contact lenses fitting for KCN

Contact lens fitting and keratoconus

Sedaghat M.R M.DMASHAD EYE RESEARCH CENTER

Khatam-al-Anbia Hospital

Natural Course• KCN typically progresses for 3 to 8 years• Difficult to predict rapidity or severity of progression • Difficult to predict termination of progression

• The end point of the progression may be: Slight corneal irregularity Moderate corneal distortion Severe corneal distortion and apical scarring

• Careful monitoring is important

Diagnosis

• Earliy diagnosis is important Early appropriate management Early adequate education

• Earlier diagnosis depends on: Awareness of clinical symptoms Awareness of clinical signs

Symptoms• Guiding symmptoms include:

Monocular diplopia or polyopia PhotophobiaHalos around lights Ghost images Distortion of lettersAsthenopic complaints Gradual decrease in visual acuity Having multiple unsatisfactory spectacles

Signs• Variable auto refractometer results

• Unsatisfactory BCVA

• Irregular retinoscopy reflexes

• Irregular keratometry mires

• Check for SLE clinical signs

• Check for localized corneal steepening in topography

PATIENT CONSULTATION• Inform the patients about the diagnosis (or possible

diagnosis) as soon as possible

• Describe the progressive nature of KCN

• Describe the algorithm of therapy including corneal transplantation

• Mention about the inevitable possible changes in the patient’s quality of life

Optical Therapy• Needs both art and science

• Management must always be tailored: Visual needs Comfort Tolerance

• Good physician- patient communication is necessary to determine the best next step in managing a particular case of KCN:

Anisometropia due to asymmetric involvement

Optical Therapy

• Most KCN patients start with wearing spectacles

• Spectacles have their best application early in the disease because:

Corneal irregularity gradually increases Spectacles do not optimally cover the irregular cornea The RE can change quite rapidly Anisometropia due to asymmetric involvement

SPECTACLE MANAGEMENT

• The management of keratoconus usually begins with spectacle correction

• There are two methods of refraction: Objective:

Your reasurement, irrespective of the patient's responses Subjective:

Measurement is mainly dependent on the patient’s responses to your questions

Optical Therapy

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

Contact Lens Management

Contact lens wear:

• Improves VA by creating a regular anterior refractive surface• Does not prevent progression of KCN • May occasionally induce or hasten progression of KCN


• CL therapy should never be withheld for fear of causing progressive KCN

• Many KCN patients are successfully fitted or refitted if: Reasonable patient motivation Physician and patient patience Fitting expertise Access to all available contact lens modalities

Contact Lens Management• In 1888, a French ophthalmologist, Eugene Kalt, tried to correct

keratoconus by compressing the steep conical apex of a keratoconic cornea by a glass shell

• This was the first known application of a contact lens for the correction of keratoconus

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

cases of KCN• As KCN 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

• Acceptable fitting results require a high level of patience Explaining this to the patient at the initial fit is helpful in

establishing an effective, long lasting relationship between the patient and the physician


• The CL management of keratoconus is most often in the form of rigid gas-permeable (RGP) CLs

• RGPs improve VA by neutralizing much of the distortion/optical aberrations of the anterior corneal surface

• There are reports suggesting that rigid CLs may cause keratoconus due to mechanical pressure and hypoxia, but

It is difficult to establish a cause-and-effect relationship The patients may have been corrected with contact

lenses before being diagnosed as KCN


• Keratoconic patients who are no satisfied with CLs may need PK: Studies have shown that more than 70% of keratokonic

patients referred for PK can avoid surgery and remain satisfied by refitting CLs

• Multiple fitting algorithms are available to assist in fitting the keratoconic cornea– The process is as much an art as a science– These lenses may be fitted

Steep or flat Large or small Spheric or Aspheric


• Three objectives are required for successful CL fitting in KCN: Minimal physical trauma to the cornea Stable visual acuity during the entire wearing schedule All day wearing comfort

• It may be impossible to meet all of these objectives for every patient, but do your best to achieve the best possible outcomes


