MT1 CL2 Flashcards
Regular Astigmatism
Meridians are 90 degrees apart
Ways to stabilize SCL
Prism ballast, peri-ballast, dual slab off, truncation, toroidal back surface
How is CL different for myope
less sphere and cylinder
how is CL different for hyperope
more sphere and cylinder
What are ranges for cyl
.75 to 2.25. Go up in .50 steps.
Prism ballast
Allows the watermelon effect (the lens to squeeze CL down with upper eyelid). Have 1-1.50 BD.
Peri Ballast
Prism lens with prism taken from central.
Double Slab off
Only prism left in the central portion. The top and bottom edges are very thin. Lids stabilize. Overall thinner lens. use with tight lids or small fissures.
Truncation
have a small amount of prism ballast and cut the edge off. This is a last resort as poor comfort.
Back surface toric
Tori on back of lens. Done to line up with patient;s own astigmatism to stabilize.
How much rotation is one clock hour?
30 degrees of rotation
Young
First to describe astigmatism in his own eye
Donders
First to study and classify different RE conditions. I.e. myopia, hyperopia, astigmatism.
Typical axis in dx set
Full circle in 10 degree steps.
What will a SCL do that a GP lens will not
neutralize lens cyl. GP only neutralizes cornea cyl.
Are patient very sensitive to axis good SCL topic wearers?
NO.
How do SCL normally Ride
Temporal. Due to nasal sclera being slightly more elevated
Affects of SCL decenterization
Optic center not in correct place.
Normal corneal diameter
11.8 mm
Scleral drop of torics
Typically 1.25. Want more stabilization
When to vertex
If above 4 D
How to allows go about correcting the astimatism
UNDER correct
Cause of decreased vision if marker at 6 o’clock
RE, overtaxing errors, lens draping effect, cylinder masking, Tear lens effects.
Induced astigmatism and rotation
increases with amount of degrees rotated.
What is SCORx not repeatable
Suspect a poor fit, everted lenses, switched lenses.
The aging eye
reduced tear production, loss of contrast, reduced transparency of lens and cornea, decreased pupil size, increased lid flaccidity, inability to cope with reduced light, reduction in retinal sensitivity, greater visual expectation.
What RE epidemiology change do we see with aging
more hype ropes.
Presbyopic options
Single vision lenses with near add, mono vision, center near design, center distance design, segmented design, concentric CD design.
How many presbyopes use the Distance CLs and reading glasses?
43%
how much of the population does mono vision work for?
70%
which eye is which with monovision
dominant eye=distance
nondominant=near
Criticism of monovision
decreased stereopsis, decreased depth perception, legal consideration
Poor monovision
amblyopes, topic SCL wearers, critical visual requirements.
swinging plus test
give them +1.50 and see which is more comfortable.
what are complaints with failing monovision
decrease in stereopsis or ghost images at distance
Are new or previous CL wearers more successful with monovision
Those that have previous experience
Does add factor into success of monovision
no
Modified Monovision
Center distance for distance and center near for near. Vision is 20/30 at distance i near instead of 20/60.
Who does simultaneous vision work best for
Younger is better. Older cannot filter out (above 48)
Pupil size of 50
3.5
Pupil size and simultaneous vision
If pupil too small may not be able to see more than one zone
Where is line of sight in eye
nasal to geometric center.
Decentered Optics
Let lens go where CL with go and put optics up and 1 mm nasal. Will get perfect vision.
Multifocal for myopia
Distance in middle and near out. Works great with their large pupil. Use decentered optics.
What happens as keratoconus increases
Cornea thins and have an increase in myopia and regular or irregular astigmatism.
Is teratology more common in M or F
Equal
When does keratoconus normally begin
12 to 32
How many patient with KC undergo transplatn
10%
When to do transplant with KC?
When patient can no longer be fitted with cl, when cl no longer provide acuity visual acuity due to scaring, patients who require sharp vision for their job.
Associated condition with KC
Atopic disease, general allergic disposition, eye rubbing, hereditary.
Is keratoaconus nomoral symmetrical?
no!
Hallmarks of KC
Decline in VA, increased myopia, change in cylindrical power and axis, squeezing of the eyelids artificially creates a pinhole, appearance of halos around street light.
Puberty onset keratoconus
begins in early adolescence age 12-16. Usually bilateral but worse in one eye. The younger the patient the more severe the disorder.
Late onset keratoconus
Usually begins in late 20s or early 30s. Both eyes can be affected the same. The incidence of progression reduces greatly with the age of onset.
Karatoconus Fruste
A mild non progressive form KC. Can occur anytime throughout life. No positive tilt lamp finding associated with KC. Normal corneal thickness.
Vertical striae
Seen with KC.
Fleischer’s Ring
Iron outlines where ectasia taking place. Iron is where the tears meet.
Munson’s Sign
See a droplet when patient looks down
Increased visibility of corneal nerve fibers
occurs with KC. The n. fibers are dilated.
Irregular superficial corneal opacities
Majority occur down from geometric center. Scaring=breaks in bowman.
Cascade Hypothesis
stromal collagen fibers are degraded due to UV light, mechanical trauma, and atopic disease. Lead to disruption in bowman, thin the storm, and scarring.
How to limit oxidative stress
UV protection, NSAIDS, allergy meds, best cl fit.
Ruptures in descent’s membrane
occurs when thinning is so bad. 5% with KC get this. Get acute hydras.
