|Year : 2015 | Volume
| Issue : 2 | Page : 31-38
Normal range values of ocular axial length in adult Sudanese population
Sahar Ibrahim Albashir, Mahgoub Saleem
Department of Ophthalmology, Faculty of Medicine, Al-Neelain University, Khartoum, Sudan
|Date of Web Publication||17-Dec-2015|
Department of Ophthalmology, Faculty of Medicine, Al-Neelain University, Khartoum
Source of Support: None, Conflict of Interest: None
Background: The axial length is one of the essential ocular biometric parameters which is to be done prior to any cataract surgery based on ultrasound. These ocular axial length (OAL) values can be influenced by sex, age, race, ethnicity, genetics, and refractive errors.
Objectives: The aim of this study is to determine the normal ranges values of OAL in adult Sudanese population and to define the effects of age, gender, and tribal ethnicity on axial length.
Materials and Methods: This is descriptive multi-center hospital-based study, carried out over a period of 6 months from January 2015 to June 2015. The study takes place in five study areas: Three in Khartoum and two in Omdorman. These centers are Khartoum Eye Hospital, Makkah Eye Complex, Alwalidain Eye Hospital, and Omdurman Military Hospital and Sudan Eye Center. The study population was recruited from patients presenting to the mentioned five Hospitals Biometric Departments or volunteers who accepted to be enrolled in the study. One thousand Sudanese adults participants (n = 1000), 507 female and 493 male, with ages ranging from 18 to 105 years were included. Patients with vitreoretinal diseases, intraocular surgery, recent trauma and staphyloma were excluded. All participants underwent systematic OAL measurements by A-scan ultrasonography. Effect of age, gender, and tribal ethnicity on OAL was analyzed.
Results: The study showed that the average axial length was 23.09 mm ranging from 18.13 mm to 29.09 mm. It was longer in males (average 23.29), ranging from 20.31 mm to 28.48 mm and shorter in females (average 22.81), ranging from 18.31 mm to 29.09 mm. In the four main Sudanese tribes, the Nubian group had the longest axial length (23.23 mm), followed by the African group (23.15 mm), and then the Arab group (23.09 mm). Bejja group had the shortest axial length (22.85 mm).
Conclusion: OAL in Sudanese adults was within the international standard but with a wider range (18.13–29.09 mm). Males' OAL was longer than the OAL of females. No significant age OAL variations, but the tribal ethnicity factor was clear, so tribal ethnicity had a major influence on Sudanese OAL.
Keywords: Bijja, cataract, Nubian group, ocular axial length, ocular biometry, staphyloma, tribal ethnicity
|How to cite this article:|
Albashir SI, Saleem M. Normal range values of ocular axial length in adult Sudanese population. Albasar Int J Ophthalmol 2015;3:31-8
| Introduction|| |
Cataract surgery is the most commonly performed surgical procedure in the world,,, especially on aging individuals, boasting an extremely high success rate. Modern cataract surgery has become a refractive process with very high patient postoperative expectations, so accurate preoperative ocular biometric assessments are the crucially significant issues for successful cataract surgery (Royal College of Ophthalmologists Cataract Surgery Guidelines, September 2010).
Ocular axial length (OAL) is one of the major variable basic ocular biometric parameters. It is defined as the distance from the posterior corneal surface to an interference peak corresponding to retinal pigment epithelium/Bruch's membrane., OAL has great impact on successful cataract surgery , and refractive corrective procedures, besides its diagnostic role of many ophthalmic conditions.
Error in OAL measurements is the most significant error in intraocular lens (IOL) power calculation, which can affect the surgery outcome and patient's expectations. Ocular biometric parameters, in practically OAL, can be influenced by race, ethnicity, and genetics, age, sex, and height  across different populations. Although there is no clear environmental or socioeconomically factors on change in OAL, however, Wong and his colleagues (Chinese Tanjong Pagar Survey, 2002) demonstrated an indirect role of education, socioeconomic status due to increase close work and reading, in elongation of OAL due to myopic shift.