• Three rigid lens-to-cornea fitting relationships are proposed in KCN:

Apical bearing (Reshape or splint method) Apical clearance Three-point touch

Contact Lens Management Apical Bearing

• A large diameter lens with flat base curve radius (BCR) is fitted

• The fluorescein pattern shows excessive central bearing accompanied by mid peripheral and peripheral pooling

Contact Lens Management Apical Bearing

• Fitters believe that:– it slows down or halts progression of KCN – they are treating KCN, not just correcting the

induced RE

• Excessive pressure on the thin fragile apex causes distortion, scarring, and swirl staining

• This method is rarely used today

Contact Lens Management Apical Bearing- Flat fitting

• The flat fitting method places almost the entire weight of the lens on the cone

• The lens tends to be held in position by the top lid

• Good visual acuity is obtained as a result of apical touch

• Wide edge stand-off cannot usually be eliminated


• Alignment can be obtained in early keratoconus; however, flat fitting lenses can lead to progression/ acceleration of apical changes and corneal abrasions

• This type of fitting philosophy is useful where the apex of the cone is displaced


Contact Lens Management Apical Clearance

• A small, steep lens is fitted

• The lens leans on the slope of the cone, and vaults over the thinned apex

• There is no mechanical rubbing on the thinned corneal apex


• Fitters who follow this philosophy believe that apical contact by a lens will increase the likelihood for corneal compromise and scarring

• If apical clearance lens fitting is utilized, the fluorescein pattern should be monitored to ensure that peripheral seal-off and adherence of lens to cornea do not occur



• In this type of fitting technique, the lens vaults the cone and clears the central cornea, resting on the paracentral cornea

• This type of lens was suggested as it was argued that apical clearance would minimise trauma to the central cornea

• These lenses tend to be small in diameter and have small optic zones; the small BOZD can result in glare problems


• The potential advantages of reducing central corneal scarring are outweighed by the disadvantages of:– poor tear film– corneal oedema– poor visual acuity as a result of bubbles becoming

trapped under the lens

Contact Lens Management Apical Clearance vs Apical Bearing

• In a study 30 keratoconic eyes were fitted with an apical clearance lens design:

The average wearing time increased from a baseline of 10.5 h daily to 13.7 h daily at 12 months

There was no decrement in visual acuity in comparison with the baseline values

In only one eye of the 22 completing the study scarring developed

Contact Lens Management Apical Clearance vs Apical Bearing

• In a study seven keratoconus patients without corneal scarring were fitted randomly such that one eye had the apical clearance design and the other eye had the apical bearing design

• At the end of 1 year: 4/7 eyes with apical bearing had scarring None of the eyes with the apical clearance had

scarring

Contact Lens Management Three-point Touch



• A relatively flat fitting method in which the CL leans on a relatively large area

• There is a mild (feather) touch over the cone apex accompanied by, at least, two other areas of touch at the corneal mid periphery

• Four zones are created: Slight apical touch Paracentral clearance Mid-peripheral bearing Peripheral clearance

Contact Lens Management Three-point Touch-steep fitting


• The proven role for lenses in the keratoconic eye is to improve visual function

• Fitters should choose the approach they are most comfortable with

• The relatively flat-fitting RGP with light apical touch (three point touch technique) remains the mainstay of contact lens treatment for keratoconus


• Contact lens fitting in keratoconus is described separately for:

Early keratoconus Advanced keratoconus

KeratoconusTopographic Characteristics

• Early keratoconus is characterized by initial steepening mid-peripherally below the corneal midline, while the superior cornea remains relatively normal

• As the condition progresses, individual corneas show different topographical shapes:

Nipple Oval Globus

Early & Advanced keratoconus

Early Keratoconus

• There are two fitting methods for early keratoconus:

Superior alignment fitting technique The intra-palpebral three point touch fitting technique

Early Keratoconus Superior Alignment Fitting Technique

• The goal is to provide a superior alignment fitting relationship across the more normal portion of the keratoconic cornea

