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Static and repeated accommodation may reduce IOP significantly
Study authors theorized that ciliary muscle contraction and aqueous outflow system as a whole acts as a mechanical pump that mediates IOP, flow.
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IOP was significantly lower after static and repeated accommodation, but frequent accommodation did not reduce IOP significantly more than static accommodation, according to a study.
“One important finding was that IOP decreased significantly from baseline after both the static and repeated mode of accommodation,” Jørgen Krohn, MD, PhD, the corresponding author, told Ocular Surgery News. “That we could find a similar decrease after the repeated mode [and static mode] was a new finding.”
In the Journal of Glaucoma, Dr. Krohn and Frank Jenssen, MD, hypothesized that alternating contraction and relaxation of the ciliary muscle during repeated accommodation may promote uveoscleral outflow of aqueous humor, in addition to outflow through the trabecular meshwork.
The additional IOP reduction afforded by repeated accommodation did not provide conclusive evidence that ciliary muscle contraction contributed to uveoscleral outflow, Dr. Krohn said.
“There are two major outflow systems from the eye. One is through the trabecular meshwork and one is through the uveoscleral pathway,” he said. “We know that the ciliary muscle is also important when it comes to the uveoscleral outflow. It could be that repeated accommodation in some way could increase the uveoscleral outflow as well. But this is just a theory, so we don’t know exactly.”
Patients and parameters
The prospective, randomized study included 33 volunteers with a median age of 24 years. Seventeen participants underwent IOP measurement after static accommodation followed by repeated accommodation. Sixteen participants underwent IOP measurement after repeated accommodation followed by static accommodation. Subjects with more than 2 D of myopia or hypermetropia, history of ocular disease, or systemic medication use were excluded.
Static accommodation testing involved subjects focusing on a near target for 3 minutes; the target was adjusted to induce a 3-D accommodative demand. Repeated accommodation involved subjects alternately focusing on a near and distant target for 3 minutes.
An infrared photorefractor was used to monitor accommodative responses. IOP was measured immediately after static and repeated accommodation.
“We monitored the level of accommodation objectively and continuously with a photorefractor during the experiments. That makes it different from other studies,” Dr. Krohn said.
The researchers evaluated refraction, best corrected visual acuity, anterior chamber depth, central corneal thickness and anterior chamber volume.
Results and findings
Study results showed that for both groups combined, mean IOP was 15 mm Hg at baseline, 13.4 mm Hg after static accommodation, and 12.7 mm Hg after repeated accommodation.
The difference between mean IOP after static accommodation and repeated accommodation was statistically significant (P = .04).
IOP decreased by 1.76 mm Hg after static accommodation and 2.06 mm Hg after repeated accommodation, but the difference in IOP reduction was not statistically significant.
Further study with a larger patient sample is warranted, the researchers said.
“Because we had a very small sample size and perhaps the way we performed the accommodative procedures may have led to this result. We don’t know,” Dr. Krohn said. “So far, we have no firm proof that repeated accommodation will have a significant influence on the IOP. We will continue on this work and try to find out more about this.” – by Matt Hasson
Reference:
- Jenssen F, Krohn J. Effects of static accommodation versus repeated accommodation on intraocular pressure. J Glaucoma. 2012;21(1):45-48.
For more information:
- Jørgen Krohn, MD, PhD, can be reached at Department of Ophthalmology, Haukeland University Hospital, N-5021 Bergen, Norway; email: jorgen.krohn@helse-bergen.no.
- Disclosure: Dr. Krohn has no relevant financial disclosures.