Lesson 21 - Hybrid and Scleral Contact Lenses

Question 1

Hybrid contact lens

Answer 1

A gas permeable lens center with a soft lens material skirt. It can enable people to wear contact lenses who otherwise are unable to wear them due to highly irregular corneas from corneal trauma, keratoconus, dry eye syndromes, post refractive surgery, cornea transplant surgery, and people who are uncomfortable with highly toric gas permeable contact lenses. They are for those with corneal astigmatism where most or all the astigmatism in the prescription is from the irregular corneal curvature, not from lenticular astigmatism where most or all of the prescription astigmatism is from the irregular surfaces of the lens. They allow clear, stable vision, which is not often possible with soft contact lenses. These lenses may also be fit on normal, healthy corneas since they are more comfortable than standard gas permeable contacts, as comfortable as soft contacts due to the soft skirt but allowing sharper vision than soft contacts. The center portion of the lens is essentially a conventional gas permeable lens material, and the outer skirt is a soft silicone lens material. The interface between the two zones is called the bond zone.

Question 2

Bond zone

Answer 2

The junction between the gas permeable material and the soft lens material of a hybrid lens

Question 3

Empirical lens fitting

Answer 3

Diagnostic lens fitting based on prescription, K readings, topographical, and/or OCT readings

Question 4

Lens skirt

Answer 4

The soft lens portion of the hybrid lens

Question 5

Conjunctival blanching

Answer 5

When the hybrid lens skirt is too tight, and the conjunctival vessel pattern is interrupted by the tightness of the lens edge

Question 6

DMV

Answer 6

The suction cup made for removing the rigid or hybrid contact lenses

Question 7

Optical zone

Answer 7

Central part or optical center of the scleral lens

Question 8

Transition zone

Answer 8

Zone that adjoins the optical zone and the landing zone of the scleral lens

Question 9

Landing zone

Answer 9

The only portion of the scleral lens that touches the ocular surface

Question 10

There are several manufacturers of hybrid lenses, so many of them provide fitting kits. It is possible to call the manufacturer to give them your prescription, corneal diameter, and K readings, and they will send you a diagnostic pair of lenses. This is called ___. We usually start with a base curve of 0.10-0.15 steeper than the ___ keratometer reading. The diameter of the lens will depend on the ____ and what is available from the manufacturer.

Answer 10

There are several manufacturers of hybrid lenses, so many of them provide fitting kits. It is possible to call the manufacturer to give them your prescription, corneal diameter, and K readings, and they will send you a diagnostic pair of lenses. This is called empirical fitting. We usually start with a base curve of 0.10-0.15 steeper than the flattest keratometer reading. The diameter of the lens will depend on the diameter of the patient’s cornea and what is available from the manufacturer.

Question 11

Hybrid lens fitting starts similarly to how to fit a gas permeable contact lens. It is recommended to start with what?

Answer 11

It is recommended to start with keratometry readings, topographical, or OCT maps of the cornea.

Question 12

Use ___ to assess the hybrid lens fit. Remember, the center of the lens is a gas permeable lens, so you would assess the fit with ___ exactly as you would a gas permeable lens. Be sure the edge of the soft lens skirt lies flat on the ___ and is not too tight. If it’s too tight, you see what? If the lens skirt is too tight, you should order what?

Answer 12

Use fluorescein dye to assess the hybrid lens fit. Remember, the center of the lens is a gas permeable lens, so you would assess the fit with fluorescein exactly as you would a gas permeable lens. Be sure the edge of the soft lens skirt lies flat on the sclera and is not too tight. If it’s too tight, you see an indentation on the conjunctiva and the blood vessels are interrupted (conjunctival blanching). If the lens skirt is too tight, order a flatter curve and/or larger diameter lens.

Question 13

When assessing hybrid lens fit, also be sure that the skirt is not so loose that there is ___ of the edge or ___ at the lower lid margin, which will cause discomfort and an unstable lens alignment.

If the skirt is too loose, you should order what? Ensure the lens is centered well on the cornea with the proper amount of ____ using fluorescein and a good edge fit. The lens should move at least ___ with the blink. Assess the vision. Change the lens power if needed to obtain the best visual acuity. These lenses come in spherical and multifocal designs. Assess the patient’s comfort. As with gas permeable lenses, there will be an adaptation period with increased wearing time.

