|Year : 2014 | Volume
| Issue : 2 | Page : 82-85
Estimation of the Eyeball Volume on Magnetic Resonance Images in Zaria, Nigeria
Philip Oluleke Ibinaiye1, C Obinna Maduforo2, Dominic Chinda3
1 Department of Radiology, Ahmadu Bello University Teaching Hospital, Zaria, Nigeria
2 Department of Radiology, University of Port Harcourt Teaching Hospital, Port Harcourt, Nigeria
3 Department of Ophthalmology, Ahmadu Bello University Teaching Hospital, Zaria, Nigeria
|Date of Submission||31-Jul-2013|
|Date of Acceptance||23-Feb-2014|
|Date of Web Publication||16-Jul-2014|
Philip Oluleke Ibinaiye
Department of Radiology, Ahmadu Bello University, Zaria
Background: Decrease or increase in eyeball volume (EV) may indicate ocular pathology. Unfortunately the reference values utilized for EV in Nigeria has been that of Caucasians. There is paucity of literature on EV measurements in Nigeria and none (to the best of our knowledge) on magnetic resonance imaging (MRI) EV biometry in Nigeria. Aim: To establish the normal EV in healthy population in Zaria using a reliable MR imaging. Patients and Methods: The EV volumes of 100 consecutive 'normal' patients who had MRI scan done (using Siemens MR imaging permanent magnet, 0.2T) were calculated. The dimensions were obtained at mid-ocular axial slices with maximum anterior-posterior dimension and maximum size of the eye lens. Results: The mean EV of the right eye was 6.75 ± 1.01 cm 3 while that of the left was 6.74 ± 0.95 cm 3 . The mean EV in the males' right eye was 6.86 ± 0.98cm 3 while that of the left eye was 6.97 ± 0.99 cm 3 . Whereas, the mean ± right VE in the females was 6.61 ± 1.03 cm 3 while that of the left eye was 6.52 ± 0.86. VE correlated with the patients' age with P < 0.001 for both sides. Conclusion: The EV of males is larger than that of females but not statistically significant. EV was observed to increase with age, but it declined after age 40 years. The study also established EV in a sample of normal population in Zaria with the hope that it will serve as reference values in that local environment.
Keywords: Magnetic resonance imaging, Normal eyeball volume, Zaria
|How to cite this article:|
Ibinaiye PO, Maduforo C O, Chinda D. Estimation of the Eyeball Volume on Magnetic Resonance Images in Zaria, Nigeria. Sub-Saharan Afr J Med 2014;1:82-5
|How to cite this URL:|
Ibinaiye PO, Maduforo C O, Chinda D. Estimation of the Eyeball Volume on Magnetic Resonance Images in Zaria, Nigeria. Sub-Saharan Afr J Med [serial online] 2014 [cited 2021 Jan 22];1:82-5. Available from: https://www.ssajm.org/text.asp?2014/1/2/82/136817
| Introduction|| |
Eyeball volume (EV) plays an important role in some ocular diseases such as microphthalmus, buphthalmus, macrophthalmus, congenital glaucoma, etc.  Therefore, it can be useful to know the eyeball volume in order to monitor the effects of some diseases and plan treatment or surgical application.  Consequently, attempts were made to determine the dimensions of the eyeball by utilizing various methods including radiography, angiography, ultrasonography, computed tomography, magnetic resonance imaging, and photography.  Gravimetric method of ocular volume measurement was described by Wales,  but this method requires enucleating a diseased eye and extrapolating the volume of the normal eyes from the value obtained. Gravimetric method is rather destructive and is not practicable in most clinical situations. Intra-ocular lens (IOL) Master can also be utilized in ophthalmological clinics to determine eyeball axial length measurements from which EV can be calculated.  However, it is only available in few ophthalmic clinics in our environment. 
Sectional imaging modalities have provided an opportunity for volumetric quantification of the VE.  MRI is the best method of EV measurement because it offers optimal soft tissue contrast resolution and multiplanar capability without the use of ionizing radiation. 
