CONTACT LENS MANAGEMENT IN KERATOCONUS

KAMAL THAKUR3RD YEAR BSC OPTO

NETHRADHAMA SCHOOL OF OPTO

KERATOCONUS

Non-inflammatory, progressive thinning of the cornea that results in apical protrusion (ectasia) resulting in a high degree of irregular myopic astigmatism with observable structural changes appearing in later stages.

Shape and position of coneThis may be helpful when selecting the design of contact lens to fit the cornea.1. Nipple cone: are round and small. usually occur near the optical axis or slightly decentred inferonasally.

2. oval cone: area of the cone is larger than nipple cones usually displaced infero-temporallyLarger diameter contact lenses are required.

3. Globus cone: Globus cones are the largest, involving up to 75 per cent of the cornea most challenging type to fit.

SPECTACLE MANAGEMENT Mild keratoconus in early stage can be

corrected with spectacles.

As the cornea steepens and becomes more irregular, glasses not capable of providing adequate visual improvement.

Once glasses fail to provide adequate visual function, contact lens fitting is required.

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Contact Lens ManagementContact lens wear:

Improves VA by creating a regular anterior refractive surface

Does not prevent progression of Keratoconus. May occasionally induce or hasten progression of

Keratoconus.

Contact Lens Management Contact lenses give sharper vision than spectacles even in mildest

cases of Keratoconus. As Keratoconus progresses spectacle best corrected acuity

becomes unsatisfactory.

Contact lens fitting in a keratoconic cornea is much more difficult Because of the irregular anterior surface of the keratoconic

cornea.

CONTACT LENS FITTING OBJECTIVES

• Provide best possible vision• Minimize interference with corneal

physiology• Optimize lens comfort• Relocate lens bearing area to the mid-

peripheral cornea.

Contact Lens fitting keratoconus

Soft contact lenses play a very limited role in the correction of keratoconus. In the early stages of the progression, soft lenses may provide acceptable visual correction, Especially if used in combination with an astigmatic spectacle over-correction.

Rigid gas permeable lenses

Cost effective, easily available, suitable for mild to moderate keratoconus.

Mostly they are spherical back toric. Spherical back curve with peripheral toric

for high corneal astigmatism.

Keartoconus-fitting philosophies

Three different general fitting philosophies .

1. Apical bearing.2. Apical clearance.3. Three point touch.

Apical bearing The lens is fitted so that it bears heavily against the

apex of the cone. This fitting technique was widely used in earlier times when it was thought that a large flat rigid lens could reshape the cornea and halt the progression of keratoconus. Because this technique is more likely to cause corneal scarring, apical bearing has fallen from favour in recent years.

Flat fitting RGP lenses, especially if the fit results in heavy bearing on the cornea, can also result in corneal abrasions, epithelial breakdown over the bearing area, and lens intolerance .

The apical bearing fitting technique often yields good vision, possibly due to corneal reshaping and/or masking of irregular astigmatism.

Apical Bearing- Flat fitting

Apical clearance The lens back surface vaults (clears) the cone

apex . Lens support or bearing is redirected to the paracentral cornea, away from the cone apex. The risk of scarring is reduced with this type of fitting. However, it may result in variable vision due to uncorrected corneal astigmatism.

Three point touch The lens rests lightly against the cone apex and is

also supported on the nasal and temporal corneal zones by the mid-periphery of the lens back surface.

It is a balance or compromise between apical bearing and apical touch.

This fitting technique is also known as ‘divided support’, and the weight of the lens is distributed over as large an area of the cornea as possible.

Three-point touch is the preferred lens fitting technique as it provides stable fitting and vision, with long-term comfort, and increased wearing time. It appears to give the best results in almost all degrees of keratoconus, from mild to the most advanced.

Aspheric RGP Gradually flatten from the centre towards the

periphery, approximating the steep cone and flat periphery curvature relationship seen in keratoconus

 Indicated for small to moderate nipple cones.

Various parameters of aspheric lenses can be adjusted to achieve the best fit. The more advanced and steeper the cone the greater the rate of peripheral flattening required for the lens to approximate the corneal shape.

if patient cannot tolerate RGP lenses

Combined lens system Piggy back system. Hybrid lens system.

Piggy back system Rigid lens fitted over a hydrogel lens,

increases comfort resulting in adequate wearing time with good vision

Hybrid lens system.

A hybrid lens has a rigid central portion with the optical neutralizing properties of a normal rigid lens and a soft peripheral portion for improved wearer comfort.

Rose K lenses •Unique keratoconus lens design with complex computer-generated peripheral curves based on data collected by Dr Paul Rose of Hamilton, New Zealand.

•Standard diameter: 8.7 mm•BOZD decreases and axial edge lift increases as base curve steepens

ROSE K2 FAMILY OF LENSESRose K2The Rose K2 keratoconus lens design is the most widely prescribed keratoconus lens in the world.  It is a multi-spherical posterior design with aberration control aspheric optics across the back and front optic zone diameters and is available in any toric lens design.Rose K2 ICRose K2 NC Nipple Cone

Standard lens designs with fixed optical zones (OZ) do not ideally fit the cone shape of keratoconus patients. A standard lens that will yield unwanted pooling at the base of the cone and peripheral bearing that can seal off and cause corneal problems.

Smaller optical zone to fit the cone contour. The design results in little tear pooling at the base of the cone and shows an even distribution of tears under the lens.

ROSE K2 FAMILY OF LENSES

Rose K2 NC Nipple ConeThe latest addition to the Rose K2 range of lenses for keratoconus. The Rose K2 NC primary indication is for advanced and moderate nipple cones and secondary application for any defined nipple cone. The design characteristics are a very small aspheric back optic zone diameter which decreases as the base curve steepens and a very rapid peripheral flattening from the back optic zone.Rose K2 Post GraftThis lens is designed for postoperative recovery and improvement in vision. It is a multi-spherical posterior design with some reverse curve geometry and aberration control aspheric optics across the back and front optic zone diameters.

Scleral and Mini-Scleral lens

An advantage of this type of lens is that it rests on the sclera and can bridge the cornea. A rather advanced cone can be cleared with a scleral lens, so that the lens doesn't touch the cone, but rather vaults over it.

Scleral Lens Design

1. The optic zone2. The transitional zone3. The landing zone

Contact Lens Spectrum; Dec. 2009

Mini scleral lensesLens diameter:15.0mm and 18.0mm

1) bear on the sclera and 2) vault the cornea

Cornea is completely vaulted and almost perfect opposite corneal shape is created by tears pooling between the cornea and back surface of the lens creating an equal and opposite keratoconic surface ultimately restoring uniform optical lens and elimination of astigmatism.

Design to fit all irregular corneas which don’t tolerate any other RGP or hybrid lens.

Keratoconus fitting consideration

Cone position, Cone size and shape, Degree of myopia and corneal astigmatism

Corneal radius (central and steepest), Corneal toricity.

Corneal topography Disease progression - degree - rate Visual acuity Contact lens tolerance

THANK YOU!!!