The Lens Flashcards
The lens: Anatomy (summary)
Transparent; Avascular; Biconvex
- Anterior pole; Posterior pole
- Equator:
- Suspensory ligament
- Fossa hyaloidea
The lens: Components
- Lens capsule
- Anterior epithelium
- Cortex & nucleus
The lens: Capsule
Elastic envelope
The lens: Anterior epithelium
- Produced the lens cells
- Limited regeneration
- Active transport of nutrients
The lens: Lens cells
- Regular arrangement
- Lens sutures
The lens: Matrix
Cement substance
- 35% protein; 65% water
- Capsule rupture/Liquefaction of cement substance →
- Proteins reach the aqueous → Immune-mediated uveitis
- Aqeuous reach the matrix → Swelling of the lens & opacity
The lens: Developmental abnormalities
- Microphakia (Smaller lens)
- Aphakia (Ø lens)
The lens: Cataract - Definition
Any local or diffuse opacity in the lens
The lens: Cataract - Pathogenesis
Biochemical cause of opacity; Failure of:
- Lens nutrition
- Lens protein metabolism
- Lens energy metabolism
- Lens osmotic balance
Classification of cataracts: By aetiology
- Metabolic
- Hereditary
- Associated
- Nutritive
- Infectious
- Traumatic
- Toxic
Classification of cataracts: By maturity
- Early
- Immature
- Mature
- Intumescent
- Hypermature
- Morganian
Classification of cataracts: By time of onset
- Congenital
- Juvenile
- Senile
Cataracts: CSx
- Uncertain movement of the animal; Hitting objects
- Grey-white colourisation in the pupil
- Determination of the opacity with the slit lamp
Cataracts: Treatment
Surgery only
- Expensive & difficult
- Careful patient selection
- Pre- & postoperative management is important
Cataracts: Development of surgeries
- Intracapsular lens extraction (ICE)
- Extracapsular lens extraction (ECE)
- Phacoemulsification (PHACO)
- PHACO + intraocular lens (IOL) implantation
Intracapsular lens extraction
Extracapsular lens extraction
Phacoemulsification
Cataract surgery: Define phacoemulsification
- Ultrasound chopping/fragmentation of the lens cortex & nucleus
- Sucking of these fragments
The lens: Subluxation & luxation
Partial/complete displacement of the lense from the fossa hyaloidea
Lens luxation/subluxation: Aetiology
Primary: Hereditary
Secondary:
- Glaucoma
- Cataracts
- Intraocular tumour
- Traumatic injuries
Lens luxation/subluxation: Congenital predisposition
- Fox terrier
- Jagd terrier
- Welsh terrier
- Tibetian terrier
- Mini Schnauzer
- Poodle
Lens luxation/subluxation: Pathogenesis
- Cause
- Partial/complete rupture of the zonules
- Lens displacement:
- Anterior lens lux.
- Posterior lens lux.
- Subluxation
Lens luxation/subluxation: CSx
- Partial discplacement
- Impaired vision; Uni-/bilateral
- Vitreous humour present in the chamber
- Edge of the lense may be observed (“Aphakic crescent”)
Anterior lens luxation: CSx
- Impaired vision
- Lens & vitreous presentation in the anterior chamber
- Narrow anterior chamber
- Corneal opacity
- Uveitis
Posterior lens luxation: CSx
- Impaired vision
- Iridodenesis; Concave iris
- Unusually deep anterior chamber
- Lens in the vitreous humour
- Uveitis
Lens subluxation: Treatment
- Observation
- Medication (miotics; anti-inflammatory drugs)
Anterior lens luxation: Treatment
- Observation
- ICE
- ICE + IOL
- Reclination
Posterior lens luxation: Treatment
Medication
- Miotics
- Anti-inflammatories
