Animal models of cataract serve as essential instruments for investigating pathological mechanisms and evaluating pharmacological interventions. The precision of lens opacity grading is contingent upon the congruence between anatomical characteristics and the employed grading system. Presently, clinical grading frameworks are primarily developed based on human ocular anatomy; however, notable anatomical disparities exist among animal species. For instance, the mouse lens diameter measures approximately 1.2 ± 0.1 mm, in contrast to the human lens diameter of 8.5–9.5 mm, with mice exhibiting a relatively smaller nuclear region. Similarly, the corneal curvature in rabbits is 7.2 ± 0.1 mm compared to 8.0 ± 0.2 mm in humans, and the zebrafish lens lacks the conventional nucleus-cortex differentiation observed in mammals. These anatomical differences contribute to issues such as dimensional redundancy, detection bias, and grading distortion when applying human-based clinical grading systems to animal models. This review article examines various methods for inducing cataracts in animal models, systematically evaluates how the aforementioned anatomical variations affect the suitability of existing grading systems, and proposes tailored strategies to enhance grading accuracy. Specifically, it recommends employing a modified Lens Opacities Classification System III (LOCS III) or a simplified grading approach for mice, developing a grading system focused on nuclear opacity for rabbits, and utilizing grayscale value quantification techniques for zebrafish. These customized methodologies aim to establish more precise grading standards to support cataract research utilizing animal models.