- Amsler
grid: each square is 1 degree at 33 cm
- 1
M unit (1.54mm) is 1 minute of angle at 1 meter
- 1
20/20 Snellen letter is 5 minutes at 6 meters
-
resolution of Snellen letter is 1 minute at 6 meters (i.e. 6M)
- resolution
of Snellen letter is 6M
-
each 20/20 Snellen letter is 30M
Goldman 3 mirrors: 59-67-73
(gonio is 59)
Fluorescein:
excitation:
490
emission:
520
filter:
500
ICG:
835?
DDx of monocular diplopia
1)
astigmatsm
2)
keratopathy
3)
cataract
4)
subluxated lens
5)
iris atrophy
6)
vitreous disease
7)
iridectomy
8)
malingering
Steep (“tight”) contact lens
1)
fluctuating acuity
2)
better acuity with blink (moves liquid out)
3)
more comfortable
4)
poor nutrient exchange
5)
persistant astigmatism
6) CL
doesn’t fall out
7)
little mvt with blink
8)
central hypoxia (microcystic edema, PEK)
9)
lens low
10)
symptoms: burning, photophobia, tearing
11)
congested vessels
12)
corneal vascularization (pannus)
Signs of flat contact lens
1)
clear vision
2)
worse acuity with blink (moves)
3)
discomfort
4)
nutrient exchange adequate
5) no
astigmatism
6)
lose CL easily
7)
movement with blink
8)
central corneal abrasion (stain)
9)
lens high
10)
symptoms: f.b. sensation
Change that can be made on a CL
1)
flatten peripheral curve
2) PMMA
lenses: adjust power by +/- 0.50 D
Treatment of prismatic effect of ADD
A) Prismatic
effect
1)
slab-off more myopic lens (BU effect)
2)
reverse slab off hyperopic side (BD effect)
3)
Fresnel vertical prisms
4)
permanent vertical prisms lens
B) Types
of add
1)
round top for some plus lens (executive)
2)
flat top for some plus lens (waiter) - no jump
-
makes prismatic effect worse
3)
flat top for minus
4)
dissimilar segments (eg. round and flat)
C) Centration
1)
different center for each lens (bicentration)
2)
decenter both distance lenses downward
3)
raise ADD closer to center
D) Different
pairs
1)
contact lenses
2)
separate reading glasses
Prentice Rule
- to
correct, assume eye looks down 8mm and nasal 2mm
Increased with the rule astigmatism post-op
1) tight
sutures
2)
many sutures
3)
deep bites
4)
long bites
5)
anterior incision
6)
fine sutures (eg. 10-0) - don’t loosen
7)
non-absorbable sutures
Contact lens correction
-
soft originally for sports, occasional wearers, occasional overnite wearers
-
now, for 90% of CL wearers
- RGP
better for astigmatism, young progressing myopes
-
mulifocals: distance CL for dominant eye; near for non-dominant eye
Types of multifocals contact lenses
1)
multifocal aspheric, near in center (soft and hard)
2)
bifocal near below
3)
multifocal in periphery which moves when eye looks at near to center over pupil
(CL moves)
4)
diffractive lenses
Types of multififocal IOL’s
1)
multifocal aspheric, near in center (soft and hard)
2)
distance- near - distance ( 3 rings)
3)
diffractive
4)
bifocal below?
6
ways to use slit lamp
1)
diffuse
2)
slit beam
3)
indirect - turn knob on arm
4)
sclerotic scatter
5)
retroillumination
6)
specular reflection
Ultrasound wavelengths
1) A
scan: 8-15 MHz “reflective”
2) B
scan: 8-15 MHz “echogenic”
3) UBM:
50-100 MegaHz
Ultrasound lesion description
1)
shape
2)
echogenicity
3)
homogeneity (regularity)
4)
vascularity (dynamic) - seen in melanoma, not angioma or mets
5)
dynamic movement: eg RD, PVD
Decrease meridional magnification by
1)
decrease cylinder power
2)
rotate axis to 90 or 180
3)
decrease vertex distance
4)
minus cylinder lenses
5)
consider CL
Lens Aberrations
1) Spherical aberration
- the
most important aberration in the eye
-
increases with the 4th power of the pupil
-
image is focused anterior to expected location
- increase
as object moves away from optical axis
2) Coma
-
cause rays from a point to be focused over a small area
- increase
as object moves away from optical axis
3) Off-axis astigmatism
- increase
as object moves away from optical axis
4) Chromatic aberration
-
blue is bent more than red
-
yellow sits on retina
-
red-blue interval: 1.50 D
-
red-green interval: 0.50 D
5) Curvature of Field
-
image focused on cuved surface
-
advantageous in the eye (only one)
6) Distortion
-
different points of the object are magnified dif’t amounts
-
e.g. pincushion, barrel distortion
