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
What type of cataract develops as a result of blunt trauma?
Stellate or rosette cataract involving posterior lens capsule
Anesthesia of terminal branches of facial nerve
van Lint block
Anesthesia of CN VII trunk as it exits stylomastoid foramen between mastoid process and mandibular ramus
Nadbath-Ellis block
Anesthesia of CN VII anterior to tragus at mandible
O’Brien block
Anesthesia of temporofacial branch along inferior border of zygoma toward top of ear
Atkinson block
What complications result from inadvertent intravenous injection of retrobulbar anesthesia?
Cardiac arrhythmia, seizures, respiratory arrest, brainstem anesthesia
What is most commonly isolated from cultures of patients with cataract surgery-associated endophthalmitis?
Staph epidermidis
What complication is associated with reverse “S-shaped” insertion of aspheric single-piece IOL?
Loss of asphericity and refractive surprise (small myopic shift)
What is the most common enzyme deficiency that causes galactosemia?
Galactose 1-phosphate uridyltransferase (Gal-1-PUT)
What is a benefit of retrobulbar over peribulbar anesthesia?
More rapid anesthesia
The majority of high-energy phosphate bonds for lens metabolism are provided by what pathway?
Anaerobic glycolysis
What percentage of lens glucose passes through citric acid cycle?
3%
What leads to age-related nuclear sclerosis?
Formation of protein-to-protein and protein-to-glutathione disulfide bonds (aggregation and accumulation of insoluble proteins)
What is a risk factor for intraoperative iridodialysis?
Floppy iris syndrome
What clinical test tests macular function in patient with dense cataract precluding visualization of fundus?
Maddox rod testing (loss of red line of Maddox glass = scotoma suggesting macular disease)
Where is the germinative zone of the lens epithelium?
Immediately anterior to the equator
Risk factors for suprachoroidal hemorrhage (7)
Hypotony, high myopia, age, hypertension, tachycardia, cardiovascular disease, longer operating times
Minimum visual acuity threshold for PAM to accurately estimate potential vision
> 20/200
Macular issues (AMD, edema, scarring), serous RD, glaucoma, amblyopia can make PAM testing unreliable
