Comparison of Aqueous Outflow Facility Measurement by Pneumatonography and Digital Schiøtz Tonography

Abstract

PurposeIt is not known if outflow facilities measured by pneumatonography and Schiøtz tonography are interchangeable. In this study we compared outflow facility measured by pneumatonography to outflow facility measured by digital Schiøtz tonography.MethodsFifty-six eyes from 28 healthy participants, ages 41 to 68 years, were included. Intraocular pressure (IOP) was measured in the sitting and supine positions with a pneumatonometer. With the subject in the supine position, IOP was recorded for 2 minutes by using a pneumatonometer with a 10-g weight and for 4 minutes by using a custom digital Schiøtz tonometer. Outflow facility was determined from the changes in pressure and intraocular volume and a standard assumed ocular rigidity coefficient for each instrument, respectively, and by using an ocular rigidity coefficient calculated by measuring pressure without and with a weight added to the pneumatonometer tip.ResultsThe outflow facility was 0.29 ± 0.09 μL/min/mm Hg by Schiøtz tonography and 0.24 ± 0.08 μL/min/mm Hg by pneumatonography (P < 0.001) when using the standard assumed constant ocular rigidity coefficient. Mean calculated ocular rigidity coefficient was 0.028 ± 0.01 μL−1, and outflow facility determined by using this coefficient was 0.23 ± 0.08 μL/min/mm Hg by Schiøtz tonography and 0.21 ± 0.07 μL/min/mm Hg by pneumatonography (P = 0.003). Outflow facilities measured by the two devices were correlated when the ocular rigidity was assumed (r = 0.60, P < 0.001) or calculated (r = 0.70, P < 0.001).ConclusionsOutflow facilities measured by pneumatonography were correlated with those measured by Schiøtz tonography, but Schiøtz tonography reported approximately 10% to 20% higher facilities when using the standard method. When ocular rigidity was determined for each eye, differences were smaller. Measurements from these devices cannot be compared directly.

Comparison of Corneal Wave Speed and Ocular Rigidity in Normal and Glaucomatous Eyes

“…Because of possible effects of IOP on ocular rigidity, our subjects were IOP matched. Ocular rigidity coefficient in our cohort of normal eyes was 0.0252/μL which was consistent with a previous study 17 in normal subjects (0.0276/μL). In the literature, the mean calculated ocular rigidity coefficient in normal eyes ranges from 0.0126 to 0.0280/μL.…”

“…Ocular rigidity coefficient in our cohort of normal eyes was 0.0252/μL which was consistent with a previous study17 in normal subjects (0.0276/μL). In the literature, the mean calculated ocular rigidity coefficient in normal eyes ranges from 0.0126 to 0.0280/μL 17,29–35. While there is currently no gold standard for ocular rigidity measurement, and different measurement techniques can produce different results, comparison of results using a single technique can still provide useful information.…”

Comparison of Corneal Wave Speed and Ocular Rigidity in Normal and Glaucomatous Eyes

“…Because of possible effects of IOP on ocular rigidity, our subjects were IOP matched. Ocular rigidity coefficient in our cohort of normal eyes was 0.0252/μL which was consistent with a previous study 17 in normal subjects (0.0276/μL). In the literature, the mean calculated ocular rigidity coefficient in normal eyes ranges from 0.0126 to 0.0280/μL.…”

“…Ocular rigidity coefficient in our cohort of normal eyes was 0.0252/μL which was consistent with a previous study17 in normal subjects (0.0276/μL). In the literature, the mean calculated ocular rigidity coefficient in normal eyes ranges from 0.0126 to 0.0280/μL 17,29–35. While there is currently no gold standard for ocular rigidity measurement, and different measurement techniques can produce different results, comparison of results using a single technique can still provide useful information.…”

Comparison of outflow facility before and after the microhook ab interno trabeculotomy

“…The retrospective study design, relatively small number of subjects, lack of a control group, absence of medication wash-out and short but various follow-up periods are other study limitations. The C value of 0.27 µl/min/mmHg preoperatively in this study was close to the C values of 0.29 µl/min/mmHg by Schiøtz tonography and 0.24 µl/min/mmHg by pneumatonography estimated in the non-glaucomatous subjects [6]; normal range IOP preoperatively explains the relatively high C value for glaucoma subjects in our study. Inclusions of normal tension glaucoma and eyes under use of multiple antiglaucoma medications can be another explanation.…”

Differing Associations between Optic Nerve Head Strains and Visual Field Loss in Patients with Normal- and High-Tension Glaucoma

