1
Contact Lens
Clinical Pearls
Pocket Guide
2
CONTENTS
Vertex Conversion Chart 3
Spherical GP Lenses 4
Soft Toric Lenses 5
GP Back Surface and Bitoric Lenses 7
Multifocal Lenses 9
Orthokeratology 12
Keratoconus 14
Scleral Lens Fitting and Handling 15
Diopter to Radius (mm) Conversion Chart 20
Special Thanks
To the GP Lens Institute Advisory Committee
and especially
Stephen Byrnes, Greg DeNaeyer, Tim Edrington,
Chris Gilmartin, Bob Grohe, Lynette Johns,
John Laurent, Norman Leach, Derek Louie,
Miles Press, Jack Schaeffer,
Christine Sindt, Eef van der Worp,
Michael Ward, and Frank Weinstock
www.gpli.info
3
Vertex Conversion Chart
minus plus
-3.87
4.00
+4.25
-4.00
4.25
+4.50
-4.25
4.50
+4.75
-4.50
4.75
+5.00
-4.75
5.00
+5.25
-5.00
5.25
+5.62
-5.12
5.50
+5.87
-5.37
5.75
+6.12
-5.62
6.00
+6.50
-5.75
6.25
+6.75
-6.00
6.50
+7.00
-6.25
6.75
+7.37
-6.50
7.00
+7.62
-6.62
7.25
+8.00
-6.87
7.50
+8.25
-7.12
7.75
+8.50
-7.25
8.00
+8.87
-7.50
8.25
+9.12
-7.75
8.50
+9.50
-7.87
8.75
+9.75
-8.12
9.00
+10.12
-8.37
9.25
+10.37
-8.50
9.50
+10.75
-8.75
9.75
+11.00
-8.87
10.00
+11.37
-9.37
10.50
+12.00
-9.75
11.00
+12.75
-10.12
11.50
+13.37
-10.50
12.00
+14.00
-10.87
12.50
+14.75
-11.25
13.00
+15.50
-11.62
13.50
+16.12
-12.00
14.00
+16.75
-12.37
14.50
+17.50
-12.75
15.00
+18.25
-13.00
15.50
+19.00
-13.50
16.00
+19.75
-13.75
16.50
+20.50
-14.12
17.00
+21.50
-14.50
17.50
+22.25
-14.75
18.00
+23.00
-15.12
18.50
+23.75
-15.50
19.00
+24.75
4
SPHERICAL GP LENSES
Before the Fit
Present adaptation with terms such as “lens awareness” and “lid
sensation.”
Use a topical anesthetic prior to initial lens application.
Empirical versus Diagnostic Fitting
Diagnostic fitting has the benefit of obtaining an optimum
fit and power through the application of lenses.
Empirical fitting has the benefit of often having the first
experience with GP lenses be a very positive one visually.
Fitting Pearls
Use a cobalt blue filter in combination
with a yellow (Wratten) filter for optimum
evaluation of the
fluorescein pattern.
Strive for an alignment fit. This is often
achieved with a base curve radius
(BCR) equal to the flatter K reading
(termed “on K”) or slightly flatter than K due to the asphericity of
the cornea.
Increasing the optical zone diameter (OZD) increases sagittal
depth and
effectively steepens the fit. Decreasing the OZD decreases
sagittal depth and effectively flattens the fit.
Flattening the peripheral curve radius (PCR) and/or increasing the
curve width will
increase edge clearance.
Steepening the PCR and/or reducing the curve width will
decrease edge clearance.
When you make a design change, make it a significant one.
Alignment Fit
5
o Change the base curve by ≥0.50D; OAD/OZD ≥ 0.3mm;
center thickness ≥0.03mm;
peripheral curve radius/width ≥1.0/0.2mm.
Order a plus lenticular to reduce edge thickness on all high minus
(≥ -5.00D) and a minus lenticular on all plus and low minus (≤ -
1.50D) lenses to increase edge thickness.
o The use of a lenticular, when indicated, in combination
with an ultrathin center thickness, will reduce the risk of
inferior decentration.