Answer 13

When assessing hybrid lens fit, also be sure that the skirt is not so loose that there is bubbling of the edge or edge lift at the lower lid margin, which will cause discomfort and an unstable lens alignment:

If the skirt is too loose, order a tighter base curve for the skirt and/or smaller diameter. Ensure the lens is centered well on the cornea with the proper amount of central bearing using fluorescein and a good edge fit. The lens should move at least .5 mm with the blink. Assess the vision. Change the lens power if needed to obtain the best visual acuity. These lenses come in spherical and multifocal designs. Assess the patient’s comfort. As with gas permeable lenses, there will be an adaptation period with increased wearing time.

Question 14

Troubleshooting hybrid lens issues: lens is too flat

Answer 14

The solution is to steepen the base curve by 0.12 or 0.25 steps until you achieve the optimal amount of corneal bearing using the fluorescein test.

Question 15

Troubleshooting hybrid lens issues: lens is too steep

Answer 15

The solution is to flatten the base curve by 0.12 or 0.25 diopter steps until you achieve the optimal amount of corneal bearing based on the fluorescein test.

Question 16

Troubleshooting hybrid lens issues: lens skirt is too loose

Answer 16

The solution would be to select a tighter lens skirt.

Question 17

Troubleshooting hybrid lens issues: lens skirt is too tight

Answer 17

The solution would be to select a flatter skirt curvature.

Question 18

Troubleshooting hybrid lens issues: lens is uncomfortable

Answer 18

Discomfort with these lenses is usually caused by poor fit: The base curve may be too steep or too flat. The skirt may be too tight or too loose. The lens may be dirty. The junction between the soft skirt and the rigid portion of the lens may be torn. Some studies have shown that the cornea can flatten over time wearing these lenses.

Question 19

Troubleshooting hybrid lens issues: poor vision

Answer 19

Vision is not usually an issue with rigid lenses. However, if the lenses are not fit correctly or if the lenses are coated, old, or not cleaned properly, vision will become an issue.

Question 20

Troubleshooting hybrid lens issues: tearing and coating

Answer 20

The bond between the soft skirt and the rigid contact lens may tear. These lenses are to be replaced every 6 months, because the risk for this to occur and the surface of the lens becomes more coated and difficult to clean over time.

Question 21

Troubleshooting hybrid lens issues: frequency of replacement cost

Answer 21

Because of the buildup of coatings on the lens surface despite daily cleanings, the eye can become irritated and risk for infection increases if the lenses are not replaced every 6 months. These lenses are not inexpensive, so the cost of these lenses may be a disadvantage.

Question 22

How to clean hybrid lenses

Answer 22

Begin by washing your hands with soap and water. Use either a hydrogen peroxide-based contact lens disinfecting solution or a soft lens multipurpose solution, depending which the doctor recommends. There is some evidence that hydrogen peroxide solutions should not be used daily and perhaps only weekly, since daily use has been reported to produce white deposits on the soft lens portion of the lens.

Rub the lens with the solution in the palm of the hand for about 5-10 seconds, then follow the directions for soaking overnight. Rinse the lens thoroughly with sterile saline solution prior to reinsertion.

Question 23

Hybrid lenses require specific techniques to insert and remove the lens. What are they?

Answer 23

Hybrid lenses also require specific techniques to insert and remove the lens. Insertion of this lens requires filling the bowl of the lens with sterile saline first. Removal of the lens requires a rubber suction cup (“DMV”), specifically made to remove rigid gas permeable lenses.

Question 24

Scleral lenses

Answer 24

Scleral lenses are very large-diameter gas permeable lenses that are larger than the corneal diameter and vault over the irregular shaped cornea. They are fit when the cornea surface is irregular and enables the cornea to have a “new” spherical surface with good vision without surgery. The scleral lens can also solve dry eye issues by allowing the cornea to bathe in the tear fluid reserve that is under the dome. Scleral lenses are a frequent solution for patients who have had poor outcomes from refractive surgery, who have had corneal transplants, or who have keratoconus. They can also reduce the risk of corneal scarring from these conditions and avoid the mechanical stress on the cornea that occurs with other contact lens designs.

Scleral lenses have been frequently used in some sports when there is a risk for other types of contact lenses falling out, such as water skiing and water polo.

Other uses of scleral lenses are for eye protection when glasses or shields won’t work in high-dust environments and the entertainment industry, in movies, as well as for cosmetic uses for people with cornea or eye deformities that will allow them to appear normal.

Question 25

Scleral lens materials are the same as conventional gas permeable lenses. Increased oxygen permeability can be obtained by ordering ____, although caution should be taken with the ___ lenses, as they can warp easily.