There is paucity of literature on VE measurements in Nigeria  and none (to the best of our knowledge) on MR imaging VE biometry in Nigeria. Consequently, most of the reference values utilized in Nigeria are based on Caucasian eyes.  In the present study, we estimated the volume of eyeball in normal healthy males and females using the MRI with the hope that our findings can serve as normal reference values for population in Zaria.
| Materials and Methods|| |
The study group consisted of 120 patients (67 males, 53 females) with age range of 1 month to 77-year old (mean, 30.31 ± 19 years) who were referred to MR imaging unit of radiology department of Ahmadu Bello University Teaching Hospital, Zaria, Nigeria, between January, 2010 and December, 2010, for brain MR imaging. All the subjects were thoroughly examined by an ophthalmologist, and were excluded if they had any history of serious head trauma, metabolic or systemic diseases and glaucoma or other ophthalmologic diseases such as microphthalmus, buphthalmus, and macrophthalmus. Twenty subjects were excluded from our study according to our criteria. In this study 100 (57 males and 43 females) subjects were analyzed. The participants' age ranged between 1 month and 77 years (mean 30.4 ± 19 years). The males' age ranged between 2 months and 77-years old while the females 1 month and 77-years old.
Approval for the study was granted by the ethical committee of our institution. All participants provided informed written consent.
The MR imaging was performed using 0.2 Tesla permanent MR imaging (Siemens, Wittelsbacherplatz, Germany) system with an orbital surface coil used for acquisition of images. The examination was carried out with subject in supine position. Children less than 10 years were sedated using intravenous diazepam and intramuscular paraldehyde to avoid movement during the scan. The radiofrequency coil (orbital surface coil) was then applied and the field of view centered on the nasion in the midline. T1- and T2-weighted spin echo sequences in the axial, coronal, and sagittal 3-mm thick sections with 0.3-mm intersection gap were obtained with MR system by the used of orbital surface coil. The scan range in the axial plane spanned from the foramen magnum to the vertex and the matrix size was 256 × 256.
The imaging of the orbit was performed sequentially with that of the brain. The axial plane corresponded to the line joining the genu and splenium of the corpus callosum while coronal plane was perpendicular to the same line, and sagittal plane was parallel to the corpus callosum. 
The EV was determined by first defined the margins of the eyeball by the outer border of the sclera and included the anterior chamber.  The slices chosen for eyeball measurements were mid-ocular slices showing the maximum axial size of the eyeball and which also showed the maximum size of the lens. Eyeball dimensions were obtained with axial length or anterior-posterior diameter of the eyeball (defined as the distance through the visual axis from the anterior corneal surface to the posterior wall of the choroid in axial view and it included the anterior chamber depth, lens thickness, and vitreous length). The width or transverse diameter was defined as the maximum transverse distance between the temporal and nasal ends of the eye in axial view [Figure 1]. These two dimensions were used to calculate the total volume of the globe. The dimensions were measured twice by the two researchers and the average recorded.
|Figure 1: T1W axial brain MRI at the level of the lens showing the sites of measurements|
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Although the eyeball is slightly ellipsoidal, it is assumed to be spherical for volume estimation. This reduced the error margin likely to be introduced. These measurements were recorded and the largest diameters were used to estimate the volume using the following formula: V = 4/3πr3 (cm 3 ),  where r = (AP + TR)/4; AP = anterio-posterior diameter (cm), that is, axial diameter of the eyeball, TR = transverse diameter (cm) of the eyeball.
The data was analyzed using SPSS software version 17 (SPSS Inc, Chicago) for statistical analysis. Values were expressed in terms of the mean and standard deviation (SD). The difference in VE between genders was analyzed using the independent t test. The differences of the estimated volumes obtained by right and left sides were compared using paired t test. Correlation between different parameters was tested by Pearson correlation test. The P < 0.05 is considered statistically significant.
