Lens Flashcards
Lens definition
Transparent biconvex structure with iris and pupil anterior and vitreous body posterior
Functions (3)
Second refracting unit of the eye - converging power 15 - 20D - refractive index 1.38 - 1.4 Accommodation Barrier (infection, aqueous, vitreous)
General structure
10mm diameter, 4mm thick
Capsule (collagen IV and glycoprotein matrix to maintain shape + accomodation)
Epithelium (cuboidal anterior capsule and highly mitotic at equator; energy production, metabolism, transport and secretion of capsular material)
Nucleus and cortex (lens fibres from epithelium and proteins alpha, beta and gamma crystallins)
Suspended by suspensory ligaments and zonules
Accommodation
Cilliary muscle contracts
- Lens becomes more globular/convex
- Miosis via PNS to limit light
- Convergence via medial rectus to prevent diplopia
Cataract definition
Lens becomes opaque
Cataract causes
Senile Congenital (i/3 AD, 1/3 trauma, galactosemia) Infectious (rubella, toxo) Metabolic (DM, galactosemia) Trauma Steroids (predforte, FML, dexamethasone) Atopy Hypocalcemia
Cataract morphology
Nuclear (deepening, diffuse brunescence)
Subcapsular (opacification beneath capsule, commonly post. causes included steroid tx, antidepressants, amiodarone CVS medication)
Cortical (discrete, spoke-like opacities)
Cataract presentation
Visual disturbances ie gradual loss of clarity
Progressive myopia due to increased nuclear density
Glare esp at night while driving
Bilateral/unilateral
Children don’t complain - incidental finding
Cataract examination
VA for level of impairment
Fundoscopy for retinal health (do visual fields if no fundoscope)
U/S for mass or retinal detachment
EUA in infants with leukocoria
Leukocoria differential
Retinoblastoma Cataract Corneal opacification ROP Retinal dysplasia
Cataract surgery complication
Posterior capsulorrhexis
Cataract surgery types
ICCE
ECCA
Phacoemulsification
Cataract surgery indications
Improve visual fx
Diabetic retinopathy
Lens-induced glaucoma
Uveitis
Cataract surgery considerations
Choice of anesthesia
Incision type
Technique
Aphakia correction
Cataract surgery prognosis
80% get 6/12 vision
Failure is due to preexisting disease
If subsequent posterior capsular opacification, tx is laser capsulotomy (YAG)
Ectopia lentis definition
Partial/complete dislocation of lens from physiological position
Associated with glaucoma
Acquired causes - trauma + syphilis
Hereditary causes - Marfan’s syndrome
Myopia
Near/shortsightedness
Eyeball AP is too long or lens is too strong -> image focused in front of retina
Correct with biconcave lens
Hypermetropia
Farsightedness
Eyeball AP is too short or lens is too weak -> image is focused behind the retina
Correct with biconvex lens
Biconcave lens makes eyes look…?
Smaller
Biconvex lens makes eyes look…?
Bigger
Presbyopia
Loss of accommodation
Lens loses elasticity
Correct with bifocal/reading glasses
Meaning of anisometropia?
Unequal refractive errors between two eyes
Monocular diplopia
Diplopia persists when one eye is closed
Binocular diplopia
Diplopia only seen when both eyes are open
What must you be careful of when treating a child born with discharge in the eye?
Ointment causes blurry vision which can induce amblyopia so always use in both eyes!
Meaning of binocular single vision?
Slightly dissimilar images from both retinas are fused centrally to be interpreted by the brain as a single image
Causes of isolated nerve palsies
Vascular disease (diabetes mellitus, hypertension, aneurysm, cavernous sinus thrombosis)
Trauma
Orbital disease
Neoplasia
Raised ICP (false localising, 3rd, 6th)
Inflammation (sarcoidosis, vasculitis, infections, GBS)
Extra-ocular muscle diseases
Dysthyroid eye disease Myasthenia gravis Ocular myositis Ocular myopathy Brown's syndrome Duane's syndrome
Pseudoesotropia
Diagnosis of exclusion
Small interpupillary distance (IPD)
Epicanthal folds
Flat nasal bridge
Pinch nasal skin and then check light reflex
Infantile esotropia
Assessment and treatment
Fixation reflex
Cover uncover test
Refraction by cycloplegic drugs
Fundoscopy to evaluate any organic disease eg retinoblastoma
Treatment = surgical recession of both medial recti
Accommodative esotropia
Often seen in pt with moderate hypermetropia
Attempt to focus eyes -> converge at same time
Causes of intermittent exodeviations
Divergence excess
Convergence weakness
Causes of constant exodeviations
Congenital
Sensory
Consecutive
Right hypertropia may clinically appear as…?
Right pseudo-ptosis
Types of amblyopia?
Strabismic
Anisometropic
Deprivation (cataracts, corneal scarring)
What typically is the cause of corneal scarring in children?
Forceps injury during birth
Which patient are you most suspicious of retinoblastoma in?
Child born with straight eyes that develops a squint by age 2
