A review of ocular perfusion pressure and retinal thickness: A case for the role of systemic hypotension in glaucoma

Background: Ocular perfusion pressure (OPP) is defined as blood pressure (BP) minus intraocular pressure (IOP). Low OPP may result in decreased ocular blood flow (OBF) and oxygen to the optic nerve head (ONH) and retina.Aim: To review the role of systemic hypotension and similar conditions in OPP and its influence on retinal nerve fibre layer (RNFL) thickness and the ganglion cell complex (GCC).Method: A literature search was conducted using the following search terms: ‘systemic hypotension’; ‘glaucoma’; ‘retinal nerve fibre layer’; ‘optic nerve’; ‘ocular blood flow’ and ‘ocular perfusion pressure’.Results: The Los Angeles Eye Study and Barbados Eye Study found that decreased OPP and BP increased the risk of glaucoma development by up to six times. Reduced retinal perfusion with resultant thinning of the RNFL in conditions with a similar mechanism, such as obstructive sleep apnoea syndrome, has indicated the importance of reduced OPP in retinal thickness. In the absence of any study directly showing the effect of systemic hypotension on OPP and retinal thickness, a working hypothesis proposes that reduced BP with or without normal-to-raised IOP will reduce OPP. The reduced OPP and OBF in those with systemic hypotension may result in oxidative stress and hypoxia which may then cause retinal ganglion cell death and the resultant retinal thinning.Conclusion: The increased risk of glaucoma development and progression relating to decreased BP and OPP has been proven to be of importance. Monitoring patients with systemic hypotension and evaluating the macula, ONH RNFL and GCC thickness may alert clinicians to possible glaucomatous changes.

The Effect of Ocular Perfusion Pressure on Retinal Thickness in Young People with Presumed Systemic Hypotension

Low ocular perfusion pressure (OPP) may increase the risk of optic neuropathy. This study investigated the effects of OPP on the ganglion cell complex (GCC) and optic nerve head-retinal nerve fibre layer (ONH-RNFL) thickness in presumed systemic hypotensives (PSH). Fifteen participants with PSH and 14 controls underwent automated sphygmomanometry and Icare tonometry to calculate OPP: mean OPP (MOPP), systolic OPP (SOPP), and diastolic OPP (DOPP). ONH-RNFL and macula GCC thickness were evaluated using the Optovue iVue optical coherence tomographer. Statistical analysis comprised independent t-tests, the Mann–Whitney U test and binary logistic regression analysis. There was no significant difference when comparing ONH-RNFL and macula GCC thickness between both groups. Increased MOPP (OR = 0.51; 95% CI: 0.27–0.97; p = 0.039) and SOPP (OR = 0.79; 95% CI: 0.64–0.98; p = 0.035) were significantly associated with a decreased risk of reductions in GCC total thickness. Increased SOPP (OR = 0.11; 95% CI: 0.01–0.89; p = 0.027) was significantly associated with a decreased risk of reductions in the average ONH-RNFL thickness. The study found no significant retinal thickness changes in PSH’s, in comparison to the controls. The study established that, by increasing MOPP and SOPP, there was a decreased risk of reductions in the total GCC thickness and average ONH-RNFL thickness. Higher SOPP may decrease the possibility of retinal thinning of the GCC and ONH-RNFL. However, higher MOPP may decrease the odds of thinning of the GCC before ONH-RNFL changes.

HIOP-Reader: Automated Data Extraction for the Analysis of Manually Recorded Nycthemeral IOPs and Glaucoma Progression

Purpose: Nycthemeral (24-hour) glaucoma inpatient intraocular pressure (IOP) monitoring has been used in Europe for more than 100 years to detect peaks missed during regular office hours. Data supporting this practice is lacking, partially because it is difficult to correlate manually drawn IOP curves to objective glaucoma progression. To address this, we deployed automated IOP data extraction tools and tested for a correlation to a progressive retinal nerve fiber layer loss on spectral-domain optical coherence tomography (SDOCT). Methods: We created and deployed a machine-learning image analysis software to extract IOP data from hand-drawn, nycthemeral IOP curves of 225 retrospectively identified glaucoma patients. The relationship between demographic parameters, IOP and mean ocular perfusion pressure (MOPP) data to SDOCT data was analyzed. Sensitivities and specificities for the historical cut-off values of 15 mmHg and 22 mmHg in detecting glaucoma progression were calculated. Results: IOP data could be extracted efficiently. The IOP average was 15.2±4.0 mmHg, nycthemeral IOP variation was 6.9±4.2 mmHg, and MOPP was 59.1±8.9 mmHg. Peak IOP occurred at 10 AM and trough at 9 PM. Disease progression occurred mainly in the temporal-superior and -inferior SDOCT sectors. No correlation could be established between demographic, IOP, or MOPP parameters and SDOCT disease progression. The sensitivity and specificity of both cut-off points (15 and 22 mmHg) were insufficient to be clinically useful. Outpatient IOPs were non-inferior to nycthemeral IOPs. Conclusion: IOP data obtained during a single visit make for a poor diagnostic tool, no matter whether obtained using nycthemeral measurements or during outpatient hours.

