Cataract Flashcards
Location of lens
between the iris anteriorly & vitreous body posteriorly
Posterior chamber
space between the iris & lens
Retro-lental fluid space
Separates lens from vitreous face
Suspensory ligament (the zonule)
Maintains position of lens
Measurement of lens
9 mm diameter
3-4 mm thickness
Weight of lens
At birth = 60 mg
linear progression
By 70 yrs = 250 mg
Measurement of curvature
Radius of anterior surface = 10 mm
Radius of posterior surface = 6 mm
Refractive index of lens
Cortex = 1.38
Nucleus = 1.40
Refractive power of lens
16-22 dioptres (inside eye)
60-70 dioptres (in air)
Lens composed of 3 portions which are?
- Lens capsule
- Lens epithelium
- Lens fibres
- lens cortex
- nucleus
Lens capsule
Very elastic transparent non cellular membrane
- thickest near equator
- thinnest at ant. & post. poles
Lens epithelium
Ant. = single layer of cubical cells
No post. epithelium
Lens fibres & cement substance
Composed of successive laminae of fibres
- cement substance with same refractive index as fibres
Lens cortex
Concentric lamellae of long hexagonal transparent fibres
- arranged in structure of an onion
Nucleus
Compressed central portions of lens cortex -> undergoes sclerosis -> becomes denser & harder than cortical fibres
Function of lens
- Static dioptric function
- Dynamic dioptric function
- Protective function
Static dioptric function
Converge parallel light rays from distant object to focus on photoreceptors layer of retina
Dynamic dioptric function
- refractive power of lens varies with distance of object so perfect image is formed on retina
- accommodation = by change in curvature of lens
Protective function
Protects retina by absorbing UV rays
Adult lens contains
65% water
34% protein
1% inorganic compounds
Accommodation
Act of altering dioptric power of lens to keep image in sharp focus on retina when gaze directed from far to near objects
How is accommodation achieved?
Increasing curvature of lens surface particularly anterior surface -> changing refractive power
Mechanism of accommodation
- active contraction of ciliary muscle
- passive change of shape of lens
Definition of cataract
Cloudiness/opacity of lens substance or capsule
- vacuoles, water clefts, dens areas reflecting/refracting light
Mostly cataract is due to aging (senile), but what is the causes of acquired cataract?
- ocular pathology
- metabolic defects
- systemic disease
- trauma
- toxins
Visual acuity examination
Distant & near vision tested
- affected mostly by nuclear cataracts
Pupillary response?
Direct and consensual are affected
Examination of lens by direct focal illumination
Lens opacities appear in pupillary area (grey/white) against black background
Slit lamp biomicroscopy
Extent, density, type & location determined
Retinoscopy
Confirmed lens opacities are cause of ptn poor vision
Examination of red reflex
Dull/irregular in early cataracts
Completely absent in mature cataracts
White (leukocoria like) in congenital cataracts
Examination of iris shadow (oblique focal illumination)
Immature = positive (shadow present)
Mature = negative (shadow absent)
A-scan ultrasound
- measures axial length for Intraocular length (IOL) power calculation before surgery
- normal = 22-24 mm
- increased = myopia; decreased = hyperopia
B-scan ultrasound
To rule out any retinal or vitreous pathology in mature cataract before surgery
Cataract associated with which Intraocular diseases?
- uveitis/inflammation
- glaucoma
- retinal detachment/degeneration
- micro-ophthalmus
- retinoblastoma
- high myopia
- retinal anoxia (burger’s disease, takayasu’s arthritis)
Anterior segment necrosis
Cataract associated with which systemic diseases?
- metabolic = DM, galactosemia, hypoparathyroidism, wilson’s, homocystinuria
- renal = lowe’s and alport’s
- skin = congenital ectodermal dysplasia, atopic dermatitis
- connective tissue/skeletal = myotonic dystrophy, Marfan syndrome, bone dysplasia
- CNS = marinesco sjogren syndrome, neurofibromatosis type 2
Cataract associated with which ionizing radiation?
X-ray
UV rays
Infrared rays
Microwaves
Cataract associated with which drugs?
- steroids
- naphthalene
- triparanol
- lovastatin
- thallium (acetate & sulfate)
- dimethyl sulfoxide
- dinitrophenol
- psoralens
- mitotic s
Congenital cataract
Present at birth/within 3 months after birth
Developmental cataract
Not evident at brith but may form during infancy/adolescence
Causes of developmental cataract
- Hereditary (dominant type)
- Maternal nutritional deficiency (accompanied with rickets)
- Maternal infection (e.g rubella)
- Deficient oxygenation (e.g repeated placental hemorrhage)
- Familial incidence
Symptoms of developmental cataract
- parents notice pupil being white
- child holds things too close to eyes
Senile cataract
Age-related bilateral progressive pacification of lens (> 50 years)
Symptoms of senile cataract
- Gradual diminution of vision w/o pain/discharge
- Uniocular diplopia/polyopia
- Myopia
- +ve scotomata
- Glare
- Altered color perception
Signs of senile cataract
Whitish opacity within pupillary area
Late = white pupil (leukocoria)
Intumescent cataract
Immature stage -> lens absorb increasing amount of fluid from aqueous -> becomes swollen
Swollen -> push iris forward -> reduce depth of anterior chamber -> block angle -> tendency to secondary glaucoma
Mature cataract
Complete opacification of fibres extend to capsule
Complications of hyper mature cataract
- Secondary glaucoma - phakomorphic/phakolytic glaucoma
- Uveitis
- Subluxation & dislocation of lens
- Rupture of lens
Cataract associated with which metabolic disturbances?
- Diabetic cataract
- Galactosemic cataract
- Hypocalcemic cataract
- Hypothyroidic cataract
- Myotonic cataract
- Deficiency cataract
Cataract associated with which skin diseases?
- Atopic dermatitis
- Poikiloderma atrophicans (Rothmund syndrome)
- Sclero-poikiloderma (Werner syndrome)
- Anhidrotic ectodermal dysplasia
Steps of extracapsular cataract extraction
- Anterior capsulotomy
- Completion of incision
- Expression of nucleu
- Cortical cleanup
- Careful not to aspirate posterior capsule accidentally
- Polishing of posterior capsule
- Injection of viscoelastic substance
- Grasping of IOL & coating with viscoelastic substance
- Insertion of inferior haptic & optic
- Insertion of superior haptic
- Placement of haptics into capsular bag& not into ciliary sulcus
- Dialling of IOL into horizontal position
Phacoemulsification
- Small incision made (point where cornea & conjunctiva meets)
- Probe (ultrasound waves) used to break up (emulsify) cataract
- Suction out fragments
2 things that happen during surgery?
- Clouded lens removed
- Clear artificial lens implanted to replace original clouded lens
What is the lens implant made of?
PMMA, plastic, acrylic/silicone
