Toric soft contact lenses by optom ankit varshney

Soft Toric Lens Fitting
Optom. Ankit S. Varshney
M.Optom, Ph.D. in Optometry (pursuing) Fellow of IACLE (Aus.), Fellow of ASCO(Mum.)
Prof. at (Shree Bharatimaiya College of Optometry & Physiotherapy, Surat)
Life Member of Indian Optometric Association (IOA)
Associate Member of Association of Schools and Colleges of Optometry(ASCO)
Member of Optometry Council of India(OCI)
Educator Member of International Association of Contact lense Educators (Australia)(IACLE)
Mail id: ankitsvarshney@yahoo.com
Whatsapp no. +918155955820

Course objectives
 Upon completion of this presentation, you will
know
– The need for soft toric lenses
– Patient selection for soft toric lenses
– Soft toric designs and stabilizing forces
– Power selection for soft toric lenses
– Fit evaluation
– Problem solving
 Resultant cross cylinder
 LARS compensation
14 July 2020 Optom. Ankit Varshney 2

Astigmatism
Defined as a refractive condition.
It is the difference in refractive
power between the 2 principal
meridians of the eye
Powermeridian
Objectat


Classification & its type
1. Classification by focal line
2. Classification by structure
3. Classification by type
4. Classification by orientation- meridional
5. Classification by magnitude

 Regular
‒ principal meridians, 90 ° apart
 Irregular
‒ principal meridians not 90o apart
‒ >2 principal meridians
‒ no principal meridians
‒ often acquired (i.e. secondary to)
‒ trauma
‒ disease

 Corneal
 Lenticular
 Other internal astigmatism
 Total

 Simple hyperopic astigmatism (SHA)
 Compound hyperopic astigmatism (CHA)
 Simple myopic astigmatism (SMA)
 Compound myopic astigmatism (CMA)
 Mixed astigmatism (MA)

 Regular
‒ with-the-rule (WTR)
‒ against-the-rule (ATR)
‒ oblique

 Negligible 0.75 D Cyl
 Low 1.00 to 1.50 D Cyl
 Moderate 1.75 to 2.50 D Cyl
 High > 2.50 D Cyl

Contact lens options to
correct astigmatism
1. Soft SCLs
2. Spherical RGP lenses/ Toric RGP lenses
3. Toric Soft lenses

Flashback..
Patient
walking in..

Flashback..
Patient walking
out..

Day Before Yesterday..
 Only Spherical Soft
Contact Lenses
 On top cylindrical
spectacle correction
 4 : 1 Sphere – cylinder
ratio

Yesterday..
 Entry of Toric soft contact lenses
 Initial reluctance of the practitioners
 Lengthy fitting procedure
 Unpredictable outcome
 Low satisfaction level

Today..
 About 7% of total soft contact lens market
 More competent practitioners
 Positive approach
 Increased awareness amongst consumers on
toric lens option
 Increased No. of patients moving to
disposable modality

Today..
Superior Products

Lesson We Learnt..
There is nothing in a caterpillar that tells us
it’s going to be a butterfly

Why should we prescribe soft toric lenses?
 Refractive astigmatism
 Spherical SCLs failed to mask
corneal astigmatism
 Induced residual astigmatism
from RGP lenses
 RGP lenses causing too much discomfort

Who should wear soft torics?
 - Poor Quality of vision with spherical soft lenses,
just not clear
- Refractive astigmatism > 0.75 D
- Refractive astigmatism > 25 % of sphere power

Who should wear soft torics?
– Cylinder power should be between 1.00 to
3.00 diopters
– Cylinder axis should be with or against the
rule, and not oblique
– Not hyper-sensitive to axis shift

Twist Test
sensitivity to axis fluctuations
 Have refraction in phoropter
 Rotate the best cylinder correction until the
patient reports a blur in vision
 Determine the amount of degrees the cylinder
can be “off axis” and not effect vision
 Less than 5 degrees indicates high sensitivity and
may NOT be a good candidate for soft toric
lenses.14 July 2020 Optom. Ankit Varshney 21

TORIC SOFT CONTACT LENSES
 Supply a full compensation for each of the eye’s
principal meridians
 Neutralize meridional refractive errors  bring
light from all meridians to a common focus on the
retina
 For optimum vision  toric SCLs must maintain
their correct meridional orientation on the
eye
 Different methods and designs for stabilization
 To maintain normal eye physiology  the toric
lens still has to move on the eye

