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Flashcards in Optics COPY COPY Deck (48):
1

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

2

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

3

Causes of acquired astigmatism

K:
- tight suture
- limbal dermoid
- ptyregium
- KC, pellucid
- corneal trauma

Lid:
- ptosis
- lid masses (tumors)
- chalazion

4

Inadequate accommodation

- cycloplegic drops
- night myopia
- convergence insufficiency
- convergence paralysis
- microspherophakia
- increasing age (latent hyperopia)

5

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)

6

4 ways to calculate IOL power after LASIK

1. Historical method: K = pre-op K + (refraction preop - refraction postop)
2. RGP: K = base curve of CL + power + refraction (with CL) - refraction (without CL)
3. Topography: use central 1 mm effective power from the Holladay diagnostic summary map (not sim K readings)
4. Online calculators/formulas

7

What abx did EVS use

Intravitreal: amikacin and vanco
Sub-conj: vanco and ceftaz
Topical: amikacin and vanco

8

What did we learn from EVS (2)

1. No benefit of IV abx in addition to tap+inject
2. Only do vitrectomy if Va is LP

9

What kind of endophthalmitis does EVS apply to

Post-cataract surgery

10

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

11

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

12

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

13

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.

14

Define vossius ring

In blunt trauma, the pupil sticks to anterior lens capsule and leaves behind a ring of pigment

15

Most common organism in endophthalmitis after cataract surgery

Coag neg staph

16

Most common organism in endophthalmitis after trab

Strep pneumo or H flu

17

Most common organism in endophthalmitis after trauma

B Cereus

18

Most common organism in endogenous endophthalmitis

Candida

19

Most common organism in dacryocystitis

Staph and strep

20

Most common organism in dacryoadenitis

Staph

21

Most common organism in canaliculitis

Actinomyces

22

Most common organism in angular blepharitis

Moraxella or staph

23

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.

24

How do you reduce rates of endophthalmitis from cataract surgery

1. Pre-op abx (e.g. 3 days)
2. Treat pre-op blepharitis, +/- oral doxy (weeks)
3. Pre-op iodine to lashes and to the surface of the eye
4. Intra-cameral or sub-conj abx
5. Post-ob abx drops
6. Tell the patient to practice good hygiene after surgery
7. Drape lashes well during surgery

25

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

26

What are the dimensions of an adult lens? Infant?

adult 9x5 mm
infant 3.5 x 6.5 mm

27

How does the index of refraction of the adult lens change with age?

Increases with age (nucleus becomes more dense)

28

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

29

What are the 3 types of lens metabolism and relative contribution of each

Glycolysis 80%
Pentose 10%
Sorbitol 10%

30

Which lens metabolic pathway is used more in diabetics, leading to diabetic cataracts

Sorbitol

31

What type of congenital cataract is most common

Lamellar

32

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

33

What are the side effects of phospholine iodide

Iris cysts
ASC cataract

34

What lens materials give you the most PCO

PMMA > Silicone > Acrylic

35

What lens edge designs give you most PCO

Round > square edges

36

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

37

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

38

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)

39

Define LASER

Light amplification through stimulated emission of radiation

40

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)

41

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)

42

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)

43

How do you organise colour vision defects

Anomalous vs absent cones
By colour (red, green, blue)

44

What colour vision defect is most common

Deuteromaly

45

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

46

What colour vision is more sensitive for macular dz vs optic nerve dz

B/Y is macular
R/G is optic nerve

47

3 types of intra-ocular hemangiomas and systemic associations

Retinal capillary hemangioma - VHL
Diffuse choroidal hemangioma - SWS
Cavernous hemangioma - idiopathic

48

List mitochondrial dz in ophthalmology

LHON
CPEO

MIDD, MERF, MELAS