To predict the lens power, take the spherical refractive value at
the corneal plane. If selecting a BCR flatter than K, add the
corresponding amount of plus power. If fitting steeper, add minus
power (SAM/FAP or steep add minus, flat add plus). Ignore the
cylinder power and the steeper K value.
o Example:
Rx -4.50 -0.75 x 180; K’s 43.00 @ 180/ 43.75 @ 090
BCR 42.50D (0.50D flatter than K)
The predicted power is -4.25D (-4.50D at the corneal
plane) + 0.50D (FAP) = -3.75D
Resources
Resources on fitting and problem-solving GP lenses are available at
www.gpli.info.
SOFT TORIC LENSES
Before the Fit
Patients with as low as 0.75D refractive cylinder are often good
candidates.
If a patient has ≥ 0.75D cylinder and is wearing a spherical lens,
provide them with a toric lens to compare the quality of vision.
One method of determining how good a candidate someone is for
soft toric lenses is the “Becherer Twist.” With the patient’s
subjective refraction in the phoropter, twist the cylinder axis knob
until the acuity chart first blurs. If the twisting is > 20 ˚ in each
direction, 90% of the patients will be successful. If it blurs at 15 ˚,
90% success is achieved with two lenses. At 10˚, 70% will be
Spherical GP Lenses cont’d
6
successful with 3 lenses. If there is blur with < 5˚
rotation, success is unlikely.
The Fitting Process
Select diagnostic lenses as close to the refractive power at the
corneal plane as possible.
o Example: a patient with a refraction of: -4.75 -1.50 x
180 should be fit with a diagnostic lens of -4.50 -1.25 x
180 (the powers at the corneal plane). If the exact
cylinder power is not available, select the lower cylinder
power lens. For instance, if the patient has -1.50 x 180
cylinder power at the corneal plane and the soft toric
lens cylinder is available in either -1.25 or -1.75 x 180,
select the -1.25 x 180 lens.
Allow the lens to settle for a minimum of 10 minutes prior to
evaluation.
To determine the amount of lens rotation, use a degree scale on
the biomicroscope to line up an optic section with the axis mark
on the lens. With this method, an exact amount of
rotation can be
read directly off the degree scale. If this scale is not available, the
clock
approach can be used to estimate the amount of rotation.
With this method, each hour on a clock is equivalent to 30 ˚.
To determine the axis of the final lens, use the “left add, right
subtract” (LARS) technique. If the patient has a refraction of -2.00
-1.25 x 180, and a lens with these identical parameters is applied
to the right eye and rotates 10˚ to the observer/practitioner’s right
(nasally), a lens with an axis of 170˚ should be fit. If it rotates 10˚
to the observer’s left
(temporally), a lens with a 10˚ axis should be fit.
Subtract the amount of rotation from the prescription, not the
diagnostic lens. Also, the final lens ordered should fit in the same
skewed position as the diagnostic lens.
Rx axis at 180° and
no rotation; Order
Lens Axis at 180°
Rx axis at 180° and 10°
right rotation; Order
Lens at Axis 170°
Rx axis at 180° and 10°
left rotation; Order
Lens at Axis 010°
Soft Toric Lenses cont’d
7
Poor Visual Response
If reduced vision is present with a spherical over-refraction (OR), a
sphero-cylindrical OR should be performed. To
determine the recommended cylinder power and axis based upon
the OR, use one of many available cross cylinder
calculators. These may be found on the AOA Contact Lens and
Cornea Section web site, www.eyedock.com, as well as many soft
lens company web sites.
If the patient experiences a persistent problem with vision due to
lens rotation or other reasons, a GP lens should be
considered.
GP BACK SURFACE AND BITORIC LENSES
Before the Fit
Good candidates are individuals with > 2.00D of corneal
cylinder who do not achieve good centration and/or have a poorly
aligned fit, are dissatisfied with their vision from soft
toric lenses, or have critical vision needs.
Decision-Making Process
○ A back surface toric lens induces a cylinder equal to
almost half of the back surface toricity with the same
axis (the exact amount depends upon the refractive
index of material).
○ When the cylinder is corrected on the front surface, it
results in a bitoric lens.
○ A back toric design (spherical front surface) is
recommended when the residual astigmatism is
approximately one half of the back surface toricity and
has an axis equal to the flat K reading. This should
also be considered when the patient’s refractive
cylinder is approximately 1½ times the corneal cylinder.
