Optics Flashcards Preview

Ophthalmology > Optics > Flashcards

Flashcards in Optics Deck (48)
Loading flashcards...
1
Q

Causes of acquired myopia

A

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
Q

Causes of acquired hyperopia

A

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
Q

Causes of acquired astigmatism

A

K:

  • tight suture
  • limbal dermoid
  • ptyregium
  • KC, pellucid
  • corneal trauma

Lid:

  • ptosis
  • lid masses (tumors)
  • chalazion
4
Q

Inadequate accommodation

A
  • cycloplegic drops
  • night myopia
  • convergence insufficiency
  • convergence paralysis
  • microspherophakia
  • increasing age (latent hyperopia)
5
Q

Causes of night myopia (4)

A
  • 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
Q

4 ways to calculate IOL power after LASIK

A
  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
Q

What abx did EVS use

A

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

8
Q

What did we learn from EVS (2)

A
  1. No benefit of IV abx in addition to tap+inject

2. Only do vitrectomy if Va is LP

9
Q

What kind of endophthalmitis does EVS apply to

A

Post-cataract surgery

10
Q

What doses of abx do we use for treating endophthalmitis

A

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
Q

Define cyclodialysis and what to do about it

A

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
Q

Define angle recession and what to do about it

A

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
Q

Define iridodialysis and what to do about it

A

Separation of the iris root from the CB. Needs surgical fix if its symptomatic (or coloured contact lens). Otherwise just leave it.

14
Q

Define vossius ring

A

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

15
Q

Most common organism in endophthalmitis after cataract surgery

A

Coag neg staph

16
Q

Most common organism in endophthalmitis after trab

A

Strep pneumo or H flu

17
Q

Most common organism in endophthalmitis after trauma

A

B Cereus

18
Q

Most common organism in endogenous endophthalmitis

A

Candida

19
Q

Most common organism in dacryocystitis

A

Staph and strep

20
Q

Most common organism in dacryoadenitis

A

Staph

21
Q

Most common organism in canaliculitis

A

Actinomyces

22
Q

Most common organism in angular blepharitis

A

Moraxella or staph

23
Q

Define alpha, beta, gamma hemolsysis with examples

A

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
Q

How do you reduce rates of endophthalmitis from cataract surgery

A
  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
Q

What are the measurements of Gulstrand’s model eye

A

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
Q

What are the dimensions of an adult lens? Infant?

A

adult 9x5 mm

infant 3.5 x 6.5 mm

27
Q

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

A

Increases with age (nucleus becomes more dense)

28
Q

What type of collagen makes up the lens capsule?

A

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
Q

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

A

Glycolysis 80%
Pentose 10%
Sorbitol 10%

30
Q

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

A

Sorbitol

31
Q

What type of congenital cataract is most common

A

Lamellar

32
Q

What is characteristic/weird about doing cataract surgery on a child with a rubella cataract

A

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
Q

What are the side effects of phospholine iodide

A

Iris cysts

ASC cataract

34
Q

What lens materials give you the most PCO

A

PMMA > Silicone > Acrylic

35
Q

What lens edge designs give you most PCO

A

Round > square edges

36
Q

What are the risk factors for suprachoroidal hemorrhage

A
High IOP pre-op
Sudden drop in IOP during surgery
Age 
HTN, high HR
Obesity
High myopia
Chronic ocular inflammation
37
Q

What are the different types of visual acuity measurements

A

“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
Q

Compare and contrast peristaltic vs venturi pumps

A

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
Q

Define LASER

A

Light amplification through stimulated emission of radiation

40
Q

What are the properties of laser light

A
  • single wavelength (monochromatic)
  • spatial coherence (all comes to a point)
  • temporal coherence (all waves are in sync with each other)
  • amplified (high intensity)
41
Q

Wavelengths of ophthalmology lasers

A

Excimer: 193 nm
Blue-green argon: 475-525 nm
Diode: 820 nm
ND:YAG: 1064 nm (freq doubled YAG = 523 nm)

42
Q

What does it mean if someone has a ‘protanomaly’

A

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
Q

How do you organise colour vision defects

A
Anomalous vs absent cones
By colour (red, green, blue)
44
Q

What colour vision defect is most common

A

Deuteromaly

45
Q

What colour vision tests are there and what do they test

A

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
Q

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

A

B/Y is macular

R/G is optic nerve

47
Q

3 types of intra-ocular hemangiomas and systemic associations

A

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

48
Q

List mitochondrial dz in ophthalmology

A

LHON
CPEO

MIDD, MERF, MELAS