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ORIGINAL ARTICLE
Year : 2022  |  Volume : 25  |  Issue : 9  |  Page : 1430-1434

Distribution of ocular perfusion pressure and its relationship with intraocular pressure in patients with primary open angle glaucoma in Enugu, South East, Nigeria


Department of Ophthalmology, University of Nigeria Teaching Hospital, Ituku-Ozalla Enugu, Nigeria

Date of Submission13-Sep-2021
Date of Acceptance06-Jun-2022
Date of Web Publication22-Sep-2022

Correspondence Address:
Dr. N Z Nwachukwu
Department of Ophthalmology, University of Nigeria Teaching Hospital, Ituku-Ozalla, Enugu
Nigeria
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/njcp.njcp_1813_21

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   Abstract 


Background: Ocular perfusion pressure (OPP) has been suggested as a possible risk factor for the development and progression of primary open angle glaucoma (POAG). Aim: To determine the distribution of OPP and its relationship with intraocular pressure (IOP) in Nigerian patients with POAG. Patients and Methods: A descriptive and comparative survey was adopted. A total of 120 subjects, 60 newly diagnosed POAG and 60 non-glaucomatous (NG) subjects, aged 40 years and above, who attended the ophthalmic clinic of University of Nigeria Teaching Hospital Enugu were recruited over a six-month period in 2019. All the subjects had ocular examination, blood pressure and IOP measurements. Statistical package for social sciences software version 25 was used for data analysis. Chi-square test, independent samples t-test, and Mann-Whitney U test were used for comparison while Pearson correlation and simple linear regression were used to ascertain the relationship. A P value of <0.05 was considered significant. Result: The mean age of the participants was 57.9 + 11.9 years. The mean OPP was found to be significantly lower in the POAG subjects (Right eye, R = 43.6 ± 12.6, Left eye, L = 41.9 ± 13.3) mmHg compared with the NG group (R = 53.9 ± 10.9, L = 53.7 ± 10.9) mmHg (p < 0.001 for both eyes). A significant inverse relationship was observed between OPP and IOP in POAG subjects (p < 0.001), while there was none in NG subjects. Conclusion: OPP was lower in POAG subjects than in NG subjects. The observed relationship suggests that reduced OPP may play a role in the development of POAG.

Keywords: Intraocular pressure, ocular perfusion pressure, primary open angle glaucoma


How to cite this article:
Arinze I C, Onwubiko S N, Nwachukwu N Z, Maduka-Okafor F C, Aghaji A E, Nkwegu M O, Onwasigwe E N. Distribution of ocular perfusion pressure and its relationship with intraocular pressure in patients with primary open angle glaucoma in Enugu, South East, Nigeria. Niger J Clin Pract 2022;25:1430-4

How to cite this URL:
Arinze I C, Onwubiko S N, Nwachukwu N Z, Maduka-Okafor F C, Aghaji A E, Nkwegu M O, Onwasigwe E N. Distribution of ocular perfusion pressure and its relationship with intraocular pressure in patients with primary open angle glaucoma in Enugu, South East, Nigeria. Niger J Clin Pract [serial online] 2022 [cited 2022 Sep 29];25:1430-4. Available from: https://www.njcponline.com/text.asp?2022/25/9/1430/356659




   Introduction Top


Globally, glaucoma is the leading cause of avoidable, irreversible blindness, affecting about 64.3 million people, with a prevalence of 3.54% in those aged between 40 and 80 years.[1] The prevalence of primary open angle glaucoma (POAG) is highest in Africa (4.2%).[1] In Nigeria, it accounted for 16.7% of blindness and the leading cause of functional low vision.[2]

The mechanisms underlying the development and progression of glaucoma still remain uncertain.[3] Several risk factors have been implicated with intraocular pressure (IOP) being the only modifiable risk factor. Reducing IOP is effective in reducing the progression of the disease, however, progression still occurs in some cases despite adequate IOP control.[3] Vascular risk factors such as blood pressure (BP) and ocular perfusion pressure (OPP) have been implicated in the pathogenesis of glaucoma.[4] Several studies across the world have demonstrated the positive relationship between reduced OPP and increased prevalence and progression of POAG.[3],[4],[5],[6],[7],[8],[9],[10] Racial variations exist in BP and IOP,[3] the distribution of OPP and its relationship with IOP in glaucoma patients might be different among Nigerians. There is paucity of data on OPP in Nigeria, especially in the South-East region, which harbors predominantly the ethnic Ibos with the greatest risk of glaucoma associated blindness.[11]

