Disorders of the Lens Flashcards
What provides the lens with its nutrients?
The aqueous humor; some from vitreous humor
Nuclear sclerosis
compaction of fibers in the lens cetner- does NOT obstruct light // affect vision
- a normal exam finding in middle-aged dogs & cats / horses
Lens functions
Congenital Lens Disorders
Aphakia
Microphakia
Spheropphakia
Coloboma
Lenticonus
Vascular Anomalies
Aphakia (lack of lens)
Microphakia (small lens)
Spheropphakia (rounder lens, instead of oval)
Coloboma (Developmental absence of zonular fibers -> flattening of lens equator due to lack of tension -> notch develops)
Lenticonus (elongation of lens capsule & cortex, often associated with vascular anomalies)
Vascular Anomalies -> most common!
Embryonic Vascular Anomalies
STRUCTURES THAT FAILED TO REGRESS AFTER EMBRYONIC DEVELOPMENT
PPM: remants of blood vessels of the embryonic lens
Persistent Hyaloid Artery: remnants of arteries of embyronic lens
Persistent hyperplastic primary vitreous (PHPV), also known as persistent hyperplastic tunica vasculosa lentis (PHTVL) or PHPV/PHTVL, is a condition of the vitreous in which the ophthalmic embryologic vascular structures do not regress normally.
Sequela of embryonic vascular anomalies
Cataracts
Cataracts = opacity of lens => vision loss due to the obstruction of light
What are the most common causes of cataracts in dog vs. cats?
DOGS
- Genetics
- Senescence
- Metabolic (e.g., diabetes)
CATS & horses
- Chronic uveitis
Clinical Staging of Cataracts:
- Incipient
- Immature
- Mature
- Hypermature
- Incipient: less than 15% of lens is affected
- Immature: more than 15% of lens is affected, but tapetum reflex is still visible
- Mature: more than 15% of lens affected and tapetum reflec is NOT visible
- Hypermature: reabsorption of zonular fibers -> more lens-induced uveitis (lens disappears -> lens capsule degenerates / liquifies and lens proteins leak out -> uveitis)
What characterizes Hypermature cataracts?
Wrinkling of the lens capsule
Why is there no appreciable effect on PLR or Dazzle Reflex in cataracts?
B/c in cataracts, the optic nerve and retina are unaffected; only the lens is affected due to increased opacity / light obstruction / breakdown of proteins in/of the lens
Glaucoma: IOP and optic nerve compression
Cataract treatments (2 types of elective surgeries)?
Elective surgeries (elective b/c dog can still life its life with cataracts)
-
Phacoemulsification
- corneal and lens incisions -> u/s probe breaks the elns, sucks up the material and irrigates the material -> leave lens capsule open -> place artificial lens in -> close cornea -
Intracapsular lens extraction: 360º incision onto cornea and complete removal of the elns
- indicated for lens instability / luxation
Lens-Induced Uveitis
- The 2 most common causes
- Treatment
Causes
1. Cataracts (especially rapdily progressive or chronic/hypermature)
2. Lens Rupture (trauma // cat scratch laceration)
Treatment
- topical corticosteroids (short-term)
- lens removal if ruptured
Clinical signs of lens luxation
Anterior or posterior
Blephrospasms, epiphora (excessive tear production), hyperemia, edema => => diminished vision
Latanoprost is used for what in lens luxation?
Posteior lens luxation -> latanoprost = prostaglandin analog / miotic agent that traps the lens to stay in the back. Life-long eye drop
Etiologies / Signalment of lens luxation (1º versus 2º)
Anything that causes the zonular fibers to degenerate / not work. Jack Russel Terriers! Shar Peis! Age 3-7
Asteroid Hyalosis
- Vitreous degenerative disorder – senescene condition in dogs
- small, white spherical bodies (calcific / lipid deposits) wthin the vitreous humor
- sometimes associated with intraocular neoplasms
Vitreal Hemorrhage - what is the band?
