Systemic hypertension remains the most prevalent cardiovascular risk factor in indigenous African population and a major cause of cardiovascular events. This prospective cross sectional study evaluated common complications of the eye and the kidneys among hypertensive individuals. The prevalence of hypertensive retinopathy among the study participants was 78 %. This prevalence is comparable with that of Ladipo [8] who reported a prevalence of over 70 % among Nigeria hypertensive patients. Our result is also similar to prevalence of retinopathy reported among black hypertensive patients in other African countries [9, 12, 13], but higher than results among hypertensive patients in Europe [14] and blacks in United States of America [15]. On the other hand, our finding contrasts that of Akinkugbe [7] who reported that hypertensive retinopathy was a rare occurrence among African patients. Perhaps, patients’ selection and sample size may account for this difference as Akinkugbe’s study was limited by small sample size and heterogeneous nature of his sample population. Complications of hypertension such as LVH, stroke and kidney failure have been reported to be commoner among Blacks than the Whites; and retinal changes may not be an exception as shown in our study. The high prevalence of retinopathy (an indication of changes in the cerebral arteries) among study participants may also explain why there is high prevalence of stroke in our hypertensive population [16].
Patients who had retinopathy are older than those with normal retinal examination and positive correlation was observed between age and retinopathy. Age has been demonstrated as an independent predictor of retinopathy in patients with hypertension in other studies [17, 18]. Age together with other factors such as duration of hypertension, BMI, total cholesterol, LDL-c and C-reactive protein correlated with retinal changes in our patients. The clustering of cardiovascular risk factors in the patients studied could account for high prevalence of hypertensive retinopathy.
Blood pressure indices (systolic and diastolic blood pressures) have been found to be associated with risk of development of hypertensive retinal changes [19, 20]. This is because hypertensive retinopathy is a reflection of severity of blood pressure elevation and control over a period of time. However, systolic and diastolic blood pressures were similar between patients with retinopathy and those without in our study.
Analysis of renal function among the study participants showed that eGFR was lower (46.2 ml/min/1.73) in those with retinopathy than those without (55.9 ml/min/1.73), p = 0.019. Similarly, a significant negative correlation was observed between the presence of retinopathy and eGFR (R = −0.26, P = 0.001). These results show that a significant number of our hypertensive patients had reduction in their renal function and this may occur simultaneous with other end organ consequence of the disease including retinal changes. In addition, ACR showed that a significant number of the patients studied had albuminuria which is an indication of glomerular dysfunction [21]. When patients with ACR ≤ 300 mg/g were compared with those with ACR >300 mg/g, the latter have higher percentage of grades II-IV retinopathy, higher levels of serum uric acid, C-reactive protein and dyslipidaemia than the former. This is an indication of a more severe disease among those with ACR > 300 mg/g than those with ACR ≤300 mg/g. Elevated serum uric acid level is associated with increased risk of chronic kidney disease [22]. Long standing hypertension is associated with vascular changes (arteriosclerosis) which occur in all organs of the body including the eyes. Therefore, the presence of hypertensive retinopathy detected at fundoscopy may be an indication for a more extensive evaluation of function of other target organs in hypertension such as the kidneys [23].
Multi-variable adjusted odds ratios showed increased probability of retinopathy with age (odds ratio-1.08, p = 0.001) and body mass index (odds ratio-1.20, p = 0.013). Obesity is considered to be a major cardiovascular risk factor and microalbuminuria is an indication of renal disease. Indeed, retinopathy, LVH and microalbuminuria are considered as evidence of target organ damage in systemic hypertension. Our study further confirmed the beneficial role of ACEIs in the management of systemic hypertension [24]. It is worthy of note that patients on drug combinations including ACEIs had lower ACR compared with those not on this drug. ACEIs protect the kidneys and can prevent or delay onset of proteinuria in kidney disease.
This study was limited by over representation of women in our study participants which is a reflection of health seeking behaviours among hypertensive patients seen in our practice. Therefore, it may be difficult to generalize our result to our population. Secondly, direct ophalmoscopy was employed in the assessment of the retina in our patients. Although, this is not inferior to retinal photographs but might have provided opportunity for further reviews.