HAPTIC SCLERAL CONTACT LENSES

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HAPTIC (SCLERAL) CONTACT LENSES Gerald E.
Lowther, O.D., Ph.D.
USES Cosmetic shells Distorted
corneas Keratoconus, Pellucids Surface
disease Lid deformatories Decentered pupils Water
sports
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TYPES OF HAPTIC LENSES
Preformed -set parameters -usually lathe
cut Molded -made from an impression of the eye
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MOLDING PROCEDURE
SUPPLIES -Impression material-Moldite made from
alginate (a product of sea kelp used in dental
work) -rubber mixing bowl -spatula -molding
shells -sterile, distilled water (not
saline) -anesthetic -Band-aids -irrigating
solution -fluorescein (materials available
from prosthetic eye companies as AO Monoplex
Division)
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POSITIONING AND EDUCATING PATIENT
Position patient in supine position-lay patient
back in chair Determine fixation point-cover eye
to be molded and position eye with slight nasal
fixation (medial rectus flattens cornea) Dry
lower lid and place tape on lid -helps pull lid
from under shell Explain procedure to
patient -where to look, etc. May want to insert
shell if patient is apprehensive
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IMPRESSION SHELLS
Use as large a shell that can be easily
inserted Shells must have apertures so mold
material will adhere to shell and not stay on
the eye on removal Shells may have hollow handle
so impression material can be injected through
handle. There is a mark on the shell
indicating the temporal position -must
position at outer canthus
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MOLDING THE EYE
Mix distilled water with molding material in
rubber bowl -spatulate, do not beat and create
bubbles Mix to a thick, whipped cream
consistency Compound comes premeasured with a
mark on vial for amount of water INSERTION
TECHNIQUE -spatulate molding material into
shell filling it
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TAKING THE IMPRESSION-INSERTION TECHNIQUE

With shell filled, have patient look down as far
as they can Lift upper lid up and away from the
eye Insert the shell and material under upper
lid -it helps to slightly rotate the shell as
you put it in Be sure to hold shell up away from
the cornea (against back of lid) While holding
shell handle, have patient look up With patient
looking up, pull the lower lid out from
under the shell using the tape as a handle. Next
have patient look at fixation point Material will
set up in 1-2 minutes after mixing water with
it -plenty of time to insert it but can not
waste time When excess material on lid does not
stick to finger on touch it is ready to remove.
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Pulling lower lid out from under shell. If
patient has a high Rx have them hold lens in
front on other eye to hold fixation.
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IMPRESSION TECHNIQUE
Place molding shell in eye with temporal mark in
proper position Hold shell away from
cornea-have assistant hold shell Fill syringe
with the molding material Inject molding
material through handle of shell -use minimium
amount of pressure required Inject enough
material that it comes out onto lids This
technique can cause some corneal distortion
giving a less accurate impression
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REMOVING THE SHELL AND IMPRESSION
When material set, remove excess from the lids
and top of shell Loosen lids from impression
material Have patient look up, while holding
handle use the lower lid to break suction under
lower edge of impression With lower lid under
mold, remove impression -if necessary have
patient look down once lower lid is under the
impression.
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REMOVING THE SHELL AND IMPRESSION
Once impression is out of the eye place it in a
cup of water or wrap it in a wet towel to
prevent it from drying Irrigate any excess
molding material left in the cul-de-sac Remove
excess material from lids with a wet
tissue Inspect the eye with fluorescein and the
biomicroscope -will usually have some corneal
stippling
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POSSIBLE PROBLEMS DURING MOLDING
Patient has a blepharospasm and you do not get
shell all the way in. -in this case leave shell
and material in place until the material sets
up-then remove (if you try to remove it prior to
it setting up you will have a lot of material
to swab out of the cul-de-sac) Discomfort
during molding -you are pressing the edge of
the shell against the upper conjunctiva. Should
not be painful-in fact can do it without anesth
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MAKING THE EYE MODEL
A dental stone model of the eye is next
made. Dental stone comes as a powder and is
mixed with water to a consistency of
toothpaste. Impression is removed from water and
surface water blotted off. Dental stone is put
into the impression -should vibrate or tap
impression to be sure it is completely filled
without bubbles. Impression shell with
impression and dental stone is allowed to sit
and harden. -can handle in an hour but not fully
hardened for 24 hours.