Empirical Versus Diagnostic Fitting
Diagnostic fitting has the benefit of obtaining an optimum fit and
power through the application of lenses. Diagnostic fitting sets are
Soft Toric Lenses cont’d
8
typically available from your laboratory. 3.00D toricity sets are
especially popular.
Empirical fitting has the benefit of often having the first
experience with GP lenses be a very positive one visually. Mandell-
Moore and the Quinn GP Toric calculators are simple and
successful methods of calculating the base curve radii and powers
based on the refraction and K values. These guides are available
at www.gpli.info.
Fitting Pearls
Bitoric lens power determination only differs from spherical lenses
in that two tear lens power calculations are needed,
not one.
The flatter base curve is typically selected approximately 0.25D
flatter than flat K. The steeper base curve radius is
typically 1.00D flatter than steep K. This creates 0.75D of
toricity, which would simulate the ideal cornea to fit a spherical lens.
The result should be an alignment fitting relationship.
If a diagnostic lens is selected, a spherical over-refraction should be
performed and the resulting power should be added to the power in
each meridian. If the diagnostic lens powers are plano in the 180˚
meridian and -3.00D in the 90˚ meridian and the over-refraction is -
1.00D, the final powers are -1.00D and -4.00D. This lens can rotate
on the eye without affecting vision (spherical power effect).
If the patient has residual astigmatism, it is likely that a
sphero-cylindrical over-refraction will result in optimum acuity. If so,
the over-refraction in one meridian should be added to the
diagnostic lens power in that meridian. In the above
example, if the over-refraction is -1.00 -1.00 x 180, -1.00D would be
added to plano, and -2.00D (in the 90˚ meridian) would be added to
-3.00D resulting in powers of
.00D / -5.00D.
Toric GP lenses are not often indicated with irregular cornea
patients as the refractive axis differs from the corneal axis and
bitoric designs have base curve radii and corresponding
powers 90˚ apart.
GP Back Surface & Bitoric cont’d
9
MULTIFOCAL LENSES
Decision-Making Process
Explain all options to every presbyope or emerging presbyope
including single vision lenses/reading glasses, monovision, and
multifocal lenses.
o The benefits of multifocals versus monovision include
the quality of vision at all distances out of both eyes.
o Many comparison studies between soft and/or GP
multifocals versus monovision have resulted in
approximately 75% of the patients preferring
multifocals.
o Monovision is indicated when the patient either has
miotic pupils - therefore very little power effect is
obtained from the paracentral aspheric region – or
pupils larger than 6mm, which will result in visual
disturbance from the mid-periphery of the lens, and
does not have critical vision needs.
Determine what the patient’s goals are from these lenses.
o Have the patient rank the importance of distance,
intermediate, and near vision and by concentrating on
the two most important, the patient will likely be
satisfied with the vision at all distances with multifocal
lenses. But, it is best to not make any guarantees!
Patients need to be given realistic expectations.
o Most contact lens multifocal designs utilize the
simultaneous vision principle in which multiple
corrections are in front of the eye at the same time.
Some blur may be noted when compared to spectacles.
o In addition, it may take a lens exchange or two to
achieve a successful fit and acceptable vision.
o Finally, patients should never be told that they will not
require spectacles. Some multifocal wearers
appreciate a low minus over-correction when driving
while others may desire some additional plus for
reading fine print.
o If they are patient and motivated they will most likely be
successful.
10
The Fitting Process
Important tests to perform include pupil size measurement, tear
film evaluation, and determining lower lid position.
When possible, it is important that the patient’s first experience in
multifocal lenses is with lenses in their prescription so use lenses
from a soft lens inventory or empirically fit GP multifocals.
If, after performing visual acuities at both distance and near,
vision is reduced out of one eye at a particular distance,
over-refract monocularly with hand held trial lenses or a flipper
bar and with both eyes open.
When assessing vision at near, make sure the patient is
reading material (magazine, book, etc.) that is similar in font to
their everyday material and consistent with what they desire to
see well at near.
Once the lenses have been evaluated, have the patient walk
around the office and perform normal visual tasks. Encourage
binocular viewing. Discourage viewing monocularly
(the “contact lens salute”).
