context of Gypsies and Travellers
3.7 The relevance of notions of ‘ the other’
3.7.4 The ‘other’s other’
ALOKA proSound SSD-3500 ultrasound scanner with 7.5MHz linear array transducer was used for the study.
After the procedure had been explained and consent obtained from the participants, they were asked to lie in the supine position with eyes closed but not squeezing the eyelids and were requested to look straight ahead. Then, copious coupling gel was applied over the closed eyelid and a 7.5MHz linear transducer was placed over the eyelid.
Extra care was taken in order not to indent the anterior surface of the cornea by gently put the probe on the eyelid. The depth was adjusted for optimum visualization of the globe. Gain was also adjusted to achieve acceptable imaging. Both globes were scanned in both vertical and horizontal planes.
The vertical scan was obtained by placing the probe face directly over the center of the cornea. It was the easiest orientation to identify because the resulting B-scan image included the lens and was bisected by the optic nerve
Commented [x8]:
Who did these? In the Radiology Department. If not done by you, then who? Who paid for it? How the you ensure compliance?
Commented [x9]: With head supported or unsupported? Was the procedure explained or why not explained before instruction?
Did you confirm vision in both eyes before your scan?
Commented [x10]: Describe its orientation of images as described for Horizontal and vertical scans
displaying the anterior portion of the eye at the top of the screen and the optic nerve at the bottom (Fig. 3). The measurements of the axial length were taken from the anterior surface of the cornea to the retina along visual axis of the eye with iris, lens and the optic nerve as the landmarks.
In the horizontal B-scan, the probe was placed over the eyelids with the pointer of the probe placed in the direction of the operator. The ultrasound beam was directed through the vitreous traversing the lens and producing a cross-section of the eye that resulted in an image with the temporal and nasal aspects of the globe displayed. The maximum transverse diameter of the eyeball in this plane represented the width while the anteroposterior (AP) diameter represented the distance from the cornea to the retina (Fig 4).
Both eyes were assessed with two readings taken for each measurement. The mean values of these readings were used to compute the ocular volume.
Ocular volume was determined from anteroposterior diameter (AP), width and axial length using ellipsoid formula as follows:
Ocular volume =/6 x anteroposterior diameter x width x axial length. (= 22/7)
.
Figure 3: Ultrasound scan of the eye in vertical plane showing measurement of the axial length (arrow) from the anterior surface of the cornea (a) to the retina (b) along visual axis of the eye with iris (c), lens (d) and the optic nerve (e) as landmarks.
Axial length a
c d
b
e
Figure 4: Ultrasound scan of the eye in horizontal plane showing biometric measurements of the width and anteroposterior (AP) diameter (white lines).
The width measures the maximum transverse diameter of the eyeball while the AP diameter measures the distance from the anterior surface of the cornea (a) through the centre of the iris (b) and the lens (c) to the retina (d).
Anteroposterior diameter
Width a
b c
d
Limitations of Study
The sample was not sufficiently heterogeneous due to the fact that the study population in this study consisted of civil servants alone. This limited heterogeneity in participants’ demographic characteristics which could have affected both the nature and the extent of the variables.
Secondly, due to the time limit, this study was conducted on a small size of population. Therefore, to generalise the results for larger groups, the study should have involved more participants in all the geopolitical zones of the country.
RESULTS
Four hundred participants were recruited into the study. The age distribution is presented in Table 1 & 2 and Figure 5. The age of participants ranged from 25 to 60 years with a mean age of 38.8 ± 9.3 years and a modal age of 29 years. Participants within the age group 30-39 years constituted the majority (n=150 or 37.5%) of the study population, followed by those within the 40-49 years age group (n=114 or 28.5%).
The gender distribution is shown in Figure 6. Two hundred and forty two (60.5%) were males while 158 (39.5%) were females. The mean ages were 38.8 ± 9.2 years and 38.7 ± 9.3years in males and females respectively.
