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Neurology & Special Senses > 1.2 The Blind Eye > Flashcards

1.2 The Blind Eye Flashcards

1
Q

What are the main causes of blindness?

A
  1. symblepharon
  2. karatitis
  3. PPM (persistent pupillary membranes)
  4. uveitis
  5. cataracts
  6. glaucoma
  7. posterior segment disease (PSD)

note: PSD is comprised of both vitreal diseases and fundic diseases

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2
Q

What forms the fibrotic tunic of the eye?

A

the cornea and the sclera (and episclera) - covers the whole of the globe and give it its shape

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3
Q

What forms the uvea of the eye?

A

formed by the iris, ciliary body, and choroid- vascular layer that provides the blood supply to the eye

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4
Q

What forms the neural layer of the eye?

A

composed of the retina which is continuous with the optic nerve

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5
Q

Explain the path of light as it travels through the eye and into the brain

A

Light travels through cornea → aqueous humour →lens →
vitreous humour, where it spreads out and hits the retina.

This light impulse is then transformed into an electrical impulse which moves from the retina towards the optic nerve → optic canal → optic chiasm → optic tract → lateral geniculate nucleus → optic radiation → occipital cortex

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6
Q

What is symblepharon?

A

Symblepharon is a pathologic condition where the bulbar and palpebral conjunctiva form an abnormal adhesion to one another, or to the cornea. Most cases of symblepharon are acquired, though it can rarely be congenital, as sometimes seen in cases of cryptophthalmos.

More common in cats than dogs, usually secondary to FHV

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7
Q

What is keratitis?

A

inflammation of the cornea (immune mediated or secondary to irritation)

e.g. Pigmentary Keratopathy (pigment on the cornea) - common in brachycephalic and 2º to entropion, trichiasis, euryblepharon (large palpebral fissure)

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8
Q

What is PPM?

A

Persistent Pupillary Membrane

Embryologic membrane which give blood supply to the lens (alonside the hyaloid artery) as it develops

  • both should regress
    after birth
  • remains instead leading to corneal / lens opacity

note: if the hyaloid artery persists this can (but not always) lead to vision imparement, or cataract associated with the lens attachment

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9
Q

From which structure does a PPM originate?

A

originates from the iris collarete

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10
Q

What are the 4 types of PPM?

A

Type 1: (least severe) little dots on the surface of the lens, usually incidental finding

Type 2: iris to iris, cannot see through iris regardless, so little effect on vision

Type 3: iris to lens

Type 4: most severe form, iris to cornea

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11
Q

What is the normal function of the uvea?

A

The uvea (iris, ciliary body and choroid) is the only structure in the eye that supplies blood to the cornea, lens, vitreous, and retina

It holds the lens in place at the level of the ciliary body (which forms the aqueous humor) and forms the blood ocular barrier

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12
Q

What is uveitis?

A

uveitis is inflammation of the middle layer of the eye, called the uvea or uveal tract. It can cause eye pain and changes to your vision

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13
Q

What are the clinical signs of uveitis?

A
  • 1st stage: aqueous flare (Tyndall Effect): aqueous humor is normally clear but during uveitis, the blood aqueous barrier is disrupted leading to blood contents reaching the eye
  • Hypopyon / Hyphema - WBC / RBCs in the anterior chamber (not necessarily infection)
  • Synechia
  • Ocular pain and blindness (↓ IOP → if chronic then ↑ IOP)
  • Corneal edema
  • Miosis
  • Conjunctival / episcleral hyperemia
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14
Q

What are the complications of chronic uveitis?

A
  • cataracts – uveitis can cause cataracts due to poor nourishment of the lens - however, cataracts can also cause uveitis (lens induced uveitis) due to protein leakage
  • other complications: retinal detachment, glaucoma (due to 360 posterior synechia), lens luxation (most common in cats)
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15
Q

What can cause uveitis?

