GP LENSES

When to Recommend Extended Wear Lenses

Here are specific cases in which you should consider recommending extended wear lenses.

By Jeffrey Sonsino, O.D., F.A.A.O., Nashville, Tenn.

Patients with contact lens complications tend to accumulate in academic medical centers. At the Vanderbilt Eye Institute we see roughly four severe contact lens-related complications each month. A severe contact-lens related pathology is one in which the patient loses vision potential due to microbial keratitis. A significant number of these cases are related to contact lens abuse and extended wear.

In well-designed, case-controlled prospective studies, the annual incidence of microbial keratitis in daily wear hydrogel lenses was 3.1 to 4.1 per 10,000.^1,2 This jumped to 9.3 to 20.9 per 10,000 for extended wear hydrogel lenses.

Unfortunately for the contact lens industry, the incidence of microbial keratitis didn't decline with silicone hydrogel materials. The incidence of microbial keratitis with extended wear silicone hydrogel lenses is 18.2 per 10,000 (annualized).³

Because of these numbers, we typically don't prescribe extended wear lenses based on convenience for the patient. However, in certain cases, the extended wear option becomes much more justifiable.

For instance, in pediatric cases in which amblyopia is eminent if refractive therapy fails, extended wear lenses may improve visual outcomes. Also, if an adult contact lens wearer is involved in an occupation that makes avoiding sleeping in lenses difficult, we prescribe extended wear, though we spend significant time educating the patient on proper care and hygiene.

Here are some specific cases in which extended wear lenses benefitted patients.

Pediatric aphakia

D.A.'s ophthalmologist first referred him for a contact-lens fitting when the boy was age two-and-a-half.

His ocular history was remarkable for persistent hyperplastic primary vitreous (PHPV), optic nerve colobomas, microphthalmos and surgical aphakia at eight months of age.

D.A.'s entering visual function was central, unsteady, maintained O.D. and central unsteady, unmaintained O.S. This visual function typically has a moderate prognosis for development, somewhere in the 20/60 to 20/100 range.

At D.A.'s first visit, we performed auto-keratometry, gross inspection of the anterior segment with a magnifying lamp and retinoscopy.

His keratometry was 32.00/33.25 @ 120 O.D. and 33.50/35.37 @ 96 O.S. Retinoscopy results revealed +15.50 sphere (sph) O.D. and+16.00 sph O.S. His visible iris diameters were 8.5mm O.D. and 10.0mm O.S.

The empiric lenses we initially ordered were: Standard Tricurve 10.22/+17.75/8.5 Boston XO and Standard Tricurve 9.78/+18.50/9.0 Boston XO.

Upon dispensing the lenses, corrected Allen visual acuity measured 20/120 O.D. and 20/200 O.S. No significant over-refraction appeared.

We prescribed full-time polycarbonate bifocal correction of pl O.U. add +3.25 for protection and near function. We chose a one-week extended wear schedule to minimize the amount of manipulation of D.A.'s eyes.

The benefits of an extended wear lens in a young child include less emotional trauma caused by an adult approaching and manipulating the eyes, less introduction of pathogens from a potentially infected lens storage case and minimizing lens loss due to physical manipulation and parental convenience.

Risks include bacterial keratitis, endothelial cell loss, corneal molding and increased lipid and protein deposition due to less cleaning.

Given D.A.'s age and the aforementioned listed benefits, we felt he'd achieve success in an extended wear schedule.

D.A.'s mother has been very proactive, continuing to bring the child for follow-up visits. Prior to his most recent examination this year, D.A.'s Snellen visual acuity astoundingly developed into 20/50 O.D. and 20/40 O.S. Unfortunately, he had a retinal detachment O.D. as a complication following pars plana vitrectomy and tube shunt that left him with a visual acuity of 20/100 O.D.

Pathologic myopia

K.S.'s mother noticed her two-year-old daughter's eyes turned in and as a result, brought her to their local eye doctor for assessment. He noticed a dim reflex with retinoscopy and referred her to our practice's ophthalmologist. The ophthalmologist, in turn, referred K.S. to us for a contact lens fitting for pathological myopia.

Retinoscopy showed an estimated prescription of -32.00D O.D., O.S. We fit KS in a tricurve GP lens. We initially ordered Standard Tricurve 7.3/22.00/9.0/7.5/0.35/8.80/0.40/10.30 Boston XO Blue.

We prescribed the lenses for a two-week extended wear schedule. In addition, we instructed K.S.'s parents to remove the lenses after two weeks, clean them with solution and reinsert them. The solution system we prescribed offers separate cleaning and rewetting components. Given that K.S. would be wearing the lenses on an extended-wear basis, we felt a cleaning solution with more "grit" would enhance the mechanical cleaning of the GP lens.

Further, we educated K.S.'s parents on the warning signs of complications associated with extended wear, such as red eyes, tearing, photophobia, etc.

K.S. has achieved success in her extended wear GP lenses through the past five years. At the start of her lens fitting, her visual acuity was unknown. By the time she reached three-and-a-half years old, she was able to identify Snellen letters and read 20/60 O.U. Her follow-up schedule has been every six months.

In 2007, K.S.'s corrected visual acuity was 20/50 O.S. (see figure 1). I believe one of the reasons KS achieved success with these lenses is because both her parents complied to my directions to the letter. They even established a relationship with a local optometrist to help with any acute problems, since seeing us required they drive 115 miles.

Figure 1: Final result of a bilateral GP fit on patient K.S., a seven-year-old child with pathologic myopia.

This child's best-corrected visual acuity was 20/50 O.S. The medical literature has described amblyopia in high myopia.⁴ In children younger than age 10 who have greater than 6.00D of myopia, amblyopia was present in 75% of cases. However, this is not a bilateral phenomenon.

Bilateral amblyopia is probably not a large factor in high myopia as there is always a real image created at the near point, albeit at a very close working distance. Rather, researchers and clinicians generally agree that visual loss with pathological (or degenerative) myopia is due to macular involvement of a posterior staphyloma.⁵ With the physiological limitation, the goal is to maximize visual acuity in each eye. Contact lenses are currently the most effective means of maximizing refractive correction in highly myopic children.^6,7

Occupational

In certain cases, it is appropriate to recommend extended wear lenses to adults for whom it is not feasible to remove lenses prior to sleeping.

We typically see residents, fellows and faculty from the orthopedic trauma service, emergency department, neurosurgery and cardiothoracic surgery as patients. Depending on the discipline, their on-call duties may require them to sleep in the hospital. Specifically, such calls may require them to awake from sleep and act immediately. As a result, they don't have time to insert lenses. Emergency responders, such as firefighters, may be good candidates for extended wear lenses as well.

We now know that two major components of avoidance of microbial keratitis are hygiene and compliance.⁸ In fact, research has shown that poor adherence to cleaning schedules increases the rate of microbial keratitis by two to 16 times.⁹ Still, the most highly predictive risk factor for microbial keratitis remains the extended wear modality.

As the demand for extended wear lenses continues to grow, so do many of its risks, in particular microbial keratitis. Given the additional risk factors, patient selection is paramount in deciding whom you should place in this modality.

Although many patients desire extended wear lenses for convenience, be sure to weigh the risk and benefits for each individual patient.

As the above cases illustrate, the extended wear modality is extremely beneficial for certain patient populations for not only improving visual function, but also quality of life. OM

References furnished upon request.

Dr. Sonsino is an assistant professor at Vanderbilt Eye Institute, Nashville, Tenn. He has particular expertise in difficult-to-fit or complex contact lens cases. E-mail him at jeff.sonsino@Vanderbilt.Edu.