GP Toric (M1) Flashcards
What are the things that are required to put in the order for a front surface toric GP?
- base curve
- diameter
- prism (with dot at base) about 1.25pd
- power in spherocylindrical notation with axis
What are the traits of a low toric simulation fit?
- BC aligns (+/- 0.25D) with flat meridian and undercorrects steep meridian
- diameters bigger
- toric lacrimal lens
If a spherical lens is fit too flat or too steep what does it cause?
corneal molding
What are the readings for the lensometer for a front surface GP toric? 1. Readings for radioscope? 2
- some cyl
2. spherical
What is the most common type of toric GP lens?
bitoric GP
What is the cyl on the eye lead to on a back surface toric GP? 1. What does the cyl measured on the radioscope measure? 2. Cyl on the lensometer? 3
- induced cyl
- base curve toricity
- air cylinder
How is the power for a bitoric GP lens written?
specify BC and power for each meridian but not in spherocylindrical form and no need for axis specification
What is the equation to find the center thickness of a toric GP lens?
use power than yields largest CT (most plus)
CT(minus lens) = 0.18 + 0.01(power)
CT(plus lens) = 0.18 + 0.02(power)
When is it best to used a back surface toric GP lens?
spectacle astigmatism is about 1.5X corneal toricity (3:2:1 rule, 3 cyl power (lenso), 2 BC toricity (radioscope), 1 induced cylinder (on eye))
What are the readings for the lensometer for a bitoric GP? 1. Readings for radioscope? 2
- cyl
2. cyl
What are the readings for the lensometer for a back surface GP toric? 1. Readings for radioscope? 2
- cyl
2. cyl
What is the bitoric where the difference in the BC is not the same the difference in lens power? 1. What does this mean? 2
- cylindrical power effect (CPE)
2. rotation induces cylinder power
When calculating bitoric lenses empirically, what is used?
- optical crosses
2. Mandell-Moore Bitoric worksheet
What type of corneal toricity is best for a low toric simulation fit?
K toricity greater than 2.50D (better WTR astig)
When are GP toric lenses required?
- spherical GP’s do not correct all refractive error (tear lens does not correct all astig)
- corneal cyl does NOT equal refractive cyl
How do you adjust the a CPE bitoric to make it SPE?
adjust powers of lens (creates more visually acceptable residual astigmatism)
When calculating bitoric lenses diagnostically, what is used?
- spherical trial lens
2. SPE trial lens
What type of corneal toricity is best for a full alignment (or saddle fit)?
2.00 to 2.50D K’s
What is the bitoric where the difference in the BC is the same as the difference in lens power? 1. What does this mean? 2
- spherical power effect (SPE)
2. any cyl induced rotation is corrected by tear lens
What are the traits of a full alignment (or saddle fit)?
- on K for each meridian
- tighter fit, more centered so smaller diameter (interpalpebral fit)
- spherical lacrimal lens
What type of astigmatism do soft toric lenses correct?
refractive astigmatism
What are the two aspects that make up the refractive astigmatism?
- corneal astig
2. lenticular astig
When ordering a toric GP lens, what should be the peripheral curve BC? 1. How wide? 2
- BC + 3.0mm
2. 0.2mm wide
What are the three types of GP toric lenses?
- front surface GP toric
- back surface GP toric
- bitoric GP
What occurs as a result of a back surface toric?
lens induces cyl created by changes in index of refraction from lens material to tears
Where is the cylinder induced by a back surface toric located?
flat meridian of CL
What is used to determine if the bitoric lens resulted in SPE or CPE?
difference in bace curve and difference in the power of the lens
What are the indications for a front surface toric GP?
- 1 D or more residual astig
- 2 D or less corneal toricity
- poor fit with soft toric
When ordering a toric GP lens, what should be the secondary curve BC? 1. How wide? 2
- BC + 1.0mm
2. 0.4mm wide
