red eye Flashcards
things that cause a CL associated red eye
CHADS
- compliance
- hypoxia
- allergies
- dry eyes
- solution sensitivity
what CL should be ordered for this patient? Ks -OD: 47.00/45.50 @ 090 -OS: 47.00/45.50 @ 090 SUBJ -OD:-6.50 -2.00 x 090 20/20 -OS:-6.50 -2.00 x 090 20/20
-6.00 -1.75 x 090
make sure to do a power cross and use the vertex equation in both meridians and then figure out the Rx
vertex=(P/1-dP)
after the SCLs are placed on the eye, you note the right CL rotes 10 degrees clockwise and the left lens rotes 10 degrees counterclockwise, resulting in BCVA 20/25 each eye. What new CL axis should be ordered in each eye to improve the patient's BCVA? Ks -OD: 47.00/45.50 @ 090 -OS: 47.00/45.50 @ 090 SUBJ -OD:-6.50 -2.00 x 090 20/20 -OS:-6.50 -2.00 x 090 20/20
OD axis 100
OS axis 080
LARS from dr perspective
clockwise=left
counterclockwise=right
LARS only works if the lens consistently rotates to the same spot each time.
which of the following available BCs is most appropriate to use for the initial CL fitting for this patient? Ks -OD: 47.00/45.50 @ 090 -OS: 47.00/45.50 @ 090 SUBJ -OD:-6.50 -2.00 x 090 20/20 -OS:-6.50 -2.00 x 090 20/20 CL RX -OD: -6.00 -1.75 x 090 -OS:-6.00 -1.75 x 090
8.3, 8.6, 9.0, or none of these?
8.3
this patient has a fairly steep K that are best fit with a smaller (steeper) BC (measured in mm). remember that as the radius of curvature increases, the cornea becomes flatter and the K values become lower.
Bercher Twist test
rotate the cyl in the phoropter. if the patient cannot tolerate less than 5 degrees of rotation, he likely will not be successful in a soft toric CL
DK
refers to oxygen permeability of a CL material. a higher DK results in greater oxygen permeability. A higher DK is healthier for the eye because it allows more oxygen to be transmitted to the cornea
DK/t
transmissibility. a thicker lens results in a decrease in oxygen transmissibility
hydrogel and DK
DK increases as water content increases
siHy and DK
as water content increases, DK decreases
siHY CLs have Dk values that are greater than traditional hydrogels (>60)
PMMA and Dk
they have 0 oxygen permeability and are no longer RXed
loose lens
flat BC
smaller diameter
decreased sag
tight CL problems
central bubbles
mucin balls
poor comfort on insertion but improved comfort after wearing, improved vision immediately after a blink, and perilimbal injection after many hours of wear
loose CL problems
may show increased drop fo the CL inferiorly on upgrade (>2mm), poor comfort (esp with a blink), and blurred vision immediately after a blink that improves between blinks
SM and hyperopes and aphakes
corrected with + lenses. SM increases as vertex distance increases for a + lens. Mag will be decreased in Cl compared to specs
myopes and SM
corrected with - lenses. SM decreases as vertex distance increases for a mins lens. therefore, in myopes, mag will be increased in CL compared to specs
myopes + CL
more convergence and accommodation
myopes and glasses
gives BI, decreased convergence and accommodation
hyperopes and CL
less convergence and accommodation
solution sensitivity
toxic
- follicles
- infiltrates
- diffuse SPK
- redness
- most common causes: thimerosal and chlorhexidine
saline solution
it is ok for wetting CL, but it does not clean or disinfect
tap water and CL
never use due to acanthamoeba
management for solution sensitivity
- switch to a different MPS as they may be less sensitive to other preservatives
- hydrogen peroxide solutions such as clear care neutralize to saline after 6 hours; therefore no chemicals are present when the CL is inserted on the eye
- dailies worn only for one day before being thrown away, thus eliminating the need for CL solution
GP BC
the curvature of the back surface of the optical zone of the CL. Recall that steepening the BC will results in a steeper CL fit and flattening the BC will results in a flatter CL fit. for every 0.5mm change in BC,the power of the CL should be adjusted by 0.25D to account for the change in the steepness of the fit.