What are soft toric lens design characteristics?
 Front Surface Toric
- spherical back surface
- toric front surface
 Back Surface Toric
- spherical front surface
- toric back surface
 Bitoric (uncommon)

Front-Surface Toric CL Design
180
Rx: –2.00 / –3.00 x 180
Spherical BOZR90
Front
(+47.00)
(+44.00)
90
Back
180
(–49.00)
(–49.00)
90
BVPs
180
–2.00
–5.00

n = 1.43
tc = 0.15
+

Back-Surface Toric CL Design
Rx: –2.00 / –3.00 x 180
Spherical FOZR90
Front
180
(+48.00)
(+48.00)
90
Back
180
(–50.00)
(–53.00)
90
BVPs
180
–2.00
–5.00
n = 1.43
tc = 0.15

+

Soft toric design
considerations
• Stabilization
• Reference marks
- type
- position
• Lens thickness variation
• Water content
• Material properties  influence lens flexibility and
rotational ability14 July 2020 Optom. Ankit Varshney 26

How are soft toric lenses
stablized?

Stabilization Methods
 Prism ballast
 Peri-ballast
 Double slab-off
 Reverse prism

Watermelon seed principle
Stabilization Techniques
Lid force on the lens

Prism Ballast
 1 to 1.5 prism dioptres, base down
 Lens stabilized by lid forces acting on
the prism-induced thickness differences
 Reduced O2 transmissibility in areas
of greater thickness
 Discomfort along lower lid margin 
increased thickness of prism base
TORIC SOFT CL STABILIZATION

 Minus carrier converted into a prism base
down effect
 Orientation principle similar to prism ballast
 Prism-free optic
 Uses thickness differences as the
stabilizing component  thinner
superiorly, thicker inferiorly
 Discomfort with lens-lid interaction at
the thicker, inferior half
 Reduced oxygen transmissibility in
thicker regions
Peri-Ballast

 Better comfort because of reduced lens
thickness
 Thin zones superiorly and inferiorly
 Lens is prismless and symmetrical
 Thinner than alternative designs available
 Dynamic stabilization  thin zones
(upper and lower) interact with the lids
(especially the upper lid) to position and
stabilize the lens on the eye
Double Slab-Off/ Thin zones

 May not be as reliable in patients
with loose lids
 Great reliance on lid interaction 
may need to use larger total lens
diameters
Double Slab-Off: Disadvantages

 Incorporating both prism (base down)
and the inferior chamfer (base up) 
integrated design
 Should be thinner and more
comfortable
 Base-to-base line is located below the
geometric centre of the lens  upper
lid plays a greater role in lens
orientation
 Cylindrical component is usually
limited to the prismless optical zone
Reverse Prism Designs

How does stabilization method
affect fit and physiology?

 Prism ballast designs have greater:
- thickness variation
- lens mass
- localized pressure on cornea at prism base
 This results in:
- increased central, temporal and inferior
corneal thickness
- greatest corneal compromise at
inferior limbus
Thickness Variations

Implications for Oxygen Transmissibility:
Harris and Chu (1972)
 Thickness differences mean Dk/t can vary greatly
 Increased thickness differential indicates a decline in oxygen
transmissibility from one lens region to the next
Average Thickness Measurements:
Wechsler(1985)
• Average lens thickness a better indicator of Dk/t
• WTR lenses have lower average thickness than ATR in
prism ballast designs
Thickness Variations

Physiological Considerations
 Complications such a corneal edema and corneal
neovascularization more likely due to increased lens
thickness

The Challenge:
 Need stable cylinder axis location for good vision
 Predictable interaction between lid forces and toric lens
shape
Must assess:
 Patient spectacle Rx and VA
 Visual demands
 Keratometry
 Degree of astigmatism/axis
TORIC SOFT CONTACT LENS FITTING

Soft Toric Contact Lenses
 Does this patient need a soft toric lens?
 Which type of soft toric is appropriate?
 What parameters should be used?
 Does the lens fit?
 What power should be ordered?