There was no statistically significant difference in age distribution between the genders (P=0.849 for independent t-test) (Table 3). The gender distribution of mean values of all the variables is shown in table 4 and revealed that mean age, height, weight and ocular volumes were higher in males while mean BMI was higher in females.
Table 5 shows statistical difference in mean ocular volumes between right and left eyes in both sexes. Significant differences (p <0.05) were found in both sexes.
The mean eyeball volume for both sexes across all age groups is presented in Tables 6 & 7. The mean eyeball volume was shown to be larger in males than females. (Males: Right eye=5.71cm3, Left eye=5.62cm3, Females: Right eye=5.58 cm3, Left eye= 5.53cm3).
Table 6 and 7 also show that there was a gradual increase in eyeball volume with age in both males and females up to the fourth decade after which there was a gradual reduction. The finding was more pronounced in males.
Table 8 shows that the ocular volumes were found to be larger on the right than left in all age groups. However, the differences were statistically significant (P<0.05).
Table 9 demonstrates decreased ocular volume in the age group above 40 years in both males and females. The differences were statistically significant (p<0.05). The group above 40 years was shorter in both males and females (male; p=0.639, female; p=0.303). The group above 40 years was heavier in both males and females. However the differences were not statistically significant (male; p=0.279, female; p=0.552). The group above 40 years was more obese in both males and females. There was statistically significant differences in both males and females (male; p=0.010, female;
p=0.019).
With respect to the relationship between ocular volume and BMI, the data was grouped into two with upper limit of normal BMI (24.9kg/m2) set as the reference point (Table 11). The group with the BMI value less than or equal to 24.9kg/m2 had smaller ocular volumes in both right and left eyes. The result showed statistically significant differences in the ocular volumes in both eyes (p=0.013, p=0.047).
The Pearson correlation of all the variables with ocular volumes is presented in table 12 and showed positive correlations with all the variables in decreasing order as follows; weight (r= 0.492), height (r =0.473), age (r=0.325) and BMI (r=0.303).
Scatter plots of each variable are presented in figure 7-10 which also showed positive correlations with ocular volume in this order (weight > height > age >
BMI).
Figure 5: Bar chart showing age distribution of participants.
78(19.5%)
150(37.5%)
114(28.5%)
48(12.0%)
10(2.5%) 0
20 40 60 80 100 120 140 160
20-29 30-29 40-49 50-59 >60
Frequency
Age (yrs)
Figure 6: Pie chart showing gender distribution of participants.
Male 242 60.5%
Female 158 39.5%
Table1: Age and sex distribution of participants Age group Frequency (N)
(Years) Males (%) Females (%) Total (%) 20-29 43 (17.8) 35 (22.2) 78 (19.5) 30-39 97 (40.1) 53 (33.5) 150 (37.5) 40-49 65 (26.9) 49 (31.0) 114 (28.5) 50-59 32 (13.2) 16 (10.1) 48 (12.0)
≥60 5 (2.1) 5 (3.2) 10 (2.5) Total 242 (60.5) 158 (39.5) 400 (100.0)
Table 2: Age and gender distribution of the participants Gender Frequency (%) Mean Age
(Years)
Minimum Maximum
Males 242 (60.5) 38.8±9.2 26 60
