Introduction

Considerable variations in retinal vasculature in terms of waviness or tortuosity can be observed in young healthy subjects. Even though there is little evidence to support the prognostic value of a single fundoscopic examination ,incidental observations of remarkable degrees of straightness or tortuosity of retinal blood vessels may be considered as potential signs of morbidity. (Cheung et al.,2011) Decreased retinal arterial tortuosity has frequently been associated with hypertension. (Hayreh et al.,1989) Recent studies have demonstrated that less tortuous retinal arteries are linked with increased risk of death from ischaemic heart disease, independent of systolic blood pressure.( Witt et al.,2006) Few studies have been performed on the normal variation in retinal vessel tortuosity and its association with fitness and well being. The relative contribution of demographic and health indices on retinal vessel tortuosity, and the association between retinal vascular morphology and development of systemic risk factors in healthy adults can serve as a means of monitoring health before clinical disease outcomes

Methods

Participants
The cross-sectional study comprised of 80 Fundus (Right and Left eye) of 40 adults of north Indian origin (18 M, 22 F ; aged 18 to 45 years; mean age 35.1years ) who reported at ophthalmology dept of BHU ,Varanasi, UP, India during the period of June to August, 2012. Systemic exclusion criteria were known diabetes, hypertension or cardiovascular disease. Ophthalmic exclusion criteria included cataract and lens opacities near the optical axis of the eye and other manifest eye diseases. To avoid confounding of undiagnosed diabetes or residual hypertension, all participants underwent screening through an oral glucose tolerance test and Blood Pressure (BP) evaluation using digital monitors. Hypertension was defined as systolic BP >/=140 mmHg or diastolic BP >/=90 mmHg and /or current use of antihypertensive medicine. Individuals with systolic BP 120

Results

All eyes included had a visual acuity of at least 0.9.
Retinal arterial tortuosity grading demonstrated that 10(25%) subjects had predominantly straight arteries (grade1), 12(30%) had wavy arteries (grade 2), and 18 (45%) had tortuous arteries (grade 3). (Table 1)

Table 1

Retinal arteriolar tortuosity distribution pattern in a study group comprising of normotensives and pre-hypertensives.(N=80; Mean age 35.1 years): Vascular wavy pattern is inversely related with blood pressure values and all subjects with straight arteries are invariably pre-hypertensive.

Figure 2

Retinal arteriolar tortuosity distribution pattern (Straight:Wavy:Tortuous) in a study group comprising of normotensives (25:30:45%) and pre-hypertensives  (66.66: 20: 13.33%)

Table 2a

Gender dimorphism in retinal arteriolar tortuosity of young healthy Indian adults (left eyes) ; N=40; 18 M and 22F; Mean age 35.1 years.

*Gender wise Mann Whitney test

Table 2b

Gender dimorphism in retinal arteriolar tortuosity of young healthy Indian adults (right eyes) ; N=40; 18 M and 22F; Mean age 35.1 years.

*Gender wise Mann Whitney test ** p value significant

The arteriolar wavy pattern or tortuosity was similar on both eye sides in the study subjects except for Superior Temporal arteries where statistically significant differences were observed between right and left eyes. Left side was predominantly wavy while right side was mainly straight.(Table 3)

Table 3

Right versus left sided dimorphism in retinal arteriolar tortuosity of young healthy Indian adults (N=40; 18 M and 22F; Mean age 35.1 years)

*Wilcoxon sign rank test sidewise
** p value significant

Age was not a determinant of retinal arterial wavy layout in our study population.(Table 4)

Table 4

Correlation of tortuosity with age in retinal arteries of young healthy Indian adults (N=40, 18 M and 22F; mean age 35.1 years)

*Not significant for all, showing that age is not associated with changes in retinal arterial wavy patterns among young healthy adults.

Discussion

The results of the present study demonstrated that wide variations in retinal arterial tortuosity may mostly be explained by the effect of demographic factors and health indices. Our findings established that BP status, age, gender and even side of the eye may affect tortuoisity patterns, even though BP levels exerted the highest degree of correlation with tortuosity while age, sex and right vs left laterality had minimalistic association. Population based studies establish that retinal venules are significantly more tortuous than retinal arterioles and less arteriolar tortuosity is independently associated with older age, higher blood pressure and higher body mass index. (Cheung ,2011) Our findings disagree with earlier studies in context of having found no effect of age on retinal arterial tortuosity. Perhaps age does matter, as quoted by others; but only after a certain period of time and maturity. Our study subjects were quite young (mean age 35.1 years) and physically healthy. Advancing age does take its toll on retinal vasculature; but more frequently in old aged or diseased individuals, particularly diabetics and hypertensives. Another research on retinal vascular morphology had findings similar to ours and recorded no change in tortuosity with respect to age in subjects 'without' hypertension. (Wang et al.,2006) In this study, pre-hypertensives, who had BP levels bordering around the upper limit of the clinically 'normal' range had strong inclination for straight arteries; or in other words, one can assume that BP levels are inversely related to tortuosity and less tortuosity might be an indicator of future cardiovascular events. Cheung et al(2011) found that retinal arteriolar tortuosity alterations were associated with higher levels of BP and BodyMassIndex and that venular tortuosity was associated with lower HDL levels. The role of arterial hypertension in modulating retinal arterial caliber, dilation and tortuosity is particularly interesting. Experiments on canines show that in response to increased transmural pressure, carotid artery dilates and elongates. (Van,1977) Qualitatively, one would naturally expect such effects from a flaccid elastic tube and observation of such passive behaviour in retinal arteries may indicate exhausted auto regulatory capacity in hypertensives, leading to arterial straightening. The exact mechanisms underlying the development and later modulation of the retinal vascular network are largely unknown. Retinal arterial tortuosity demonstrates strong heritability without adjustment for covariates among first order blood relations; especially twins.( Taarnh

Conclusion

The retina is a unique site where 'in vivo' microvasculature can be directly visualized and monitored repeatedly. Advances in retinal imaging techniques have facilitated the development of computer-assisted methods to measure and quantify subtle variations and abnormalities in the retinal microvasculature. These assessments can be applied to large populations in the community and clinic settings. Retinal arteriolar tortuosity is variable; it may change with age, gender, right to left laterality and ethnicity. Fluctuations in BP levels strongly affect vascular morphology even in normotensives, with a predominantly straightening effect. Fundus photography may be used in the evaluation of a persons