Anatomy & Fitting Basics
This is the formula used to calculate the total Lens Diameter (LD)
The mathematical formula: LD = OZD + 2(SCw) + 2(PCw).
This substance is used to evaluate the tear layer profile and the relationship between the lens and the cornea
Fluorescein
This is the term for the lens created by the tear fluid trapped between the back surface of a GP lens and the cornea
Lacrimal Lens
The maximum amount of corneal toricity that can usually be successfully fitted with a spherical GP lens
2 to 3 Diopters
The fitting method that involves ordering a lens based on spectacle refraction and keratometry data without using trial lenses
Empirical Fitting
The recommended Lens Diameter for a corneal GP lens
2 to 2.5 mm less than the Horizontal Visible Iris Diameter (HVID)
This is the characteristic appearance of a spherical GP lens on a toric cornea
asymmetric pattern
The formula used to determine the relationship between Diopters (D) and Radius (r) in millimeters
D = 337.5 / r
How much corneal astigmatism is neutralized by the lacrimal lens of a non-flexing spherical GP lens
all corneal astigmatism
The Base Curve (BC) of a lens is flatter than K, this is the resulting power of the Lacrimal Lens
Negative (minus power).
The three primary types of lens-to-cornea relationships observed during a fitting evaluation
Touch, Alignment, and Clearance
In a With-The-Rule (WTR) cornea, a spherical lens that is flatter than the cornea in the vertical meridian will show this specific pattern.
Apical Touch
If the corneal power is 45.00 D, what is its radius of curvature in millimeters
7.50 mm
This is the term for the astigmatism that remains manifest while the patient is wearing the contact lens
Residual Astigmatism (RA)
the formula for calculating the power of the Lacrimal Lens (LL)
LL = BC - K
The initial Base Curve (BC) selection formula for a lens with a 9.2 mm diameter?
BC = Kave – 0.50D
Where does a GP lens typically sit on an Against-The-Rule (ATR) cornea, often leading to poor comfort?
Temporal or Nasal (lateral) position
This mnemonic is used to remember how to compensate the contact lens power when the Base Curve is changed
SAM-FAP (Steeper Add Minus, Flatter Add Plus)
This is the formula to calculate predicted Residual Astigmatism
RA = SRcyl - Kcyl
This formula represents the entire rigid contact lens system, including over-refraction, lens power, and tear lens?
ORv + CLP + LL = SRv
This type of lens consists of a rigid gas permeable center and a soft peripheral skirt
Hybrid contact lenses
A lens fitted steeper than the corneal curvature (K) will result in this fluorescein pattern characteristic.
Apical Clearance
This optical adjustment must be performed for all spectacle refractions greater than ±4.00 D
Vertex Distance
The primary cause of residual astigmatism if the corneal astigmatism is fully corrected by the tear lens
Internal (lenticular) astigmatism
When correlating empirical and diagnostic data, the two calculated lens powers should agree within this margin.
±0.25 D.