Eye Prosthesis

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

TYPES OF HAPTIC LENSES

Preformed -set parameters -usually lathe cut Molded -made from an impression of the eye

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)

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

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

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

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.

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.

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

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.

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

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

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.

Dental stone in envelope, rubber bowl, vibrator.

Dental stone eye model

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

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.

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.

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.

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 corneal shim

model with corneal and haptic shims

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.

Other types of presses that can be used.

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

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.

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.

EDGING THE LENS Shape the edge with a file and then remove file marks with a fine emery paper.

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.

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.

FENESTRATING THE LENS 1. Drilling fenestration with 1 mm handheld drill bit.

3. Polishing the fenestration with a felt-tipped cone using CL polish. 2. Beveling the fenestration opening

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 on know radius

Lap too flat

Lap too steep

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.

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.

DETERMING THE FIT OF THE LENS

Lens with central touch

After additional central grind-out of back optic giving more clearance

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

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.

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.

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.

Lens is mounted on a lathe and the front radius is cut. The front surface is then polished as is done with RGP’s. Most RGP labs can do this.

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.

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

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.

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.

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

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.

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.

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/

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 23:259-263, 1997)

Preformed lenses can be modified as described for molded lenses using grinding and polishing tools.