A New Rigid Contact Lens Fitting Tool: An Internet Contact Lens Simulation

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A New Rigid Contact Lens Fitting ToolAn
Internet Contact Lens Simulation

• Jay M. Rumsey, OD, FAAO
• Chris Woodruff, OD, FAAO
• Nova Southeastern University
• College of Optometry

2
Introduction

• This project was developed as an internet based
  simulation to aid in teaching rigid contact lens
  design to optometry students.
• The simulation allows the development of an
  unlimited variety of patient cases.
• Students can review relationships of CL fitting
  whenever and wherever they have internet access.

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Traditional Fitting Limitations

• Number of students
• Variety of corneas
• Inexperience

• Typically limited to size of laboratory
• 15 of 30 at a time if group fits each other
• Larger lab sizes may lead to some students being
  over-looked

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Traditional Fitting Limitations

• Number of students
• Variety of corneas
• Inexperience

• Often more myopes and near emmetropes
• Distribution of spherical and astigmatic corneas
  may vary in groups

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Traditional Fitting Limitations

• Number of students
• Variety of corneas
• Inexperience

• Inexperienced fitters and wearers lead to
• Excessive blinking
• Excessive tearing
• Lens flexure
• Transient acuity changes
• Lens discomfort
• Potential for abrasions

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Simulation Fitting Advantages

• Removes many of the variables associated with
  Traditional Lens Fitting
• Allows students to see how changing some CL
  parameters effects the fit and fluoroscein
  patterns.
• Multitude of initial parameters can be adjusted
  to create unique situations.

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Simulation Variables Initial Program Definitions

• ltapplet code"CLParams" height430 width390gt
• ltparam name"ShowTF" value"1"gt
• ltparam name"ShowCD" value"0"gt
• ltparam name"KhD" value"45.00"gt ltparam
  name"Khm" value"180"gt
• ltparam name"KvD" value"45.00"gt ltparam
  name"Kvm" value"090"gt
• ltparam name"BCsR" value"7.5"gt ltparam
  name"BCsD" value"45.00"gt
• ltparam name"BChR" value"7.5"gt ltparam
  name"BChD" value"45.00"gt
• ltparam name"BCvR" value"7.5"gt ltparam
  name"BCvD" value"45.00"gt
• ltparam name"FCsR" value"7.5"gt ltparam
  name"FCsD" value"45.00"gt
• ltparam name"FChR" value"7.5"gt ltparam
  name"FChD" value"45.00"gt
• ltparam name"FCvR" value"7.5"gt ltparam
  name"FCvD" value"45.00"gt
• ltparam name"OAD" value"9.0"gt ltparam
  name"OZ" value"7.0"gt
• ltparam name"PsD" value"0.00"gt
• ltparam name"PhD" value"0.00"gt ltparam
  name"PhM" value"180"gt
• ltparam name"PvD" value"0.00"gt ltparam
  name"PvM" value"090"gt
• Cannot perform 'java' operations on your system.
• lt/appletgt

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Contact Lens Simulation Variables

• Overall diameter
• Optic zone diameter
• Base curve radius
• Corneal curves

• Parameter Name OAD
• Entered as mm value

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Contact Lens Simulation Variables

• Overall diameter
• Optic zone diameter
• Base curve radius
• Corneal curves

• Parameter Name OZ
• Entered as mm value

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Contact Lens Simulation Variables

• Overall diameter
• Optic zone diameter
• Base curve radius
• Also, if necessary
• Front and/orBitoric curves
• and Contact Lens powers
• Corneal curves

• Parameter Names (Rradii in mm. Dpower in
  diopters)
• Back Curves
• BCsR and BCsD
• BChR and BChD
• BCvR and BCvD
• Front Curves
• FCsR and FCsD
• FChR and FChD
• FCvR and FCvD
• Powers
• PsD
• PhD and Phm
• PvD and Pvm

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Contact Lens Simulation Variables

• Overall diameter
• Optic zone diameter
• Base curve radius
• Corneal curves

• Parameter Names (D in diopters, meridian in
  degrees)
• KhD and Khm
• KvD and Kvm

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Simulation Limitations

• Any simulation of a contact lens fitting on a
  human eye has limitations.
• While an effort has been made to present a
  realistic demonstration of the dynamics and
  interactions of CL fitting parameters, there are
  some of the limitations to the accurate
  presentation of a real fit.

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CL Fit Simulation Limitations

• Spherical Curves
• Lid Interactions
• Edge Design
• Thickness
• Peripheral Curve and Width
• Index of Materials

• Only spherical formulas are used in the
  calculations.
• There are no adjustments for corneal asphericity
  nor manufacturer non-sphere lens designs.

