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Ophthal > Cataract > Flashcards

Cataract Flashcards

(54 cards)

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1
Q

Location of lens

A

between the iris anteriorly & vitreous body posteriorly

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2
Q

Posterior chamber

A

space between the iris & lens

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3
Q

Retro-lental fluid space

A

Separates lens from vitreous face

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4
Q

Suspensory ligament (the zonule)

A

Maintains position of lens

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5
Q

Measurement of lens

A

9 mm diameter
3-4 mm thickness

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6
Q

Weight of lens

A

At birth = 60 mg
linear progression
By 70 yrs = 250 mg

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7
Q

Measurement of curvature

A

Radius of anterior surface = 10 mm
Radius of posterior surface = 6 mm

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8
Q

Refractive index of lens

A

Cortex = 1.38
Nucleus = 1.40

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9
Q

Refractive power of lens

A

16-22 dioptres (inside eye)
60-70 dioptres (in air)

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10
Q

Lens composed of 3 portions which are?

A
  1. Lens capsule
  2. Lens epithelium
  3. Lens fibres
    - lens cortex
    - nucleus
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11
Q

Lens capsule

A

Very elastic transparent non cellular membrane
- thickest near equator
- thinnest at ant. & post. poles

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12
Q

Lens epithelium

A

Ant. = single layer of cubical cells
No post. epithelium

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13
Q

Lens fibres & cement substance

A

Composed of successive laminae of fibres
- cement substance with same refractive index as fibres

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14
Q

Lens cortex

A

Concentric lamellae of long hexagonal transparent fibres
- arranged in structure of an onion

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15
Q

Nucleus

A

Compressed central portions of lens cortex -> undergoes sclerosis -> becomes denser & harder than cortical fibres

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16
Q

Function of lens

A
  1. Static dioptric function
  2. Dynamic dioptric function
  3. Protective function
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17
Q

Static dioptric function

A

Converge parallel light rays from distant object to focus on photoreceptors layer of retina

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18
Q

Dynamic dioptric function

A
  • refractive power of lens varies with distance of object so perfect image is formed on retina
  • accommodation = by change in curvature of lens
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19
Q

Protective function

A

Protects retina by absorbing UV rays

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20
Q

Adult lens contains

A

65% water
34% protein
1% inorganic compounds

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21
Q

Accommodation

A

Act of altering dioptric power of lens to keep image in sharp focus on retina when gaze directed from far to near objects

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22
Q

How is accommodation achieved?

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A

Increasing curvature of lens surface particularly anterior surface -> changing refractive power

23
Q

Mechanism of accommodation

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A
  • active contraction of ciliary muscle
  • passive change of shape of lens
24
Q

Definition of cataract

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A

Cloudiness/opacity of lens substance or capsule
- vacuoles, water clefts, dens areas reflecting/refracting light

25
Mostly cataract is due to aging (senile), but what is the causes of acquired cataract?
- ocular pathology - metabolic defects - systemic disease - trauma - toxins
26
Visual acuity examination
Distant & near vision tested - affected mostly by nuclear cataracts
27
Pupillary response?
Direct and consensual are affected
28
Examination of lens by direct focal illumination
Lens opacities appear in pupillary area (grey/white) against black background
29
Slit lamp biomicroscopy
Extent, density, type & location determined
30
Retinoscopy
Confirmed lens opacities are cause of ptn poor vision
31
Examination of red reflex
Dull/irregular in early cataracts Completely absent in mature cataracts White (leukocoria like) in congenital cataracts
32
Examination of iris shadow (oblique focal illumination)
Immature = positive (shadow present) Mature = negative (shadow absent)
33
A-scan ultrasound
- measures axial length for Intraocular length (IOL) power calculation before surgery - normal = 22-24 mm - increased = myopia; decreased = hyperopia
34
B-scan ultrasound
To rule out any retinal or vitreous pathology in mature cataract before surgery
35
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
36
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
37
Cataract associated with which ionizing radiation?
X-ray UV rays Infrared rays Microwaves
38
Cataract associated with which drugs?
- steroids - naphthalene - triparanol - lovastatin - thallium (acetate & sulfate) - dimethyl sulfoxide - dinitrophenol - psoralens - mitotic s
39
Congenital cataract
Present at birth/within 3 months after birth
40
Developmental cataract
Not evident at brith but may form during infancy/adolescence
41
Causes of developmental cataract
1. Hereditary (dominant type) 2. Maternal nutritional deficiency (accompanied with rickets) 3. Maternal infection (e.g rubella) 4. Deficient oxygenation (e.g repeated placental hemorrhage) 5. Familial incidence
42
Symptoms of developmental cataract
- parents notice pupil being white - child holds things too close to eyes
43
Senile cataract
Age-related bilateral progressive pacification of lens (> 50 years)
44
Symptoms of senile cataract
1. Gradual diminution of vision w/o pain/discharge 2. Uniocular diplopia/polyopia 3. Myopia 4. +ve scotomata 5. Glare 6. Altered color perception
45
Signs of senile cataract
Whitish opacity within pupillary area Late = white pupil (leukocoria)
46
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**
47
Mature cataract
Complete opacification of fibres extend to capsule
48
Complications of hyper mature cataract
1. Secondary glaucoma - phakomorphic/phakolytic glaucoma 2. Uveitis 3. Subluxation & dislocation of lens 4. Rupture of lens
49
Cataract associated with which metabolic disturbances?
1. Diabetic cataract 2. Galactosemic cataract 3. Hypocalcemic cataract 4. Hypothyroidic cataract 5. Myotonic cataract 6. Deficiency cataract
50
Cataract associated with which skin diseases?
1. Atopic dermatitis 2. Poikiloderma atrophicans (Rothmund syndrome) 3. Sclero-poikiloderma (Werner syndrome) 4. Anhidrotic ectodermal dysplasia
51
Steps of extracapsular cataract extraction
1. Anterior capsulotomy 2. Completion of incision 3. Expression of nucleu 4. Cortical cleanup 5. Careful not to aspirate posterior capsule accidentally 6. Polishing of posterior capsule 7. Injection of viscoelastic substance 8. Grasping of IOL & coating with viscoelastic substance 9. Insertion of inferior haptic & optic 10. Insertion of superior haptic 11. Placement of haptics into capsular bag& not into ciliary sulcus 12. Dialling of IOL into horizontal position
52
Phacoemulsification
1. Small incision made (point where cornea & conjunctiva meets) 2. Probe (ultrasound waves) used to break up (emulsify) cataract 3. Suction out fragments
53
2 things that happen during surgery?
1. Clouded lens removed 2. Clear artificial lens implanted to replace original clouded lens
54
What is the lens implant made of?
PMMA, plastic, acrylic/silicone

Ophthal (18 decks)

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