contact lenses fitting for KCN

Contact lens fitting and keratoconus Sedaghat M.R M.D MASHAD 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
Photophobia
Halos around lights
Ghost images
Distortion of letters
Asthenopic 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
M anagement must always be tailored :
V isual needs
Comfort
T olerance
Good physician- patient communication is necessary to determine the best next step in managing a particular case of KCN:
A nisometropia due to asymmetric involvement

Optical Therapy
Most KCN patients start with wear ing spectacles
Spectacles have their best application early in the disease because:
Co rneal irregularity g radual ly increases
Spectacles do not optimally cover the irregular cornea
The RE can change quite rapidly
A nisometropia due to asymmetric involvement

SPECTACLE MANAGEMENT
The management of keratoconus usually begins with spectacle correction
Ther e are two methods of refraction:
Objective :
Your r easurement , irrespective of the patient's responses
Subjective :
Measurement is mainly depende nt o n 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 :
I mproves VA by creating a regular anterior refractive surface
D o es not prevent progression of KCN
M ay 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

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 lenses give sharper vision than spectacles e ven in m ildest cases of KCN
A s 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) CL s
RGPs improve VA by neutrali zing much of the distortion/optical aberrations of the anterior corneal surface
There are reports suggesting that rigid CL s may cause keratoconus due to mechanical pressure and hypoxia , but
I t is difficult to establish a cause-and-effect relationship
The patients may have been corrected with contact lenses before being diagnos ed as KCN

Keratoconic patients who are no satisfied with CLs may need PK:
S tudies have shown that more than 70% of keratokonic patients referred for PK can avoid surgery and re main satisfied by refitting CLs
Multiple fitting algorithms are available to assist in fitting the keratoconic cornea
T he process is as much an art as a science
These lenses may be fit ted
S teep or flat
L arge 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
N one of the eyes with the apical clearance had scarring

Contact Lens Management Three - point Touch

Contact Lens Management Three - point Touch
A relatively flat fitting meth od in which the CL leans on a relatively large area
The re 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 i s described separately for :
E arly keratoconus
A dvanced keratoconus

Keratoconus Topographic Characteristics
E arly keratoconus is characteri zed 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 f i tting methods for early keratoconus:
Superior a lignment f itting t echnique
The i ntra- p alpebral t hree p oint t ouch f itting t echnique

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:
C entral keratometry (“K”) readings are of little valu e
T he 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
T he 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 t his lens on the cornea and evaluate th e fluorescein pattern
S uperior 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
T he BCR should be steep enough to provide slight touch mid peripherally at 3 and 9 o’clock
The re might be slight bearing at the apex of the cornea
The re 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 touch es mid-peripherally at 3 and 9 o’clock
Th is 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 Keratoconus RGP 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:
S light clearance across the corneal apex with no fixed, mid-peripheral bubbles
T ouch in mid-peripheral cornea at 3 and 9 o’clock
M inimal impingement across the flatter superior cornea
S light lower edge lift is common:
I ntermittent bubbles inferiorly
Any attempt to decrease the inferior edge lift by :
S teepening the base or peripheral lens design
M ay result in a tight lens fit superior ly

Having achieved the desired fit :
Perform over-refraction to determine the final CL power
O rder t he lens in a moderate to high Dk RGP material
T he diagnostic lens design should match the final lens
M anufactur ers follows slightly different aspheric lens design s

Best – fit contact lens / KCN

Best – fit apical 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
E arly keratoconus is characteri zed 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 Keratoconus Topographic 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 Keratoconus Topographic Characteristics, Oval Cone
The most common type
A pex is displaced below midline:
I nferior mid-peripheral steepening
N ormal or flat 180 degrees away

Advanced Keratoconus Topographic Characteristics, Globus Cone
T he largest (often nearly 75% of corneal surface )
N early all keratoscopy rings are located within the ectatic area
Almost n o island of normal cornea above or below the midline

Advanced Keratoconus Fitting 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 Keratoconus Fitting 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:
I t is often necessary to increase the amount of posterior lens asphericity , due to :
R apid topographical flattening from center to periphery

