Ophthalmology Flashcards
What is the Globe?
The Globe is an eyeball that consists of fibrous tunic, vascular tunic, neural tunic and transparent media that coats the outside of the eye
What is the fibrous tunic?
The cornea/sclera
The cornea is transparent
The fibrous tunic/sclera is collagen.
What is the Vascular Tunic?
The vascular tunic consists of the iris, ciliary body and choroid
The iris moves in and out, and changes the size of the pupil
The ciliary body is the vascular and muscular body behind the iris, that attaches to the lens.
Flexing of the ciliary body, pulls on the ligament and changes the shape of the lens.
The choroid wraps around the back of the eye and is a cup shaped structure. It is purely vascular.
What is the neural tunic?
The neural tunic consists of the ciliary body epithelium and retina.
The epithelium derives from neural tissue, coating the ciliary body. This becomes the retina.
Nerve fibers run from the retina to the optic nerve. The optic nerve is an extension of the brain.
Neural tissue: Extension of the optic nerve
What is transparent media?
Transparent ocular media consists of the aqueous humour, lens and vitreous humour.
The cornea can be included as it is transparent.
Aqueous humour is a water like fluid that lies in front of the lens. Vitreous humour is a gel-like substance that lies behind the lens and in front of the retina.
Maintain ocular pressure and shape of the eyeball.
The lens is a clear, proteinaceous material
What is the adnexa?
The adnexa is ocular appendages/structures around the eye.
This includes the:
Eyelids: Several layers: Skin, muscle, connective tissue, conjunctival layer, modified hairs
Conjunctiva: IS an epithelial layer that lines the lids, reflects and covers the sclera. Folded structure within: Third eyelid.
Nictitans: Covered with conjunctival tissue and connected tissue cover.
Lacrimal tear glands
Lacrimal drainage apparatus
What is the orbit?
The orbit is the area behind the globe. Refers to the boney socket of the skull in which the eye and its adnexa sit.
Contents of the boney socket:
Orbital Cone
Extraconal orbital tissue
What is the orbital cone?
The orbital cone is defined by extra-ocular muscles that attach onto the side of the eye and attach to the back of the orbit.
This is to turn the eye one way and then the other way. Up and down as pulleys under voluntary control.
Lots of blood vessels and nerves
What is the extraconal orbital tissue?
This is within the orbit but outside the orbital cone.
This is fatty tissue padding things out and filling the space.
Other blood vessels and nerves here
This has an effect on the orbit and eye position.
Describe the basic cell layers
In the embryo there are layers of tissues called the ectoderm and endoderm. The mesoderm is in between
In the eye the ectoderm modifies and becomes the neuroectoderm: Forming neural tissues.
Describe the ectoderm, mesoderm and neuroectoderm in the eye
The ectoderm is the ocular epithelial tissue and the lens. The epithelial covering of the cornea and epithelial conjunctiva. Formation of skin on the lids
The mesoderm is connective tissue filling the spaces. Ocular subepithelial, connective vitreal, vascular tissue
–> Forms the primary vitreous: Large vascular area of vitreous, filling the gab.
The neuroectoderm is the central nervous system. The neural tunic of the eye.
–> The neuroectoderm forms the neutral tube. This punches off and becomes an actual tube which form optic pits.
–> The neural tube forms optic buds/optic vesicles.
–> The ectoderm forms a modified patch of cells called the lens placode. As the optic vesicle grows out: The lens placode grows in. This forms an optic cup.
The cup (ball of cells from ectoderm) grow and pinch off inside the eye, this forms the lens and neural tunic.
Describe the anterior chamber/corneal epithelium
The anterior chamber forms from the regression of the ectoderm. From here the skin is developed with hair and pigment.
Then there is a clear layer of epithelium forming over the cornea. The corneal epithelium is a modification of ectoderm-derived skin.l
Layer of cornea forms the conjunctiva: That covers the cornea and eyelids.
Describe the final differentiation in ocular embryology
The pupillary membrane, tunica vasculosa lentis and secondary vitreous are all mesoderm derived.
Waiting on full development of choroid and sclera
The vascular tissue regresses around the lens. The pupillary membrane regresses to form the proper pupil.
There is regression of the pupillary membrane, tunica vasculosa lentis and secondary vitreous.
The lens buds of the ectoderm. The ectoderm derived tissue forms a clear transparent gel.
Neural area of the eye formed from mesodermal tissue.
Final differentiation:
Ectoderm, mesoderm and neuroectoderm
Form around the optic cup from the neural tube.
Describe blood supply and drainage to the eye
The choroid is made of a specific blood vessel network. There is a high blood supply and turnover to the ciliary body and choroid.
Blood vessels in the iris, ciliary body and choroid should not be leaky
If it is leaky: Larger molecules and cells will leak into the eye.
Do not want lots of protein/cells or will get a cloudy media and unclear vision to the back of the eye
Usually smaller molecules such as glucose, anions and cations can go: Nutrient fluid.
Blood-aqueous barrier and blood retina barrier prevent this.
Tight junctions allow proteins and immune cells to get into transparent media to take away antigens
But inflammation can cause the break down of these barriers causing protein and cells entering into the vitreous chamber and clouding things up.
Describe aqueous production and drainage
Blood will not pass through the blood retinal barrier.
Thus, Aqueous is produced instead. Blood is primarily circulating through the ciliary body, and is then turned into the fluid, followed by going into the posterior chamber.
It goes through to the anterior chamber and into spongy gabs.
As it goes through each smaller and smaller chamber, the blood stream in the sclera is taken away.
This must be balanced for pressure in the eye to be correct.
Aqueous humour is produced by the ciliary body and drains out close to the front of the eye: Cornea and iris.
Vitreous humour does not have an active production and drainage as it is a static structure.
