Contact Lens Options in

KERATOCONUSHira Nath Dahal

Institute of MedicineMaharajgunj, Kathmandu

COE: Advanced Contact lens Practice

Introduction

• 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.

• Mild to marked impairment of vision occurs, depending on

• extent of induced irregular astigmatism

• Protrusion of cornea

• Bilateral in approximately 96% of the cases.

• No gender predisposition

Rabinowitz YS. Keratoconus. Surv Ophthalmol 1998;42(4):297-319

Zadnik K, Barr JT, Edrington TB, et al. Baseline findings in the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study. Invest Ophthalmol Vis Sci 1998;39(13):2537-46.

Management

Varies depending on state of progression of ectasia

Does spectacle works in Keratoconus?

• Yes and No

• 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.

Then, does soft contact lens work?

• It is not better than spectacle lens but it works in piggy back system

• At very early stage, this way work as equal to spectacle does.

• But patient may not be satisfied with the level of vision he has even though it is 6/6

• Shadow effect of texts• Ghosting of image• Poor night vision• Eye fatigue on prolong reading

Do they have to suffer from visual impairment ????

No.... Research in contact lens has brought tremendous achievements

• Conventional RGP • Aspheric RGP—latest Mc Aspheer

• Piggy back system

• Hybrid lens system

Promising options

• Rose K family of lens

• Mini –Scleral lenses

• Rose K XL

• Mc Aspeer

• Boston prose treatment

Optics of contact lens!!

Eliminate corneal irregularities with pre-corneal tear lens formed by these lenses

thus provides better visual correction

Rigid gas permeable lenses

• Mostly they are spherical back toric, • Spherical back curve with peripheral toric for

high corneal astigmatism• Multicurve or aspheric design also available

(Mc Aspheer)

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

Divided support or three point touch

• An apical contact area of two to three millimetres, a intermediate clearance zone and mid peripheral contact annulus with conventional edge clearance at the periphery.

Woodward EG. Contact lenses in abnormal ocular conditions—keratoconus. In: Phillips AJ, Speedwell L, eds. Contact Lenses.

• Fitting: three point conventional fitting philosophy

• Because of three point touch, bearing on irregular cornea, corneal haze is likely on long standing cases Latest: superior edge alignment with

modified edge design (S- curve design)

On basis of shape and position of cone

This 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. Sagging (oval) cone:

area of the cone is larger than nipple cones usually displaced infero-temporally

Larger 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.

Aspheric RGP

• Gradually flatten from the centre towards the periphery, approximating the steep cone vs. 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

So, what if patient cannot tolerate RGP lenses??

Ans: 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

• With availability of super-Dk silicone hydrogel and RGP lens materials, use of piggyback system has become better in terms of enhanced oxygen availability to cornea and reduced risk of complication.

Potential problems ????Handling and care of two different types of lenses, Hypoxia and Neovascularisationdifficulty in obtaining centration of the  rigid lens.

Better options than Piggy back !

Hybrid Lens system

• One way to overcome the problems with piggy-back lenses, yet have the optics of a rigid lens with the comfort of a hydrogel, is to fuse a soft rim onto a hard central portion.

• combine the benefits of rigid lens optics, including better lens centration and decreased aberrations, along with the comfort of a soft lens

Potential complications… • flexure of the GP centre lens (leading to

astigmatism and decreasing visual results), • difficulties with insertion and removal of the

lenses, and• tearing at the GP lens and hydrogel skirt

junction.

Fully keratoconic designed lenses??

•Rose k family of lens

•Scleral and Mini scleral lens

Rose K

• 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 K1 Vs Rose K2

ROSE K1

ROSE K2

Aspheric back surface

Multiple back curves

• Every individual Rose K2 lens has its own aspheric (ecc)

• value on the front and back, computer designed to

minimize spherical aberration

Rose K2 Family of lenses

Rose K2 Xl

• Indications: Keratoconus, Pellucid Marginal Degeneration, Post Graft, Corneal Rings, Post-LASIK ectasia and dry eye

Rose K2

• Indications: Oval Keratoconus, Nipple Keratoconus & early Pellucid Marginal Degeneration

Rose K2 NC

Indications: Moderate & Steep Nipple Cones

Rose K2 IC

• Indications: Pellucid Marginal Degeneration, Keratoglobus, Oval Keratoconus, LASIK-induced Ectasia and Post Graft

Rose K2 PG

• Indications: For patients who have undergone penetrating keratoplasty, Oval Keratoconus, Nipple Keratoconus and Lasik

Scleral and Mini-Scleral lens

Mini scleral lenses

• Lens diameter:15.0mm and 18.0mm

1) bear on the sclera and

2) vault the cornea

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

Optics of Mini scleral lens !!

• 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.

• This result in less ghosting and much crisper vision

Advantages

• better comfort,

• Less mechanical trauma to the cornea,

• better vision. 

Boston (PROSE) scleral lens

• PROSE is an acronym for "prosthetic replacement of the ocular surface ecosystem".

• customized prosthetic corneo-scleral devices for each patient’s condition and unique eye shape

• Prosthetic devices used in prose are transparent domes, about the size of a nickel, made of gas permeable plastic (Boston XO2 and Menicon Z) that allows oxygen to reach the ocular surface

PROSE creates:

• A new transparent, smooth optical surface over the irregular, damaged or diseased cornea

• An expanded artificial tear reservoir that provides constant lubrication while maintaining necessary oxygen supply

Finally…

• Contact lens care of keratoconus patients is often

challenging, complex, and involved, requiring cost and time on the part of both practitioner and patient.

•But rewarding too• However, contact lens wear can restore vision without the need for surgery throughout the lifetime of most keratoconus patients (90%). 

THANK YOU!!!