• Use aspherical lens designs with: OAD of 9.5 mm OZD of 8.3 mm



• In superior alignment fitting technique:

Central keratometry (“K”) readings are of little value The more normal nasal, temporal, and superior mid-

peripheral cornea is the most important fitting consideration


• Topography of a patient with early keratoconus

• Inferior steepening and superior flattening

• Central K readings : 46.25 / 49.75 D

• Inferiorly, the cornea steepens to 51.25 D and superiorly it flattens, to 42.00 D


• If a standard spherical contact lens is fitted on flat K (46.25 D) or steeper than flat K : There is discrepancy

between the lens and the more normal superior cornea

The lens will not show acceptable centration


• If a standard spherical contact lens is fitted on flat K (46.25 D) or steeper than flat K : There is discrepancy

between the lens and the more normal superior cornea

The lens will not show acceptable centration


• Choose a diagnostic lens with BCR equal to the radius of curvature 4.0 mm to the temporal side of the cornea

• Place this lens on the cornea and evaluate the fluorescein pattern

• Superior alignment fitting technique is possible only in the early stages of keratoconus because:

In advanced central ectasia, It causes greater apical bearing


• The ideal fitting should have the following characteristics:

The BCR should be flat enough to provide lens alignment across the flatter superior cornea

The BCR should be steep enough to provide slight touch mid peripherally at 3 and 9 o’clock

There might be slight bearing at the apex of the cornea

There might be slight edge lift across the inferior steeper portion of the cornea

Early Keratoconus Three Point Touch Fitting Technique

The ideal fitting characteristics: The BCR should be steep enough to provide three touch

point: A slight central apical touch Two slight touches mid-peripherally at 3 and 9 o’clock

This lens will most likely position centrally or slight low on the cornea


• Select a spherical lens design with: OAD of 8.0 to 8.5 mm OZD of 6.4 to 6.9 mm BCR equal to the flat K

• Place this lens on the cornea and evaluate the fluorescein pattern


• Four zones are created:

• Slight apical touch• Paracentral clearance• Mid-peripheral bearing• Peripheral clearance


• Three-point-touch actually refers to the area of apical central contact and two other areas of bearing or contact at the mid-periphery in the horizontal direction

• This type of fitting philosophy works very well for small central cones

Early KeratoconusRGP Fitting Approach

• Perform and evaluate the topography• Identify the steepest (red) and the flattest (blue) areas of

the cornea, quantitatively: Location Size Shape

• Identify the dioptric curvature of the corneal apex• Select a diagnostic lens with a BCR equal to the dioptric

curvature of the corneal apex • Place this lens on the eye and evaluate the fluorescein

pattern


• An ideal fitting should have the following characteristics: Slight clearance across the corneal apex with no fixed,

mid-peripheral bubbles Touch in mid-peripheral cornea at 3 and 9 o’clock Minimal impingement across the flatter superior cornea

Slight lower edge lift is common: Intermittent bubbles inferiorly

Any attempt to decrease the inferior edge lift by :Steepening the base or peripheral lens designMay result in a tight lens fit superiorly



Having achieved the desired fit: • Perform over-refraction to determine the final CL power

• Order the lens in a moderate to high Dk RGP material

• The diagnostic lens design should match the final lens

• Manufacturers follows slightly different aspheric lens designs

Best – fit contact lens / KCN

Best – fitapical clearance and good

fluorescein circulation

Excessive vaulting with trapped bubble

Inadequate vaulting with apical touch

TIPS FOR PARAMETERS SELECTION IN KCN

THREE POINT TOUCH NORMAL LENS DESIGN ROCK & EXCSSIVE EDGE LIFT

Advanced Keratoconus Topographic Characteristics

• Early keratoconus is characterized by initial steepening mid-peripherally below the corneal midline, while the superior cornea remains relatively normal

• As the condition progresses, individual corneas show different topographical shapes, e.g.