There are close relationships between OAL and some other biometric values like central corneal thickness, anterior chamber depth (ACD), corneal refractive power, axial length of myopia, intraocular pressure (IOP) and susceptibility to glaucoma.
There is a positive correlation between OAL and ACD; in younger people where there is longer OAL, the ACD tends to be deeper. But in older people the ACD is found to be shallower and OAL is shorter OAL. Contrarily, there is an inverse correlation between OAL and the corneal power, age, and lens thickness, so the OAL is found to be shorter (shorter eyes) with thick lenses in older patients.
Also OAL plays an important role in refractive status in different age groups as both they have shared genetic loci, so as refractive errors are not uncommon in communities, and Sudan is not an exceptional; we need to plot Sudanese OAL's Map to direct our optical techno needs and business.
The mean adult values for OAL are 22–25 mm, which remain almost unaltered before the age of 40, then started to have slight but steady change towards hyperopia (shorter eye), after the 40 s.
In spite of the vast improvement in ophthalmic technology to invent error-free electronic biometric machines, still there are minor errors in OAL assessments  that occur due to variations in optical refraction  (hyperopic shift after the age of 40) and refractive index in different ocular media with age., IOL master partial coherence interferometry biometer is one of the most accurate machines; it was proved that it may yielded an OAL measuring error between −0.043 mm and +0.089 mm. Although these errors are quite small, but it may affect the IOL power calculation; 0.1 mm of OAL error corresponds to error in the power of the IOL around 0.25 D, these errors are expected to be higher for very high OAL values.
Although A-Scan, regular ultrasound, and IOL master are the popular machines for OAL measurements, OAL can also be measured by magnetic resonance imaging, which almost matches reliably with A-scan ultrasonography.
| Materials and Methods|| |
This is descriptive multi-center hospital-based study, carried out over a period of 6 months from January 2015 to June 2015. The study takes place in five study areas: Three in Khartoum and two in Omdorman (Sudan). These centers are Khartoum Eye Hospital, Makkah Eye Complex, Alwalidain Eye Hospital, Omdurman Military Hospital and Sudan Eye center. The study population was recruited from patients presenting to the mentioned five Hospitals Biometric Departments or volunteers who accepted to be enrolled in the study.
One thousand Sudanese adults Sudanese participants (n = 1000), 507 female and 493 male [Figure 1], with age ranging from 18 to 105 years were studied, from January to June 2015. Simple random sampling technique was adopted. Patients with vitreoretinal diseases, intraocular surgery, recent trauma and staphyloma were excluded. All participants underwent routine ophthalmic examination and systematic OAL measurements by A-scan ultrasonography. The effect of age, gender, and tribal ethnicity on OAL was analyzed.
The study subjects were classified into different ethnic and racial groups according to our modified. “Current Sudan Tribal composition;” and “Sir Harold MacMichael (1922) Sudan tribal classification in his History of the Sudan and some account of the people who proceeded them and the inhabiting Darfur."
The whole study individuals were grouped in five groups and other subgroups; as follows:,,,,,,,,,,
The Arab origin groups
- Ga'alin Groups: (Gaalin, Shaygia, Rubatab, Mirafab, Batahin, Bedayria, Gumoyia, Gemie, Geme'aab)
- Guhayna Groups: (Kawahla, Kinaniah, Salahalbia, Gaafrah, Arakia, Halaween, Shokriah, Kababeesh, Jabriah, Misayriah, Gowamaha, Hasaniah, Taaysha)
- Others: (Ashraf, Rikabia, Masalamya, Rashaida, Konooz, Hamran, Hawawer, Kenana, Magharba).
The African origin groups
- The non-Arab races of Darfur: (Fur, Bedayat, Kura'an, Zaghawa, Tama, Mido, Berti, Tungur, Dagu, Begu, Burghad, Mima, Mararit, Fallata, Masaleet, Erenga, Mun, Hadahid, Fertit, Tungur, Omba-Raru)
- Nubian tribes in Southern Kordufan
- Mapan tribes in Southern Blue Nile
- Angassana tribes in Southern Blue Nile
- Southern Nilotic tribes
- Western African group: (Hawsah, Brgaw, Falata, Barnu).
