthalmos

3. microphthalmos

4. phthisis bulbi

5. buphthalmos

When performing regional anesthesia in large animals, what drugs can we use?

1. lidocaine

2. carbocaine

3. bupivacaine

What are the motor blocks and their use for large animal regional anesthesia?

1. facilitate exam and procedures

2. CN VII (auriculopalpebral nerve)

What are the sensory blocks and their use for large animal regional anesthesia?

1. facilitate procedures

2. frontal nerve (CN V)

3. lacrimal nerve (CN V)

What nerve covers sensory for the medial 2/3 of the upper eyelid?

frontal nerve

What part of the exam is helpful for identifying a retrubulbar mass?

retropulsion

What diagnostics can be used for eyelids?

1. palpebral and dazzle reflexes

2. skin scrapings

3. biopsy

4. culture and cytology

What are the functions of the pre-corneal tear film?

1. cleanse and lubricate

2. provide nutrition and oxygen

3. antimicrobial defense

4. maintains uniform surface

What makes up the portions of the pre-corneal tear film?

1. aqueous component from lacrimal glands

2. lipid component from meibomian glands

3. mucin component from conjunctival goblet cells

What is the order of the tear film from outer to inner?

lipid -> aqueous -> mucin

What does STT measure?

quantitative measure of aqueous portion of tear production

When do you perform STT?

always prior to instillation of topical solutions

What is normal and deficient tear production?

1. <15 mm/minute is deficiency

2. up to 30 mm/minute is normal

What tests are used for the mucin fraction of the tear film?

1. tear film break-up time (TFBUT)

2. rose bengal or lissamine green test

How does the TFBUT test work?

1. topical fluorescein added and time from blink to appearance of dry spot

2. without mucin layer the acqueous portion evaporates faster

3. deficiency with less than 10 seconds

What tests can be used for the nasolacrimal drainage apparatus?

1. fluorescein passage (Jones test)

2. nasolacrimal flush

3. dacryocystorhinography

What are the layers of the cornea?

1. epithelium

2. stroma

3. descemets membrane

4. endothelium

Which layer of the cornea is highly regenerative?

epithelium

What contributes to corneal clarity?

1. avascular

2. anhydrous

3. absence of pigment

4. non-keratinized anterior epithelium

5. regular arrangement of stromal collagen fibrils

6. small size of stromal collagen fibrils

What is an important function of the endothelium of the cornea?

actively pumps out fluid

When do you want to take your culture sample?

before instillation of solutions

What are the indications for culture of the cornea?

1. ulcers with depth

2. cellular infiltrate

3. collagenolysis

4. delayed healing

What type of culture is run from the cornea?

aerobic with maybe fungal especially in horses

When is fluorescein stain used?

1. corneal ulcers

2. nasolacrimal patency

3. tear film break-up

4. aqueous leakage

5. angiography and blood aqueous barrier

When is rose bengal or lissamine green stain used?

1. cornea and conjunctival cell degeneration

2. mucin layer deficiency

What do we need to do before placing a patient on a topical steroid?

flourescein stain

What is the Siedel's test?

uses fluorescein to evaluate for aqueous leakage

What is the Jones' test?

evaluate patency of the nasolacrimal apparatus

What is a test for tear quality?

rose bengal

What does rose bengal stain?

devitalized cells and healthy cells not covered by tear film

How do you evaluate the anterior segment?

bright, focal light source, slit beam on ophthalmoscope or slit lamp

What makes up the uvea?

1. choroid

2. iris

3. ciliary body

What is the central aperture of the iris?

pupil

What is the function of the iris?

controls amount of light entering the eye

What are the two zones of the iris?

1. pupillary zone

2. ciliary zone

3. collarette is the division between

What makes up the iris stroma?

1. small collagen fibers

2. pigment cells

3. extensive vascular network

What is the iris made of?

1. stroma

2. dilatory and constrictor muscles

3. posterior pigmented epithelium

4. no anterior epithelium

What makes up the muscle in the iris?

1. smooth muscle in mammals

2. skeletal muscle in avians and reptiles

What are the two portions of the ciliary body?

1. pars plicata

2. pars plana

What is the function of the ciliary body?

1. produces aqueous humor

2. anchors the fibers that suspend the lens

3. contributes to AqH outflow

4. lenticular accomodation

5. blood aqueous barrier

Which part of the ciliary body produces the aqueous humor?

non-pigmented epithelium on ciliary processes

What is the function of the aqueous humor?

supplies nutrition to lens and cornea

How do aqueous humor drain?

through uveoscleral outflow and iridocorneal angle

What maintains intraocular pressure?

balance between production and outflow of aqueous humor

What is a tool that we can use to visualize the iridocorneal angle?

gonioscopy

What is miosis indicative of?

anterior uveitis

What can cause mydriasis?

1. drug induced

2. glaucoma

3. retinal disease

What causes dyschoria?

1. synechia

2. uveitis

3. mass lesions

How do you estimate the anterior chamber depth?

1. view from the front and side

2. use slit or focal beam of light

3. use iris as reference point

4. compare the two eyes

What is the normal range for IOP?

10-25 mmHg

When do you want to perform tonometry?

prior to pharmacologic mydriasis

What is important about measuring tonometry and position?

head should be above the heart

What are the types of tonometry devices?

1. digital is not reliable

2. applanation (Schiotz, Tonopen)

3. Rebound (Tonovet)

In acute onset glaucoma, is the pupil big or small?

mydriatic

2 multiple choice options

What are the layers of the lens?

1. epithelium

2. capsule

3. cortex

4. nucleus

5. sutures

What is unique about the lens cortex?

made of collagen fibers that are constantly being produced and do not slough away

What is a normal age related change with the lens?

nuclear sclerosis due to densely packed collagen

What helps maintain lenticular transparency?

1. highly organized fibers

2. maintained in avascular environment

3. fibers are kept dehydrated (deturgescence)

4. large percent of soluble proteins

What is loss of transparency with the lens?

cataract