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Tonometry yields accurate IOP through silicone hydrogel lenses
There was no statistically significant difference found in a study of 10 volunteers who were measured with soft contact lenses and without.
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Accurate measurement of IOP by Goldmann applanation tonometry through a silicone hydrogel contact lens may be attainable without the need for patients to remove their contact lenses, according to a cohort study by researchers in the United Kingdom.
Previous studies investigating IOP through conventional soft therapeutic lenses confirmed that accurate IOP could be recorded in normal eyes and in eyes with abnormal anterior segments. Obtaining accurate measurements through soft contact lenses, however, can be influenced by factors such as water content and center thickness of the lens.
 Richard J. Allen |
Richard J. Allen, FCOptom, and colleagues measured the IOP of 20 eyes in 10 volunteers with a Goldmann applanation tonometer (Haag-Streit) without a contact lens and repeated the measurement with a silicone hydrogel contact lens in situ. Their findings were published in Contact Lens & Anterior Eye.
“We knew that we were able to [measure] it with hydrogel lenses,” Mr. Allen told Ocular Surgery News in a telephone interview. “It was just a question of confirming with the modern lens material silicone hydrogel that we could measure it just as accurately as we could in the past.”
Methodology
In the study, the researchers examined 10 healthy volunteers with no ocular pathology and a mean age of 31.4 years.
Measurements were taken using a Goldmann applanation tonometer with proxymetacaine hydrochloride 0.5% and fluorescein sodium 0.25% mixed minims without contact lens in situ and again using a Goldmann applanation tonometer with a –0.5 SS PureVision (Bausch & Lomb) silicone hydrogel contact lens.
“We evaluated intraocular pressure before and again with and without the lens in situ on the eye through snapshots and measurements,” he said.
Before each measurement, the operator reset the tonometer scale to 10 and took the measurement while the scale was obscured from his vision by a small screen. To reduce the risk of bias, an independent technician then recorded the measurement.
After insertion of the silicone hydrogel contact lens, IOPs were retested within 20 to 30 minutes by the same operator, Goldmann applanation tonometer and slit lamp.
The researchers then performed a statistical analysis using the paired t-test and calculated a correlation coefficient.
They found no statistically significant difference between the two groups.
Improves patient care
Mr. Allen said he hopes that the findings have a positive effect on patient care.
“I think it improves the care of patients,” he said. “That means we can successfully use silicone hydrogel contact lenses as therapeutic contact lenses in many patients, knowing that we could measure their intraocular pressure accurately and improve their long-term care.”
Mr. Allen said it is imperative that ophthalmologists have an accurate method of measuring IOP and that patients can have the option of not having to remove their lenses. By doing so, he said clinicians no longer have to risk damaging the fragile epithelium.
A follow-up study is being planned that will re-examine various parameters of therapeutic contact lenses, he said.
“Thickness didn’t change, but if we start measuring through contact lens patient use for refractive purposes, myopes and hyperopes will have different thicknesses of contact lenses, and that will alternate the pressure readings. … That study would have to be done on a larger scale because we would be evaluating contact lens power as well,” Mr. Allen said.
For more information:
- Richard J. Allen, FCOptom, can be reached at Essex County Hospital, Colchester, Essex C03 3NB, United Kingdom; 44-1206-744656; fax: 44-1206-744646; e-mail: richard.allen@colchesterhospital.nhs.uk. Mr. Allen has no direct financial interest in the products discussed in this article, nor is he a paid consultant for any companies mentioned.
Reference:
- Allen RJ, Dev Borman A, Saleh GM. Applanation tonometry in silicone hydrogel contact lens wearers. Cont Lens Anterior Eye. 2007;30:267-269.
- John Misiano is an OSN Correspondent based in Bordentown, N.J.