Circadian Variation of Ocular Perfusion Pressure in Primary Open Angle Glaucoma- A Cross-sectional Study

Introduction: Various haemodynamic factors have been implicated as pathophysiological mechanisms in Primary Open Angle Glaucoma (POAG) other than raised Intraocular Pressure (IOP). However, the exact relationship still remains unclear. Aim: To examine the circadian pattern of Blood Pressure (BP), IOP and Ocular Perfusion Pressure (OPP) with the aim of understanding their relationships in a cohort of patients with POAG. Materials and Methods: A cross-sectional study was conducted in which 44 cases of newly diagnosed, non-hypertensive patients with POAG were enrolled and categorised based on the severity of glaucoma. Recording of BP and IOP were done every 4th hourly during a 24 hour hospital stay. The Mean OPP (MOPP) was calculated as 2/3×Mean Arterial Pressure (MAP)-IOP. Systolic OPP (SOPP) was calculated as Systolic BP-IOP and Diastolic OPP (DOPP) was calculated as Diastolic BP-IOP. The diurnal, nocturnal and 24 hour fluctuations were derived from the difference between the highest and lowest values within each period. Data was analysed using Statistical Package for the Social Sciences (SPSS) version 16.0. Univariate and multivariate regression analysis of the variables with age and severity of POAG were performed Results: Significant positive correlation of the nocturnal fluctuations in MAP (r=0.533), SOPP (r=0.835), DOPP (r =0.768), MOPP (r=0.685) and 24 hour fluctuation in MOPP (r=0.636) were noted with severity of glaucoma on multivariate analysis. No significant correlation of these parameters with age was noted on multivariate analyses. Conclusion: Nocturnal dip in OPP was an important observation among patients with POAG, potentially contributing to its pathophysiology.

Rhythm of 24-h Intraocular and Perfusion Pressure in Patients With Ocular Hypertension

AIMThe aim of the present study was to characterize the rhythm of 24-h intraocular pressure (IOP) and ocular perfusion pressure (OPP) in patients with ocular hypertension (OHTN), in order to provide a reference for the clinical diagnosis and treatment of OHTN. METHODSAccording to the diagnostic criteria, 107 patients with OHTN were included, and an age- and sex-matched healthy control group (71 patients) was selected. The IOP and blood pressure (BP) of the OHTN and the healthy control groups were recorded every 2 h over a 24-h period. BP was measured using a digital automatic BP monitor, and IOP was measured using a non-contact tonometer. RESULTSThe maximum, minimum and mean IOP were significantly higher in subjects with OHTN than in the healthy control group (P<0.05), and the maximum, minimum and mean MOPP were significantly lower in the OHTN group than in the healthy control group (P<0.05). The minimum and mean SOPP and DOPP values of the OHTN group were lower than those of the healthy control group (P<0.05), and the IOP, MOPP, SOPP and DOPP diurnal and nocturnal fluctuation values were significantly greater in the OHTN group than in the healthy control group (P<0.05). The peak and trough IOP times of the two groups coincided, which tended to be low during the day and higher at night. The peak and trough MOPP and SOPP times of the two groups also coincided, and were primarily higher during the day and lower at night. The 24-h DOPP in the healthy control group was generally higher during the daytime and lower at night, with peak values between 19:00-23:00 h, and trough values between 3:00-7:00 h. No obvious day-to-night fluctuations were observed in the OHTN group. CONCLUSIONThe OPP of patients with OHTN is lower, and the 24-h OPP fluctuates more than that of healthy control subjects. This may be an important blood flow factor for the progression to primary open angle glaucoma in patients with OHTN.