Lens and cataract Flashcards
Where does the lens receive all of its nutrients from?
Aqueous entirely. There is no blood supply to the lens except during development.
What is the length and depth of an average adult human lens?
9mm by 5mm Cataract surgeons work 9 to 5
What natural aging process might cause a lens to be more myopic (increased refraction)? Hyperopic?
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.
What is the equatorial region of the lens called where lens epithelium begin to elongate and migrate losing their organelles?
The bow region
What percentage of the lens is protein?
33%
Of the water soluble proteins in the lens, what the the 3 major types?
Alpha, beta, and gamma (from order of largest to smallest)
What is the main energy source of the lens (what fuel)?
glucose, depends on anaerobic metabolism
What are the basics of the Helmholtz theory of accomodation?
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
What is believed to be the principle cause of presbyopia?
Hardening of the lens
What are primary lens fibers?
Lens fibers (from posterior) that elongate and fill the lumen of the newly created lens vessicle. These form the embryonic nucleus.
What are secondary lens fibers?
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.
What is the reason the lens fails to develop in congenital aphakia, primary type? Secondary type (the more common type)?
lens placode fails to form; spontaneous absorption of the lens
Epicapsular star
Tiny colored, star shaped anterior capsule remnant of the anterior tunica vasculosa lentis
Why would cycloplegics be the medication of choice for secondary angle closure caused in microspherophakia?
Relaxation of the ciliary muscles tightens the zonular fibers causing the spherical lens to flatten
What is the most common type of congenital cataract?
Lamellar
Which direction is ectopia lentis usually in homocystinuria?
Down and in (opposite from Marfans)
Ectopia lentis et pupilae
Lens and pupil are both displace in opposite directions
Vacuoles proceed what type of cataract?
Cortical
PSC’s are associated more with distance or near visual complaints?
Near
What type of cataract is often seen in patients with AKC?
Anterior subcapsular
Do myopes or hyperopes experience “second site” due to myopic shift caused by cataracts?
Hyperopes
If refractive error and no ocular pathology besides cataracts is noted, axial length difference between both eyes should be no great than what?
0.3
Contact applanation technique to determine axial length can artificially increase or decrease the true axial length?
Decrease, because the examiner may indent the cornea too much
What percentage of CME following cataract surgery will spontaneously resolve?
95%
Cavitation
formation of gas bubbles at the tip of the phaco needle
What is “chatter” in phaco terms?
Energy from the phaco tip (repulsive) vs vacuum holding power causes a back and form movement of lens material. It is not desirable.
What is “duty cycle” in phaco terms?
The period when phaco power is being delivered.
What is “load” in phaco terms?
The mass of nuclear material in contact with the phaco tip
Power is directly proportional to what in phaco terms?
The stroke length of the phaco needle
What meridion (steep or flat) is a LRI placed?
steep
When using a toric IOL, each degree off mark will reduce the astigmatism correction by how much (percentage wise)?
3% for each degree off from the desired mark
How much astigmatism can an LRI correct?
Up to 0.5 D
What is the important reducing agent in the lens?
glutathione
What percentage of patients will have a PCO at 5 years post cataract surgery?
25%
What type of IOL material is more likely to form a PCO? Least likely?
PMMA; acrylic
What does BAT stand for?
Brightness acuity test
How is the definitive diagnosis of epithelial downgrowth made?
Argon laser to membrane which will blanch white
What is the easiest and best solution for lens-iris diaphragm retropulsion syndrome in which there is a “reverse pupillary block”
Gently lift the iris off of the anterior capsule
“Glistening” of IOL’s is most common in what type of IOL material?
acrylic; glistening is an influx of water in hydrophobic optic material
Snowflake degeneration seen as progressive degeneration of IOL material is most common in what type of IOL material?
PMMA
What does a traumatic cataract characteristically look like?
Star, located posteriorly
In general, are low myopes or low hyperopes better candidates for multifocal IOL?
low hyperopes
What type of lens abnormality is seen in Alport’s syndrome?
Anterior lenticonus (bilateral); A in Alport and Anterior
Why would Marfans and PDX have an increase rate of anterior capsule phimosis?
Loose zonules that allow the anterior capsule to contract
What type of cataract occurs in congenital rubella?
Nuclear cataracts that appear pearly white; they also have retained nuclei
Sun exposure is mostly correlated with what type of cataract?
Cortical
Snowflake cataract is characteristic of what underlying process?
Acute onset diabetic cataract. Should think diabetes in a young person with acute, bilateral cataracts.
What is the inheritance pattern of anterior polar cataracts?
AD, usually are not visually significant