Females 158 (39.5) 38.7±9.3 25 60
N=400
Table 3: T-test of mean age between males and females Gender Frequency (%) Mean Age
(Years)
t-test P-value Males 242 (60.5) 38.8±9.2
Females 158 (39.5) 38.7±9.3 0.191 0.849
Table 4: Gender distribution of mean values of the age and anthropometric parameters
Variables Age (Years) Height(m) Weight(Kg) BMI(Kg/m2) Males 38.8±9.2 1.69±0.06 70.56±6.52 24.71±1.38
Females 38.7±9.3 1.64±0.06 67.03±6.36 24.92±1.63
T/Mean 38.8±9.3 1.67±0.06 68.79±6.44 24.81±1.51
Table 5: Mean ocular volume in the right and left eyes in both sexes and statistical significance (independent t -test)
Ocular Volume(cm3)
Gender Right Left t- test P-value
Males 5.71±0.16 5.62±0.17 6.650 0.000
Females 5.58±0.16 5.53±0.16 3.333 0.001
Table 6: Mean ocular volume for both eyes across age groups in both male and female participants
Age (Years)
Sex Frequency Ocular Volume (cm3) Right Left
20-29 Males 43 5.61±0.08 5.52±0.10
Females 35 5.41±0.20 5.39±0.17
30-39 Males 97 5.76±0.16 5.67±0.19
Females 53 5.56±0.12 5.45±0.13
40-49 Males 65 5.88±0.15 5.73±0.18
Females 49 5.69±0.04 5.67±0.05
50-59 Males 32 5.72±0.04 5.65±0.07
Females 16 5.60±0.03 5.52±0.05
≥60 Males 5 5.57±0.06 5.53±0.01
Females 5 5.65±0.02 5.62±0.04
Total Males 242 5.71±0.10 5.62±0.11
Average 5.67±0.11
Total Average
Females 158 5.58±0.08
5.56±09
5.53±0.09
Table 7: Comparison of right and left ocular volumes of the study population across age groups with statistical significance
Ocular Volume(cm3) t-test P-value Age Group
(Years)
Frequency Right Left
20-29 78 5.52±0.18 5.46±0.15 7.625 0.000
30-39 150 5.69±0.18 5.59±0.20 14.688 0.000
40-49 114 5.80±0.15 5.70±0.15 5.375 0.000
50-59 48 5.68±0.07 5.61±0.09 10.870 0.000
≥60 10 5.61±0.06 5.58±0.05 2.616 0.028
Table 8: Age group distribution of all the variables below and above 40 years and statistical significance.
Sex ≤40years >40years t-test p-value Right Ocular Volume(cm3) Males 5.82±0.16 5.72±0.16 4.278 0.000 Right Ocular Volume(cm3) Females 5.69±0.17 5.51±0.05 6.932 0.000 Left Ocular Volume(cm3) Males 5.69±0.18 5.64±0.17 2.068 0.042 Left Ocular Volume(cm3) Females 5.58±0.16 5.50±0.08 8.732 0.000
Height(m) Males 1.70±0.06 1.69±0.06 0.470 0.639
Height(m) Females 1.65±0.05 1.64±0.08 1.041 0.303
Weight(Kg) Males 70.42±7.11 71.53±5.77 1.088 0.279 Weight(Kg) Females 67.00±6.55 67.83±6.26 0.599 0.552 BMI(Kg/m2) Males 24.37±1.52 25.04±1.18 2.650 0.010 BMI(Kg/m2) Females 24.61±1.57 24.91±1.81 2.420 0.019
Table 9: Ocular Volume and BMI
Ocular volume(cm3)
BMI(Kg/m2) t- test p-value Slim—
standard (BMI≤ 24.9)
Overweight—
obese(BMI>24.9)
Right 5.63±0.17 5.71±0.20 3.998 0.013
Left 5.55±0.17 5.64±0.20 4.152 0.047
Table 10: Pearson correlation of all the variables with ocular volume
Parameter Ocular Volume R p-value
Age Right ocular Volume 0.325 0.000 Left Ocular Volume 0.288 0.000 Height
Right ocular Volume 0.473 0.000 Left Ocular Volume 0.425 0.000 Weight
Right ocular Volume 0.492 0.000 Left Ocular Volume 0.563 0.000 BMI
Right ocular Volume 0.303 0.000 Left Ocular Volume 0.297 0.000
Figure 7: Scatter plot showing relationship between ocular volume and age.
42 Age (years) Ocular volume (cm3)
Figure 8: Scatter plot showing relationship between ocular volume and height.
43
Height (m) Ocular volume (cm3)
Figure 9: Scatter plot showing relationship between ocular volume and weight.
