Introduction: This paper presents a comparative study of an optical system of a smartphone-based ophthalmoscope to improve the image quality of retinal imaging photoplethysmography (iPPG). Methods: This study has developed two optical systems using WinLens 3D software. Design I employed the combination of best forms and aspheric lenses while Design II was formed by combining achromatic and 20D lenses. These optical systems were developed to observe: (i) illuminating path when the rays travel from light source to the retina and (ii) imaging path when the ray travel from the retina back to the image sensor of the smartphone camera. Results: The outcomes of the observations were presented as the image metric quantities: (i) spot diagram, (ii) transverse ray aberration, and (iii) 3D wavefront plot that represent the image quality of the optical system. Also, the illumination and imaging paths were demonstrated with different focal lengths and similar lens selections to observe the image quality. Conclusion: The results showed that Design II has better performance than Design I. The simulation results have provided enough information to verify the performance of the optical design.