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CL Fit Simulation Limitations

• Spherical Curves
• Lid Interactions
• Edge Design
• Thickness
• Peripheral Curve and Width
• Index of Materials

• Currently, the positioning of the lens within the
  palbepral fissure or pressure changes due to
  upper or lower lid interactions are not
  represented in the program.

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CL Fit Simulation Limitations

• Spherical Curves
• Lid Interactions
• Edge Design
• Thickness
• Peripheral Curve and Width
• Index of Materials

• The use of different plus or minus carriers is
  not implemented
• Edge lift adjustments for different manufacturer
  specifications are not currently utilized.

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CL Fit Simulation Limitations

• Spherical Curves
• Lid Interactions
• Edge Design
• Thickness
• Peripheral Curve and Width
• Index of Materials

• The effects of positioning and flexure of the
  lens is not simulated.

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CL Fit Simulation Limitations

• Spherical Curves
• Lid Interactions
• Edge Design
• Thickness
• Peripheral Curve and Width
• Index of Materials

• Only two curves (base and peripheral) are used in
  the display calculations.
• Modern lens design may implement numerous curves
  with varying widths that may effect appearance.

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CL Fit Simulation Limitations

• Spherical Curves
• Lid Interactions
• Edge Design
• Thickness
• Peripheral Curves
• Index of Materials

• Modern materials are used to control
• Thickness
• Flexure
• Oxygen transmission
• This simulation does not show effects of material
  changes.

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Implementation

• Simulation program and examples are located at
• http//www.nova.edu/hpd/otm/cl/fit/

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Advantages of Simulation

• Dynamic creation of effects of CL modifications
  to OAD, OZ, BC (and FC) for specific corneal
  conditions.
• Reduced memory allocation for storage of images
• Quick view of effect of changes without delay for
  insertion and lens adaptation.

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Example Simulated CL Fitting

• Set corneal curves
• Initialize CL parameters
• Apply lens
• Adjust CL variables and repeat steps 3-4 until
  satisfied.

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Reset display to Initial conditions
Alterative simulation conditions (adds button
functions below)
OAD
Display of current contact lens Parameters after
last Apply
OZ
Effective Base Curve estimate From latest CL
parameter changes
Display of current Corneal Curves
Tear Film lens effect (if displayed)
Increase / Decrease Optic Zone
Increase / Decrease Horizontal /
Vertical Keratometry values
Increase / Decrease Overall Diameter
Increase / Decrease Base Curve
Toggles Keratometry and Base Curve Changes by
0.25 and 1.00 Diopters
Toggles OAD and OZ Changes by 0.5 / 0.1 / 0.05 mm
Toggles Display between Radii in mm and Diopters
Apply latest changes To simulated contact lens
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Sample Simulation Patterns
Sphere BC on Toric Cornea
Back Toric BC on Toric Cornea
Front Back Toric BC On Toric Cornea
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Toric Corneas
Sphere CL
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Toric Corneas
Back Toric CL
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Toric Corneas
Bitoric CL
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Survey Results1Strongly Agree .. 2Agree ..
3Neutral .. 4Disagree .. 5Strongly Disagree

• 1. Overall, the contact lens fitting simulation
  was useful
• 2. The contact lens fitting sumulation was easy
  to use
• 3. The difficulty of case was appropriate for
  entry level 4th year clinics
• 4. The cases were realistic
• 5. Using the simulation could help me improve my
  rigid CL fitting skills
• 6. The simulation would be useful in teaching 3rd
  year optometry students
• 7. The example case was useful
• 8. The fluorescein simulation was useful
• 9. The keratometry conversion was useful
• 10. The estimated thickness calculator was
  useful
• 11. The Bennett Tricurve Nomogram was useful
• 12. The lens diameter selection guideline was
  useful

1.50 1.83 1.83 1.83 1.33 1.83 1.80 2.00 1.40 1.4
0 1.50 1.50
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Survey Comments

• This will definitely help 3rd year students
  understand more what they are suppose to be
  doing. Initially, this material can be a little
  confusing for some students. The conversion
  charts are great.
• I think it was hard.
• Overall, this was a useful simulation.
• It was very helpful!

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Student Comments

• I found it to be very helpful.
• Overall I think this is a great learning tool
  for students and doctors alike.
• I think it is excellent
• It is user friendly
• it would be great to have to help with
  learning how to fit RGPs

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Thank You!
Jay Rumsey, OD, FAAO rumsey_at_nova.edu Chris
Woodruff, OD, FAAO chrisw_at_nova.edu