Resolving hydrops
Have FC acuity and most cases will resolve after 3 weeks. Can cause reduction in keratoconus after
Diopter power diagnosis for KC
greater than 10D
Corneal eccentricity for KC
> .80
Inferior superior average curvature
Abnormal if >1.50 diopters
Surface Asymmetry Index for KC
Abnormal if greater than 1
Surface regularity index
abnormal if >1
Corneal GP for KC
If patient have 350 nm or less of corneal elevation difference
Scleral GP for KC
If patient have greater than 350 nm of corneal elevation difference
3 point touch technique
Most commonly KC lens. Distribute CL weight evenly between the cone and cornea.
Apical clearance with KC
want to vault cone and cornea to decrease damage.
KC lens eccentricity
Range for .8 to 1.60. Remember circle is zero.
Quadrant specific lens design
Can change eccentricity for each quadrant. Aspheric
Aspheric lens
change curvature from central to periphery
OR with KC
use +/- big steps.
Contumacy Material for SCL
Lathe able (made to order), daily wear, DK=60. Water content is 74 to decrease corneal swelling.
HEMA vs. SiHY
Need SiHY for KC lenses to decrease corneal swelling
Determining BC for KC
Identify the mean K and add 1.0 mm.
Hybrid lenses and KC
Soft skirt with hard front.
Calculating scleral lens saggiato depth
Low angle=low sag. High angle=high sag.
Soft KC fittingy by sagitall height
If lens diameter is 14.2 add 500 microns to saggital height at 14.2 sag. If lens diameter is 14.8 add 1,000 microns to 14.8 sag.
Piggy back lens and staining in KC
stops the 3 and 9 staining.
Ideal fit for GP
.75D to 1D WTR astigmatism
A GP spherical lens on a >2D topic cornea
Will have poor vision, poor contraption, lens flexure, stable fit, lens rocking on flat, corneal dessication
Topography of good astigmatism with GP toric
want limbus to limbus.
GP flexure on topic conrnea
will have inconsistent VA.
Spectacle blur and GP
Spherical lens on topic cornea will mold the cornea and create less cylinder.
When to consider topic GP
Significant amount of cornea toxicity or significant residual astigmatism.
Topic GP options
Spherical power effect, cylindrical power effect, base curve topic, front surface topic, thin flex
Spherical power effect lens
Biotic. Compensating power on front surface. Back surface for a good fit.
When to pick Spherical power effect
corneal toxicity greater than 2. Residual astigmatism .75 to 1 with spherical GP. Corneal toxicity is equal to spectacle astigmatism (can rotate)
Lens rotation and spherical power effect
Behaves like a spherical lens. Tear lens compensates for rotation.
Advantages to spherical power effect
good for highly toxic. But expensive and many parameters to specify.
How to know if a SPE lens
If change in BC=change in CL power
If same meridian cylinder in OR
add to the power of steep meridian or add sphere if indicated. No longer a SPE design.
Cylinder Power Design
Topic back surface and toric front surface. The front surface is greater than the back.
Measurements with SPE
toxicity in lensometer=toricity in radiuscope
Is toxicity in lensometer equal to toxicity in radarscope with CPE
NO.
When to use CPE
Corneal toxicity greater than 2D. Corneal cylinder is not equal to refractive cylinder.
Is stability important with CPE
YES.
CPE is identical to SPE but
Compensating for residual astigmatism by adding extra cylinder in steep meridien.
Base Curve Toric
Spherical front surface. Topic back surface
When to use base curve topic.
Corneal toxicity greater than 2D. Refractive cylinder 1.5X greater than corneal topic or with non flexing spherical GP reveal residual cylinder (.75D or greater). No compensating optics on front surface for induced astigmatism or residual astigmatism.
Base curve topic and acuity
Most pt. will not get optimal acuity. Relies on CL and tear lens to induce a minus cylinder. However, induced cylinder rarely corrects the residual.
What relationship should refractive cylinder and corneal toxicity have with base curve topic?
Refractive cylinder should be 1.5X greater than corneal toxicity.
Higher index of refraction and base curve toric
will induce greater cyliner
123 rule
To get 1D of cylinder on the eye you will need 2D of toxicity on CL and you will measure 3 in the air.
Topic Peripheral curves
Normally the peripheral curves of a topic lens will be spherical. Necessary if the peripheral pattern of the GP is minimal in one meridian
Front surface toric
Prism ballast and trunction
When to use FST
When an optimum lens fit can be achieved with spherical lens design. When refractive astigmatism is greater than corneal (.75D)
Flexure
Thickness is critical. As lens becomes thinner the possibility increases. May negate value. Increases with corneal toxicity.
Thin-Flex
Planned flex that corrects corneal toxicity. Neutralize 30% corneal astigmastims
SynergyEyes Multifocal
use near segments surrounded by distance. However, have complications due to low DK skirt.
SynergEyes Duette
Have a skirt with higher DK.
Pupil size and add power
Lower add with lower pupil
Add effect
Front surface yields higher add effect than back surface. Steeper BC yields higher add effect. Higher indices of refraction yield higher add.
Flex lens GP design
Standard spherical or aspheric design. High Dk material. Minimal center thickness. Diameter is 1 mm smaller than cut out diameter.
Soft perm Hybrid lens designs
Has a soft skirt. Will increase diameter but low DK so caused complication. Discontinued.
