Retina, part I

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Retina, part I

• Björn Ekesten
• Department of Clinical Sciences, SLU
• 2006

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Anatomy
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Cells in the neuroretina

• Five major cell types
• Photoreceptors
• Rods and cones
• Horizontal cells
• Lateral communication
• Bipolar cells
• Vertikal communication
• Amacrine cells
• Lateral communication
• Vertical communication
• Ganglion cells
• Glia, chiefly Müller cells

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Rod pathways
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Cone pathways
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Retinal pigment epithelium (RPE)

• Not neuronal cells
• Cytoplasm surrounds the outer segments of the
  photoreceptors
• Phagocytizes shedded material
• Important for the metabolism of vitamin
  A-derivatives (retinol/11-cis-retinal)
• Essentiell for maintenance of photoreceptor
  function
• Non-pigmented over tapetum lucidum

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Postretinal pathways
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Examination of ocular fundus

• Ophthalmoscopy
• Direct
• Indirect
• Electroretinography
• DNA-testing

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Direct ophthalmoscopy

• Pros
• High magnification
• Cat 20x
• Dog 17x
• Horse 8 x
• Different apertures and colors
• Dioptric power can be adjusted
• Refractive error compensation
• Depth estimates
• Examination of more anterior parts
• Cons
• Close to the teeth
• Small field of view - periphery, eye movements
• No stereopsis
• Image marred by opacities

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Direct ophthalmoscopy

• Use the same eye that you are about to examine
  (OD-OD etc).
• Find the fundus reflex at 1/2 m distance.
• Follow the reflex and go closer until you see the
  fundus.
• Adjust the dioptric power settings until you have
  a focused image.
• Wait until the right area comes into the field.

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Indirect ophthalmoscopy

• Pros
• Large field of view
• Stereopsis
• Image less affected by opacities
• Safer working distance
• Can be used for inspection and magnification of
  other tissues
• Cons
• Lower magnification
• 20 D ger 1/10 x compared to direct
• More difficult to master technically
• More expensive

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Indirect ophthalmoscopy

• Inverted, mirror image
• Working distance approximately 50 cm
• Start with 20 / 30 D
• Hold the lens about 5 cm from the patients eye.
• Adjust the distance until the image fills the
  lens.
• Tilt the lens and adjust the size of the light
  beam to get rid of reflexes.

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Diseases of the ocular fundus

• Hereditary
• Congenital
• Not congenital

• Acquired
• Infections and inflammations
• SARD
• Toxic conditions
• Metabolic diseases
• Cardiovascular diseases
• Glaucoma
• Neoplasias

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Some congenital diseases

• Collie eye anomaly
• Retinal dysplasia
• Night blindness
• Optic nerve hypoplasia / micropapilla

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Collie eye anomaly

• Syndrome in the
• Collie
• Shetland Sheepdog
• Border Collie
• Australian Shepherd
• Three types of defects
• Chorioretinal dysplasia
• Go normals
• Coloboma
• Retinal detachment
• Secondary signs
• Intraocular hemorrhage

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Retinal dysplasia

• Abnormal proliferation causing folds and rosettes
  in neuroretina
• Multifocal form (tapetum)
• Geographic form (tapetum)
• Complete (detached / non-attached)
• Hereditary condition in several Retriever and
  Spaniel breeds etc
• Induced
• Radiation (therapy)
• Infection with canine herpesvirus

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Complete retinal dysplasia

• Important to look for during pre-purchase exam of
  pups
• Impaired vision
• Abnormal direct PLR
• Microphthalmia
• Esotropia
• Nystagmus
• Intraocular hemorrhage
• Examine with a focal light
• Look for abnormal behavior

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Night blindness

• Night blindness / RPE 65 defect in the Briard
• Night blindness and slowly progressive impaired
  daylight vision
• Enzymatic defect in the vitamin A-metabolism
• Recessive inheritance
• Initially normal fundic appearance
• Appaloosa
• Night blindness and dorsomedial strabismus
  (squinting)
• Usually not progressive
• X-chromosome linked

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Optic nerve hypoplasia / micropapilla

• Fewer gnaglion cells
• Congenital malformation
• Sporadic finding in all breeds
• Reported to be inherited in the Poodle
• Usually uniocular
• Hypoplasia impaired vision
• Mikropapilla no clinical signs
• Aplasia total absence

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Amblyopia and strabismus

• Abnormal development of visual areas in the
  cortex
• Secondary to severe strabismus
• Minature breeds
• Cattle
• Receives little attention

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Amaurosis

• Central nervous blindness
• Congenital malformations
• Head trauma
• Encephalitis / meningoencephalitis
• Neoplasias
• Precise diagnosis may be difficult
• MRI
• Electrophysiology
• Always guarded prognosis