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Dental stone in envelope, rubber bowl, vibrator.
Dental stone eye model
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COPYING THE EYE MODEL
A copy of the eye model can be made in case the
original is broken in the process of making the
lens. Clay dam made around the eye model, model
is coated with a releasing agent and more dental
stone poured onto the model.
Eye model with clay dam.
Negative of eye model
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COPYING THE EYE MODEL
Silicone impression material can be used to make
a copy. It is mixed and placed into a cup or
holder. The eye model is placed in the soft
material. The material will set and be a solid
rubber material.
Dental silicone modeling material. Silicone
negative.
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OBTAINING THE PROPER CLEARANCES
Final lens must have clearance over the cornea
and limbus. If lens rests on cornea or limbus it
will be uncomfortable. Need about 0.20 mm
corneal clearance. Haptic needs to be flatter
than sclera or it will fit too tight. Use thin
plastic shims (0.10 mm thick) to achieve this.
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OBTAINING THE PROPER CLEARANCES
With no shims there would be no clearance over
the cornea and the lens would adhere.
Need clearance over whole cornea and limbus.
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OBTAINING THE PROPER CLEARANCES
Corneal shim is 0.2 mm thick, haptic shim 0.10
mm. Can use plastic sheets obtainable from a
hardware.
Eye model model with model
with corneal corneal
shim and haptic shims
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FORMING THE SHIMS
Shim material put on PMMA plastic sheet with
grease in between and heated until pliable. Then
pressed over the eye model. The corneal shim is
then cut out using a razor blade.
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Other types of presses that can be used.
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FORMING THE SHIMS
The procedure is repeated with a thinner piece of
shim material for the scleral shim. A 1.0 mm
piece of plastic is used on top of the thin
material. This thicker portion will become the
lens.
Heating the plastic
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REMOVING EXCESS PLASTIC AND SHAPING LENS
Excess plastic is ground off using grinder or
hand held Dremel type tools. Can not cut the
plastic off as it will crack.
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REMOVING EXCESS PLASTIC AND SHAPING LENS
A coarse file is used to further finish the lens.
Once the general shape is reached, the bottom is
filed flat in order to eventually achieve a
uniform edge.
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EDGING THE LENS
Shape the edge with a file and then remove file
marks with a fine emery paper.
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EDGING THE LENS
Once shaped the edge needs to be polished. A rag
buff or just a sponge tool as used to edge RGP
lenses can be used.
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With the edge finished, the lens can be put on
the eye to determine the fit and where to place
the fenestration (aperture). The fenestration
allows flow of tears under lens and releases
suction. Using a permanent ink, felt pen mark a
spot over the pooling at the temporal limbus
just below the upper lid for the
fenestration. This position makes the
fenestration relatively unnoticeable.
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FENESTRATING THE LENS
1. Drilling fenestration with 1 mm hand- held
drill bit.
3. Polishing the fenestration with a felt-tipped
cone using CL polish.
2. Beveling the fenestration opening
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DETERMING BACK OPTIC RADIUS
Back radius should be about 0.3 mm flatter than
cornea. Can determine by coating back surface
with ink and then touching the lens down on
polishing lap, changing laps until it matches the
back surface.
Lap too flat Lap too steep
Lap on know radius
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FINISHING BACK OPTIC
Once the radius is determined, the back surface
is roughed in using a diamond lap with water or
tape lap with a grit such as Pumice or a compound
used to rough surface spectacle lenses. It is
then polished with contact lens polish on tape or
on a wax tool. Double rotation technique as when
doing peripheries of RGP lenses should be used.
