Optics Flashcards
Causes of acquired myopia
All refractive shift can be broken into cornea, lens, and eyeball:
Corneal changes
- overcorrected hyperopic lasik
- undercorrected myopic lasik
- keratoconus
Lens changes
- anterior dislocation of the lens (ectopia lentis)
- microspherophakia
- nuclear sclerosis
- diabetes
- night myopia
Anterior shift of the lens-iris diaphragm:
- choroidal effusions
- PRP
- topamax, other sulfa drugs
- pregnancy
- miotic drops
Eyeball changes
- posterior staphyloma
- scleral buckle
- congenital glaucoma
Causes of acquired hyperopia
All refractive shift can be broken into cornea, lens, and eyeball:
Cornea:
- overcorrected myopic LASIK
- undercorrected hyperopic LASIK
Lens:
- posterior dislocation of the lens
- cycloplegic drops
- aphakia
- 3rd nerve palsy (with internal ophthalmoplegia)
- PRP (can’t accomodate)
Eyeball:
- CSR
- choroidal tumors
- retro-orbital masses or hardware
Causes of acquired astigmatism
K:
- tight suture
- limbal dermoid
- ptyregium
- KC, pellucid
- corneal trauma
Lid:
- ptosis
- lid masses (tumors)
- chalazion
Inadequate accommodation
- cycloplegic drops
- night myopia
- convergence insufficiency
- convergence paralysis
- microspherophakia
- increasing age (latent hyperopia)
Causes of night myopia (4)
- Dilated pupil (spherical aberration, irregular astigmatism)
- Dark focus (poor distance and near targets cause poor focus)
- Purkinje shift (spectral sensitivity shifts toward shorter wavelengths at lower light, and chromatic aberration moves the focal point more anteriorly)
- May have undercorrected them with your rx (20 ft lane gives 1/6 D under-minused correction for distance)
4 ways to calculate IOL power after LASIK
- Historical method: K = pre-op K + (refraction preop - refraction postop)
- RGP: K = base curve of CL + power + refraction (with CL) - refraction (without CL)
- Topography: use central 1 mm effective power from the Holladay diagnostic summary map (not sim K readings)
- Online calculators/formulas
What abx did EVS use
Intravitreal: amikacin and vanco
Sub-conj: vanco and ceftaz
Topical: amikacin and vanco
What did we learn from EVS (2)
- No benefit of IV abx in addition to tap+inject
2. Only do vitrectomy if Va is LP
What kind of endophthalmitis does EVS apply to
Post-cataract surgery
What doses of abx do we use for treating endophthalmitis
Vanco 1 mg/0.1 ml
Ceftaz 2.25 mg/0.1 ml
+/- dex
+/- ampho-B if you suspect fungal
Topical fortified vanco 25 mg/ml + tobra 15 mg/ml
Define cyclodialysis and what to do about it
Separation of the CB from scleral spur
Often as a result of trauma or surgery
Dilate the pupil, wait to see if it resolves
Define angle recession and what to do about it
Separation of the longitudinal and circular fibres of the CB
Higher risk of glaucoma so watch and see
only 5-10% of people with traumatic hyphema will get glaucoma
Define iridodialysis and what to do about it
Separation of the iris root from the CB. Needs surgical fix if its symptomatic (or coloured contact lens). Otherwise just leave it.
Define vossius ring
In blunt trauma, the pupil sticks to anterior lens capsule and leaves behind a ring of pigment
Most common organism in endophthalmitis after cataract surgery
Coag neg staph
Most common organism in endophthalmitis after trab
Strep pneumo or H flu
Most common organism in endophthalmitis after trauma
B Cereus
Most common organism in endogenous endophthalmitis
Candida
Most common organism in dacryocystitis
Staph and strep
Most common organism in dacryoadenitis
Staph
Most common organism in canaliculitis
Actinomyces
Most common organism in angular blepharitis
Moraxella or staph
Define alpha, beta, gamma hemolsysis with examples
Alpha = little hemolysis (turns green). E.g. strep viridans, strep pneumo
Beta = lots of hemolysis (ring of yellow around the culture). E.g. strep pyogenes
Gamma = no hemolysis. Plate stays red.
How do you reduce rates of endophthalmitis from cataract surgery
- Pre-op abx (e.g. 3 days)
- Treat pre-op blepharitis, +/- oral doxy (weeks)
- Pre-op iodine to lashes and to the surface of the eye
- Intra-cameral or sub-conj abx
- Post-ob abx drops
- Tell the patient to practice good hygiene after surgery
- Drape lashes well during surgery