The Nubian groups in the far North
Danagla, Mahas, Halfaween.
The Bejja groups
Hadandawa, A'Marar, Beshare'een, Bane-Amir, Halnga.
Coptic, Mawaleeds, Ethiopians, Somalia's, Greece, etc.,
A modified “WHO world standard population distribution; age-structure for 10-year age groups (instead of 5-years)” was adopted  to design seven age groups: (1) 18–20 years, (2) 21–30 years, (3) 31–40 years, (4) 41–50 years, (5) 51–60 years, (6) 61–70 years, (7) the last age group was above 70 years [Table 1] and [Figure 2].
|Figure 2: Distribution of patients according to age age-structure groups|
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Data was analyzed by IBM SPSS Inc. (IBM SPSS Statistics) Software Group's Business Analytics Portfolio. The study was approved by Makkah Research Center ethics committee (MRCEC). Official letters were sent to the five hospitals administrations where the study was done. All participants were treated in accordance with the Declaration of Helsinki and verbally to each patient.
| Results|| |
In total, 1000 (n = 1000) Sudanese adults with diverse tribal origins were examined during this study. Both sexes were almost equal, with slight insignificant predominance of females. Out of the total, females were 507 individuals (n = 507; 50.7%) whereas males were 493 (n = 493; 49.3%) [Figure 1]. The mean age of the study group was 62.86 ± 22.86 years (range: 18–107 years). The numbers of subjects in the different seven age-structure groups resulted in 20 subjects (n = 20; 2%) in the age group below 20 years (18–20 years), 33(n = 33; 3.3%) in the age group (21–30) years, 22 (n = 22; 2.2%) in the age group (31–40) years, 91 (n = 91; 9.1%) in the age group (41–50) years, 246 (n = 246; 24.6%) in the age group (51–60) years, 361, as the majority (n = 361; 36.1%) in the age group (61–70) years, the last age group comprising 227 subjects (n = 227; 22.7%) in the age group above 70 years. These results comprised only 16.1% of the study groups were below the 5th decade while 83.4% were above the 5th decade of age, which appears the majority of older population [Table 1] and [Figure 2].
The tribal distribution scale had shown that the Arab origin groups represented the majority of the study population of 716 subjects (n = 716; 71.6%) whereas the African origin groups represented only 152 subjects (n = 152; 15.2%).
The Arab origin groups which encompass three sub-groups: The Ga'alin Groups represent 307 subjects (n = 307; 31.4%), Guhayna groups represent 367 subjects (n = 367; 37.8%) forming the majority of population within the Arab origin groups. The remaining other Arab origin groups collectively represent 42 subjects (n = 42; 4.1%).
The African origin groups constituting the minority of the whole study population as compared with the Arab origin groups; only 152 subjects (n = 152; 15.2%). Distributed as follows: 58 (n = 58; 5.8%) to non-Arab races of Darfur, 40 (n = 40; 4.0%) to Nubian tribes in Southern Kordufan; and 54 (5.4%) to Western African groups.
The Nubian groups in the far North represented 100 (n = 100; 10%). While the Bejja tribes in the Eastern Sudan represented only 15 subjects (n = 15; 1.5%) [Figure 3]. No study subject presented the fifth Sudanese minorities: Coptic, Mawaleeds, Somalia's, Greece.
Ocular axial length
The overall average of the OAL in the studied adult Sudanese population was computed to be 23.09 mm, ranging from 18.13 to 29.09 mm.
Altogether, Arab origin groups mean value of the OAL was 23.09 mm (males 23.37 mm and females 22.81 mm). Ga'alin group OAL was found to be 23.13 mm (males 23.51 mm and females 22.78 mm), that of Guhayna groups was 23.00 mm (males 23.27 mm and females 22.90 mm), and that of other Arab groups was 23.16 mm (males 23.34 mm and females 22.75 mm) [Table 2].
|Table 2: Average ocular axial length in both sexes of all Sudanese different tribes|
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The African origin groups OAL was found to be 23.15 mm (males 23.28 mm and females 22.67 mm), while the non-Arab races of Darfur was averaging OAL of 23.26 mm (males 23.28 mm and females 22.47 mm). The Nubian tribes in Southern Kordufan OAL was 22.92 mm (males 23.21 mm and females 22.55 mm) and that of Western African group being the longest OAL, was 23.29 mm (males 23.35 mm and females 23.01 mm) [Table 2].
