Orthokeratology

Orthokeratology

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

2. Contents Introduction History Conventional Geometry Reverse Geometry Mechanism Patient selection Indication /Contraindications 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 K flat 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 m m 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

12. 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 ”). T his 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.

13. 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 ).

14. 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

15. Myopia

16. Treatment diameter vs dioptric change for a fixed sagittal depth change Treatment depth(Flattening / 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

17. 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

18. 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

19. 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

20. 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

21. 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

22. 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

23. Reference IACLE module 8.9 ICLE power point presentation 8.9

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