Unit 2 - The Lens and Vitreus Flashcards by Jessica Carson

In utero, what does the pupillary membrane develop from?

The iris

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In utero, what does the tunica vasculosa lentis develop from?

The hyaloid artery

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T/F: Vasculature from in utero development of the eye atrophies by the time of the eyelid opening.

True

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T/F: Lens growth stops at the end of puberty.

False - it continues throughout life

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Explain how the lens grows throughout life.

The lens epithelial cells form the cortex and new fibers force the older ones to the center

The nucleus hardens with age resulting in nuclear sclerosis

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What are the components of the lens?

Lens capsule

Anterior epithelium

Lens fibers

Equator

Nucleus

Cortex

Y sutures

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How big is the lens capsule of the anterior lens in the dog?

50-70 microns

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How big is the lens capsule of the posterior lens in the dog?

2-4 microns

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What are the Y sutures?

The location where the lens fibers come together - as long as there is no cataract associated with them, they are not a problem

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How are the Y sutures oriented on the anterior lens? Posterior lens?

Anterior - upright Y

Posterior - upside down Y

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What is the lens suspended by?

Zonules from the ciliary body

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The lens is _________ and (avascular/vascular). It recieves its nutrition from ________ ______. Its primary function is _______ of light to focus on the retina.

Transparent

Avascular

aqueous humor

refraction

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What are the categories of abnormalities that the lens can have>

Congenital defects

Nuclear sclerosis

Cataract

Lens luxation/subluxation

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What congenital defects are associated with lens abnormalities?

Lens coloboma

Microphakia

Spherophakia

Aphakia

Cataract

Persistent fetal vasculature

Persistent pupillary membrane

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What is lens coloboma?

Defect/notching of the lens equator

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What is microphakia?

small lens

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What is spherophakia?

Spherical lens

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What is aphakia?

Absence of a lens

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What persistent fetal vasculature can there be in the lens?

Persistent hyaloid artery

Persistent tunica vasculosa lentis

Persistent hyperplastic primary vitreous

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T/F: Nuclear sclerosis is a normal aging process.

True

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What does nuclear sclerosis look like?

Grayish blue haze of the lens - can be seen in dogs that are greate than 6 years of age

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T/F: Nuclear sclerosis has minimal effect on vision.

True

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What is it important to differentiate nuclear sclerosis from?

Cataracts

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What is a cataract?

An opacity in the lens or lens capsule

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What are cataracts classified based on?

Etiology Age of onset Location in the lens Stage of development

A patient with only a cataract should have a normal \_\_\_\_.

PLR

Nuclear sclerosis or cataract?

Cataract

Nuclear sclerosis or cataract OU?

Nuclear sclerosis

Nuclear sclerosis or cataract OU?

Nuclear sclerosis

Nuclear sclerosis or cataract?

Nuclear sclerosis

Nuclear sclerosis or cataract?

Cataract

Nuclear sclerosis or cataract?

Cataract

Nuclear sclerosis or cataract?

Nuclear sclerosis

Nuclear sclerosis or cataract?

Cataract

Nuclear sclerosis or cataract OU?

Cataract

Nuclear sclerosis or cataract OS?

Cataract

Nuclear sclerosis or cataract OD?

Cataract

What are the causes of cataracts?

Hereditary Metabolic Secondary to uveitis Traumatic Radiation Toxic

What is the most common cataract cause in dogs?

Hereditary

What are the metabolic causes of cataracts?

Diabetees mellitus (dogs) Galactosemia Milk replacer Hypocalcemia

What species commonly get cataracts secondary to uveitis?

Cats and horses

What traumatic situations can result in cataract formation?

Blunt or penetrating trauma Electric cord shock or lightening strike

What toxins can result in cataract formation?

Ketoconazole Retinal degeneration (due to toxin)

Where can a cataract be located?

Capsular Subcapsular Nuclear Perinuclear/lamellar Cortical Equatorial Axial Anterior/posterior

How do you differentiate the location of a cataract?

Dilate the pupil and differentiate by direct exam and retroillumination

What are the four stages of a cataract?

Incipient. iimmature, mature, hypermature

What is an incipient cataract?

Punctate opacity, \<15% of the lens

What is an immature cataract?

15% to 99% opacification Some tapetal reflection remains +/- vision

What is a mature cataract?

Complete (100%) opacification No tapetal reflection visible and blind

What is a hypermature cataract?