44
Ocular volume (cm3)
Weight (kg)
Figure 10: Scatter plot showing relationship between ocular volume and BMI.
45 BMI (kg /m2) Ocular volume (cm3)
DISCUSSION
Ultrasonography was used in this study to determine the ocular volume due to its non-invasiveness, ease of access, quick and reliable information and real-time characteristics. In addition, US is cheap, readily available, easy to perform, and can be carried out easily in the clinic setting. Thus, US is quite often, the first imaging modality used in eye and orbit assessment where direct clinical assessment is impossible or of little value4,11.
The age range of the participants was 25 to 60 years with a mean age of 38.8 years (SD ± 9.3) and modal age of 29 years. This may be due to recent recruitment of young new staff in the last 3 years in UITH. Participants within the age group 30-39 years constituted the majority (n=150 or 37.5%) of the study population, followed by those within the age group 40-49 years (n=114 or 28.5%). This may be due to the fact that these age groups constitute the bulk of the workforce of the Federal Civil Service.
There were more male participants (60.5%) than females (39.5%) in this study. This finding is contrary to the observation made by Ogbeide et al4 in South-South Nigeria whereby more females (62%) were included in the study population than males (38%). The gender distribution of mean values of all the variables showed mean height, weight and ocular volumes that were higher in males than females while mean age and BMI were higher in females.
Previous studies have shown that males were generally taller and have larger ocular volume44,46,47. The higher BMI in females may be due to hormonal
influence which predisposes them to obesity which has been reported to be around the waist in black women50.
The ocular volume changes during human lifetime as observed in this study51. This study showed that there was a gradual increase in eyeball volume with age in both males and females up to the fourth decade after which there was a slight reduction. Similarly, Ogbeide and Omoti4 in a study carried out in Benin City, South-South zone of Nigeria using ultrasound also reported gradual decrease in ocular volume after the 4th decade which agrees with results from the present study carried out in the North-Central zone of Nigeria.
This may be due to the fact these two studies were conducted in the same geographical location. Contrary to this, Igbinedion et al51 in a study carried out in Benin City using CT reported decrease in ocular volume after the 5th decade. This may be due to different imaging modalities use in both studies.
In addition, the growth of the eyeball has been reported to be similar to the growth curve of the brain and central nervous system rather than to the general body growth and that the eye shares with the brain the peculiarity of having a precocious growth20,26.
In contrast, Hahn et al16 in a study carried out in United Kingdom reported that rapid growth of the eyeball was noted during the first 24 months of age reaching its peak at the third decade, suggesting an earlier age at which maximum ocular diameter is reached after which there was a reduction.
Lim et al26 however, reported a decrease in eyeball diameters and volume at the 6th decade in a study carried out in South Korea. This present study
however, showed positive correlation between ocular volume and age (r=0.325).
Furthermore, the measurement of eyeball volume in all the studies has not been done using a universal method4. The difference being that the eyeball has been assumed to be either slightly ellipsoidal or spherical for eyeball volume estimation4. Many authors had also used different imaging modalities and different techniques to estimate ocular volume.
US has also been used for ocular volume determination by different authors using different methods and modes. Fanny et al25 and Osuobeni et al27 made use of A-mode ultrasound while Ogbeide and Omoti4 used B-mode ultrasound. B-mode ultrasound was also used for the estimation of ocular volume in this study.
The differences in ocular volume among workers who used ultrasonography may be due to age group studied, racial variations in eyeball sizes, method of eyeball diameter measurement (contact or non-contact, A- or B-mode ultrasonography), or a combination of all these factors4.
All these factors explain the different mathematical formulae used to calculate eyeball volume in different studies and the resultant difficulty to corroborate the findings in these studies. Furthermore, the eyeball volume was usually estimated with measurement of only one or two or three eyeball diameters1. Ogbeide and Omoti4 used two eyeball diameters for the estimation of ocular volume.
