Sudden Blindness

Question 1

describe the relationship between vision and PLR

Answer 1

1. vision itself is a brain function accomplished by the visual cortex
2. PLR peels off before vision so is considered subcortical
   -PLR can be used to determine if the retina/optic nerve work
3. PLR does not mean visual!!
   -can have a PLR and be bind
   -can have no PLR and be visual
4. can use a maze test to assess
   -but lots of things can confound

Question 2

what do we need for vision?

Answer 2

1. light must enter eye
2. passes through cornea, aqueous humor, lens, and vitreous to hit the retina
3. photoreceptors must be activated and send message to retinal ganglion cells
4. message conveyed via axos to optic nerve head to optic nerve
5. goes to chiasm, partial cross over
6. optic tracts to visual cortex which processes image and stars response

Question 3

desribe basic assessment for vision

Answer 3

1. is cornea, aqueous, lens, and vitreous transparent?
   -just need retroillumination
   -tapetal reflex means some vision should be present

Question 4

describe corneal causes of blindness

Answer 4

1. severe edema
   -end stage so highly unlikely to be acute presentation
2. severe pigmentary keratopathy
   -no tapetal reflex
   -dark orbs of doom

Question 5

describe anterior chamber causes of blindness

Answer 5

1. breakdown of the blood aqueous barrier can result in acute blindness
   -some manifestation of uveitis
2. opaque aqueous:
   -hyphema
   -severe hypopyon
   -lipid
   -uveitis: miotic pupil and hazy aqueous (flare = functional blindness)

Question 6

describe iridial causes of blindness

Answer 6

1. severe miosis
2. iridial tumor
3. severe iridociliary cysts

Question 7

describe lens causes of blindness

Answer 7

1. traumatic lens rupture
2. cataract:
   -rapid onset is often associated with juvenile or diabetic cataracts

Question 8

describe vitreal causes of blindness

Answer 8

1. severe vitritis (panophthalmitis)
2. vitreal hemorrhage

Question 9

describe retinal causes of blindness

Answer 9

1. sudden acquired retinal degeneration syndrome
2. retinal degeneration
3. retinal detachment
4. chorioenteritis

Question 10

describe sudden acquired retinal degeneration syndrome

Answer 10

1. aka SARDS
   -acute photoreceptor death
2. signalment:
   -usually middle aged dogs
   -females predisposed
   -all breeds affected
3. associated clinical signs:
   -often have weight gain, PU/PD/PP for weeks to months prior to vision loss
   -cushing’s like signs
4. clinical signs:
   -acute vision loss: often over 24hr period
   -dilated pupils at rest
   -minimal to no PLR (although clients bringing in earlier now so may have a relatively normal PLR)
   -normal fundic exam
5. diagnosis:
   -electroretinogram to confirm loss of photoreceptor function
   -may have elevated ALP or other cushing’s-like changes on bloodwork but rarely positive for cushing’s
6. treatment/prognosis;
   -no treatment, will have permanent blindness
   -fundus will develop opthalmoscopically visible signs of degeneration over time, similar to PRA
   -may also acutely lose sense of smell = very debilitating to lose vision + smell

Question 11

describe neurophthalmic exam of SARDs

Answer 11

1. no menace
2. negative dazzle reflex
3. reduced or normal PLR
4. positive blue PLR, negative red
   -specific wavelengths from a colorimetric PLR machine, still not gold standard diagnosis like electroretinogram (ERG)
5. normal fundic exam
6. flat ERG

Question 12

describe progressive retinal atrophy

Answer 12

1. not an acute form of blindness but can present as acute vision loss if environment changes cause owners to acutely notice
   -furniture move, trip to another environment, etc.
2. marked vessel attenuation, hyperreflectivity, myelon loss on nerve head
3. no acute treatment that will change the course of the disease (just like with SARDS)
   -so in ER setting you won’t screw the pooch if you miss these

Question 13

describe neurophthalmic exam of retinal degeneration

Answer 13

1. +/- PLR
2. negative menace
3. negative dazzle
4. fundoscopy:
   -tapetal hyperreflectivity
   -retinal vascular attenuation
5. low ERG

Question 14

describe neuropthalmic exam of retinal detachment

Answer 14

1. negative direct PLR
2. negative menace
3. negative dazzle if complete detachment
   -may be weakly positive if partial
4. fundoscopy:
   -partial or complete retinal elavation
5. hypertensive cats are the queens of acute vision loss due to retinal detachment
   -treat hypertension!!!!
   -any old cat with acute vision problems = BP is first thing to check

Question 15

describe optic nerve causes of blindness

Answer 15

1. optic neuritis
   -hopefully will have a good eye to compare to on the aniamal
   -negative PLR, menace, dazzle
   -fundoscopy: elevated, hyperemic, fuzzy optic nerve head
   -normal ERG
2. traumatic optic neuropathy

Question 16

describe causes of brain/cortical-associated blindness

Answer 16

1. brain tumor
2. cortical hypoxia
3. GME

Question 17

what can mouth gag use in cats lead to?

Answer 17

1. maxillary artery blockage
2. vision often returns
   -was lack of bloodflow to brain and eye

Question 18

describe central blindness

Answer 18

1. no menace
2. +/- dazzle reflex
3. positive PLR
4. normal fundic exam
5. normal ERG