Addressing scleral lens clinical concerns

November 11, 2016

While scleral lenses offer more stability than traditional lenses, there are still many controversies about their use that may give practitioners pause

Anaheim, CA-While scleral lenses offer more stability than traditional lenses, some concerns may give practitioners pause, according to panel discussion at the American Academy of Optometry’s annual meeting in Anaheim, CA.

Oxygen delivery

A common concern for optometrists when fitting contact lenses is oxygen flow. Oxygen transport is a necessity for all contact lenses to ensure adequate corneal health. Although the increased size of scleral lenses can improve vision and stability, says panelist Langis Michaud, OD, FAAO, the increased size and thickness of scleral lenses creates problems with oxygen delivery.

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In particular, he says that lens thickness and clearance can be significant factors in causing edema and disrupting the endothelial cell layer. Excess thickness prevents oxygen transport and creates hypoxic stress in eye tissues. In turn, the cornea will suffer from the lack of oxygen, so when the stress is removed, the cornea overconsumes oxygen to regain its status

“What is the long-term effect of putting the cornea under chronic hypoxic stress for 12 hours a day? The answer is simple-we don’t know,” Dr. Michaud says.

To be safe, practitioners can begin by fitting patients in scleral lenses with limited thickness and limited clearance to support the health of the cornea to ensure that excessive strain isn’t placed on the eye.

 “It’s all about the risk-benefit ratio,” he says.

While scleral lenses are becoming popular with patients seeking alternatives to standard contact lens options, practitioners need to assess all the pros and cons of various lens sizes and thickness before fitting patients.

“The clinical recommendation is certainly to fit with limited lens thickness-200 µm,” Dr. Michaud says.

Keep in mind that misaligning lenses on the conjunctiva by using an incorrect thickness may create visual distortion.

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Tear exchange

Unlike other lens types, scleral lenses offer a range of tear exchange fitting options to practitioners.

However, this range can be confusing to those unfamiliar with scleral lenses, says panelist Jason Jedlicka, OD, FAAO. Depending on the optometrist’s approach to fitting a scleral lens, the result can range from no tear exchange to an excessive amounts of exchange.

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Typically, there are two goals for tear exchange in traditional gas permeable (GP) corneal and soft contact lenses:

• Increase oxygen flow behind the lens

• Remove metabolic by products that stagnate between the lens and the cornea

Although these goals are essential to other styles of GP and soft contact lenses, Dr. Jedlicka says tear exchange for scleral lenses may be less important. And as scleral lenses feature tear reservoirs, tear exchange may be unnecessary altogether.

Because fitting scleral lenses too tightly to the eye may lead to hypoxia, fitting them to allow tear exchange would seem to be the safer option. But that tear exchange can actually pull in debris and metabolic byproducts, Dr. Jedlicka says.

“The drawback is debris in the tear reservoir, which affects acuity,” he says.

Having debris behind the lens may also impact the health of the ocular surface, and at times there are concerns with excessive tear exchange.

“It would seem that tear exchange in scleral lenses seems to create more problems than it solves,” Dr. Jedlicka says. “Most often, when we have excessive amounts of tear exchange, patients are symptomatic.”

He says that the patient’s unique health factors (such as the cornea being at risk for edema) may indicate a need for some tear exchange, but it’s up to the practitioner to make the final call. Both sides have advantages; providers must work with their patients to find a fitting solution that is viable for the patient’s visual health while still being comfortable for patients during their daily routines.

 

Sclerals for normal corneas

Scleral lenses are known to be good options for patients with irregular astigmatism or irregularly shaped corneas, but they are also an option for patients with regular corneas and refractive error.

Scleral lenses are growing in popularity. Some patients seek them out in search of better vision, some enjoy their stability for sports, and others (who haven’t had success in traditional lens options) may be curious about them as well.

Related: Using toricity with scleral lenses

Scleral lenses follow many of the same rules as regular contact lenses, but practitioners must still be cautious when prescribing sclerals, says panelist Dr. Melissa Barnett, OD, FAAO.

Fitting goals for lenses are the same for both scleral candidates and those with normal corneas:

• Lens must be completely supported by the scleral conjunctiva

• Even clearance

• No impingement or blanching

Other variables, such as contact lens care and daily wear schedules, are likewise similar. No special equipment is required to fit patients into scleral lenses-a slit lamp is all practitioners need.

With these in mind, Dr. Barnett posed the question of whether it was time to fit normal cornea patients into scleral lenses.

Essentially, it’s up to the practitioner.

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While the contact lens rules of care should be reviewed with every patient, scleral lenses share many similarities with other lens types. Dr. Barnett recommends that practitioners who want to fit patients with normal corneas should determine the proper scleral lens size.

The lens can be a little smaller, and that’s OK,” she says. “These patients have a more regular corneal surface.”

She says that these options are generally mini-sclerals that are supported by the conjunctiva.

Other points to consider include:

• Lens handling

• Lens cost

• Possible complications with the lenses

Conjunctival prolapse

Conjunctival prolapse occurs when the conjunctiva is pulled from its position outside the limbus, over the limbus, and on to the cornea.

It is commonly seen when different fluid forces are under the lens, says panelist Michael Lipson, OD, FAAO. It is thought to be caused by excessive clearance.

Dr. Lipson says that clinical observations determine that conjunctival prolapse is reversible, temporary, and benign. While it seems to be more bothersome for optometrists than patients, doctors should strive to avoid it.

“Over a long period of time, theoretically, if you have conjunctival tissue overlying the cornea, there’s a potential that it could be vascularized,” he says.

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Dr. Lipson suggests several fitting methods that may change the fluid forces acting on the conjunctiva:

• Reduce the clearance of the lens over the limbal area

• Change diameter of the lens

• Add toric peripheral curves

• Reduce edge compression

“The goal is to balance the bearing of that scleral lens evenly, 360 degrees around the sclera,” he says.

While the conjunctival prolapse appears benign, long-term studies haven’t yet been performed, and more research is needed.

“As much as we’ve learned about scleral lenses, there are more questions still to be answered,” he says.

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