No individuals were found from Mapan, Angassana, and Southern Nilotic from the division of “The African origin groups”.
The average OAL of the Nubian groups in the far North Sudan was 23.23 mm (males 23.49 mm and females 22.68 mm) [Table 1]. While the Bejja tribes average OAL was 22.85 mm being the shortest (males 23.10 mm and females 22.66 mm) [Table 2], Figure 4] and [Figure 5].
|Figure 4: Average ocular axial length in of all Sudanese different tribes|
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|Figure 5: Average ocular axial length in of all Sudanese different sub-tribes|
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| Discussion|| |
Racial differences in population regarding “Refractive Errors”, a survey which was done by late Duke-Elder (1949), who pointed that myopia which always represented biometrically by longer OAL, are common among Chinese, Japanese, Jewish, Egyptian, and Arabs. While he noted that Nubians and Sudanese are free from myopia, while most of the other Africans are more prone to hyperopia which indicative of shorter OAL.
OAL found to be 16–18 mm at birth., It enlarges to 20 mm by the end of 12 months with continuous rapid growth until 2 years age, then increases to 23 mm between the age of 3 years to adolescence, then slowly increases to 24 mm by adulthood till 24 years of age to be stable and remains fixed in the range of 24.00–25 mm in normal adult people, as reported by Goldschmidt (1992, cited by Bhardwaj and Rajeshbhai, in reference no. 1). However, Lim et al. (1992, cited by Obgeide and Omoti, in reference no. 15) reported that OAL remains practically unaltered in adult normal population till the fifth decade where it declines due to the start of the dramatic eye-aging processes.
Some physiological basic studies demonstrate too small (15–40 μm; micron) diurnal axial length fluctuations in some vertebrates and human eyes with the maximum OAL at mid-day. This is thought to be as part of numerous daily normal ocular physiological, noncircadian rhythms, which include variations in visual sensitivity, melatonin production, photoreceptor disc shedding, IOP, pupil size  and corneal epithelial thickness diurnal rhythms.,
In the current study, the average OAL of Sudanese adults was found to be 23.09 mm, which was longer by 0.49 mm (2.12%) than that of Nangia et al. in the adult population of central rural India (2010), where they recorded a mean OAL of 22.6 ± 0.91 mm (range, 18.22–34.20 mm). The difference between our lowest OAL and the upper one was 10.96 mm whereas the Indian one showing a difference of 15.98 mm. Both studies showed high range difference, more than 10 mm in the current study and more than 15 mm in the Indian one.
On the other hand, the Sudanese OAL was smaller by 0.05 mm (0.217%) than that of the adult Iranian (Shahroud, 2012) study of Hashemi et al. whom they recorded an OAL of 23.14 mm (ranging from 23.11 to 23.17 mm) in a larger study population of 4869 subjects. The difference between their lowest length and the upper one was only 0.06 mm which showed very low range difference which is far less than ours and that of the central rural India study (Nangia et al.; 2010):10.96–15.98 mm difference.
In all the above two results (the current and the central rural Indian studies ), there were large variations in the OAL; the possible explanation was that: The most affecting causes could be the diverse age [Figure 2] and tribal ethnicity ranges of both study samples. An assumption which can be supported by other similar studies: The Meiktila Eye Study in Rural Myanmar  and the “older White population study" of Fotedar et al. OAL measurements decrease with age, so the highest OAL is seen in younger adult groups (18–30 year) in contrary to old age group, as the lowest OAL value belongs to older age population of more than 70 years of age, a conclusion that supports the concept of older people move towards hyperopia by getting a decrease in their OAL when they get older.