Answer 25

Scleral lens materials are the same as conventional gas permeable lenses. Increased oxygen permeability can be obtained by ordering higher Dk materials and/or thinner lenses, although caution should be taken with the thinner lenses, as they can warp easily.

Question 26

Diagnostic lens fittings are most easily done with ___ provided by several scleral lens manufacturers. Typical diameters range from ___ to as large as ___, depending on the extent of the corneal problem. Excessive diameters may cause what? The ____ is less sensitive than the cornea, so these lenses tend to be more comfortable than gas permeable lenses, easier to adapt to, and less likely to cause irritation or create corneal distortions.

Answer 26

Diagnostic lens fittings are most easily done with fitting sets provided by several scleral lens manufacturers. Typical diameters range from 14.5 mm to as large as 24 mm, depending on the extent of the corneal problem. Excessive diameters may cause lens decentration. The conjunctiva is less sensitive than the cornea, so these lenses tend to be more comfortable than gas permeable lenses, easier to adapt to, and less likely to cause irritation or create corneal distortions.

Question 27

What is required for fitting scleral lenses?

Answer 27

Corneal topography, as well as the OCT, is required for fitting scleral lenses.

Question 28

There are three main fitting zones specified when fitting the lens. What are they?

Answer 28

The optical zone (central portion)

The transition zone (intermediate or limbal zone)

The landing zone

Question 29

Scleral lens fitting: optical zone

Answer 29

Fitting the optical zone may prove to be a bit difficult, since most corneas will not be spherical. The best option would be to start with a lens diameter of .2 mm larger than the corneal diameter and back optic zone radius slightly flatter than the flattest K reading. The OCT is needed to ensure that the corneal clearance should be at least 200-300 microns. Wait about 30 minutes before assessing the lens clearance, since the lens will sink. Ensure that there is no air bubble in the central portion of the lens.

Question 30

Scleral lens fitting: transition zone

Answer 30

This is between the outer edge of the optical zone and the beginning of the landing zone. For typical large-diameter scleral lenses, the transition zone will vault over both the cornea and the limbus.

Question 31

Scleral lens fitting: landing zone

Answer 31

This is the most important portion of the scleral lens, because it is the only portion of the lens that touches the ocular surface. It is also called the haptic or scleral zone. The alignment of this portion of the lens must mimic the surface curvature of the sclera, and the weight must evenly distribute over the surface of the sclera. It should be about 3 mm wide, and the diameter can be increased in order to increase comfort. Remember that this lens should not move with the blink, unlike other lens designs. Avoid conjunctival blanching as with the hybrid lens.

Question 32

Scleral lenses come in what designs?

Answer 32

These lenses come in front and back surface toric, quadrant specific, and multifocal designs.

Question 33

How to insert a scleral lens?

Answer 33

Lens placement: Ensure that the face is parallel to the surface of a table. You may want to place the mirror on the flat table. There are two ways to insert the lens: using fingers or an insertion tool. Using your fingers, form a tripod with the thumb, forefinger, and middle lens to hold the lens. Fill the lens to the top with sterile saline. There is also an insertion tool available that fits on the finger like a ring. Ensure there are no air bubbles under the lens, because bubbles will interfere with vision and are unlikely to disappear spontaneously. If an air bubble exists, the lens must be removed and reinserted.

Question 34

How to remove a scleral lens?

Answer 34

Removing the lens is best done with a rubber suction device, larger than the DMV used for a standard gas permeable lens. Since the scleral lens is large, you should place the suction cup at the bottom of the lens, lift up to break the seal, and gently pull up and out to remove the lens. Fingers can also be used by placing your two fingertips on either side of the lens and gently squeezing the lens to break the seal.

Question 35

How to clean the scleral lens?

Answer 35

Cleaning scleral lenses is similar to cleaning gas permeable lenses, since the solutions are the same. Place the lens in the palm of one hand, apply a few drops of cleaning solution in the bowl of the lens, and rub for a few seconds in the palm of the hand. Rinse with sterile saline solution and store in the recommended disinfecting solution.

Always use fresh solution to store lenses. The case should be cleaned with disinfecting solution daily, wiped with a new, clean tissue, and turned upside down to air dry.

Question 36

Typically scleral lenses last how long? How often should they be replaced?

Answer 36

Typically scleral lenses last one to three years but should be replaced every year, since coatings, scratches, and deposits accumulate on the surface that are not possible to clean off and will affect vision and increase the risk for infection.