The values obtained by Ogbeide and Omoti4 were 5.43±0.28 and 5.31±0.37 cm3 in males and females respectively while in this present study 5.67±0.11 and 5.56±0.09cm3 were recorded in males and females respectively. The difference observed between the two studies may be due to method of eyeball diameter measurement or the age group studied or difference in the gender distribution of the study population or a combination of all these factors.
Studies done have showed that the calculation of all three diameters as done in this study have a better result in estimation of eyeball volumetry16,52.
In this study, ocular volume was higher in males across all age groups.
This is consistent with other previous studies that reported larger ocular volume in males than females4,30,45. This may be due to the fact that anthropometric parameters (height, weight etc.) have been shown to be associated with the increase in ocular volume and these prarameters are usually higher in males26-30,53,54. Contrary to this finding, Chau et al18 stated that volumes of the eyeballs showed no significant gender difference (p>0.05).
The mean eyeball volume reported in this study was less than what has been reported in several studies in Caucasian populations16,18,28-30,45. The mean eyeball volume in the Caucasians ranges from 6.70cm3 to 9.26cm
16,18,28-30,45.. This wide range might be due to different imaging modalities and methods used as well as racial differences16,18,20,28-30.
Ocular biometric parameters and their anthropometric and physiological determinants are known to vary considerably across racial groups and populations29,53. Recent population-based studies have suggested that the
dimensions of the eyeball are associated with general anthropometric parameters such as body height29,45,46. Body height showed significant relationship with ocular parameters in the previous studies45,46,53. In the present study, body height also showed positive correlation with ocular volume confirming the findings of the previous studies (r=0.473). In the Singaporean Tanjong Pagar Study, adult height was related to the size of the eye and it was observed that taller persons were more likely to have longer globes, deeper anterior chambers, thinner lenses and flatter corneas28. Similarly, the ocular volume was also found to be larger in taller participants in this study.
In the Meiktila Eye Study (Myanmar), body weight was significantly correlated with age, gender, corneal curvature, axial length, anterior chamber depth, lens thickness and vitreous chamber length46. Song et al14 also reported increased in ocular dimensions with weight. Ocular volume also showed strong correlation with body weight in this present study (r=0.492).
BMI is an anthropometric measure that de-emphasises the effect of height on body weight and correlates closely with the degree of obesity27. In this study, obese participants had larger ocular volume than those with normal BMI. This finding is consistent with Wong et al28 observation whereby the heavier and more obese participants had larger ocular volume. In addition, the current study also showed positive correlation between ocular volume and BMI (r=0.303).
CONCLUSION
This study has provided ocular volumes in a sample of Nigerian adults that can be used as reference values especially in North Central Nigeria.
These values were lower than what has been reported in the Caucasian eyes.
There was gradual increase in ocular volume with age reaching the peak at the 4th decade.
The right ocular volume was larger than the left in all age groups. The ocular volume was larger in males than females. This study also showed positive correlation between ocular volume and weight, height, sex, age and BMI in decreasing order.
These results may be of help in recognising eye abnormalities such as microphthalmos and macrophthalmos. It may also assist in early detection of refractive errors as well as in monitoring changes in ocular dimensions following treatment of some ocular pathologies with subsequent improvement in prognosis.
This study was able to determine the ocular volume and its relationship to age, sex, body height, body weight and body mass index (BMI), among the black Africans in Ilorin, North Central zone of Nigeria which may serve as reference values among Nigerian adults.
RECOMMENDATIONS
Variation in eyeball volume among those who used ultrasonography may be due to racial differences in eyeball sizes, method of eyeball diameter measurement (contact or non-contact, A- or B- mode ultrasonography, two or three eyeball diameter measurements), age group studied or a combination of all these factors. Therefore, a multi-centre controlled study involving the six geopolitical zones in Nigeria is recommended in order to generate more generally acceptable reference values among Nigerians.
The significant correlation of body weight and height with ocular volume in this study may indicate that the inclusion of body weight and height in the list of diagnostic variables and risk factors of some ocular diseases may be helpful. This may be an area for further research.
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