Lens Flashcards
What type of cataract is characteristic of ischemic ocular conditions?
Posterior subcapsular
Chronic UV radiation exposure typically causes what type of cataract?
Cortical
What are the most radiosensitive structures in the eye?
Lens > cornea > retina > optic nerve
How much radiation exposure leads to cataract formation? How long does it take to develop cataracts after radiation?
2 Gy in 1 fraction, 2-3 years
What lens capsule finding is seen when operating on patients with aniridia?
Thinner than normal lens capsule -> makes capsulorrhexis challenging
What is responsible for postoperative myopic shift?
Capsular contraction or phimosis
What complication is more common after intracapsular CEIOL than extracapsular?
Retinal detachment
What is posterior infusion syndrome or posterior fluid misdirection syndrome?
Occurs after hydrodissection -> fluid misdirected into vitreous cavity leading to anterior displacement of lens and shallowing of anterior chamber
Not associated with pain
What types of IOLs have been associated with highest rates of corneal decompensation?
Closed-loop ACIOLs, iris-clip lenses
Flexible/open-loop ACIOLs at less risk
What can be done to reduce increased risks of cataract surgery in patient with COPD?
Small-incision surgery: reduces risk of suprachoroidal hemorrhage and iris prolapse
Reverse Trendelenburg position may help patient breathe more easily
After performing LASIK in myopic patient, how will central corneal power differ when measured by keratometer versus topography?
Corneal curvature is overestimated by keratometry compared to topography (keratometry only measures central 3 mm)
What IOL is most likely to cause negative dysphotopsia?
Smaller square-edge PCIOL in the bag
What IOL pathology is associated with positive dysphotopsias?
Decentered PCIOLs
What carbohydrate metabolism change occurs in lens in presence of high levels of glucose?
Aldose reductase activity increases
What is the rate-limiting step in glucose phosphorylation in the lens? What occurs when glucose concentration increases in the lens?
Hexokinase reaction
Sorbitol pathway activated when glucose concentration increases -> aldose reductase is key enzyme in this pathway
What kind of patient would benefit from Trendelenburg positioning for cataract surgery?
Kyphotic patients
What should be done during cataract surgery for eye containing silicone oil?
Inferior iridotomy to prevent pupillary block from silicone oil migration into anterior chamber through zonules
What should be done for nanophthalmic eyes undergoing cataract surgery to reduce risk of uveal effusion? (3)
Suture all incisions, administer mannitol preoperatively to dehydrate the vitreous, use lower aspiration rate or higher infusion pressure
When performing phacoemulsification on patient with zonular incompetence, what change in settings would most effectively reduce chances of complications?
Lower aspiration flow rate -> diminishes fluctuation and turbulence in AC depth, reduces risk of vitreous prolapse
What average IOP-lowering effect is expected from phacoemulsification in eye with high IOP?
10-30% IOP lowering (can consider cataract surgery as stand-alone procedure in eyes with early to moderate glaucoma)
What is viscosity of OVDs? What factors determine viscosity?
Resistance to flow, thickness and thinness of a fluid
Determined by molecular weight and concentration
What is elasticity of OVDs?
Ability to return to original tape after being stressed
What is surface tension of OVDs?
How readily fluid sticks to another surface
Inversely proportional to coatability: low surface tension is better at coating tissue, but more difficult to remove from the eye
What pattern of Nd:YAG laser reduces risk of lens dislocation?
Spiraling circle