How should Lens Parameters be
Selected?
 Base curve
– Be sure lens fits!… Equilibration can take up to
30 minutes. Fit the flattest base curve that is
stable
 Over all diameter
– larger sizes allow scleral support, more stable.
Normal size is 14.2 to 14.5

How should Lens Parameters
be Selected?
 Cylinder axis
– Close to axis of glasses
 Cylinder power
– Close to the cylinder amount of glasses. Remember
vertex distance conversion.
 Sphere power
– Close to sphere power of glasses.
– Remember vertex distance conversion.14 July 2020 Optom. Ankit Varshney 42

Fitting Toric Soft Lenses
1. Three fitting techniques:
1. Diagnostic
2. Trial
3. Empirical
4314 July 2020 Optom. Ankit Varshney

 Use a trial lens which incorporates cylinder
 Stabilization features of the trial lens should be
representative of any lens ordered from the same
series
 Most reliable technique for toric SCL fitting
Toric Trial Lens Method

 Measure refractive error; correct for
vertex distance if necessary
 Choose a toric trial lens as close as
possible to this Rx
 Assess the lens fit
 Determine orientation behaviour of the
lens
 Consider any angular mislocation in the
final prescription
Toric Trial Lens Method

 Average lens rotation is 5 – 10 nasal
- anticlockwise for RE
- clockwise for LE
 Large individual variations
 Lens affected by lens/eye relationship
and lid anatomy/ Tears
 Lens allocation affected by lens
thickness profile
Most lenses stabilize within 0 – 15 nasally
(Irvins, 1984)
Predicting Lens Rotation

Good vision with any kind of toric lens needs
stable cylinder axis location!
1. The magnitude and
direction of any mislocation
must be determined
2. Use this to compensate the
ocular astigmatic axis for
any regular mislocation

How do you determine amount
of rotation?
 Look at markings
– Lens Marks denote THICKEST part of the lens
– Lens Marks do NOT indicate the power axis
– Stable lens rotation, to a position other than 6 o’clock
is OK
– >20 degrees rotation is BAD FIT
 Measure rotation:
- narrow slit-lamp beam
- protractor scale eyepiece graticule
- Estimate the degree of lens rotation (clock hours)

Soft toric markings: AOCLE guide

References marks (prism base or thin zone) are
used to assess lens orientation in situ
Lens Rotation

 Reference mark on lens at 3 and 9 o'clock or 6 o'clock
 Lens markings are for reference only
 Measure rotation:
- narrow slit-lamp beam
 Estimate the degree of lens rotation (clock hours)
 Note consistency of lens marking position
 Push lens around to determine settling position
Measurement of Lens Rotation

Lens deviation is measured as:
 Deviation from the vertical
(markings at 6 o’clock)
OR
 Deviations from the horizontal
(markings at 3 and 9 o’clock)
Measurement of Lens Rotation

Rotation of lens: Compensation: (degrees)
Clockwise (Left)  ADD
Anticlockwise (Right)  SUBTRACT
Compensation for Lens Rotation
L A R S
Add or subtract amount of rotation to the
axis of the contact lens Rx

Lens Rotation Terminology: Practitioner View
left
anti-clockwiseclockwise
right
12
6
9 3
Terminology: practitioner viewTerminology: practitioner view
Left
Add
Right
Subtract

 Patient requires cyl axis 90° OD
 Lens marking (6 o’clock) mislocates
15° to the right
 Right = subtract (Anti-clock)
therefore requires 90° – 15° = 75°
order
75°
105°
15° mislocation
Example of Lens Rotation
Target location in this case is 90°
Right Eye

 Patient requires cyl axis 70° OS
 Lens marking (6 o’clock) mislocates
10° to the left
 Left = add (clockwise)
therefore requires 70° + 10° = 80°
Target location in this case is 70°
Left Eye
order
80°
60°
10° mislocation 70° = desired
axis
Example of Lens Rotation

Rotation & Axis Compensation
Rotation Amount Axis Compensation
0 to 09 degrees No compensation, order
spectacle cyl axis
10 to 20 degrees Left add, Right subtract to
spectacle cyl axis
> 20 degrees Change lens design or fit

How to make the patient see
 Do spherical over refraction first
 If VA not acceptable, do sphere-cylinder over
refraction
 Use cross cylinder calculators from labs
 Or use the lensometer cross cylinder technique

 Within 1 line of spectacles
 If 1 – 2 lines from spectacles, use clinical
judgement:
- patient expectation
- visual demand
- monocular vs binocular VA
- visual comfort
Visual Success Criteria:

Induced power due to axis
rotation
 Induced cylinder power equals ½ the contact
lens cylinder when lens is rotated 15 degrees.
 CLP= -1.00-2.00x180
 Rotates 15 degrees
– Induces about -1.00 cylinder!
 Lower powers (<1.25) not as significant as
higher powers.

