Zulu ocular biometry differs fundamentally from that of Europeans - A modelling analysis

The accuracy of ocular refraction calculations depends on reliable biometry and the validity of the models upon which the calculations are based. Most models are based on European eyes, so their validity in sub-Saharan Africans may be questioned, potentially contributing to suboptimal postoperative outcomes. Hence, this study developed an optical eye model tailored to a Zulu cohort.

Ocular biometry data were collected from 192 near-emmetropic (i.e., non-cycloplegic spherical equivalent within ±1D) young individuals of Zulu descent in Durban, South Africa. Key biometric parameters, including axial length, corneal thickness, anterior chamber depth, crystalline lens thickness and vitreous chamber depth, were measured and input into Bennett's and Royston's equations to develop the eye model. This model was subsequently compared to the eyes of 32 near-emmetropic young European adults that were used previously to help develop the SyntEyes model. Statistical analysis was performed to identify significant differences in ocular structural parameters between the models.

Zulu eyes exhibited marked differences compared to European eyes. On average, Zulu eyes had deeper anterior chambers (+0.28 mm, t-test, p < 0.001), thinner crystalline lenses (-0.19 mm, p < 0.001) and lower corneal power (-0.83 D, p = 0.001). However, the total ocular power of Zulu eyes was greater due to a more powerful crystalline lens (+2.60 D, p < 0.001). No significant difference in refractive error or axial length was observed between the two populations.

The ocular biometry of the Zulu population differs significantly from that of the European population, particularly in corneal and crystalline lens power, lens thickness and anterior chamber depth. This has important implications for intraocular lens power calculations, glaucoma risk assessment and other diagnostic procedures. Accurate, population-specific references are essential for optimising vision correction and enhancing ophthalmic healthcare outcomes in regions with populations underrepresented in the literature.