Ocular Biometry is an essential part of Ophthalmic evaluation of patients. Many eye diseases and conditions can be predicted by looking at the axial length, corneal curvature and anterior chamber depth of the eye. Researchers indicated that long axial length is associated with primary open angle glaucoma(POAG)(1) while short ocular axis and shallow anterior chamber predispose individuals to primary angle-closure glaucoma (PACG)(2).In a study done in India patients with POAG were found to have longer Axial length and flatter corneas as compared to age matched control(3). The Singapore Malay Eye Study (SMES) conducted by Shamira A Perera et al. in Malay population of Singapore, also demonstrated an association between increasing AL and POAG, thus suggesting axial myopia as a potential risk factor for POAG(4).
Refractive errors are major causes of visual impairment worldwide, (5) and a good understanding of ocular biometric parameters, like axial length (AL), is crucial for understanding the risk factors and determinants of ammetropia (6,7,8) .
Anterior chamber depth(ACD ) is an important parameter in the evaluation of the anterior segment of the eye. Central ACD less than 2.5 mm has been regarded as shallow ACD, which is a main risk factor for PACG. Measurement of axial ACD has been used in population screening for angle closure(9). In one study done in China the PACG prevalence was 25% when ACD is between 2.1–2.3 mm but the prevalence was 100% when ACD is less than 1.5 mm (10). Aung T et al also reported ACD as the strongest predictor of PACG(11) .
Another most important use of ocular biometry is for the calculation of the power of Intra ocular lenses implanted during cataract surgery. The quality of cataract surgery is largely dependent on implantation of the accurate power of Intra ocular lens which is variable for each patient undergoing the surgery. The critical step in ocular biometry to attain the desired post-operative refractive outcome requires standardization of techniques to ensure accurate measurements important in providing correct calculation of required IOL power for cataract surgery(12,13).
A-scan ultrasound is the traditional technique for measuring anterior chamber depth, axial length and lens thickness. It involves passing an ultrasonic beam via a transducer through the eye, and as this is returned after hitting intraocular structures a trace of ocular spikes is displayed on the monitor from the cornea to the orbital fat(14). Biometry values can be obtained either by contact (applanation), immersion or optical methods. The contact/applanation technique is a widely used method which requires placing an ultrasound probe on the central cornea; this slightly indents the surface leading to various degrees of corneal compressions which may introduce errors into the values(15).The immersion A-scan biometry uses a saline filled scleral (Prager) shell between the probe and the eye; it is relatively observer independent. The optical method is a non-contact technique by partial coherence interferometry (PCI) that is highly reproducible, observer-independent and therefore potentially more accurate(16).The immersion and optical methods give comparative results(17).
Ophthalmological epidemiology on biometry had been studied continuously on the world stage For example the Handan eye study(18) and the Beijing eye study(19) in the northern China, the Liwan eye study(20) in the southern China. In Nepal one study reported a mean axial length and IOL power to be 22.68 and 21.60 respectively(21).
In our Continent there are few studies on ocular Biometry. One study which was done in Nigeria revealed a mean axial length of the study groups to be 21.7(22).There are also few or no data on the average value of the main parameters of ocular biometry in Ethiopia in large population based study. so this research will provide a normative data on the ocular biometry of Ethiopian patients and also will be taken as reference for many patients in Africa. Knowing the average value of the axial length and the average power of the IOL is especially important in a resource limited countries like ours where there is an extreme scarcity of most important Ophthalmic instruments like automatic keratometer and A- SCAN.
The main objective of the study was to report on the main parameters of ocular biometry such as keratometry, axial length and anterior chamber depth and Intra ocular lens power of patients attending a cataract surgical program in Eastern Ethiopia.