Fitting soft contact lenses requires considering many patient-specific factors to achieve excellent vision and ocular health. A proper fit involves selecting the correct total diameter, base curve, thickness, and material based on the patient's prescription, corneal shape, lifestyle, and health. Trial lenses are used to evaluate fit parameters like coverage, centration, movement, comfort, and vision to optimize on-eye performance while avoiding issues like tightness or looseness that could impact ocular health or vision. The goal is to find a lens that provides optimum vision and good comfort without causing any ocular insult.

1. Soft Contact Lens Fitting
1

2. Why is fitting the “whole patient”
necessary?
• Successful fitting involves complete set of
parameters
• Most critical, patient must achieve excellent vision
and maintain ocular health
• Many factors must be considered for success:
– Compliance to lens wear and care
schedules
– Lifestyle issues and environment
– Overall patient physical health
3

3. Soft Contact Lens Fitting
Parameter Selection
• Total diameter
• BOZR ( Base Curve)
• Centre thickness
• Water Content
• Material Selection
• Method of manufacture
4

4. Contact Lens Fitting Guidelines
• Selection of lens type –Conventional/ Disposable
• Determine Lens Power
• Total Diameter Selection
• Base Curve selection (if required)
• Trial fitting
5

5. Lens Power Determination
• Subjective refraction
e.g - -4.00/-1.00 X 180
• Spherical equivalent
• Vertex distance compensation
6

6. Spherical Equivalent`
• If a patient has low astigmatic refractive
errror in addition to myopia or hyperopia, a
spherical soft lens may be prescribed. The
Rx is based on a calculation known as the
“spherical equivalent.”
SE = Sphere + ½ Cylinder
7

7. Vertex Distance Compensation
• Effective lens power changes depending on
the distance from the cornea; e.g.spectacle
vs. contact lens
• Utilize vertex distance compensation chart
to determine proper contact lens power
from spectacle refraction
8

8. Soft Contact Lens Fitting
Total Diameter Selection
• Measure HVID (Horizontal Visible Iris Diameter)
Then either:
• Add 2mm to HVID and select trial lens
set with nearest diameter or
• Follow manufacture's recommendation
and select suggested diameter
9

9. Soft Contact Lens Fitting
Total Diameter Selection
10

10. Soft Contact Lens Fitting
Effects of Diameter
S2 > S1 > S3
same BOZR
S 1
S2
D
1
D2
‘Original Fit’ ‘Steeper’
flatter BOZR same BOZR
S 4
S 3
D
4 D 3
‘Same’ ‘Flatter’
S11 S 44
D 11 D 44
11

11. Soft Contact Lens Fitting
Rule of Thumb`:
(Soft Lenses)
TD 0.5 mm BOZR 0.3 mm
(increase) (increase)
12

12. Soft Contact Lens Fitting
Base Curve Selection
Measure Ks (mm) then add either:
• 0.8 mm to flattest K
• 1 mm to average of Ks
• 4 D flatter than average K
Select lens of nearest Base Curve from trial set
or . . .
Select Trial lens Base Curve as per manufacturer’s recommendation
13

13. Soft Contact Lens Fitting
Trial Lens Fitting
• Regarded as essential by some
• Allows the 'feel' of a lens experience
• Patient reaction is assessable
• Needs to be performed in average illumination
(pupil size)
- assessments made with the aid of good
illumination
- low to moderate magnification
• Now easier and safer - disposable trial lenses
15

14. Soft Contact Lens Fitting
Trial Lens Fitting
• Select trial BVP nearest to vertex corrected
spectacle Rx result
• If only ± 3.00 D (or similar) available use
appropriate type ( ie plus or minus)
• If Rx high but only low Rx trial lenses available,
consider getting more appropriate trial lenses )
• If large difference between trial and Rx, remember
to correct over-Rx for vertex distance
16

15. Soft Contact Lens Fitting
Empirical Prescribing
Patient data required for lens choice:
• HVID
•
• Ks
•
• Spectacle Rx
•
• Vertex distance
•
•
17

16. Optimizing On-Eye Performance
• Trial Lens is placed on the eye and allowed to
settle 10-15 minutes
• On-eye lens performance is evaluated based on
the universal fitting criteria:
– Corneal Coverage
– Centration
– Lens movement
– Comfort
– Vision
18

17. SOFT LENS FITTING
The need for Corneal Coverage
• Mechanical, prevention of trauma
•
• Physiological
- corneal exposure
- corneal dessication
- tear film disturbance, lens & eye wettability
• About 1 mm symmetrical overlap is ideal
19

18. Soft Contact Lens Fitting`
Corneal Coverage
20

19. Soft Contact Lens Fitting
Centration
Good Optical performance
Based on Lens Diameter,
Edge Design
If decentered
- Large lens
- Steep BC
21

20. Soft Contact Lens Fitting
Why is Movement Required?
Movement
• Removes and disperses ocular debris
•
• Promotes tear exchange (minimal)
•
• Possibly aids epithelial wetting by
•
mucin spreading and smoothing
23

21. Soft Contact Lens Fitting
Assessment of Mobility?
• Movement on a blink
• Lag following eye movement
• Movement on up-gaze blink
• Lower lid push-up test
24

22. Soft Contact Lens Fitting
Movement
25

23. Soft Contact Lens Fitting
Movement
26

24. Soft Contact Lens Fitting
Lens Lag
A steep lens is very stable
and there is hardly any lag
A flat lens is less stable
and therefore will lag more
27

25. Comfort
• A critical factor of contact lens success
• Steeper (tighter) fitting lenses may be more
comfortable
• Flat (loose) fitting lenses may cause lid
sensation and discomfort
28

26. Vision
29

27. Soft Contact Lens Fitting
Effect of a Blink
Too Steep : Vision CLEARS after blink
Steep lens
Before Blink Lens conform to
central cornea after
Blink (due to lid force)
30

28. Soft Contact Lens Fitting
Effect of a Blink
Too Flat : Vision BLURS after blink
Flat lens Lens decenters
Before Blink because of force
of lid
31

29. Soft Contact Lens Fitting
Tightness: What is Acceptable?
33

30. Soft Contact Lens Fitting
Tightness: What is Acceptable?
• Lens Immobile
• Conjunctiva Indentation
• Blood flow constriction in
peri-limbal vessels
• Low grade inflammation
• Vision better immediately after blink
34

31. Soft Contact Lens Fitting
Summary
Choose lens that gives...
35

32. Optimum vision
36

33. Good comfort
37

34. No ocular insult
38