Advanced Keratoconus Fitting Process, Nipple Cone

Advanced Keratoconus Fitting Process, Nipple Cone, Fitting Set

Advanced Keratoconus Fitting Process, Oval Cone
The oval cone consists of an inferior steepening with varying degrees of normal superior cornea l topograph y
C areful attention to the status of the superior and horizontal corneal topography is important
I f the superior and horizontal topography are relatively normal :
C onsider superior alignment fitting technique similar to that described for early keratoconus
S uperior alignment fit is sufficient ly supported by the normal cornea at 9, 12, and 3 o'clock

Advanced Keratoconus Fitting Process, Oval Cone

Advanced Keratoconus Fitting Process, Oval Cone, Fitting Set

Advanced Keratoconus Fitting Process, Globus Cone
The globus cone consists of ectasia involving cornea , almost total ly
T he 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 mm
OZD of 6.5 mm

Advanced Keratoconus Fitting Process, Globus Cone

Advanced Keratoconus Fitting Process, Globus Cone, Fitting Set

Keratoconus Fitting Process, Over Refraction
Over-refraction is an integral part of diagnostic fitting
M oderate to high amounts of residual astigmatism is not uncommon for keratoconus patients wearing RGPs:
Correcti o n with glasses often improves visual acuity three to four lines
Front surface toric RGP s may also be fitted in this situation

Keratoconus Fitting Process, Lens Dispensing
All keratoconus contact lenses should be ordered in a moderate to high Dk RGP material to avoid :
E pithelial hypoxia
C orneal erosion
Before dispensing the lens c arefully evaluate :
B ase 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 R GP lens designs may not provide the desired centration, optics , or comfort
Semi-scleral lenses have proven to be extremely beneficial for H ighly irregular and/or asymmetric keratoconic corneas

Semi-Scleral GP Lenses Fitting Process
The u se of a diagnostic set is mandatory
S elect a diagnostic lens with a BCR equal to the steepest K reading
The ideal fitting relationship is one in which :
T he re is apical clearance across the central cornea
The re is a 1.0 mm band of pooling adjacent to the limbus , in the area of the scleral curve

Semi-Scleral GP Lenses Fitting 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

Keratoconus Soft 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

Keratoconus Soft CL
Few new soft lens designs have made it possible to correct some complex optics created by keratoconu s
The most common use of soft lenses in keratoconus is the combination of these with rigid lenses:
Piggyback designs
Traditional
Custom
Hybrid designs

Keratoconus Traditional Piggyback Lenses
These consist of a high Dk silicone hydrogel soft lens over which a high Dk RGP lens is fitted

Keratoconus Traditional 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

Keratoconus Traditional Piggyback Lenses, Fitting Process
The ideal GP lens fitting should accomplish three fitting objectives:
Apical clearance :
T o prevent the lens from rocking and pivoting over the corneal apex
Lens contact ( landing zone ) at 3 and 9 o’clock:
T o 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 Traditional Piggyback Lenses

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 :
I nsert 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
T o 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:
A n 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
I deal for patients with early keratoconus
SynergEyes KC :
S pecifically 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

Contact lens fitting and keratoconus

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
Woodward KC3

Different types of RGP lens designs for KCN
Moderate/Advanced keratoconus:
Kera II/III
Profile K (J Allen)
Advanced keratoconus:
Large diameter lenses
S-Lim (J Allen)
Dyna-intra limbal (No.7)

Soper contact lens / KCN bicurve-10 lenses Apical clearace manner

VAULTING EFFECT (sagittal value of lens )

McGuire contact lens / KCN BCR -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 success complex 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

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 / KCN 3 separate BCRs -1 PCR

Bennett contact lens / KCN Three point touch fitting

Contact lens / KCN problem solving

CLEK contact lens / KCN mild to moderate KCN -

KCN TRIAL LENSES

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contact lenses fitting for KCN

by Hossein Mirzaie on Dec 30, 2008

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contact lenses fitting for KCN Presentation Transcript