Hence the decision to conduct this survey aimed at generating comparative values of OPP in normal and glaucoma Nigerian subjects, as well as establishing the relationship between OPP and IOP in patients with POAG. Additionally, this study intends to establish the relevance or otherwise of OPP as a routine data in the management of POAG in Nigeria or elsewhere with similar setting.


   Materials and Methods Top


Study area: The study was conducted at the University of Nigeria Teaching Hospital (UNTH) Ituku-Ozalla, Enugu. The hospital was established in 1960 and is located in the South-Eastern geo-political region of Nigeria. It functions as a referral centre in all aspects of medicine and surgery, for the entire South-East, South-South, North-Central, and other parts of Nigeria.

Study design: A descriptive and comparative analytical hospital-based survey was adopted. Sixty consecutive newly diagnosed POAG and 60 aged-matched non-glaucomatous (NG) subjects who attended the eye clinic of UNTH from January to July, 2019 and voluntarily gave their consent were recruited for the study.

Inclusion criteria: Newly diagnosed POAG patients aged 40 years and above attending the eye clinic of UNTH, Enugu who had not commenced anti-glaucoma medications and gave an informed consent were recruited for the study. Diagnosis of POAG was based on presence of open angles on gonioscopy as well as:

  1. Vertical cup to disc ratio ≥0.6 or disc asymmetry >0.2.
  2. Glaucomatous visual field loss observed on two or more central visual field analysis.


NG aged-matched patients (40 years and above) attending the eye clinic, who had refractive error or presbyopia and gave their consent were equally recruited for the study.

Exclusion criteria: Patients with co-existing ocular pathologies, systemic vascular diseases such as hypertension, diabetes mellitus, migraine or those on anti-glaucoma and/or anti-hypertensive medications were excluded.

Ethical clearance

Approval for the study was obtained from the Health Research and Ethics Committee (institutional review board) of the University of Nigeria Teaching Hospital, Ituku-Ozalla, Enugu, according to the tenets of the Helsinki Declaration as amended.

Informed consent

Written informed consent was obtained from each participant. Participation in the study was voluntary and at no cost to the patient, who also had the freedom to withdraw from the study at any time they deemed fit.

Sample size calculation

The minimum sample size was calculated using the formula below:[12]



Where,

N = Minimum sample size of each of the study group.

α = Probability of making type one error.

B = Probability of making type two error.

Zα/2 = Level of significance of type one error probability determined from a statistical table based on the value of level of significance α; for this study it was set at 0.05. The 95% confidence interval = 1.96 for a two-tailed test (standard normal deviate).

Zβ = This is type two error probability corresponding to standard normal deviate for a stated power of the study to detect a significant difference.

For this study, a power of 80% was used therefore Zβ = 0.84.

C (r) = correlation between OPP, IOP, and BP (r = 0.40).



N = 52

Correcting for an attrition rate of 10% = 5.2.

Minimum sample size = 52 + 5.2 (attrition rate) = 57.2 ≈ 57.

57 for POAG patients and 57 for non-glaucomatous group.

The total minimum sample size was 114 which was approximated to 120 (60 newly diagnosed POAG and 60 NG subjects).

Sampling technique: To obtain the required sample size, consecutive enrolment was used. All consecutive, consenting patients who met the inclusion criteria were enrolled into the study until the estimated sample size was obtained for the two groups.

Study procedure: New patients diagnosed with POAG were evaluated for eligibility and recruited into the study, as well as the non-glaucoma patients. After obtaining consent, a pre-tested, structured questionnaire comprising of two sections: sociodemographic and clinical sections were administered by the researchers. Thereafter, each participant had the following examinations.

Blood pressure: Subjects were allowed to rest for at least 2 hours after arriving at the hospital to ensure a stable hemodynamic condition before measuring BP on the upper arm. BP was measured with an automated BP monitor (Dinamap model). The mean of two measurements taken in a sitting position at least 30 min apart with the appropriate cuff placed around the upper arm was recorded.

