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Lens and Cataract > Lens and cataract > Flashcards

Lens and cataract Flashcards

1
Q

Where does the lens receive all of its nutrients from?

A

Aqueous entirely. There is no blood supply to the lens except during development.

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2
Q

What is the length and depth of an average adult human lens?

A

9mm by 5mm Cataract surgeons work 9 to 5

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3
Q

What natural aging process might cause a lens to be more myopic (increased refraction)? Hyperopic?

A

The lens becomes more thick/dense and possibly more curved causing it to be more myopic. However, its index of refraction also decreases with age thus causing it to be more hyperopic.

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4
Q

What is the equatorial region of the lens called where lens epithelium begin to elongate and migrate losing their organelles?

A

The bow region

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5
Q

What percentage of the lens is protein?

A

33%

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6
Q

Of the water soluble proteins in the lens, what the the 3 major types?

A

Alpha, beta, and gamma (from order of largest to smallest)

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7
Q

What is the main energy source of the lens (what fuel)?

A

glucose, depends on anaerobic metabolism

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8
Q

What are the basics of the Helmholtz theory of accomodation?

A

Anterior lens becomes more convex when ciliary muscle contracts as this causes the zonules to relax which normally have a constant tension on the lens

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9
Q

What is believed to be the principle cause of presbyopia?

A

Hardening of the lens

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10
Q

What are primary lens fibers?

A

Lens fibers (from posterior) that elongate and fill the lumen of the newly created lens vessicle. These form the embryonic nucleus.

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11
Q

What are secondary lens fibers?

A

Lens fibers that begin to elongate near the equator to evelope the newly developed embryonic nucleus (formed from primary lens fibers). These form the fetal nucleus.

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12
Q

What is the reason the lens fails to develop in congenital aphakia, primary type? Secondary type (the more common type)?

A

lens placode fails to form; spontaneous absorption of the lens

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13
Q

Epicapsular star

A

Tiny colored, star shaped anterior capsule remnant of the anterior tunica vasculosa lentis

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14
Q

Why would cycloplegics be the medication of choice for secondary angle closure caused in microspherophakia?

A

Relaxation of the ciliary muscles tightens the zonular fibers causing the spherical lens to flatten

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15
Q

What is the most common type of congenital cataract?

A

Lamellar

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16
Q

Which direction is ectopia lentis usually in homocystinuria?

A

Down and in (opposite from Marfans)

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17
Q

Ectopia lentis et pupilae

A

Lens and pupil are both displace in opposite directions

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18
Q

Vacuoles proceed what type of cataract?

A

Cortical

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19
Q

PSC’s are associated more with distance or near visual complaints?

A

Near

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20
Q

What type of cataract is often seen in patients with AKC?

A

Anterior subcapsular

21
Q

Do myopes or hyperopes experience “second site” due to myopic shift caused by cataracts?

A

Hyperopes

22
Q

If refractive error and no ocular pathology besides cataracts is noted, axial length difference between both eyes should be no great than what?

A

0.3

23
Q

Contact applanation technique to determine axial length can artificially increase or decrease the true axial length?

A

Decrease, because the examiner may indent the cornea too much

24
Q

What percentage of CME following cataract surgery will spontaneously resolve?

A

95%

25
Q

Cavitation

A

formation of gas bubbles at the tip of the phaco needle

26
Q

What is “chatter” in phaco terms?

A

Energy from the phaco tip (repulsive) vs vacuum holding power causes a back and form movement of lens material. It is not desirable.

27
Q

What is “duty cycle” in phaco terms?

A

The period when phaco power is being delivered.

28
Q

What is “load” in phaco terms?

A

The mass of nuclear material in contact with the phaco tip

29
Q

Power is directly proportional to what in phaco terms?

A

The stroke length of the phaco needle

30
Q

What meridion (steep or flat) is a LRI placed?

A

steep

31
Q

When using a toric IOL, each degree off mark will reduce the astigmatism correction by how much (percentage wise)?

A

3% for each degree off from the desired mark

32
Q

How much astigmatism can an LRI correct?

A

Up to 0.5 D

33
Q

What is the important reducing agent in the lens?

A

glutathione

34
Q

What percentage of patients will have a PCO at 5 years post cataract surgery?

A

25%

35
Q

What type of IOL material is more likely to form a PCO? Least likely?

A

PMMA; acrylic

36
Q

What does BAT stand for?

A

Brightness acuity test

37
Q

How is the definitive diagnosis of epithelial downgrowth made?

A

Argon laser to membrane which will blanch white

38
Q

What is the easiest and best solution for lens-iris diaphragm retropulsion syndrome in which there is a “reverse pupillary block”

A

Gently lift the iris off of the anterior capsule

39
Q

“Glistening” of IOL’s is most common in what type of IOL material?

A

acrylic; glistening is an influx of water in hydrophobic optic material

40
Q

Snowflake degeneration seen as progressive degeneration of IOL material is most common in what type of IOL material?

A

PMMA

41
Q

What does a traumatic cataract characteristically look like?

A

Star, located posteriorly

42
Q

In general, are low myopes or low hyperopes better candidates for multifocal IOL?

A

low hyperopes

43
Q

What type of lens abnormality is seen in Alport’s syndrome?

A

Anterior lenticonus (bilateral); A in Alport and Anterior

44
Q

Why would Marfans and PDX have an increase rate of anterior capsule phimosis?

A

Loose zonules that allow the anterior capsule to contract

45
Q

What type of cataract occurs in congenital rubella?

A

Nuclear cataracts that appear pearly white; they also have retained nuclei

46
Q

Sun exposure is mostly correlated with what type of cataract?

A

Cortical

47
Q

Snowflake cataract is characteristic of what underlying process?

A

Acute onset diabetic cataract. Should think diabetes in a young person with acute, bilateral cataracts.

48
Q

What is the inheritance pattern of anterior polar cataracts?

A

AD, usually are not visually significant

Lens and Cataract (1 decks)

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