Resorption of cataractous lens Highly variable appearance: sparkling, wrinkled capsule

What is the pathogenesis of Diabetic cataracts?

Normally, glucose is metabolized by anaerobic glycolysis. High blood glucose increases lens glucose and overwhelms hexokinase enzyme. The excess glucose is metabolized by aldose reductase system to sorbitol. Sorbitol accumulates within the lens and causes an osmotic effect. Fluid is drawn into the lens and causes architectural changes in the lens fibers

What species are especially susceptible to diabetic cataracts?

Mice, dogs, and rats

What is phacolytic uveitis?

The leakage of some lens proteins through an intact lens capsule resulting in mild/moderate lens-induced uveitis

Phacolytic uveitis is common in what cataract scenarios?

Diabetic, hypermature, and some juvenile cataracts

What is phacoclastic uveitis?

The rupture of the lens capsule due to trama or rapidly progressing cataracts. It is associated with severe inflammation and requirse medications and maybe surgery ASAP.

What should you monitor for in patients with phacoclastic uveitis?

Secondary glaucoma

What is the general medical therapy recommended for cataracts?

Treat/prevent lens-induced uveitis Monitor eye status and intraocular pressure Prevent diabetic cataracts

What can be given to treat/prevent lens-induced uveitis (general)?

Topical NSAID BID Topical steroid SID-QID Systemic anti-inflammatories

What is the preferred topical NSAID for the treatment/prevention of lens-induced uveitis? Other options?

Preferred: Diclofenac Other options: Flurbiprofen, ketorolac

What is the preferred topical steroid for the treatment/prevention of lens-induced uveitis? Other options?

Preferred: Prednisolone acetate 1% Other options: Dexamethasone 0.1% (Neo-Poly-Dex)

When should you refer for cataract surgery?

Refer early - when cataracts are first noted The ideal time for surgery is when cataracts are immature and there is no lens-induced uveitis

What are the components to a cataract surgery work-up?

Complete ophthalmic examination Physical examination Gonioscopy Electroretinogram Ocular ultrasound

What does a gonioscopy evaluate?

Iridocorneal angle

What does an electroretinogram evaluate?

Electrical activity of the retina

What does the ocular ultrasound evaluate?

The posterior segment

What are the post operative complications of cataract surgery?

Uveitis, glaucoma, retinal detachment, and endophthalmitis

What is the cause of primary lens luxation?

Hereditary - Terrier breeds are predisposed

What are the secondary causes of lens luxation?

Glaucoma, uveitis, trauma, introcular tumors, cataracts`

What is lens subluxation?

Partial detachment of lens zonules

What possible clinical findings are associated with lens instability?

Aphakic crescent Iridodensis Phacodensis Vitreous coming into the anterior chamber

What is lens luxation?

Complete detachment of the lens zonlues

What is anterior lens luxation? Posterior?

Anterior - lens luxation anterior to the iris (behind the cornea) Posterior - lens is posterior to the iris (deep anterior chamber)

When is an anterior lens luxation emergent?

If the lens luxation is recent and the dog/cat is visual

How do you treat emergent anterior lens luxations?

Intracapsular lens extraction +/- sulcus IOL fixation Trans-corneal reduction

What condition do you need to make sure to treat if there has been an anterior lens luxation? How is it treated?

Secondary glaucoma - mannitol IV, topical/oral carbonic anhydrase inhibitors, DO NOT GIVE MIOTICS

T/F: Secondary lens luxation is emergent.

False - it is not

What is the treatment for primary lens subluxation?

Proactive surgical lens removal OR Medical therapy BID to keep pupil miotic and lens back (prostaglandin analogs and parasympathomimmetics)

How is posterior lens luxation managed?

No management is necessary if the lens is in a fixed position Miotic therapy is warranted if possible to lens shift

Vitreous is ____ of the globe volume. Its appearance is _____ and \_\_\_\_-like. It is made up of 99% ____ and 1% \_\_\_\_\_\_\_\_/\_\_\_\_\_\_.

\>2/3 Transparent Jelly-like Water Collagen/hyaluronic acid

What is the funciton of the vitreous?

Supports lens anteriorly Maintains globe shape Transmits light to the retina Supports retina posteriorly

What vitreous abnormalities can occur?

Vitreal cells Vitreal hemorrhage Vitreal degeneration Asteroid hyalosis

What is asteroid hyalosis?

Small white particles that are calcium or phospholibids that create a snow globe effect in the eye