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Study shows similar reduction in IOP in both eyes of a single patient after LASIK
J Cataract Refract Surg. 2009;35(1):76-82.
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Reductions in IOP after LASIK were larger in eyes with higher preop IOP and smaller in eyes with lower preop IOP.
In addition, postop IOP measurements "were similar and proportional in eyes of the same patient," the study authors said.
The prospective cohort study included 312 eyes of 156 patients with myopia or myopic astigmatism who underwent LASIK. Inclusion criteria were uncorrected visual acuity of 20/20 or better and refraction within ±2.5 D of the target 6 months after LASIK; 14 patients were excluded from analysis. The final study group included 284 eyes of 142 patients ranging in age from 20 years to 48 years.
Noncontact tonometry was used to measure IOP, autokeratorefractometry to gauge keratometric power and ultrasound pachymetry to assess central corneal thickness.
Data showed significant links between high preoperative IOP, high postoperative IOP and a large post-LASIK decrease in IOP. Differences between postoperative IOP, post-LASIK decrease in IOP and the ratio of laser ablation depth to decreased IOP in the eyes of the same patient were not statistically significant.
"These findings regarding IOP measurements after LASIK treatment should be of interest to ophthalmologists when evaluating IOP measurements in patients after refractive surgery," the authors said.
I think the main take-home point is that ophthalmologists need to be more acutely aware of patients who have had LASIK eye surgery as they follow them for comprehensive management, which includes evaluation of IOP and screening for glaucoma.
It’s been known quite well that as we change the corneal curvature with LASIK, for example, we can falsely lower IOP measurements, simply due to an altered corneal curvature, perhaps altered resistance. The bottom line in terms of clinicians is if they’re following a target of 16 mm Hg, 18 mm Hg or 20 mm Hg and they’re trying to keep the pressure lower than that and the patient goes on to have LASIK, their pressure might be falsely low when in fact it’s representative of a higher pressure that might warrant treatment.
Dr. Sheng-Yao Hsu and co-authors followed a cohort of patients after LASIK surgery and they found that the IOP measurement after LASIK was greater in cases of people with higher IOPs and smaller in cases of lower preoperative IOPs. That also is an important point for the comprehensive ophthalmologist to know. What it’s basically saying is, if someone is really at low risk for the development of ocular hypertension or glaucoma, meaning they have a normal or low-normal IOP measurement before their LASIK surgery, the amount of change you’re going to see afterwards is less. But if someone has a higher IOP measurement prior to their LASIK, they are more likely to have a larger IOP measurement reduction after their LASIK surgery.
That doesn’t necessarily mean that LASIK is treating pressure or treating glaucoma or reducing the risk for patients with ocular hypertension. Rather, you’re getting a falsely lower measurement so that you might miss the development of glaucoma in those high risk patients.
– Kerry D. Solomon, MD
OSN Refractive Surgery Board Member