If satisfactory vision and fitting relationship is achieved,
schedule an appointment, at minimum, one week later to allow
the patient to become adapted to the lenses.
Soft Multifocal Lenses
Good candidates include individuals who do not have critical
vision demands, have ≤ 0.75D refractive cylinder (unless using
toric multifocals), and are satisfied spherical soft lens wearers. If
they decide to be fit with soft multifocals, they should be
informed about the GP multifocal option if vision becomes
problematic.
For the initial diagnostic lens, select the power to be equal to the
spherical equivalent of the manifest refraction at the
corneal plane (unless otherwise recommended by the
manufacturer). For example, if the refraction at the spectacle
plane is -4.50 -0.50 x 180, the initial diagnostic lens would be
equal to -4.50D.
Multifocal Lenses cont’d
11
The final lens power should be the lens that emphasizes “least
minus, most plus” if there is a range of lenses that provide
acceptable distance vision.
Allow the lenses to settle at least 10 minutes after application
before evaluation.
Be sure to consult the manufacturers’ fitting guides and
problem solving recommendations for their unique lens design.
GP Multifocal Lenses
This is a viable option for patients with critical vision demands.
Aspheric lenses
o Aspheric lenses are a viable option except for
individuals who have a large (≥ 6mm) pupil diameter.
For uninterrupted vision at distance and near,
segmented translating (bi) multifocal lenses are
recommended. Aspheric lenses should result in an
alignment fitting relationship, good centration, and
limited (1mm) movement with the blink.
o If the lens moves excessively, select a lens with a
0.50D steeper base curve radius.
Segmented lenses
○ Segmented, translating bifocal lenses typically have the seg
line positioned at or slightly below the lower pupil margin.
Many designs have an aspheric or segmented intermediate
zone, which should be positioned right above the lower pupil
margin.
○ The lens should move minimally (1mm) with the blink.
○ Poor candidates for this design would include anyone with a
low positioning lower lid.
○ When viewing through the biomicroscope, have the
patient view inferiorly and the lens should shift upward or
translate as the edge contacts the lower lid.
○ If the lens does not translate (or only does so
intermittently), increase edge clearance with a flatter base
curve radius or peripheral curve radius.
Multifocal Lenses cont’d
12
○ If the lens moves excessively, increase the prism
ballast.
For assistance with problem-solving GP bifocal
and multifocal lens designs, the Contact Lens
Manufacturers Association (CLMA) member
laboratory consultants are an invaluable resource.
In addition, the GP Lens Institute has numerous
resources, like the one pictured here, available at
www.gpli.info.
ORTHOKERATOLOGY
Before the Fit
Good candidates include < 5.00D myopia, ≤ 1.50D WTR
corneal cylinder or ≤ 0.50D ATR cylinder; < 6mm pupil
diameter.
Important screening tests include refraction, slit lamp
evaluation, and corneal topography.
Topography will rule out patients with irregular corneas as well as
provide corneal eccentricity values.
The Fitting Process
The “Jessen formula” can often be used to determine the base
curve radius.
○ It uses the FAP (flat add plus) tear lens factor to result in a
final power of +0.75D, which will allow for
regression during the day.
○ If the patient has a refractive error of -3.00 -0.75 x 180 and
keratometry values equal to 44.00 @ 180/ 44.75 @ 090, the
base curve should equal 3.75D (3.00D + 0.75D) flatter than
K, which is equal to 44.00D -3.75D or 40.25D.
○ The initial diagnostic lens is selected in an effort to achieve a
bull’s eye fluorescein pattern (central
bearing, paracentral pooling, midperipheral bearing, and
slight peripheral clearance).
Wait at least 10 to 15 minutes before evaluating the fit.
○ Good centration with minimal (≤ 1mm) lag with the blink is
desired.
The patient should be evaluated the morning after dispensing.
○ Assess the lens to cornea fitting relationship.
Multifocal Lenses cont’d
13
○ The lenses should be removed to assess corneal
integrity. If coalesced corneal staining is present, the
lens is too flat centrally. Improvement in unaided visual
acuity should be present.
○ Corneal topography should be performed and a bull’s eye
pattern (central flattening, paracentral steepening) should be
present.