Intraocular pressure: This was measured using Goldman applanation tonometer. The prism was disinfected with isopropyl alcohol 70% rinsed in sterile water and wiped dry with a clean swab. After checking the graduation and setting the calibrated dial to 10 mmHg, the patient was seated comfortably at the slit-lamp, local anesthetic drops and fluorescein strip was instilled in the lower fornix of the conjunctiva, with the patient looking straight ahead, the prism was gradually placed to rest gently on the centre of the patient's cornea, the calibrated dial on the tonometer was turned clockwise until the inner edges of the semi-circles in the prism head were seen to touch. The reading on the dial was noted and recorded.

The mean OPP was calculated from the BP and IOP using this formula:

OPP = 2/3 of the mean arterial BP - IOP, where

Mean arterial pressure = Diastolic Blood Pressure (DBP) + 1/3{Systolic Blood Pressure (SBP) – DBP}.

Mean OPP was calculated for each group.

Data management: Statistical package for social sciences software version 25 was used for data analysis. The descriptive statistics – frequency, percentage, mean, range, and standard deviation were used to summarize the data. Chi-square test, independent samples t-test, and Mann-Whitney U test, one factor independent measures analysis of variance (ANOVA), and Kruskal-Wallis H test, were used for comparison of OPP values between POAG and non-glaucoma subjects while Pearson correlation and simple linear regression were used to ascertain the relationship OPP and IOP in the two study groups. A P value of < 0.05 was used to define statistical significance at 95% confidence interval.


   Results Top


The participants comprised 77 females and 43 males with a mean age of 57.91 + 11.9 years. Comparison of the sociodemographic profile between the POAG and NG subjects revealed no statistically significant difference [Table 1].
Table 1: Sociodemographic characteristics of the subjects (n=120)

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OPP values in both eyes were higher in females than males in the NG group (RE: 54.36 ± 12.3 vs 53.05 ± 7.5; LE: 54.48 ± 12.4 vs 52.10 ± 6.8). Female OPP values were equally higher than those of their male counterparts in the POAG group [Table 2]. Those aged 70 years and above had the highest OPP (RE: 57.22 ± 11.4 and LE: 56.61 ± 10.2) among the NG group, and the least values (RE: 37.03 ± 10.1 and LE: 38.03 ± 11.1) in POAG subjects [Table 2].
Table 2: Distribution of OPP by age and sex among the subjects (n=120)

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OPP values in both eyes among the POAG subjects were significantly lower (p < 0.001) compared with those in the NG group (RE: 43.66 ± 12.67 vs 53.94 ± 10.99; LE: 41.97 ± 13.30 vs 53.72 ± 10.96) [Table 3].
Table 3: Comparison of OPP between the NG and POAG subjects

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A significant inverse relationship was observed between OPP and IOP in both eyes in the POAG group (RE: P = 0.03; LE: P = 0.002) while there was none in the NG subjects [Table 4].
Table 4: Relationship between OPP and IOP in the NG and POAG subjects

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   Discussion Top


In this study, OPP was found to be significantly lower among the POAG subjects compared with the NG group. This finding is similar to those reported in several previous studies in different countries,[3],[4],[5],[6],[7],[8],[9],[10],[13],[14] which showed that OPP values were lower among the POAG compared to their NG counterparts. Conversely, our result is not in agreement with that reported from a previous study in China,[15] which found no significant reduction in OPP among the POAG subjects. This difference could be due to racial factors as Asians have been known to have lower BP values compared to blacks and Caucasians. The significant inverse relationship observed between OPP and IOP in the POAG group supports the role of vascular factors in the aetiology of POAG. Poor perfusion of the optic nerve head, consequent upon impaired vascular autoregulation,[16],[17] and altered blood flow in the optic disc increases the risk of POAG.[18],[19] OPP is affected either by a low BP, high IOP, treatment to lower BP or IOP, or a combination of these variables. It is therefore, pertinent for OPP to be routinely assessed in glaucoma, more importantly, in hypertensive glaucoma patients. Therefore, a multi-disciplinary approach by the Ophthalmologists and the internal medicine Physicians should be deployed in the management of these patients. This will help in halting the progressive loss of the optic nerve fibres.


