6. Diseases of the lens. Neoplasia of the eye.

What is the function of the crystalline lens?

Refracts incoming light rays to a point source on the retina

Describe the anatomy of the lens.

The crystallin lens is an avascular, transparent, & highly structured tissue.

It contains only a single layer of cuboidal cells, the anterior epithelium, inside the anterior lens capsule. Cortex, nucleus and posterior lens capsule.

The lens is attached to the ciliary body by fibres

What is the composition of the lens?

66% water and 33% proteins

Where in the eye has the most intensive refraction?

1. Cornea

2. Lens

What are examples of diseases of the lens?

1. Congenital abnormalities

2. Cataracts

3. Lens luxation and subluxation

What are the congenital abnormalities of the lens?

1. Aphakia

2. Microphakia

3. Lenticonus/lentiglobus

4. Coloboma

5. Lens luxation

6. Vascular abnormalities (persistent pupillary membrane, PHTVL/PHPV)

What is aphakia?

Complete absence of the lens

What is microphakia?

Abnormally small lens

What is lenticonus/lentiglobus?

Deformity of the lens

What is coloboma of the lens?

Part of the lens is missing

What is lens luxation often in conjunction with?

Microphthalmia

What is PHTVL/PHPV?

Persistent hyperplastic tunica vasculosa lentis/Persistent hyperplastic primary vitreous, a vascular abnormality of the lens

What are the grades of PHTVL/PHPV?

• Grade 1: retro lens fibrovascular pigment/dots

• Grade 2: dot + proliferation of retro lens tissue on the posterior lens capsule

• Grade 3: plaque + persistent part of the hyaloid vessel

• Grade 4: plaque + lenticonus

• Grade 5: combination of Grades 3 and 4

• Grade 6: combination of any grade with coloboma lentis, microphakia, retro lens pigment + bleeding

What are cataracts?

Increased opacity of the lens due to clumping and accumulation of proteins

How can cataracts be classified?

1. Age

2. Aetiology

3. Consistency

4. Localisation

5. Degree of maturation

How are cataracts classified in relation to age?

1. Congenital

2. Developmental

3. Juvenile

4. Senile

5. Acquired

How are cataracts classified by aetiology and pathogenesis?

1. Primary (hereditary)

2. Secondary (traumatic, due to intraocular diseases like uveitis, nutritional, radiation, diabetes, toxic, congenital abnormalities, senile)

How are cataracts classified by consistency?

1. Soft

2. Hard

3. Watery

How are cataracts classified by localisation in the lens?

1. Anterior capsular

2. Anterior subcapsular

3. Cortical (anterior or posterior)

4. Equatorial

5. Nuclear or perinuclear

6. Posterior capsular

7. osterior subcapsular

How are cataracts classified by degree of maturation?

1. Incipient

2. Immature

3. Mature

4. Hypermature

What is an incipient cataract?

Focal opacity in the lens

What is an immature cataract?

Increased lens size and impaired vision

What is a mature cataract?

Totally opaque lens, absent fundic reflex, blindness

What is a hypermature cataract?

Wrinkling of the anterior lens capsule, crystal formation, liquefaction by proteolysis, and potential ventral settling of the lens nucleus

Which breeds are predisposed to congenital/hereditary cataracts?

Miniature Schnauzer, Boston Terrier, Old English Sheepdog, Welsh Springer Spaniel, West Highland White Terrier

What general diseases can contribute to cataract formation?

Diabetes, hypocalcaemia, and hypercupraemia

What nutritional deficiencies can contribute to cataract formation?

Arginine deficiency and use of inappropriate milk replacers

What external factors can contribute to cataract formation?

Various toxins and ionising radiation

What is the major clinical sign of cataracts?

Cloudiness of the lens. Other signs may include increased lens size and impaired/lost vision

What are the treatment options for cataracts?

1. Spontaneous recovery (rare)

2. Conservative management (topical mydriatics, aldose reductase inhibitors)

3. Surgical removal of the lens

What are the surgical techniques for cataract removal?

1. Extracapsular cataract extraction (leaving the capsule)

2. Intracapsular extraction (removing the capsule)

3. Phacoemulsification (using ultrasound to break up and aspirate the lens – the gold standard) with intraocular lens implantation

What is lens luxation/subluxation?

Dislocation (complete) or subluxation (partial) of the lens from its normal position due to pathological changes in the ciliary zonules

Which breeds are predisposed to lens subluxation?

Terrier breeds

What are the clinical signs of anterior lens luxation?

Acute signs including glaucoma and corneal oedema

What are the clinical signs of posterior lens luxation?

May be asymptomatic or cause ocular inflammation and glaucoma

What are the clinical signs of lens subluxation?

Instability of the iris and lens (half-moon-shaped edge)

How is lens luxation/subluxation treated?

Surgical removal of the lens by phacoemulsification or intracapsular lens extraction, depending on pain and vision status

What are examples of neoplasia of the eye?

1. Iris melanoma

2. Ciliary body adenoma/adenocarcinoma

3. Uveal canine lymphoma

What are some treatment options for ocular neoplasia?

Surgical excision, radiation, cryotherapy, and enucleation

What is the most common eye tumour in dogs?

Iris melanoma

What are the clinical signs of iris melanoma?

Changes in iris pigmentation, potentially causing dyscoria and glaucoma. It can metastasise.

How is iris melanoma treated?

Laser coagulation

What are the clinical signs of ciliary body adenoma/adenocarcinoma?

Pink-red mass in pupil, swollen conjunctiva, prominent third eyelid, mydriasis, detached retina, and potential glaucoma

How is ciliary body adenoma/adenocarcinoma treated?

Tumour removal

What is uveal canine lymphoma?

A secondary tumour (originating elsewhere) presenting as pink-white masses on the uvea

What are some other ocular tumours?

Dermoid, malignant melanoma on the cornea, uveal melanoma, and uveal lymphosarcoma