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DETERMING THE FIT OF THE LENS
At this point the lens can be put on the eye and
the fit evaluated. There should be clearance over
the cornea and limbus usually with a small bubble
over the temporal limbus.
The lens will settle some with time so extra
clearance initially is desirable. This
lens shows a slightly larger bubble then is
finally desired after settling.
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DETERMING THE FIT OF THE LENS
After additional central grind-out of back optic
giving more clearance
Lens with central touch
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DETERMING THE FIT OF THE LENS
Corneal shim diameter too small, need more
limbal clearance.
Can use abrasive point to grind out plastic
in localized area.
Polish with a felt cone or small polishing pad
using CL polish
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DETERMING THE FIT OF THE LENS
Excessive large, inferior bubble. Need to grind
out haptic peripheral to the bubble to allow lens
to settle back and decrease the bubble size.
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DETERMING THE FIT OF THE LENS
Too much central clearance with touch at limbus
in horizontal meridian (large amount of WTR).
Need to increase limbal clearance in horizontal
meridian which will allow lens to settle back
and decrease the central clearance.
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DETERMING LENS POWER
Use of a RGP diagnostic lens example A 7.50 mm
BCR, -3.00 D. lens is on the eye Over-refraction
-2.00 D. Haptic Lens BCR 7.80 mm Power in
haptic lens -5.00 (RGP OR) -1.75 D (from
BCR change from 7.5 to 7.8 mm) -3.25 D.
required.
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Lens is mounted on a lathe and the front radius
is cut. The front surface is then polished as is
done with RGPs. Most RGP labs can do this.
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After the front optic is cut there will be a
ledge at the edge of where they cut. This needs
to be smoothed off with a razor blade and then
polished in this area with polish.
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PERFORMED HAPTIC LENSES
ADVANTAGES -molding not required -obtainable
from a laboratory -easily reproduced -can
specific all the parameters DISADVANTAGES -may
not be able to fit a distorted eye or high
toricity
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Preformed haptic lenses usually have a central
optic, several peripheral curves to obtain
peripheral corneal and limbal clearance with a
haptic radius.
The lens may not be round but oval with largest
section going temporal. Different optic and
haptic radii are available.
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PERFORMED HAPTIC LENSES
Determine the haptic radius first using lenses
that clear the cornea and limbus. Want a close
match between haptic and sclera.
A. Haptic radius too steep. B. Haptic radius
too flat.
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To determine haptic fit apply slight pressure to
the lens and look for the blanching of the
vessels.
Blanching of vessels at junction indicating a
flat haptic radius
Blanching at the edge of the lens indicating a
steep haptic
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PERFORMED HAPTIC LENSES
Once the haptic radius is determined, use
diagnostic lenses with different central radii to
obtain central and limbal clearance. Fit should
look the same as described for the molded lenses.
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PERFORMED HAPTIC LENSES
POWER DETERMINATION Determine the power
required by refracting over a diagnostic lens and
make any compensation required for base
curve changes and add over-refraction. If
diagnostic lenses do not have finished optics you
can determine the power required as described
for molded lenses using RGP diagnostic lenses
and compensating for and base curve
change. Order lens from laboratory giving all
parameters.
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PERFORMED HAPTIC LENSES
LENS MATERIAL Up until recent years PMMA was
the only material Today fluorosilicone/acrylate
ploymers are used. -most can only be only be
lathed because they are thermosetting
plastics. Availability Boston Foundation for
Sight http//www.bostonsight.org/
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PERFORMED HAPTIC LENSES
Boston Scleral Lens Fluorosilicone/acrylate
Dk 127 c.t. 0.25-0.39 15-23 mm diameter With
lenses of Dk over 115 and ct 0.30 mm the
corneal swelling is usually less than 4 (CLAO
J 23259-263, 1997)
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Preformed lenses can be modified as described for
molded lenses using grinding and polishing tools.