A

ocular causes (more commonly lead to unilateral uveitis)

  • secondary to: complicated ulcers, penetrating ocular trauma (e.g. foreign body), blunt ocular trauma, cataracts, intraocular tumor

systemic causes (more commonly lead to bilateral uveitis)

  • vascular causes: systemic hypertension, anemia, vasculitis, etc.
  • infectious causes:
    viral: FeLV, FIV, others
    parasitic: toxoplasma, leishmania, others
    fungal: cryptococcus, others
    bacterial: pyometra, others
  • immune-mediated causes: uveodermatologic syndrome, other
  • systemic neoplasia: lymphoma, carcinoma, others
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16
Q

How do you diagnose uveitis?

A
  1. perfrom a complete ophthalmic examination (check eye pressure, rule out ulcer, cataracts, etc.)
  2. perform a complete physical exam
  3. Identify underlying cause:
    a. ocular causes may require an ocular ultrasound if the eye is opaque
    b. systemic causes – blood pressure measurement, comprehensive biochemistry and hematology, rerology for infectious diseases, full body CT (X-rays, AUS)

Tyndall Effect indicates ocular blood barrier (OBB) issue (stage 1)

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17
Q

What is the treatment for uveitis?

A

topical treatment - if ocular disease permits
* steroid/NSAID eye drop QID to treat the inflammation
* cycloplegics eye drop (to treat the ocular pain): tropicamide BID, atropine SID/EOD

systemic treatment - if concomitant disease permits
* systemic NSAID: carprofen, meloxicam, other
* systemic immune suppressive (if uveitis is secondary to an immune-mediated disease): prednisolone, other

Uveitis MUST be treated for even as results are pending due to sequelae

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18
Q

What is synechia?

A

an eye condition where the iris adheres to either the cornea (i.e. anterior synechia) or lens (i.e. posterior synechia)

may be a complication of uveitis

19
Q

What is miosis and mydriasis

A

miosis is a constricted pupil

mydriasis is a dilated pupil

word length can help you remember this

20
Q

What are cataracts?

A
  • Opacity of the lens impedes light transmission
  • All cataracts can interfere with sight BUT only complete, mature cataracts will cause blindness
21
Q

What causes cataracts?

A

many things (inherited, congenital, traumatic, metabolic, nutritional, senile, progressive retinal atrophy, etc.)

22
Q

What is nuclear sclerosis?

A

nuclear sclerosis is a normal change with age; and while can make vision slightly blurry will not impede sight or function

  • nuclear sclerosis has an even, pearly opacity with grey to blue appearance
  • cataracts appear as whitish chunks of ice that vary in size, shape, and opacity
23
Q

What is glaucoma?

A

glaucoma is a group of eye diseases that can cause vision loss and blindness by damaging the optic nerve

  • pathophysiology: problem in the drainage of aqueous humor i.e. obstruction of outflow pathways
  • increased IOP → blindness (pressure too high for optic nerve to function)
24
Q

What is the difference between primary and secondary glaucoma?

A
  • primary glaucoma is inherited - breed disposition (hereditary malformation or malfunction of the aqueous humor outflow pathways)
  • secondary develops in association with concurrent ocular disease, e.g. uveitis, lens luxation, cataract
25
Q

List the main fundic diseases.

A
  • progressive retinal atrophy (PRA)
  • acute retinal diseases (SARDS, IMR)
  • retinal detachment (RD)
  • systemic hypertension
  • optic neuritis
  • optic nerve neoplasia

specific other:
* collie eye anomaly
* enrofloxacin retinal toxicity in cats

(+) sudden acquired retinal degeneration syndrome
(++) immune mediated retinopath

26
Q

What is progressive retinal atrophy (PRA)

A
  • inherited condition
  • on exam: hyperreflective tapetum (thinning of overall retina) and vascular attenuation (thinning retinal vessels)
  • genetic test available for some breeds
  • slowly progressive - often presents in middle age dogs as night blindness
  • no treatment but not painful
  • clinical history is important, consider breed: miniature and toy poodles, cocker spaniels, and Labrador retrievers
27
Q

What is SARDS

A

sudden acquired retinal degeneration syndrome (actue blindness with no opthalmic or neurological abnormalities)

  • dazzle reflex, menace response, and PLR = negative
  • ERG (electroretinography): a flat recording
  • colorimetric PLR: absent with RED light, present with BLUE light (due to the degeneration of certain photoreceptors)
  • no treatment available
28
Q

What is IMR?

