Computed tomography obtained adult orbital and eyeball volumes in relation to age and gender at Moi Teaching and Referral Hospital.

Abstract

Background: The orbit is an intricate structure on the upper part of the face that houses the eyeball, muscles, optic nerve, lacrimal gland, orbital fat, blood vessels and nerves. Dimensions and volumes of the orbit and eyeball have not been clearly elaborated in the African population. They are crucial to ophthalmologists, reconstructive surgeons, radiologists and designers of eye protective equipment and prosthesis. The dimensions and volumes differ with various demographic factors such as age, gender and ethnicity. Few studies have been done in Sub-Saharan Africa and in the local Kenyan population. Earlier measurements were two dimensional (2D) measured directly on cadavers or skulls, afterwards volumes were obtained using mathematical formulae. The advent of three dimensional (3D) imaging such as Computed Tomography (CT) has made it possible to accurately estimate orbital and eyeball volumes using computer software. This study aims to establish the orbital and eyeball volumes for the local black Kenyan population in relation to age and gender for use in orbit-ocular related surgery, diagnosis of orbit-ocular disease and manufacture of prosthesis as well as protective equipment. Objective: To determine adult orbital and eyeball volumes in relation to age and gender at Moi Teaching and Referral Hospital using CT scan. Methods: This was a cross sectional study done at the Department of Radiology and Imaging, Moi Teaching and Referral Hospital between 1st September 2021 and 31st August 2022. Sample size of 475 adult participants was determined using Naduvilath et al, (2000) formula for estimating sample size for ophthalmology studies from a population of 1796 patients which was the total number of patients done CT scanning in the selected CT room in the previous year. Systematic random sampling was used where every third patient was selected. They were then screened for orbital and ocular anomalies and those with abnormal findings excluded. Patients underwent head CT scan at the Philips 64 slice CT scan room using protocol for the orbit. Images were then stored in a Digital Versatile Disk Read Only Memory (DVD-ROM). The discs were then singly loaded to a computer and volumes obtained using the gold standard manual segmentation method with assistance of the Eclipse software version 16.1 by tracing the edge contours of both the orbit and eyeball in two subsequent steps for each structure. A structured questionnaire was used to record data which was then entered to an Excel sheet. Continuous variables were analyzed using descriptive statistics of mean, median, standard deviation and interquartile range. Categorical variables were presented in frequency tables. Chi square and Pearson correlation was used to test for associations. A p-value of <0.05 was regarded as statistically significant. Results: The study included 458 participants with a mean age of 41.1 ± 20 years and median age of 35 years. The youngest patient was 18 years old while the oldest was 98 years old. The number of male patients was 291 (63.5%). The mean volume of the male orbit was 22.57 ± 2.98 cm³. The female orbit was smaller measuring 21.47 ± 2.87 cm³ with the difference being statistically significant (p<0.001 for both orbits). The eyeball volume for females was 5.44 ± 0.93 cm³ while that of males measured 5.41 ± 0.93 cm³ with the difference being not statistically significant (p=0.802 for the right eye, p=0.647 for left eye). There was an associated increase in orbital volume with age (r=0.0932, p=0.046 for the right orbit, r=0.089, p<0.057 for the left orbit) with no statistical significance. There was an associated decrease in eyeball volume with age but with both sides having no statistical significance (r=-0.024, p=0.612 for the right eyeball, r=-0.039, p=0.405 for the left eyeball). Conclusion: The male orbital volume was larger with a mean of 22.57 ± 2.98 cm³, while that of females had a mean of 21.47± 2.87 cm³. There was no difference in eyeball volume measurements among males and females measuring 5.41 ± 0.93 cm³ and 5.44 ± 1.14 cm³ respectively. There was no significant difference of eyeball volume with age for both genders, while there was decrease in size with increase in age for both genders. Recommendation: The observed variation of orbital volumes with gender should be taken into consideration in orbit-ocular clinical practice and implant manufacture.