2. Contact Lenses for Astigmatism

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2. Contact Lenses for Astigmatism
Biomedical science,
anterior segment diseases
and
advanced contact lenses
M i c h a e l W y s s & M i c h a e l B är ts ch i
M.Sc.Optom. et M.Med.Educ., FAAO
kontaktlinsenstudio baertschi, Bern / Switzerland
Adjunct faculty New England College of Optometry, Boston/USA
Schedule
1st Day Saturday:
Modul 1
(5 lecture hours)
2nd Day Sunday :
Modul 2, A & B, 3
(5,5 lecture hours plus
2 x 1,5 hours workshop)
3rd Day Monday :
Modul 3 & C, 4
(6 lecture hours plus
1,5 hours workshop)
4th Day Tuesday:
Modul 4, 5, 6
(7,0 lecture hours)
5th Day Wednesday:
Modul 6, 7
(5,5 lecture hours)
incl. final discussion
2. Contact Lenses for Astigmatism
•
Soft Toric Lenses
•
Front Surface Toric Rigid Lenses
•
Back Surface Toric Rigid Lenses
•
Bitoric Rigid Lenses
•
Over refraction measurement and
calculations
Duration 3 hours
3. Contact Lenses for Presbyopia
•
Monovision vs Simultaneous vs Alternating
Vision
•
Rigid & Soft Aspheric Multifocals
•
Rigid & Soft Concentric Multifocals
•
Soft Diffractive Multifocals
•
Rigid & Soft Segmented Bifocals
Duration 4 hours
2. Contact Lenses for Astigmatism
•
List the most popular Soft Toric Lenses
•
Understand and differentiate different stabilization
systems
•
Describe the fitting procedure
•
Perform astigmatism calculations
•
Be familiar with centration, movement and
stabilisation axes monitoring and evaluation
Popular Soft toric contact lenses
Cooper
CIBA Vision
Johnson&Johnson
Bausch & Lomb
Benz
Stabilization Systems for soft lenses
Prismatic
Bausch & Lomb
PCT/US1998/006106
Bi-Prismatic
Stabilization Systems for soft lenses
Dynamic
Johnson &
PCT/US2005/016824
Johnson
Patent
Johnson & Johnson
Engraving / Marks
Lines
or dots
Horizontal
or vertical
location
Fitting procedure
1.
Take Topography or Keratometry measurement
2.
Check Lid position and Lid tonus
3.
Low Lid position and weak lid tonus = Prismatic system
4.
Normal Lid position and strong lid tonus = dynamic or bi-prismatic
system
5.
Fit Silicone Hydrogel 0,6 to 0,8 mm flatter than the flat Meridian (for
OAD 14,5 mm)
6.
Fit Hydrogel 0,8 to 1,2 mm flatter than the flat Meridian (for OAD 14.5
mm)
7.
Check centration, stabilisation axes and movement (0,5 to 1 mm )
Lid position
Normal Lid position
Low Lid position
(extreme example)
Check stabilization axes
Horizontal marks
Vertical marks
2. Contact Lenses for Astigmatism
•
Understand the stabilization system of Front
Surface Toric Rigid Lenses
•
Describe the fitting procedure
•
Be familiar with centration, movement and
stabilisation axes monitoring
Stabilization system
Spherical back-curve, prismatic stabilized.
Ideal for spherical or low astigmatic corneas
with a residual optical astigmatism.
Fitting procedure
1. Take Topography or Keratometry measurement
2. Check corneal astigmatism
3. Check ametropia and total eye astigmatism
4. Fit the lens parallel to the flat meridian
5. Define the ideal over all diameter OAD
6. Check centration, stabilisation axes and
movement (1 to 2 mm )
Check stabilization axes
Horizontal marks
Vertical mark
Stabilization axes = 10°
2. Contact Lenses for Astigmatism
•
Understand the stabilization system of Back
Surface Toric Rigid Lenses
•
Describe the fitting procedure
•
Be familiar with centration, movement and
stabilisation axes monitoring
Stabilization system
Sphero-toric stabilization (peripher-toric).
Ideal for low central and higher peripheral astigmatic
corneas. Use OAD lenses > 9.8mm.
00
06
r2/0
06
r2/0
00
Stabilization system
Full toric back-curve stabilization.
Ideal for high central and complete astigmatic
corneas.
r2/1
06
06
r2/1
r2/0
06
r2/0
06
06
Stabilization system
Toric back-curve with peripheral toric stabilization.
Ideal for high central and even higher astigmatic
corneas.
r2/1
00
06
r2/1
06
r2/0
00
r2/0
Fitting procedure
1.
Take Topography or Keratometry measurement
2.
Check central and peripheral corneal astigmatism
3.
Check ametropia and total eye astigmatism
4.
Fit the flat BC parallel to the flat meridian
5.
Fit the steep BC slightly flatter than the steep
meridian (2/3 rule)
6.
Define the ideal over all diameter OAD
7.
Check centration, stabilisation axes and
movement (1 to 2 mm )
Check stabilization axes
Horizontal marks
Stabilization axes = 150°
2. Contact Lenses for Astigmatism
•
Understand the stabilization system and
working mechanism of Bitoric Rigid Lenses
•
Describe the fitting procedure
•
Be familiar with centration, movement and
stabilisation axes monitoring
Stabilization system
All three stabilization system possible :
•
Sphero-toric stabilization
•
Full toric back-curve stabilization
•
Toric back-curve with peripheral toric
stabilization
In addition, any needed toric correction on the
front optic surface in any needed axes.
Fitting procedure
1.
Take Topography or Keratometry measurement
2.
Check central and peripheral corneal astigmatism
3.
Check ametropia and total eye astigmatism
4.
Fit the flat BC parallel to the flat meridian
5.
Fit the steep BC slightly flatter than the steep meridian (e.g. 2/3 rule)
6.
Define the ideal over all diameter OAD
7.
Check centration, stabilisation axes and movement (1 to 2 mm )
8.
Check residual astigmatism and define stabilization axes
9.
Calculate final bi-toric correction and order the final lens
Topography of a Back-toric rigid lens (Falco, Switzerland)
Measured by Oculus Topography
FIT 06/06
7.75 / 7.55
=>
8.70 / 8.50
2. Contact Lenses for Astigmatism
•
Understand over lens refraction
measurement
•
Demonstrate new contact lens power
calculations with professional software
Overrefraction
Back-toric rigid lenses induces a specific refractive
astigmatism of -0.25 dpt per 0.10 mm radii
differences in the steep meridian.
-0.25 on eye/tears
-0.75 in air
Example :
FIT 7.75 / 7.55 = 0.20 mm = - 0.50 dpt in 90°
Overrefraction
1. Use defined (back, peripher) toric trial lens
until you have a perfect fit, centration and
stabilization
2. Measure stabilization axes
3. Measure the residual ametropia and
astigmatism
4. Measure vertex distance
5. Use calculation software
How to calculate the final power ?
Use existing calculation software.
(E.g. CIBA http://virtualconsultant.cibavision.com/toric_lens.jsp
or Galifa online www.galifa.ch )
Workshops
Workshops:
•
RGP lenses Fluorescein patterns
•
Soft and RGP toric lenses
•
Soft and RGP presbyopia lenses
Duration 3 x 1.5 hours
Workshops
Workshops:
•
RGP lenses Fluorescein patterns
•
Soft and RGP toric lenses
•
Soft and RGP presbyopia lenses
Duration 3 x 1.5 hours