13 steps in learning Trial Toric
SCL selection
Step 1 - Refraction and cylinder in MINUS cylinder form
e.g- R/E - -3.00 /-2.50 x 170 degrees
L/E - +3.00 /+2.00 x 160 degrees
Step 2 - Unlike spherical lenses there is no need to do
spherical equivalent
Step 3 - Do vertex distance compensation of the sphere &
cylinder separately

Toric lens fitting
e.g- RE -3.00 / -2.50 x 170 degrees
-3.00 -2.25 To be Decided

Toric lens fitting
Step 4 - Base curve is determined by Keratometry
e.g- 7.50mm / 7.70mm
Step 5 - Add 0.80 mm to the flattest meridian or the highest
reading in mm.
In the above example 7.70 mm is flatter than 7.50 mm hence
7.70mm + 0.80mm = 8.50mm
Thus the BC of the lens will be 8.50mm
Horizontal Vertical

Toric lens fitting
-3.00/ -1.75 x 180 8.50 mm

Toric lens fitting
Step 6 - You have the spherical, Cylindrical power
as well as the Base curve of the lens
Step 7- Choose a lens with its axis as the
spectacle Cylindrical axis (i.e 170 degrees)

Toric lens fitting
Step 8- Give the trial to the patient - wait for 15-20
minutes before assessing fit of the lens
Step 9 -Assess fit of the lens by assessing
– Full Corneal Coverage
– Centration
– Movement
– Comfort
– Stable vision 6614 July 2020 Optom. Ankit Varshney

Toric lens fitting
Step 10 - It is possible to show vision to a patient
as lens axis matches spectacle axis
Step 11 - If first 4 factors are fine then axis
finalization is done

Toric lens fitting
Step 12 - For axis finalization concentrate on
the 3 laser guide marks at the inferior or lower
portion of the lens

Toric axis finalisation
3 things can happen while assessing toric lens rotation
 No rotation or minimal rotation of 5 degrees
 Rotation to L.H.S ( with reference to Practitioner)
 Rotation to R.H.S (Practitioner)

Formula for Toric axis finalization
L A R S
LEFT ADD RIGHT SUBTRACT
70
C A A S
LEFT
CLOCKWISE ADD SUBTRACTANTI- CLOCKWISE

Toric axis finalisation
CASE 1
No Rotation / minimal rotation of 5 degrees
Answer - No change in spectacle axis
hence the prescription remains:-
-3.00 / -2.25 X 170 8.50mm 7114 July 2020 Optom. Ankit Varshney

Toric axis finalization
CASE 2
Rotation to L.H.S by 15 degrees
Answer - ADD 15 degrees to spectacle axis
hence the prescription becomes:-
-3.00 / -2.25 X (170 + 15 = 5 degrees) 8.50mm
150

Toric axis finalization
CASE 3
Rotation to R.H.S by 10 degrees
Answer -subtract 10 deg. from spectacle axis, hence
the prescription becomes:-
-3.00 / -2.25 X (170 -10 =160 degrees) 8.50mm
100

Example 1
 Spectacle Rx -6.00 / -3.00 x 180 8.5 mm
 Vertex Dist -5.50 / -2.50 x 180 8.5 mm
 Trial lens - -3.00 / -1.25 X 180 8.5 mm
 Rotation to R.H.S by 20 degrees
 Subtract - 180 – 20 = 160 degrees
Final lens prescription:-
74
-5.50/-2.50 x 160 degrees 8.50mm14 July 2020 Optom. Ankit Varshney

Example 2
 Spectacle pres. -3.00/-1.75 x 20 8.50mm
 Vertex Dist - -3.00 / -1.50 x 20 8.50 mm
 Trial lens - -3.00 /1.25 X 180 8.50 mm
No Rotation
Final lens prescription:-
75
-3.00/-1.50 x 20 degrees 8.50mm14 July 2020 Optom. Ankit Varshney

 Full corneal coverage,
 0.2 – 0.5 mm movement
 Easy push up test
 Minimal lens rotation
Good fit – quick return to axis if mislocated
Tight fit – slow return to axis if mislocated
Loose fit – lens orientation unstable and
inconsistent
Assessment of toric soft lens

Toric lens fitting
STEP 13 - After axis finalization the final toric
lens order is given to the manufacturer

Things to Remember
 Do not make any changes in trial lens axis
 Choose trial lens axis same as spectacle
axis or as close as possible
 Like the trial lens, final lens would also show
similar rotation

