Fitting RGPs Flashcards
on K NaFL pattern
an evenly distributed light green pattern across the cornea with a narrow band of green in the peripheral edge
what BC will allow for an on K fit? Ks -OD: 45.00/45.00 @ 090 -OS: 45.00/45.00 @ 090 SUBJ -OD:-2.25 DS -OD:-2.25 DS
- 5mm
337. 5/45
What GP lens power should be ordered for an onK fit? -OD: 45.00/45.00 @ 090 -OS: 45.00/45.00 @ 090 SUBJ -OD:-2.25 DS -OD:-2.25 DS
-2.25
what new power should be ordered if the CL base curve is steepened by 0.1mm
-2.75D
how do you always want to fit an RGP
slightly flat to allow for tear exchange
flat fit pattern
central touch with a broad green ting of NaFL underneath the peripheral portion of the lens
steep fit pattern
bulls eye pattern with central pooling of NaFL and minimal NaFL underneath the periphery of the lens
spherical GP lens fit over an ATR cornea pattern
will have a figure 8 pattern of TOUCH along the vertical meridian and pooling along the horizontal meridian and I the peripheral zone
spherical GP lens over WRT cornea pattern
dumbbell shaped pattern of TOUCH along the horizontal meridian and pooling along the vertical meridian and in the peripheral zone
a spherical GP fit over an astigmatic cornea will have pooling where
in the steep meridian and touch in the flat meridian
if you see 3 and 9 staining, what does this typically mean
riding too low
corneal desiccation
raising a GP lens
- BC closer to on-K fit
- increase diameter
- decrease center thickness by 0.03mm
- minus carrier lenticular to assist with lid attachment
- flatten the peripheral curves to increased edge lift and lid attachment
signs of keratoconnus
FIRST
- Fleischer ring
- Irregular mires
- Reflex scissors
- Striae (Vogt’s)
- Thinning of storm
high riding CL results in
corneal warpage with image ghosting
diff between flexure and warpage
flexure is ON the eye and warpage is on and off the eye
laterally displaced GP lens
its too flat. steepen the fit bit decreasing the BC, increased the OZD, or increasing the overall lens diameter. If this does not work, refit into a minus lens carrier lenticular edge design or a toric back surface design or add toric peripheral curves
two main fitting philosophies for fitting RGPs
- lid attached
2. interpalpebral
lid attached RGP fit
the edge of the GP Cl interacts with the superior eyelid margin; this is the most appropriate for patients whose superior eyelid sits at or below the limbus, and the eyelid has normal tension against the globe
interpalpebral RGP fit
the edge of the RGP DOES NOT interact with either eyelid margin; this is most appropriate if the superior eyelid is located above the limbus or the patient has tight eyelids against the globe
OAD fitting philosophy
consider the fitting philosophy and corneal curvature when determining the most appropriate OAD. an average OAD (9.4-9.6mm) is most appropriate for patients where the upper eyelid is located atop below the superior limbus (lid attachment). A smaller OAD is recommended fort patients who need an interpalpebral fit or have small interpalpebral fissures
large OAD/OZDs
steepened the GPCL
small OAD/OZD
flatten the GPCL
for every 0.4mm increase (decrease) in the OAD/OZD
flatten (steepens) by 0.25D
guidlines for fitting spherical RGPS
corneal astigmatism < 2.50D and acceptable residual astigmatism
fitting guidlines for front toric RGP
corneal astigmatism <2.50D and unacceptable residual astigmatism
fitting guidelines for back surface toric
corneal astigmatism >2.50D and spec astigmatism =1.5 x corneal astigmatism
fitting guidelines for bitoric lenses
corneal astigmatism >2.50D and spec astigmatism that does not equal 1.5x the corneal astigmatism
fitting guidelines for aspheric RGPs
consider in patients with ATR or borderline astigmatism or in patients who are hypercritical of their vision
higher amounts of corneal astigmatism and BC
steeper BC needed for adequate fit, the CT should be increased by 0.03mm with a steeper BC in order to minimize flexure
material of RGPs
higher Dk lenses have greater oxygen permeability but also more flexure; increase the CT by 0,03mm in order to minimize flexure. in general, high or hyper Dk lenses are indicated for extended wear, and low Dk lenses are acceptable for daily wear
BC guidelines
for a RGP with a 9.4mm OAD and lid attached fit
- if corneal astigmatism is < or equal to 0.75D, fit 0.50D flatter than K; for every 0.50D increase in corneal astigmatism, steepen the BC by 0.25D until a biotic CL is necessary
- because the cornea progressively flattens toward the periphery, selecting a BC that is flatter than K will result in greater alignment between GP CL and the cornea
watermelon seed effect
describes the phenomenon where the RGP is posed down and outward, most often due to tight upper lid tension
-an improvement in a lid attachment fit or an interpalpebral fit will help to minimize this effect
how to achieve a lid attached fit
large and flat RGP
how to achieve an interpalpebral fit
small and steep GP
SAM FAP
describes how to change the power of a RGP to compensate for a change in the BC of the CL. Recall that every 0.05mm change in BC, the power should be adjusted by 0.25D