Nipple Oval Globus

Advanced KeratoconusTopographic Characteristics, Nipple Cone

• The nipple form of keratoconus characteristically consists of a small, near central ectasia, less than 5.0 mm in cord diameter

Advanced KeratoconusTopographic Characteristics, Oval Cone

• The most common type• Apex is displaced below midline:

Inferior mid-peripheral steepening Normal or flat 180 degrees away

Advanced KeratoconusTopographic Characteristics, Globus Cone

• The largest (often nearly 75% of corneal surface) • Nearly all keratoscopy rings are located within the

ectatic area• Almost no island of normal cornea above or below

the midline

Advanced KeratoconusFitting Process

• Due to the varying peripheral corneal topographies No single lens design or fitting philosophy will

universally result in an optimal fit

• Different fitting approaches must be employed Based on the central and mid-peripheral corneal

topography

• Fitting approachs for advanced keratoconus based on the nipple, oval, and globus photokeratoscopy

Advanced KeratoconusFitting Process, Nipple Cone

• The lens should have multiple spherical peripheral blending curves that gradually fatten the lens periphery The resulting lens design is a non-definable aspheric

surface

• The aspheric lens fitting technique is identical to that described for the fitting of early keratoconus, but: It is often necessary to increase the amount of

posterior lens asphericity, due to :Rapid topographical flattening from center to

periphery

Advanced KeratoconusFitting Process, Nipple Cone

Advanced KeratoconusFitting Process, Nipple Cone, Fitting Set

Advanced KeratoconusFitting Process, Oval Cone

• The oval cone consists of an inferior steepening with varying degrees of normal superior corneal topography

• Careful attention to the status of the superior and horizontal corneal topography is important

• If the superior and horizontal topography are relatively normal : Consider superior alignment fitting technique similar

to that described for early keratoconus Superior alignment fit is sufficiently supported by the

normal cornea at 9, 12, and 3 o'clock

Advanced KeratoconusFitting Process, Oval Cone

Advanced KeratoconusFitting Process, Oval Cone, Fitting Set

Advanced KeratoconusFitting Process, Globus Cone

• The globus cone consists of ectasia involving cornea, almost totally

• The only normal portion of the cornea may be the superior limbal area

• Because of the large size CL fitting for globus cones requires large lenses with:

Large OAD of 9.1 mmOZD of 6.5 mm

Advanced KeratoconusFitting Process, Globus Cone

Advanced KeratoconusFitting Process, Globus Cone, Fitting Set

KeratoconusFitting Process, Over Refraction

• Over-refraction is an integral part of diagnostic fitting

• Moderate to high amounts of residual astigmatism is not uncommon for keratoconus patients wearing RGPs: Correction with glasses often improves visual acuity three

to four lines Front surface toric RGPs may also be fitted in this

situation

KeratoconusFitting Process, Lens Dispensing

• All keratoconus contact lenses should be ordered in a moderate to high Dk RGP material to avoid: Epithelial hypoxia Corneal erosion

• Before dispensing the lens carefully evaluate: Base curve, optical zone, diameter, edge, etc Every aspect of the lens design plays an integral role

in the overall success of the fitting

Semi-Scleral GP Lenses

• Semi-scleral lenses are large diameter (13.5 to 16.0 mm)

• These lenses often have a large limbal fenestration to reduce lens adhesion and facilitate lens removal

• Sometimes traditional RGP lens designs may not provide the desired centration, optics, or comfort

• Semi-scleral lenses have proven to be extremely beneficial for Highly irregular and/or asymmetric keratoconic corneas

Semi-Scleral GP LensesFitting Process

• The use of a diagnostic set is mandatory• Select a diagnostic lens with a BCR equal to the

steepest K reading

• The ideal fitting relationship is one in which: There is apical clearance across the central cornea There is a 1.0 mm band of pooling adjacent to the

limbus, in the area of the scleral curve

Semi-Scleral GP LensesFitting Process

Soft lenses• These (hydrogels, silicone hydrogels) have a limited role in

correcting corneal irregularity:– tend to drape over the surface of the cornea– result in poor visual acuity