Describe tissue transparency
There is a need to maintain clear aqueous and a clear lens.
Cloudy lens: Can be a cataract, vitreal floaters; opacities in the vitreous
The aqueous, lens and cornea should be clear and light should pass through unimpeded.
Describe the nerve functions in th eeye
Sensory and motor nerves in the eye
There is special sensory nerves for vision. Somatosensory nerves for touch, pain and temperature.
Voluntary and involuntary motor nerves.
Involuntary: E.g. pupil dilation and constriction.
Describe phototransduction
Light is absorbed by the retina and is changed into an electrical signal. This is set up by a series in neurones.
There is 10 layers in the retina. The inner side is the nerve fiber layers.
Towards the choroid there are photoreceptors (rods and coners) deep in the retina/inner layer of the retina.
–> Rods for black and white (night vision). Cones for colour. Most domestic species have less cones and prioritise night vision with more rods.
The photoreceptors convert light energy to an electrical signal.
This signal passes down the series of neurones in the nerve fiber layer. The nerve fiber layer eventually becomes the optic nerve and goes to the brain.
What are the Golden Rules of Ocular Examination?
- Use Signalment and history for ‘clues’. Age, breed and species.
- Examine both eyes, including one that does not have disease.
- Systemically ecamin all other ocular structures.
How can you describe the presenting problem?
Nature, duration (gradual or sudden onset), progression (constant or intermittent signs), previous treatment (medication, surgeries)
Nature:
Pain, changes in eyes appearance, vision problem or combination
Signs of ocular pain: Squinty eye (spasm), pawing/rubbing, excess lacrimation (tearing, watery eye)
Change in appearance: Redness, cloudiness, swelling.
Eye may be open and comfortable.
No excess lacrimation, no pawing. May be both.
If no sign of pain/change in appearance:
Blindess/vision loss
Explain General Illumination
Obvious Abnormalities
Symmetry: Frontal, Dorsal
Retropulsion
Look above and down the patient: Is eye protruding or sunken
Check Light reflexes, visual responses, cranial nerve damage if neurological problem
Explain Focal Illumination
In a darkened room using a good quality focal light source
A fiber optic device or pen torch.
Look at both eyes. Anterior to posterior, start with the lids. Move onto conjunctivia and nicitans.
Look at the lining of the lids: Push third eyelid up.
Cornea: Should be nice and clear. Iris should be nice and crisp, easy to see. Hole in iris: Pupil.
Through the pupil you can see the lens
CANNOT see back of the eye
Explain magnification combined with illumination
Light source can be swung around and can get focus on the eye
There is magnifying spectacles/loops with the light source. Magnifying apparatus/decent focal light source.
Describe Opthalmoscopy
It is to first examine the front half of the eye to the lens
Then look at the back half of the eye
What is the posterior segment of the eye
Posterior segment of the eye: Eye back to the lens: Area of the eye behind the lens to the optic nerve/retina.
Does not include the posterior chamber
What is the fundus
The fundus is the part of the posterior segment that is visible with an ophthalmoscope.
Dominated by the tapetum = colourful, reflect part of the choroid.
What is the distant direct technique of ophthalmoscopy?
Staying at a distance: Arms length of the eye.
Can see reflectiveness of the tapetum, bouncing back from the pupil.
Use retro illumination especially for screening lens changes.
Retrioillumination is the tapetal reflex/eye shine.
At arms length in an examination room with lights down and opthalmascope will cause the eye shine. Colour
If animal has opacity in its lens: Appear as black shadow against retro illumination.
Distant direct illumination easily differentiates true cataract from normal age related nuclear sclerosis.
Haziness or opalescence of the lens.
Explain the close direct technique
Close direct is a magnified, narrow angle view.
That focuses on the retina
Look around different parts of the retina and fundus
What is the monocular indirect technique
Indirect: Wide angle image that is virtual and inverted: Image will be upside down and back to front.
Image rotated 180 degrees
Condensing lens at the right length of the eye.
As it is wide angle: Huge view of all of the fundus. Aerial image of the fundus filling up this lens.
What is the bionocular indirect technique?
It is a wide angle image that is virtual and inverted
Steroscopic view
What are techniques included in vision assessment?
Conscious perception: Response
Reflex: No conscious perception. No control
Dazzle Reflex: Really bright light and clicks on/off on the eye.
Will get squeezing of the lids and withdrawal of the head.
Even in blind dogs: Will get positive dazzle reflex.
Menace response: Threaten the animal with a hand movement. Blink reaction
Cataract: Blocking all vision so will not do anything unless there is noise/wind current.
Once down 2-3 times there are less responsive to menace response.
Tracking response: Tossing cotton wool balls. Want to track object, not sound so do not use ball. Wander around the consult room and observe it.
Pupillary light reflexes: Only assess light sensation and do not assess vision.
Animal can have an intact pupillary light reflex that is blind. And ones with no light reflex that can see
What ocular signs are systemic with disease processes?
General physical examination is critical if systemic disease is a potential cause of ocular signs.
Falls into 4 categories:
Systemic Infectious disease
Systemic immune mediated disease
Endocrine Disease
Multicentric neoplasia
What is the scirmer tear test
Schirmer tear test: Strips of filter paper in the eye. Over 60 seconds track how much moisture comes down the strip.
Between lower lid and cornea, and upper lid and cornea.
What is the florescein stain
Florescein stain: Corneal ulcer diagnostic.
Orange stain that stains green.
How can topical anaesthesia be used as an ocular diagnostic aid
It can be used to do procedures on the eye. It can eliminate blepharospasm.
Local anaesthetic, small animals more comfortable and blepharospasm eliminated and easier to examine.
Blepharospasm is surface pain, closure of the eyelids