○ If superior flattening is present with an inferior arc of
steepening (“smiley face”), the lens is too flat. If little change
is present with slight central steepening (“central island”), the
lens is too steep.
○ If no obvious topography pattern is present, the patient
should wear the lenses for 2 more days and be
re-evaluated.
On average, it takes 10 days to reach the treatment goal
although it will likely be less for lower myopic and higher for more
moderate myopic powers.
Provide the patient daily disposable lenses of gradually
decreasing power to wear during the treatment period and
re-evaluate at one week.
At the end of the treatment period, the lenses should be worn on a
retainer basis. This can be anywhere from every night for higher
myopic patients to once a week for very low myopes.
Patients can self-monitor retainer wear. Whenever the
distance vision becomes blurred, they can wear the lenses
overnight.
Applying a highly viscous artificial tear prior to inserting the lens has
been found to optimize centration and lessen corneal staining.
Lens removal should not occur immediately upon awakening.
Rewetting drops should be applied before removal and the lower lid
margin can be used to gently nudge the lower lens edge to break
suction if present.
Further expertise through certification and examinations are
available at www.paragoncrt.com and www.bausch.com as well as
from the Orthokeratology Academy of America at
www.okglobal.org.
Orthokeratology cont’d
14
KERATOCONUS
Before the Fit
Hallmark clinical signs of keratoconus are Fleischer’s ring and
Vogt’s striae.
In keratoconus, the steepest area of the corneal topography is
typically >48.00D. Also, if the eccentricity value is greater than or
equal to 0.8, it is likely keratoconus.
In a moderate to advanced keratoconic patient, in the absence of a
corneal topographer, the use of a +1.25D trial lens over the
patient’s side of the keratometer will extend the range by about
8.00D. A +2.25D trial lens will extend the range by
approximately 14.00D.
The Fitting Process
If the apex of the cone is relatively small
and centrally located, a traditional small
diameter keratoconic lens can be used.
If a large oval or globus cone is present
or the apex is
decentered inferiorly, intralimbal, scleral,
piggyback, or hybrid designs have all
been successful.
With most designs, minimal apical
clearance or mild touch is desired. This
“three point touch” or bull’s eye
fluorescein pattern is most likely
achieved on a relatively
well-centered apex.
Gross apical bearing can result in
corneal staining and possibly
scarring.
Excessive apical clearance can
result in peripheral seal off.
The presence of excessive
inferior edge clearance can be
remediated with designs that allow the inferior edge to tuck
in (flat-steep, ACT, quadrant specific).
Excessive
Apical Clearance
Excessive
Apical Bearing
Three Point Touch
15
A piggyback design combination should be considered if a GP lens
alone results in either poor
centration, less than optimum
comfort, or if scarring is present.
A very low power (0.50D) silicone hydrogel soft lens can be
placed under the GP. Due to the lens combination it is
important that a hyper Dk (>100) GP material be used.
If the patient has a low corneal apex resulting in the GP lens
positioning low on the soft lens, the use of a moderate plus
power (+6.00D) soft lens may help the GP lens center due to
the thicker center of the soft lens. This should result in little
to no change in the GP power as a soft lens contributes only
about 20% of its power when used in a piggyback system.
For assistance with keratoconic patients, communicate with your
CLMA member laboratory consultant.
For resources contact the National Keratoconus Foundation
(www.nkcf.org) and the GP Lens Institute (www.gpli.info).
SCLERAL LENS FITTING AND HANDLING
Definition and Applications
Scleral lenses can be divided into the following categories based
upon overall diameter:
Corneo-scleral (12.9mm to 13.5mm)
Semi-scleral (13.6mm to 14.9mm)
Mini-scleral (15.0mm to 18.0mm)
Scleral (>18.0mm)
Scleral lenses are indicated in cases of irregular corneas although
corneo-scleral lenses have been recommended for healthy cornea
patients and scleral lenses have been successful for patients with
dry eye syndrome and
scarred, severely pathological
corneas.
Lens Handling and Patient
Education
Lens Insertion (non-
fenestrated):
Keratoconus cont’d
16
For initial fitting evaluation, the lens should be completely filled
with isotonic, non-preserved artificial tears (e.g. OPTIVE™
Sensitive, Unisol 4). Fluorescein from a strip should be added
to the filled bowl. The lens can be supported on a large DMV
scleral suction cup or equivalent. Alternatively, a tripod made
up of the thumb, middle, and index finger, can be used.