Males in all groups had longer OAL than females [Figure 3], which trigger on the fact that males have bigger anatomical features and statues, as compared to their national female communities. Scientifically, this can be well explained by the normal biological feminine and masculine difference of facial and body features on the bases of sexual dimorphism in anthropometric measurements.,,,,
In the Arab group, OAL differs slightly among the subgroups. “Other Arabs group” subdivision had the longest axial length (23.16 mm) within the whole Arabic origin groups followed by Ga'alin group (23.13 mm), whereas Guhayna group had the smallest axial length (23.00 mm) within these Arabic origin groups. The difference between the three Arab origins subgroups was not so significant [Table 2] and [Figure 5].
The African origin group (23.15 mm) had slightly bigger OAL than the Arab origin group (23.09 mm). Bejja group had the smallest axial length (22.85 mm) [Table 2], [Figure 4] and [Figure 5].
In the main Sudanese tribal divisions, the Western African group had the longest OAL (23.29 mm), followed by the non-Arab races of Darfur (23.26) and then the Nubian groups in the far north of Sudan (23.23 mm). This result goes to some extent with other African studies which show longer African OAL (Eghosasere Lyamu; 2012) reported longer OAL in Nigerian adults (23.50 ± 0.70 mm).
The Nubians of south Kordufan had the smallest OAL (22.92 mm) unlike other African origin groups; these measurements were almost similar to the Bijja tribes OAL (22.85 mm). A fact needs to be studied anthropologically; it highlights the historical hypothesis of late Sir MacMichael  who postulated the migration of the The Nubians of South Kordufan back in history from the land of Nuba in North Sudan, a land where Bijja tribe partially used to be part of its inhabitant with some possibility of racial intermix between the two groups. This dialogic point can explain why The Nubians of south Kordufan and Bijja had these low OAL readings apart from other Sudanese population and other Africans (22.93, 22.85 mm). However, it may support Duke-Elder  (1949) assumption in some part that Africans are more prone to hyperopia [Table 2]; possible Duke-Elder data collection was from North African countries (Nubians and North Sudan). On the other hand, the longer OAL which is towards mild degrees of myopia will contradict with the late Duke-Elder survey, as we found that in the Africans groups, e.g. Western African group (23.29 mm), non-Arabs of Darfur (23.26 mm) and Nigerian adults (23.50 mm; Eghosasere Lyamu (2012); all they had loner OAL.
The overall average of the OAL in the studied adult Sudanese population was computed to be 23.09 mm, ranging from 18.13 to 29.09 mm coinciding with the average OAL of Arab origin groups.
The mean OAL measurements in normal some Asians and Western populations were found to be variable; the smallest reported OAL reported in Central Rural India was found to be the smallest as 22.60 mm; and the largest was the Australians OAL measurements (25.53 mm). The Sudanese average OAL being the third smallest (23.09 mm) after Central Rural India out of 15 different Nations, going towards some Asian populations like Myanmar, Iran, Jordan  and Mongolia [Table 3] and [Figure 6]. Koreans, Singaporean  and Chinese  were in the middle of whole world populations. The average OAL measurements in normal Egyptian were found by Abdelaziz and Mousa (Cairo University, 2014) to be 23.7 mm (21–30.6 mm), the third biggest [Table 3]. Denmark mean OAL was found to be 23.47 mm (23.74 males, 23.20 females), in Southern Norway the average OAL was 23.5 ± 0.9 mm. Nagra et al. (Birmingham, UK) found a higher OAL of 24.51 mm ± 1.47. Among the Asians, Arabs, and Western contraries, females recorded the lost OAL as comparison to our study.
|Figure 6: Average ocular axial length in different international nations|
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| Conclusion|| |
OAL in Sudanese adults was found to be statistically different between males and females. It was of great difference amongst the various Sudanese tribes.
OAL study in pediatrics would be complementary to this study to report the full spectrum of Sudanese population OAL Norms. OAL measurement is a necessary requirement before cataract surgery, thus bilateral measurement should be done imperatively. IOL suppliers can put in mind these racial variation points. Encourage public and academic institutions to work for “Sudanese Records of Norms.”
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]
[Table 1], [Table 2], [Table 3]