• Soft lenses designed specifically for keratoconus have a useful role:– In early keratoconus – where a patient may be intolerant of RGP

Soft lenses

• Soft lenses tend to be more comfortable compared with RGPs:

– Kerasoft Lenses (Ultravision) (58% water content terpolymer), in four series, A,B,C and D

– Acuity K Mark I and II (Acuity Contact Lenses)

Advantages of soft contact lens• They afford higher levels of comfort and longer wearing

times, especially in:– patients intolerant of RGP corneal lenses – in monocular keratoconus

• They are useful :– where the cone apex may be displaced, especially if it is

very low– for certain groups of patients, for example airline pilots

• They are relatively simple to fit

Disadvantages of soft contact lens

• Visual acuity may be variable in cases of very high minus lenses

• Low-powered diagnostic lenses may not provide an accurate guide to the fit of the final lens, which may be extremely high powered

Disadvantages of soft contact lens

• There may be reduced oxygen transmissibility and the risk of neovascularisation if the lenses are overworn

• If the condition has progressed, it may be difficult to change to RGP’s at a later stage

KeratoconusSoft CL

• Although in theory, it seems that keratoconic corneas would benefit from soft toric lenses, but this is often not the case because: In the toric lenses, the toric curvatures and

corresponding power corrections are 90 degrees apart (orthogonal)

The keratoconus corneas typically have a high level of irregular, non orthogonal astigmatism

• Only if the cone apex is well centered and if the keratoconus is not advanced, the fitting of a bitoric is possible and has been found to be successful

KeratoconusSoft CL

• Few new soft lens designs have made it possible to correct some complex optics created by keratoconus

• The most common use of soft lenses in keratoconus is the combination of these with rigid lenses: Piggyback designs

Traditional Custom

Hybrid designs

KeratoconusTraditional Piggyback Lenses

• These consist of a high Dk silicone hydrogel soft lens over which a high Dk RGP lens is fitted

KeratoconusTraditional Piggyback Lenses, Fitting Process

• Fit the diagnostic soft lens• Determine the radii of the new corneal surface

Perform keratometry or topography over the anterior surface of the soft lens

• Selected a GP lens with BCR equal to the flat K OAD of 9.0 to 9.5 mm

• Adjusted the base curve until an appropriate lens-to-lens fitting relationship is established

KeratoconusTraditional Piggyback Lenses, Fitting Process

• The ideal GP lens fitting should accomplish three fitting objectives: Apical clearance :

To prevent the lens from rocking and pivoting over the corneal apex

Lens contact (landing zone) at 3 and 9 o’clock: To center the lens along the horizontal meridian

Unobstructed lens movement along the vertical meridian:For the lens to move with blinking

• An over-refraction is performed to determine the final power of the RGP lens



Keratoconus Custom Piggyback Lenses

• These consist of a soft lens with a circular, recessed depression in its center

• A high Dk RGP lens is fitted within the central depression of the soft lens

Keratoconus Custom Piggyback Lenses

• The system provides optimal performance by: Good optics of a well centered RGP Enhanced comfort provided by the soft lens

• The soft lens is available in a wide range of parameters : BCR from 6.00 to 11.00 mm OAD from 12.5 to 16.5 mm The recessed cutout diameter of 7.5 to 11.5 mm

Keratoconus Custom Piggyback Lenses, Fitting Process

• Goals are identical to that of any lens, with the primary fitting: objectives:

Adequate movement Optimal centration

• Select the optimal diagnostic soft lens : Insert any rigid lens into the recessed cutout to mimic

final lens weight and lid/lens interaction

• Remove the rigid lens and determine K readings over the central portion of the soft lens


• Select a diagnostic GP lens with : BCR equal to flat K OAD of 1.0 mm smaller than the cut out diameter To allow for some movement and tear exchange

within the soft lens cutout boundaries

• Place this RGP into the central cutout and evaluate the lens to lens relationship