The face should be parallel to the ground and the lids must be
retracted and well-controlled. The patient should look straight
down toward the ground. The
patient should retract the upper lid while the practitioner
retracts the lower lid and raise the lens onto the eye in one
continuous motion. The lids should be released prior to
lowering the supporting suction cup. If seated, cover the
patient’s lap with paper towels before insertion as some of the
solution and fluorescein will overflow and could stain clothing.
If a large bubble is observed after insertion, either the lens was
not inserted in one continuous motion or the lens well was not
completely filled with solution. Remove the lens and reinsert.
Lens Removal:
○ As the lens will likely be suctioned, always loosen the lens
prior to removal. An appropriate rewetting drop should be
applied and the inferior periphery of the lens should be
gently pushed in a repeated motion for several seconds.
○ With the superior lid well controlled, the inferior lid can be
used to lift the lower portion of the lens away from the eye.
○ Alternatively, a medium DMV suction cup can be used. If so,
it should be applied to the inferior lens periphery and then
pulled in a direction that is down and out with the removal
force directed perpendicular to the lens surface, not along
the visual axis.
Fitting Principles
It is important for the lens to completely vault the cornea while
aligning the lens to the bulbar conjunctiva.
Choose the Overall Diameter
○ In general, larger lenses can hold more fluid in the corneal
chamber and tend to be more forgiving for the fitter, allowing
for more clearance over the cornea.
Scleral Lens Fitting & Handling cont’d
17
○ Smaller lenses must more closely vault the cornea and
demand a more precise central fit.
○ For the most irregular corneas, choose a larger lens
diameter (mini- versus semi- or corneo-scleral diameter
when possible).
○ In addition, some manufacturers provide guidelines for
selecting an overall diameter based on horizontal visible iris
diameter.
Choose an Initial Trial Lens
○ Follow manufacturer’s fitting guide or try a more simple
approach.
○ Standing beside the patient, look at the corneal profile. If
very steep, choose a steeper base curve. If flat, choose a
flatter base curve. If average, choose an
average base curve.
○ These lenses are fit on the basis of sagittal height, so this
method can be very effective when used properly.
Examine the Corneal Fit
○ With white light and an optic section at high illumination and
medium magnification, set the slit lamp housing off axis and
examine the central corneal clearance.
○ You will see several layers in cross section. The outermost
band (dark black) is the lens. The dark area is straddled by
two hairline reflections that arise from the front and back
surface of the lens. Compare this black layer to the tear lens
(green).
○ For example, if the trial lens is known to have a
thickness of 300 microns and the tear lens appears to be
half that thickness, then the lens vaults the cornea by
approximately 100 to 150 microns, which is ideal clearance
although this varies by design and is often less if the lens is
fenestrated.
○ Apply trial lenses until an acceptable central clearance value
has been achieved.
○ Note that after applying any type of scleral lens, it will settle
into the conjunctiva over a 30 to 40 minute
period. This will decrease the corneal vault and
Scleral Lens Fitting & Handling cont’d
18
possibly lead to touch in an area that was vaulted upon initial
application of the lens.
○ A trial lens that shows gross, excessive vaulting of the
central cornea initially should be removed and replaced with
a flatter base curve.
○ However, if the corneal vault is only mildly excessive upon
initial application of the trial lens, it is best to allow the lens to
settle since it may yield an ideal corneal vault after 30 to 40
minutes.
Corneal versus Peripheral Fitting
Relationship
○ Overall, the fit of a scleral lens can be
divided into two parts; the
central fit (over the cornea called the
“corneal chamber”) and the
peripheral fit (over the
conjunctiva).
○ Examine the entire corneal
chamber under diffuse cobalt blue and
high illumination. Note any
areas of bearing just as with a
corneal GP contact lens.
○ When fitting an irregular cornea, it is
common to observe touch or bearing
in the mid-peripheral or
peripheral cornea once acceptable
central clearance has been
obtained.
○ In these cases, additional
clearance must be created in the
problem area without grossly
increasing the central clearance.