“…Third, the actual level of IOP raised via ODM varied both inter and intra subjects based on several factors: (1) the ocular pulse, 58 (2) the viscoelastic behaviour of the ONH connective tissue, 59 which may cause the level of IOP raised to fall slightly after the initial compression as observed in a study by Kazemi et al 60 and, (3) to a lesser extent, the response of the eyelid tissue to the ODM. In our current study, we observed a relatively high standard deviation of 7 mmHg for the level of IOP raised for both groups of subjects.…”

Comparison of Corneal Wave Speed and Ocular Rigidity in Normal and Glaucomatous Eyes

“…Because of possible effects of IOP on ocular rigidity, our subjects were IOP matched. Ocular rigidity coefficient in our cohort of normal eyes was 0.0252/μL which was consistent with a previous study 17 in normal subjects (0.0276/μL). In the literature, the mean calculated ocular rigidity coefficient in normal eyes ranges from 0.0126 to 0.0280/μL.…”

“…Ocular rigidity coefficient in our cohort of normal eyes was 0.0252/μL which was consistent with a previous study17 in normal subjects (0.0276/μL). In the literature, the mean calculated ocular rigidity coefficient in normal eyes ranges from 0.0126 to 0.0280/μL 17,29–35. While there is currently no gold standard for ocular rigidity measurement, and different measurement techniques can produce different results, comparison of results using a single technique can still provide useful information.…”

Comparison of outflow facility before and after the microhook ab interno trabeculotomy

“…The retrospective study design, relatively small number of subjects, lack of a control group, absence of medication wash-out and short but various follow-up periods are other study limitations. The C value of 0.27 µl/min/mmHg preoperatively in this study was close to the C values of 0.29 µl/min/mmHg by Schiøtz tonography and 0.24 µl/min/mmHg by pneumatonography estimated in the non-glaucomatous subjects [6]; normal range IOP preoperatively explains the relatively high C value for glaucoma subjects in our study. Inclusions of normal tension glaucoma and eyes under use of multiple antiglaucoma medications can be another explanation.…”

Differing Associations between Optic Nerve Head Strains and Visual Field Loss in Patients with Normal- and High-Tension Glaucoma

“…Third, the actual level of IOP raised via ODM varied both inter and intra subjects based on several factors: (1) the ocular pulse, 58 (2) the viscoelastic behaviour of the ONH connective tissue, 59 which may cause the level of IOP raised to fall slightly after the initial compression as observed in a study by Kazemi et al 60 and, (3) to a lesser extent, the response of the eyelid tissue to the ODM. In our current study, we observed a relatively high standard deviation of 7 mmHg for the level of IOP raised for both groups of subjects.…”

Comparison of Corneal Wave Speed and Ocular Rigidity in Normal and Glaucomatous Eyes

“…Because of possible effects of IOP on ocular rigidity, our subjects were IOP matched. Ocular rigidity coefficient in our cohort of normal eyes was 0.0252/μL which was consistent with a previous study 17 in normal subjects (0.0276/μL). In the literature, the mean calculated ocular rigidity coefficient in normal eyes ranges from 0.0126 to 0.0280/μL.…”

“…Ocular rigidity coefficient in our cohort of normal eyes was 0.0252/μL which was consistent with a previous study17 in normal subjects (0.0276/μL). In the literature, the mean calculated ocular rigidity coefficient in normal eyes ranges from 0.0126 to 0.0280/μL 17,29–35. While there is currently no gold standard for ocular rigidity measurement, and different measurement techniques can produce different results, comparison of results using a single technique can still provide useful information.…”

Comparison of outflow facility before and after the microhook ab interno trabeculotomy

“…The retrospective study design, relatively small number of subjects, lack of a control group, absence of medication wash-out and short but various follow-up periods are other study limitations. The C value of 0.27 µl/min/mmHg preoperatively in this study was close to the C values of 0.29 µl/min/mmHg by Schiøtz tonography and 0.24 µl/min/mmHg by pneumatonography estimated in the non-glaucomatous subjects [6]; normal range IOP preoperatively explains the relatively high C value for glaucoma subjects in our study. Inclusions of normal tension glaucoma and eyes under use of multiple antiglaucoma medications can be another explanation.…”

Differing Associations between Optic Nerve Head Strains and Visual Field Loss in Patients with Normal- and High-Tension Glaucoma

“…Third, the actual level of IOP raised via ODM varied both inter and intra subjects based on several factors: (1) the ocular pulse, 58 (2) the viscoelastic behaviour of the ONH connective tissue, 59 which may cause the level of IOP raised to fall slightly after the initial compression as observed in a study by Kazemi et al 60 and, (3) to a lesser extent, the response of the eyelid tissue to the ODM. In our current study, we observed a relatively high standard deviation of 7 mmHg for the level of IOP raised for both groups of subjects.…”