| Results|| |
The subject's ethnic distribution, indication/provision diagnosis and MRI findings are presented in [Table 1]. While [Table 2] presents the summary of data for all subjects. Also in [Table 2], there was a strong correlation between age and both right and left EV (P = 0.0001). The mean, EV in males was 6.86 ± 0.98 cm 3 and 6.97 ± 0.99 on the right and left sides, respectively. The mean, EV in females was 6.61 ± 1.03 cm 3 and 6.52 ± 0.86 cm 3 on the right and left sides respectively. Both right and left EV estimates were larger in males than females. However, there were no statistically significant differences between genders and right and left EV (P = 0.06).
|Table 1: Subject's ethnic distribution, indication/ provision diagnosis and MRI fi ndings|
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|Table 2: The summary of the data of all subject and correlation between age and volume of the eyeball|
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[Table 3] showed that the EV in both sexes and in both eyes increases with advancing age until about 40 years of age when it starts to decline.
| Discussion|| |
The volume of the eyeball changes with advancing age as observed in this study. Our findings show significant correlation between age and EV for both eyes. Our study shows that increase in EV occurred from early childhood to about 40 years of age before it starts to decline. The previous studies by Han et al., and Wong et al., recorded 30 years and 50 years as ages the eye ball volume starts to decline, respectively. Racial differences may likely responsible for this discrepancy. , Priestly Smith  stated that the cornea of elderly is thinner than that of young age group which indicates eye undergoes changes with age.
The mean EV found in our study was less than those by Hahn et al., (9.26 cm 3 ), Thaller  (8.15 cm 3 ), Bites et al., (8.94 cm 3 ). However, the methods used by these researchers to determine EV were different. Hahn et al., and Bite et al., used CT images while Thaller  used a water displacement method to find the EV.
The mean EV found by Chau et al., was 6.70 cm 3 and 6.66 cm 3 on the right and left sides, respectively. This is similar to our estimated mean EV values of 6.75 cm 3 and 6.74 cm 3 recorded for right and left eyes, respectively. It is also noteworthy that Chau's study was carried out on magnetic resonance imaging (MRI) as in our study.
The right EV is slightly larger than the left by 0.15%, but this is not statistically significant (P = 0.06). This finding is in agreement with earlier observation that the difference between paired eyes is always less than 1%.  Consequently, if the volume of one eyeball is known, then the volume of the other eyeball can be extrapolated as it will fall within the calculated value of ± 1% of the known EV.
In this study we found that the mean EV is larger in males than females, although not statistically significant (P = 0.06). This finding is in agreement with that of Chau et al., they stated that volumes of the eyeballs showed no significant gender effects (P = 0.065). This may be because males' body habitus is generally bigger than that of females with concomitant increased size of the male organs compared to females.
Sectional imaging modalities have provided an opportunity for volumetric quantification of the EV. MRI offers optimal soft tissue contrast resolution and multiplanar capability without the use of ionizing radiation.  MR imaging also shows the shape of soft tissue like the eyeball excellently. EV plays an important role in some ocular diseases such as macrophthalmus, buphthalmus, microphthalmus, etc.  Congenital glaucoma is the result of developmental obstruction of intraocular fluid drainage, so that the pressure in the eye is raised and globe becomes enlarged.  Therefore, it can be useful to know the volume of eyeball in order to monitor the effects of some diseases and plan treatment or surgical application.
| Conclusions|| |
This study has established normal VE across the ages in a sample of normal population in Zaria with the hope that it will serve as normal reference values for that local environment.
The values of eyeball volume obtained in this study could not be used for Nigerian population as whole because the sample size was small and the study population was mainly Hausa/Fulani domiciled in Zaria and environs [Table 1].
We recommended that similar study should be carried out in various centers across the country in order to establish the normal eyeball volume across the age, ethnicity, and gender for Nigerian population.
| Acknowledgement|| |
The authors wish to acknowledge contributions of staff of ophthalmology department of Ahmadu Bello University Teaching Hospital, Zaria for the selection of subjects for the study. The authors also express their gratitude to members of the MRI unit, especially Mr. Emmanuel Nwokorie, nurses, and clerks of the department of Radiology Ahmadu Bello University Teaching Hospital, Zaria.
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[Table 1], [Table 2], [Table 3]