• Adjust BCR to obtain optimal fitting• Over refract to determine final RGP power


Keratoconus Hybrid Lenses, Saturn Lens

• Work on a hybrid combination GP and soft lens design began in 1977

• In 1985 the Saturn lens was introduced: A central 6.5 mm rigid material with a Dk of 14 Surrounded by a 13.5 mm diameter, 25% water

content soft lens

Keratoconus Hybrid Lenses, Softperm Lens

• The Saturn lens was replaced by the Softperm lens in 1989

An 8.0 mm styrene center in a bi-curve lens design

Surrounded by a 14.3 mm diameter, 25% water content soft lens

Keratoconus Hybrid Lenses, Softperm Lens

• The Softperm hybrid design had limited success due to:

Complications secondary to minimal oxygen permeability

Frequent loss of adhesion between the components Limitations in lens design and parameter availability

Keratoconus Hybrid Lenses, SynergEyes

• In September 2001 a new high Dk hybrid lens called SynergEyes was introduced:

An 8.2 mm high Dk rigid center Paragon HDS 100, Dk 100 Surrounded by a 14.5 mm, 28% water content

non-ionic soft lens

Keratoconus Hybrid Lenses, SynergEyes

• The SynergEyes is available in two designs for keratoconus: SynergEyes A:

the standard aspherical design Ideal for patients with early keratoconus

SynergEyes KC :Specifically designed for advanced

keratoconus

Keratoconus Hybrid Lenses, SynergEyes, Fitting Process

• Select a diagnostic lens with a BCR equal to steep K

• Pour high molecular weight fluorescein into the bowl of the lens and place the lens

• Evaluate fluorescein pattern


• The RGP portion of the lens should exhibit: Central apical clearance Mid-peripheral lens bearing

• The soft lens skirt should exhibit 0.25 mm of blink-induced movement






KCN lens selection based on type of cone

Different types of RGP lens designs for KCN

• Early keratoconus:– Aspherics or multicurve lenses– Kera I and II (No.7)– Acuity K– Rose K (David Thomas)

• Moderate keratoconus:– Kera II– Quasar KNO7– Rose K (David Thomas)– Woodward KC3

Different types of RGP lens designs for KCN

• Moderate/Advanced keratoconus:– Kera II/III– Rose K (David Thomas)– Profile K (J Allen)

• Advanced keratoconus:– Large diameter lenses– S-Lim (J Allen)– Dyna-intra limbal (No.7)

Soper contact lens / KCNbicurve-10 lenses

Apical clearace manner

Soper contact lens / KCNbicurve-10 lenses

Apical clearace manner

VAULTING EFFECT (sagittal value of lens )

McGuire contact lens / KCNBCR -4 PCR-3 type -Apical clearace manner

Rose –K contact lens

• The Rose K is a unique keratoconus lens design with complex computer-generated peripheral curves based on data collected by Dr Paul Rose of Hamilton, New Zealand

Rose –K contact lens 85% first fit successcomplex lens geometry

computer- generated peripheral curve system


• The system (26 lens set) incorporates a triple peripheral curve system - standard, flat, steep - in order to order to achieve the ideal edge lift of 0.8mm

• The practitioner has a choice of peripheral curves


Rose –K contact lens• The design starts with a standard 8.7mm diameter

and works by decreasing the optic zone diameter as the base curve gets steeper

• It is available in base curves of 4.75- 8.mm and diameters of 7.9-10.2mm

• Toric curves are available on the front and back surfaces as well as in the periphery


• Standard lift lenses should work 70% of the time

• Peripheral curves can be configured to a toric design

• Rose K lenses are very widely used

Ni-Cone contact lens / KCN3 separate BCRs -1 PCR

Bennett contact lens / KCNThree point touch fitting

Bennett contact lens / KCNThree point touch fitting

Contact lens / KCN problem solving

CLEK contact lens / KCNmild to moderate KCN-

KCN TRIAL LENSES

Health & Medicine

contact lenses fitting for KCN