   Conclusion Top


The findings from the present study showed that OPP is inversely related to IOP and suggest that reduced OPP may play a role in the development of POAG in the Nigerian subjects. Routine assessment of OPP and co-management of glaucoma patients with the Physicians especially those with progression despite adequate IOP control is therefore, recommended.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
   References Top

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2.
Abdull MM, Sivasubramaniam S, Murthy GV, Gilbert C, Abubakar T, Ezelum C, et al. Causes of blindness and visual impairment in Nigeria: The Nigeria national blindness and visual impairment survey. Invest Ophthalmol Vis Sci 2009;50:4114–20.  Back to cited text no. 2
    
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Cherecheanu AP, Garhofer G, Schmidl D, Werkmeister R, Schmetterer L. Ocular perfusion pressure and ocular blood flow in glaucoma. Curr Opin Pharmacol 2013;13:36–42.  Back to cited text no. 3
    
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Khawaja AP, Crabb DP, Jansonius NM. The role of ocular perfusion pressure in glaucoma cannot be studied with multivariable regression analysis applied to surrogates. Invest Opthalmol Vis Sci 2013;54:4619-20.  Back to cited text no. 5
    
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Zheng Y, Wong TY, Mitchell P, Friedman DS, He M, Aung T. Distribution of ocular perfusion pressure and its relationship with open-angle glaucoma: The Singapore Malay eye study. Investig Ophthalmol Vis Sci 2010;51:3399–404.  Back to cited text no. 8
    
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Tielsch JM, Katz J, Sommer A, Quigley HA, Javitt JC. Hypertension, perfusion pressure, and primary open-angle glaucoma. A population-based assessment. Arch Ophthalmol 1995;113:216-21.  Back to cited text no. 9
    
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Memarzadeh F, Ying-Lai M, Chung J, Azen SP, Varma R; Los Angeles Latino Eye Study Group. Blood pressure, perfusion pressure, and open-angle glaucoma: The Los Angeles Latino eye study. Invest Ophthalmol Vis Sci 2010;51:2872–7.  Back to cited text no. 10
    
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Kyari F, Wormald R, Murthy GV, Evans JR, Gilbert CE; Nigeria National Blindness and Visual Impairment Study Group. Ethnicity and deprivation are associated with blindness among adults with primary glaucoma in Nigeria: Results from the Nigeria national blindness and visual impairment survey. J Glaucoma 2016;25:e861-72.  Back to cited text no. 11
    
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Machin D, Campbell MJ. Comparison of Means in Medical Statistics A Common Sense Approach. 2nd ed. West Sussex, England: John Wiley and son ltd.; 1990.  Back to cited text no. 12
    
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Bonomi L, Marchini G, Marraffa M, Bernadi P, Morbio R, Varotto A. Vascular risk factors for primary open angle glaucoma: The Egna-Neumarkt Study. Ophthalmology 2000;107:1287–93.  Back to cited text no. 13
    
14.
Leske MC, Heijl A, Hyman L, Bengtsson B, Dong L, Yang Z, et al. Predictors of long-term progression in the early manifest glaucoma trial. Ophthalmology 2007;114:1965–72.  Back to cited text no. 14
    
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Xu L, Wang YX, Jonas JB. Ocular perfusion pressure and glaucoma: The Beijing eye study. Eye (Lond) 2009;23:734-6.  Back to cited text no. 15
    
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Flammer J, Mozaffarieh M. Autoregulation, a balancing act between supply and demand. Can J Ophthalmol 2008;43:317–21.  Back to cited text no. 16
    
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Flammer J, Mozaffarieh M. What is the present pathogenetic concept of glaucomatous optic neuropathy? Surv Ophthalmol 2007;52(Suppl 2):S162–73.  Back to cited text no. 17
    
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Grieshaber MC, Mozaffarieh M, Flammer J. What is the link between vascular dysregulation and glaucoma? Surv Ophthalmol 2007;52(Suppl 2):S144–54.  Back to cited text no. 18
    
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Nicolela MT. Clinical clues of vascular dysregulation and its association with glaucoma. Can J Ophthalmol 2008;43:337–41.  Back to cited text no. 19
    



 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4]



 

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