This document provides an overview of orthokeratology (orthokeratology), which aims to temporarily reshape the cornea through the overnight use of specialized contact lenses to reduce or eliminate the need for refractive correction. It discusses the history of orthokeratology from its origins in the 1960s using conventional geometry lenses to more modern techniques employing reverse geometry lenses made of high Dk materials. The mechanisms by which orthokeratology reshapes the cornea, patient selection criteria, potential indications and contraindications are described. Advantages include reversibility and potentially slowing myopia progression in children, while disadvantages include its non-permanence and risk of non-compliance.

1. ORTHOKERATOLOGY
Rashad Ibn Muhammed
A51339214013
M Optom (Sem 4)
Amity University Haryana

2. Contents
1. Introduction
2. History
3. Conventional Geometry
4. Reverse Geometry
5. Mechanism
6. Patient selection
7. Indication /Contraindications
8. Advantages / Disadvantages

3. ORTHO KERAT OLOGY
Straight cornea knowledge
• Aim is to ‘reshape’ the cornea
▫ a non-surgical, topographical approach
to eliminate refractive correction

4. Having so many names
• Corneal Reshaping Therapy™ (CRT™)
• Vision Shaping Treatment™ (VST™)
• Corneal Refractive Therapy™
• Accelerated Orthokeratology
• Corneal Corrective Contacts
• Eccentricity Zero Molding™
• Gentle Vision Shaping System™
• Overnight Corneal Reshaping

5. History
• Dr George N. Jessen introduced “Orthofocus”
Conventional Geometry lenses in 1960
• Fontana was the first to use a reverse Reverse
Geometry lenses in 1972

6. Conventional Geometry
• First to attempt to change refractive error
• Technique used plano PMMA lenses
• Flat central fitting
(Flattest k fitting)

7. • Failed due to Disadvantages of PMMA lens
• Decentration of lens inducing astigmatism
• Took long time to achieve a small amount of
reduction
• Lens fit was unstable
• Costly

8. Reverse Geometry
• Ortho-K is used the temporary correction of low
to moderate myopia. It uses four- or five curve
reverse-geometry lenses in high Dk materials in
an overnight lens-wearing modality

9. Early RG lenses
• Fitted 0.3 - 0.5 mm flatter than Kflat
▫ depends on corneal cyl
• Width of the tear reservoir may indicate the
extent of possible further corneal change
• Steep periphery aids tear exchange and
centration
• Larger diameters may be required
• Maximum effect may take some time

10. Treatment Zone
Tear
Reservoir
Secondary
Curve
Edge Clearance
Before After
3-Zone Design

11. Modern RG
• Centre well
• Apply little or no load to the corneal apex
(5 mm clearance)
• Lens is supported by its peripheral curve
• Having different zones
1. base curve
2. reverse (steeper) curve
3. fitting (alignment) curve
4. peripheral curve

13. • Depending on the fitting philosophy of the
design being used, an initial base curve is chosen
that is 0.30 mm to 1.40 mm flatter than the
flattest corneal curvature (flat “K”).
• This optical zone width may vary from 6.0 mm
to 8.0 mm. Commonly, a posterior optical zone
diameter of 6.0 to 6.5 mm is most often used.

14. • The secondary (reverse) lens curve of the shaping
lens is chosen steeper than the base curve radius.
• This “reservoir” zone is commonly 3.00 to 5.00
diopters steeper than the base curve radius
• The width of the reverse curve ranges from 0.6 mm
to 1.0 mm
• Peripheral curve radius is slightly steeper than
conventional GP lens fits, having an edge (edge lift)
clearance of 60 to 70 microns (0.06 mm to 0.07
mm).

16. Mechanism
• The flatter central fitting relationship results in a
positive pressure or applanating force on the
cornea induces a possible compression and/or
flatenning of the corneal epithelial cells, but
there is no loss or migration of the cells.
2. The mid-peripheral epithelial cells are larger
and more oval. The thickened midperipheral
cornea maintains normal cell layers

17. Myopia

18. Treatment diameter vs dioptric change for
a fixed sagittal depth change
Treatment
depth(Flatteni
ng / thinning)
Treatment
diameter
(‘Optic zone’)
Expected
change
20μm 6.0 mm –1.75 D
20μm 5.0 mm –2.50 D
20μm 4.0 mm –3.75 D
20μm 3.0 mm –6.75 D

19. Patient selection
• High motivation is required
• Level of patient’s desire for 6/6 (20/20)
• Previous contact lens wear
• Pupil diameter
▫ measure under a range of illuminations
▫ large pupils are problematic

20. Indications
1. Age: 6-20 years
2. Spherical refractive error: -1.00 D to -5.00 D
3. Cylindrical refractive error:
a. 1.50 D or less “with-the-rule” corneal
astigmatism
b. 0.75 D or less “against-the-rule” astigmatism
5. Professionals who require good unaided visual
acuity such as police, firemen, military, deep-sea
divers, high altitude pilots, etc.
6. Free of corneal dystrophies , degeneration and
contra indication to CL wear

21. Contraindications
• Previous failure(s) with RGP lens wear
• Diseases of the cornea, conjunctiva, or adnexa
▫ e.g. dry eye
• Anterior chamber inflammation/infection
• Systemic disease that affect the eye or can be
exacerbated by lens wear
▫ e.g. diabetes
• Keratoconus

22. Contraindications
• Older patients (long-term CL wearers?)
▫ cornea less likely to respond well
• Unrealistic patient expectations
• Against the rule cylinder > 0.75 D Cyl
• Low sphere power with high cylinder
• Limbus to limbus astigmatism
• Very steep or flat K values

23. Advantages
• Reversible
• Both eyes ‘altered’ at the same time
• No disruption to vision during treatment
• Less (or no) pain compared with PRK
• Therapy can be halted if untoward effects
are experienced
• Option for children
▫ may slow myopia progression

24. Disadvatages
• Not a ‘permanent’ solution
• Patient may become a regular RGP
lens wearer, i.e. uses OK lens conventionally
• Amount of refractive error correctable by OK is
limited
• Potential for non-compliance

25. Reference
• IACLE module 8.9
• ICLE power point presentation 8.9

26. THANK
YOU