○ A reverse geometry design can be
employed to vault over the areas of
touch/bearing, but compensatory
flattening of the base curve must be
done to avoid excessive central
clearance.
Good Fit -
Down Gaze
Good Fit -
Optic Section
Good Fit
Scleral
Compression
Scleral Lens Fitting & Handling cont’d
19
○ The peripheral portion of the lens should align with the
bulbar conjunctiva.
○ Impingement occurs when there is compression or
focal blanching of blood vessels, which can occur
anywhere on the scleral haptic, not just the edge.
○ Compression, or general indentation of the conjunctiva,
whether at the edge or mid-periphery of the lens, may result
in seal off, suction and indentation.
○ When blanching occurs, flatten the peripheral curve
associated with the area of blanching.
○ Excessive movement and/or bubble formation after lens
insertion may indicate the peripheral curve(s) are too
loose; therefore, tighten the peripheral curve(s).
Over-topography
○ It is beneficial to perform computerized topography over the
contact lens in situ after it has settled for a few
minutes. This can reveal any lens flexure. More than about
0.50D of toricity can be significant and should be addressed by
increasing the center thickness if it interferes with vision.
Check for Tear Exchange
○ Before a scleral lens is dispensed, proper tear exchange must
be demonstrated. Apply the lens without fluorescein in the
filling media. After the lens has been properly applied, instill a
generous amount of fluorescein dye over the top of the lens
with a dye strip. Periodically examine the tear lens and check
for dye that has made its way behind the lens into the tear
chamber. After several minutes, there should be at least a
small amount of dye in the tear lens.
○ Tear exchange does not need to be rapid, but it is
critical for a proper fit. If in the test for tear exchange there is
no fluorescein seen in the corneal chamber
after waiting for several minutes, flatten the peripheral fit or
increase the overall diameter.
Scleral Lens Fitting & Handling cont’d
20
Diopter to Radius (mm) Conversion Chart
Diopter Radius Diopter
Radius
34.00D
9.92mm
44.00D
7.67mm
34.25D
9.85mm
44.25D
7.63mm
34.50D
9.78mm
44.50D
7.58mm
34.75D
9.71mm
44.75D
7.54mm
35.00D
9.64mm
45.00D
7.50mm
35.25D
9.57mm
45.25D
7.46mm
35.50D
9.50mm
45.50D
7.42mm
35.75D
9.44mm
45.75D
7.38mm
36.00D
9.37mm
46.00D
7.34mm
36.25D
9.31mm
46.25D
7.30mm
36.50D
9.24mm
46.50D
7.26mm
36.75D
9.18mm
46.75D
7.22mm
37.00D
9.12mm
47.00D
7.18mm
37.25D
9.06mm
47.25D
7.14mm
37.50D
9.00mm
47.50D
7.11mm
37.75D
8.94mm
47.75D
7.07mm
38.00D
8.88mm
48.00D
7.03mm
38.25D
8.82mm
48.25D
6.99mm
38.50D
8.76mm
48.50D
6.96mm
38.75D
8.70mm
48.75D
6.92mm
39.00D
8.65mm
49.00D
6.89mm
39.25D
8.60mm
49.25D
6.85mm
39.50D
8.54mm
49.50D
6.82mm
39.75D
8.49mm
49.75D
6.78mm
40.00D
8.44mm
50.00D
6.75mm
40.25D
8.39mm
50.25D
6.72mm
40.50D
8.33mm
50.50D
6.68mm
40.75D
8.28mm
50.75D
6.65mm
41.00D
8.23mm
51.00D
6.62mm
41.25D
8.18mm
51.25D
6.58mm
41.50D
8.13mm
51.50D
6.55mm
41.75D
8.08mm
51.75D
6.52mm
42.00D
8.04mm
52.00D
6.49mm
42.25D
7.99mm
52.25D
6.46mm
42.50D
7.94mm
52.50D
6.43mm
42.75D
7.89mm
52.75D
6.40mm
43.00D
7.85mm
53.00D
6.37mm
43.25D
7.80mm
53.25D
6.34mm
43.50D
7.76mm
53.50D
6.31mm
43.75D
7.71mm
53.75D
6.28mm