 Low or no spherical component
e.g. Plano / –2.50 x 180
 Oblique cylinders
e.g. – 2.00 / – 2.00 x 45
 High cylinders
e.g. +4.00 / – 6.00 x 80
Difficult Cases
TORIC SCL FITTING

 Teacher
 Age: 35 years
 Plays sport
 Spec Rx
OD –5.00 / –2.00 x 80 OS –6.00 / –1.75x110
 K readings
OD 44.00 / 43.50@ 90 OS 43.50 / 43.00@ 95
Case 1
TORIC SCL FITTING

A. Spherical RGP
B. Spherical SCL
C. Toric RGP
D. Toric SCL
What would be the
1st CL of choice?

WHY A TORIC SCL?
Spec Rx
OD –5.00 / –2.00 x 80 OS –6.00 / –1.75x110
K readings
OD 44.00 / 43.50@ 90 OS 43.50 / 43.00@ 95
Most astigmatism is NOT corneal
& is ATR
Likes to play sport

Spec Rx
OD –4.25 / –1.25 x 180 VA 6/6
OS –3.25 / –1.25 x 170 VA 6/6
K readings
OD 44.50 D (7.59 mm) @ 90 / 43.75 D (7.72 mm) @ 180
OS 44.00 D (7.67 mm) @ 80 / 43.50 D (7.76 mm) @ 170
HVID = 12 mm OU
Case 2
TORIC SCL FITTING

Use Toric Trial SCLs
RIGHT LEFT
BOZR (mm) 8.6 8.6
Total Diameter 14.0 14.0
BVP
(as close as possible to required
BVP, taking vertex distance into
account)
–4.00 / –1.00 x 180 –3.00 / –1.00 x 180

Spec Rx: OD –4.25 / –1.25 x 180 OS –3.25 / –1.25 x 170
Right Trial Lens: –4.00 / –1.00 x 180
 Patient requires axis 180°
 Reference marks: mislocate to
20° ANTICLOCKWISE
 (Mislocation   VA)
 ANTICLOCKWISE = SUBTRACT
180° – 20° = 160°
– with spherical over RX
equires axis 180°
rking: mislocates 20° to the right
ARS, therefore, require 180° – 20° = 160°
order
20°160°
20°
mislocation
180° = desired axis

Spec Rx: OD –4.25 / –1.25 x 180 OS –3.25 / –1.25 x 170
• No rotation noted
(but axis of trial lens 10° off   VA)
• No mislocation, therefore, no compensation
required (i.e. order ocular Rx axis)
• CL axis: 170° (same as spectacle Rx)
(1) Left Trial Lens: –3.00 / –1.00 x 180

RIGHT LEFT
BOZR (mm) 8.6 8.6
Total Diameter 14.0 14.0
BVP –4.00 / –1.00 x 160 –3.25 / –1.00 x 170
(if no rotation)
Final Toric SCLs to be Ordered

DELIVERY & DISPENSING
 Visual acuity OD 6/6
OS 6/6
 Fit good OU
 Care & maintenance instructions reinforced
 Note RE lens orientation
One Week Follow-up Visit
• Vision stable
• R CL locates 20° ANTICLOCKWISE (as compensated for)
• L lens  no mislocation
• Fit still good OU
• Comfort good

Over-Refraction
 If  VA with toric CL, possible reasons are:
– delivered CL not rotating to the same position as trial
CL did
– CL axis is inaccurate (±8⁰ is acceptable in
manufacturing but has significant effect on VA)
– patient’s Rx is incorrect or has changed
Perform an over-Rx to see if VA improves14 July 2020 Optom. Ankit Varshney 90

Over-Rx
 If over-Rx VA:
– add obliquely crossed-cylinders (the contact lens Rx &
the over-Rx sphero-cyl) and resultant will be new Rx
(?)
 Use a lensometer to determine the new Rx by adding the
spheres & the cylinders together
 Go online to CooperVision, CIBA Vision or J&J and use their
toric calculators to find the resultant cyl.
 See ICLC Module 3 where you will find a table that shows you
the resultant cylinders14 July 2020 Optom. Ankit Varshney 91

 Patient happy with good vision and comfort
 Best contact lens option given for this patient
As a practitioner, you can offer more
than basic contact lens practice!
OUTCOME

Thanks
 Any questions?????????????????

Toric soft contact lenses by optom ankit varshney

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