A

immune mediated retinopathy

  • similar changes to SARDS but not well characterized
  • can respond to systemic immune suppression
29
Q

What is retinal detachment, and what would you see on PE?

A

neuro-retina detaches from the retinal pigment epithelium (RPE): several causes

on exam:
- findings of a pre-chiasmal lesion (absent direct/indirect PLR and absent menace response)
- hyporeflective tapetum
- retinal vasculature remains visible and appears closer to the lens
- retina always remains attached to optic nerve

30
Q

What can systemic hypertention do to the eye?

A
  • intraocular hemorrhages: anterior chamber hyphema, vitreal and retinal hemorrhages)
  • bullous retinal detachment (retinal vessles secrete blood or fluid from hypertention into subretinal space)
  • irideal hemorrhages
  • tortuous retinal vessels
31
Q

List the main optic nerve diseases.

A

optic neuritis: meningoencephalitis of unknown etiology (MUA) or infectious disease (e.g. distemper)

  • hyperemic (pink) swollen optic nerve, vascular congestion, hemorrhages around optic nerve

optic nerve neoplasia

  • meningioma is most common neoplasia of the optic nerve
32
Q

What is retinal dysplasia?

A

the unusual development of the retina; multiple causes

  • unilateral or bilateral, but when inherited always bilateral - CKCs, English Springer Spaniel
  • 3 main types (from less→ more severe): retinal folds, geographic form, retinal detachment
33
Q

What is the “collie eye anomaly”?

A

inherited disease in Collie breeds (genetic test available)

  • combination of: choroidal hypoplasia and optic nerve head coloboma
  • can lead to retinal detachment and hyphema / vitreal bleed
34
Q

What antibiotic can cause retinal toxicity in cats?

A

enrofloxacin

  • can even happen at recommended doses
  • all fluoroquinolones should be used with caution (but pradofloxacin is considered safe)
35
Q

What is equine recurrent uveitis (ERU)?

A

non-specific immune-mediated disease leading to recurrent inflammatory episodes
- most common in draft, warmblood, and european breeds

36
Q

What are the three types of ERU

A
  • classic ERU
  • insidious ERU
  • posteroir ERU
37
Q

What are the main differences between the forms of ERU?

A
  • classic ERU: episodes of active intraocular inflammation followed by variable quiescent periods
  • insidious ERU: subclinical ocular inflammation persists without obvious signs of discomfort until severe chronic symptoms develop
  • posterior ERU: affects the retina and the choroid at the back of the eye; difficult to diagnose due to location
38
Q

How is ERU treated?

A

the aim is to preserve vision
- medical: topical NSAIDs/steroids/atropine, intravitreal/subconjunctival injections of steroids (severe)
- surgical: cyclosporine implants (suprachoroidal), pars plana vitrectomy (removes vitreous humor), enucleation

atropine dilates the pupil and relaxes the ciliary body (reduces pain from ciliary spasms associated with uveitis)

39
Q

What are cataracts?

A

opacities of the LENS which impare light transmission
- only mature cataracts cause complete blindness

40
Q

How can cataracts lead to uveitis?

A

occurs via inflammation caused by lense protein
- phacolytic: lense protein diffuses through intact lens capsule (chronic)
- phacoclastic: lens protein enters eye via lens capsule rupture (acute traumatic)

41
Q

How can uveitis lead to cataracts?

A

chronic uveitis can lead to poor nurishment of the lens capsule, eventually causing cataracts

42
Q

How do cataracts appear on illumination?

A
  • direct illumination: whitish chunks of ice that vary in size and shape
  • retroillumination: dark (tapetum reflection impeded)
43
Q

How does diabetes lead to cataract formation?

A

High blood glucose leads to high aqueous glucose. Glucose is converted into sorbitol (large molecule that cannot exit the lens). The lens swells and bursts, leading to cataract formation. 80% of diabetic dogs will acquire cataracts within the first 6 months of diagnosis.

Neurology & Special Senses (22 decks)

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