SAM FAP
if the BC is steepened, add minus power, if the BC is flattened, add plus power to the CL
GP OAD
the uncurled distance of the CL from edge to edge. the OAD is selected to minimize flare (most commonly occurs when the edge of the CL is close to the edge of the pupil), to avoid the bottom lid, facilitate lid attachment, and max comfort ( a larger OAD is more comfortable), the average OAD is 9.4-9.6mm and is adjusted in 0.4mm steps
GP OZD
the usable area of optics in the CL (avg 7.6-8.2). Increasing the OZD increases the sag, resulting in a steeper fit. th maintain the same physical alignment between the GP and the cornea, the BC should be flattened. conversely, decreasing the OZD decreases the sag depth and flattens the fit of the CL; the BC should be steepened to maintain the same physical alignment
for every 0.4mm change in OZD, the base curve should be adjusted by
0.25D
GP peripheral curves
allow alignment between the edge of the CL and the peripheral cornea. CP CL may have one (bicurve) or two (tricurve), or three (tetra curve) peripheral curves in addition to the BC
3 main functions of the perisperhal curves in GP
- prevent the edge of the CL from bearing on the cornea when the Cl moves on the eye
- promote tear exchange under the CL to maintain adequate corneal metabolism
- support tear meniscus at the edge if the CL, which promotes lens centration
edge thickness and GP
ideal edge thickness will promote lid attachment and is similar to the edge thickness of a -3.00D GP CL
- GP lenses that are more plus than -1.50D have a “plus shape” and will often drop inferiorly due to inadequate lid attachment. Plano/minus carrier lenticular can be added to thicken the CL edge and promote lid attachment
- CL that are more minus than -5.00D have excess edge thickness, causing the lens to ride higher due to excessive lid attachment. a plus lenticular or CN beveling can be added to decrease the edge thickness and promote normal lid attachment
edge lift and GP
the distance between the peripheral edge of the CL and the cornea. can be adjusted by changing the peripheral curve radii in 1mm steps. remember that steepening the peripheral curve radius and or reducing the width of the peripheral curve will decreased edge lift
center thickness and GP
influences oxygen transmissibility of the CL, flexure, and the center of gravity of the CL. the CT can be changed 0.03mm steps
thinner CT
has greater oxygen transmissibility, better centration, and more flexure (esp with 1.50D or more corneal astigmatism)
thicker CT
less oxygen transmissibility, less flexure, and tends to drop inferiorly on the eye
Dk and thickness
higher Dk values require a thicker CT in order to minimize flexure
center of gravity and GP
the center of the weight of a GP CL; it is influenced by the CL power, diameter, center thickness, and base curve. The more posterior the center of gravity, the better the centration of the CL
what causes a more anterior center of gravity for a GP lens
thicker CT
smaller OAD
“plus” shape
flatter BC
drops inferiorly on the eye
BC selection for SCL
in general, SCL are typically fit with a BC that is 4D flatter than on K
- average K (41-45): fit the median BC or the flatter BC
- for a steeper K (>45), fit the steeper BC
- for a flatter K (<41), fir the flatter BC
power of SCL
determined by the spec refraction at the corneal place and the over-refraction. Remember that the tear lens power is always Plano for a SCL, and thus does not influence the final power
diameter of SCL
measures the horizontal visible iris diameter (HVID) and add 3mm to ensure 1.5mm extension of the SCL edge beyond the limbus for 360 degrees
material of SCL
consider wear schedule and the patient needs when selecting material. daily wear CL can have a lower Dk compared to extended wear or continuous wear CL. Also consider deposits and patient complains of dry eye
