Date Published: February 5, 2018
Publisher: Public Library of Science
Author(s): Sang Yeop Lee, Hyoung Won Bae, Hee Jung Kwon, Gong Je Seong, Chan Yun Kim, Wei Li.
The utility of Goldmann applanation tonometry (GAT) for monitoring intraocular pressure (IOP) in open-angle glaucoma (OAG) patients with a history of laser refractive surgery was investigated by comparing IOP fluctuations measured using GAT and dynamic contour tonometry (DCT) on the same day. In this retrospective study, patients were divided into one of two subgroups according to IOP fluctuation values using GAT: 43 eyes in the low IOP fluctuation group (LIFG [GAT fluctuation ≤1.7 mmHg]); and 55 eyes in the high IOP fluctuation group (HIFG [GAT fluctuation >1.7 mmHg]). IOP fluctuation was defined as the standard deviation of all IOP values during follow-up. IOP parameters using GAT were compared with those of DCT. Correlation analyses were performed among IOP parameters, and between IOP fluctuation and associated factors including central corneal thickness, corneal curvature, and axial length. All IOP parameters demonstrated significantly high values in the HIFG compared with those in the LIFG. Mean and peak IOP using DCT were significantly higher than those using GAT in both groups. However, there were no significant differences in IOP fluctuation and reduction using both tonometry methods in the HIFG (p = 0.946 and p = 0.986, respectively). Bland-Altman analysis revealed similar fluctuations using GAT and DCT. In multivariate analyses, there was a significant correlation between fluctuations using GAT and DCT in the HIFG (p = 0.043). These results suggest that IOP monitoring using GAT is a reliable method of monitoring IOP change in glaucoma patients with a history of laser refractive surgery, especially those exhibiting high IOP fluctuation. Nevertheless, several factors, including central corneal thickness, corneal curvature, and axial length, should be considered when using GAT for IOP monitoring.
Increased intraocular pressure (IOP) is a well-known risk factor for the development and progression of glaucoma [1–4], as are fluctuations in IOP . Therefore, IOP measurement is a basic and essential examination for treatment and follow-up in patients with glaucoma. Although various devices have been developed for IOP measurement, Goldmann applanation tonometry (GAT) is regarded as the gold standard. However, one limitation of IOP measurement using GAT is that accuracy is influenced by biomechanical properties of the cornea, including central corneal thickness (CCT) and corneal curvature (CC) [6, 7].
This retrospective study was conducted at the Department of Ophthalmology, Severance Hospital, Yonsei University School of Medicine (Seoul, Korea), with approval from the Institutional Review Board of Severance Hospital, Yonsei University (2015.9.25). All research adhered to the tenets of the Declaration of Helsinki, and informed written consent was obtained from all subjects. The medical records of patients who visited the Glaucoma Clinic of the Department of Ophthalmology at Severance Hospital, Yonsei University School of Medicine, between January 2005 and June 2015 were reviewed. Patients who underwent LASIK or LASEK at least 3 years before initial visit to the clinic and diagnosed with glaucoma exhibiting an open angle in the clinic using anti-glaucoma topical medication were selected. The follow-up period after initial diagnosis of glaucoma should be > 12 months. IOP was measured using GAT and DCT separately on the same day. At least 6 IOP measurements using GAT and DCT and regular clinic visits were required for inclusion. Other inclusion criteria were as follows: each examination to evaluate glaucoma was performed > 3 times; best-corrected visual acuity (BCVA) was > 20/30; no medical history of systemic disease; and no history of anti-glaucoma medication before the initial clinic visit. Glaucoma patients who underwent ophthalmic surgery, such as cataract surgery, vitrectomy, or glaucoma surgery, including laser trabeculoplasty, were excluded. Additionally, patients who discontinued using anti-glaucoma medication during the follow-up period(s), those who used steroid or non-steroidal anti-inflammatory eye drops, or those with a history of using these eye drops within 3 months of the last follow-up, were also excluded.
A total of 387 eyes of 194 OAG patients with a history of LASIK or LASEK were selected after review of medical records. Among these patients, 98 eyes of 98 patients who met the inclusion and exclusion criteria were included in the present study. Patients were divided into one of two subgroups according to the IOP fluctuation value obtained using GAT. Table 1 summarizes demographic information and comparisons between LIFG and HIFG. Except for IOP parameters (mean IOP, peak IOP, IOP fluctuation, IOP reduction, and ΔIOP fluctuation), there were no significant differences in other parameters. In the between-group comparisons, all IOP parameters of the HIFG were higher than those of the LIFG, with the exception of ΔIOP fluctuation. Mean and peak IOP measured using DCT (mean DCT and peak DCT) were significantly higher than mean and peak IOP measured using GAT (mean GAT and peak GAT) in each group. IOP fluctuation and reduction measured using DCT (DCT fluctuation and DCT reduction) were significantly higher than those measured using GAT (GAT fluctuation and GAT reduction) in the LIFG (p = 0.003, p = 0.004, respectively). However, there were no significant differences in IOP fluctuation and reduction between the two types of tonometry in the HIFG (p = 0.946, p = 0.986, respectively).
IOP fluctuation is divided into long- and short-term fluctuations . Although there is no definitional or methodological consensus for these two types of IOP fluctuation, many studies have demonstrated significant correlation between IOP fluctuation and glaucoma [15–19]. Therefore, for patients who have undergone LRS, both accuracy of IOP measurement and the detection IOP changes should not be overlooked. Sung et al  investigated the clinical characteristics of glaucomatous subjects who underwent LRS. They reported similar levels of IOP reduction after using anti-glaucoma medication between glaucomatous eyes with a history of LRS and glaucomatous eyes without such a history. Their study indicated the possible validity of using GAT for detecting IOP changes in glaucoma patients who have undergone LRS. GAT is considered to be the gold standard for IOP measurement and is commonly used in the glaucoma field. Therefore, if IOP changes can be monitored using GAT, glaucoma patients with the history of LRS can receive timely examination and/or treatment for the condition.
In the present study, IOP parameters calculated using GAT and DCT demonstrated significant correlation in OAG patients who underwent LRS, although their actual value(s) was different. In the group consisting of patients with high GAT fluctuation, significant correlation between GAT fluctuation and DCT fluctuation was still verified in the multivariate analysis. IOP change is important when we monitor glaucoma patients. However, there is no established consensus as to which mode of tonometry is the most accurate for monitoring IOP in OAG patients who have undergone LRS, although DCT is regarded to be a relatively exact method for IOP measurement in this patient group. By demonstrating significant correlation between DCT fluctuation and GAT fluctuation in HIFG, our results suggest that it is acceptable to apply GAT for monitoring IOP in OAG patients with a history of LRS. However, because GAT fluctuation was correlated with CCT, AXL and CC in HIFG, these factors should be considered when using GAT for monitoring.