7) Astigmatism of oblique incidence
-
tilting of lens
Ways eye deals with spherical aberration
1)
pupil
2)
cornea is aspheric (greater central refraction)
3)
nucleus center is more refractive
Accomodation Amplitudes
0 :
18
10:
14
20:
10
30: 8
40: 6
50: 3
60:
1.5
70: 0
Retinoscopy
A)
power
- as
we approach neutrality, streak is
1)
brighter
2)
faster
3)
fatter
B)
axis
- as
we approach correct axis, there is
1)
less break
2)
less skew
3)
thinner reflex
4)
brighter intensity
Ultraviolet wavelengths
1)
UVA: 320-400 - 90% on earth
2)
UVB: 280-320 - 10% on earth
3)
UVC: <280 - negligeable
Sunglasses:
(p. 224 AAO)
1)
improve color contrast
2)
improve dark adaptation
3)
reduction of glare sensitivity (eg. polarized)
4) UV
absortion
5)
photochromic change with light (silver ions - UV)
UV absorbtion
1)
almost all dark sunglasses
2)
coated glass (clear glass transmits all above 300nm)
3)
plastic made of polycarbonate and CR-39 (transmits above 350; partial
absorption)
Regular lenses must
1) be
at least 2mm thick
2)
withstand 5/8 inch steel ball dropped from 50 inches
Industrial lenses must
1) be
at least 3 mm thick
2)
withstand 1 1/8 inch steel ball dropped from 50 inches
Lens material
1)
glass (high density, high index)
2)
high density glass
3)
plastic (low density, low index)
4)
high density plastic
5)
polycarbonate (low density high index)
When to prescribe polycarbonate lenses
(AAO
p.229); - “shatter proof”?
-
discovered in 1950’s
-
lighter, stronger lenses
1)
sports
2)
industrial
Components of Hyperopia
1)
Total: Manifest + Latent
2)
Manifest: Absolute + Facultative
AC/A ratio
1)
normal = 4-6
2)
heterophoria method:
IPD
(cm) + [ET (dist) - ET (near)]/near (D)
3)
clinical distance-near relationship (usual);
compare
deviation at near and far (> 10 abnormal)
4)
lens gradient: compare with no lens and with
+
3.00 at near (or other variations of manipulating with lenses)
Prisms for low vision glasses
- 2
PD BI more than prescription
eg. +
10 D glasses: +12 PD BI OU
after
+ 10 single vision; available up to + 40
Lensometer:
prism moves rings towards base (1 ring per PD)
Advantage of spectacles
1)
Both hands free
2)
large field
3)
Don’t have to hold something
4)
good for hand tremor
5)
binocular
Advantage of hand lens
1)
variable magnification
2)
compact
3)
esthetic
Disadvantage of projector
1)
poor contrast
2)
fixed distance
Advantage of Keplerian telescope
1)
greater magnification
2)
greater focusability
Advantage of Galillean
1)
easier to use
2)
smaller
3)
field expander
Correction of aphakic anisoconia
1) CL
2)
decrease vertex of spectacles
3)
IOL insertion
4)
overcorrected plus CL with minus spectacle lens
5)
minus cylinder spectacle lenses
6)
decrease lens convexity?? (notes)
Fresnel lens uses
A) prism
1)
adaptation test (pre-op surgery in adult)
2)
correction of temporary deviation
3)
exercises for X(T)
4)
stable incomitant deviations
5)
nystagmus (null point)
6) VF
defects
B) plus
lens
1)
penalization
2)
accomodative ET’s
3)
temporary aphakia
4)
occupational bifocal adds
5)
low vision high power segments
C) minus
lens
1)
X(T) treatment
Multifocal lenses
1)
unwanted astigmatism in area lateral to progressive corridor
Aphakic lens problems
1)
ring scottooma
2)
jack in the box
3)
pincushion distortions
Types of plastic frames
1)
CR-39
2)
MMA (Plexiglass)
3)
Celluloid (cellulose)
4)
Nylon
5)
carbon-nylon
6)
carbon graphite
Types of Metal frames
1)
gold
2)
aluminum
3)
titanium
4)
stainless steel
5)
“nickel/silver” (German silver - nickel + copper + zinc)
Ways to hold CL in place
1)
prism ballast
2)
truncation
3)
myoflange (plus lenses)
4)
lenticular bevel ( minus lens)
Automated Refractors Metjhods
1)
optometer
2)
Scheiner principle (2 holes)
3)
laser speckle pattern movement
4)
photo of retina (screening)
5)
VEP
6)
automated phoropter
7)
automated refracting lane
Low Vision Aids
A) Near
1)
high plus glasses with BI prism
2)
hand-held magnifying lens
3)
stand magnifier
B) Far
1)
Galilean telescope
2)
astronomical telescope
C) Increase
field
1)
reverse Galilean telescope
D) Non-optical
1)
monitor
2)
large print books
3)
good lighting
4)
tinted glasses (improves contrast
5)
computers which scan text
6)
audiible books
