Optics COPY COPY 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
What are the measurements of Gulstrand’s model eye
AL = 22.5 mm
Nodal point is 5.5 mm behind cornea
Nodal point to retina is 17 mm
Cornea to focal point is 17 mm
What are the dimensions of an adult lens? Infant?
adult 9x5 mm
infant 3.5 x 6.5 mm
How does the index of refraction of the adult lens change with age?
Increases with age (nucleus becomes more dense)
What type of collagen makes up the lens capsule?
Type IV
Type I = corneal stroma
II = vitreous (remember Stickler’s is a problem with type II collagen)
III = corneal stromal scarring
IV = all BM’s
What are the 3 types of lens metabolism and relative contribution of each
Glycolysis 80%
Pentose 10%
Sorbitol 10%
Which lens metabolic pathway is used more in diabetics, leading to diabetic cataracts
Sorbitol
What type of congenital cataract is most common
Lamellar
What is characteristic/weird about doing cataract surgery on a child with a rubella cataract
Live virus particles can persist in the lens for up to 3 years. Make sure everyone in the room has been immunized against rubella.
Also, can have crazy inflammatory rxn after cataract surgery
What are the side effects of phospholine iodide
Iris cysts
ASC cataract
What lens materials give you the most PCO
PMMA > Silicone > Acrylic
What lens edge designs give you most PCO
Round > square edges
What are the risk factors for suprachoroidal hemorrhage
High IOP pre-op Sudden drop in IOP during surgery Age HTN, high HR Obesity High myopia Chronic ocular inflammation
What are the different types of visual acuity measurements
“People’s vision sometimes looks awesome”
Minimum legible = snellen
Minimum visible = VF machine
Vernier = Teller
Others:
Minimum perceptible = candy bar
Minimum separable = tumbling E
Compare and contrast peristaltic vs venturi pumps
Peristaltic = vacuum only builds when tip is occluded
Less followability, less smooth, less accurate
Venturi = need compressed gas source Vacuum bulids even if tip not occluded Better fluidics (more precise aspiration and vacuum response)
Define LASER
Light amplification through stimulated emission of radiation
What are the properties of laser light
- single wavelength (monochromatic)
- spatial coherence (all comes to a point)
- temporal coherence (all waves are in sync with each other)
- amplified (high intensity)
Wavelengths of ophthalmology lasers
Excimer: 193 nm
Blue-green argon: 475-525 nm
Diode: 820 nm
ND:YAG: 1064 nm (freq doubled YAG = 523 nm)
What does it mean if someone has a ‘protanomaly’
They have an abnormal concentration of red cones
Can still see red but have difficulties with seeing red when it is not fully saturated (e.g. mixed with other colours, the red part of the colour may not be as clear to them - i.e. they may confuse certain shades that have red in them i.e. shades of purple or orange)
How do you organise colour vision defects
Anomalous vs absent cones By colour (red, green, blue)
What colour vision defect is most common
Deuteromaly
What colour vision tests are there and what do they test
Ishihara - tests R/G defects
HRR - B/Y and R/G
100-hue - for saturation. R/G and B/Y
D-15 - shorter version of 100 hue. Also R/G and B/Y
What colour vision is more sensitive for macular dz vs optic nerve dz
B/Y is macular
R/G is optic nerve
3 types of intra-ocular hemangiomas and systemic associations
Retinal capillary hemangioma - VHL
Diffuse choroidal hemangioma - SWS
Cavernous hemangioma - idiopathic
List mitochondrial dz in ophthalmology
LHON
CPEO
MIDD, MERF, MELAS
