## 3 Glasses-Type 3D Ophthalmoscope Design
### Optical Design for Glasses-Type 3D Ophthalmoscope Lens  
In accordance with the glasses-type 3D ophthalmoscope framework, this study analyzed the specifications of the lens design, in which visible lights and near-infrared lights (985 nm and 965 nm) were used for optimization with the simulation design. These two segments of near-infrared light wavelength spectrum have good transmission through the crystal body and the organ in the human eye of the retina, effectively increasing the macular image of the retina and enabling the symptoms to be observed via the infrared wavelength penetration [10]. This design uses a large aperture to increase the amount of incident light. Figure 3 shows a right-angle prism inverted fixed focal design for visible light and the near-infrared wavelengths. Its specifications are listed in Table 6. \begin{table}
\begin{tabular}{c c} \hline \hline \multicolumn{2}{c}{**Initial Conditions of Design**} \\ \hline
**Image Height** & 2.4 mm \\ Source wavelength & Photonic 5 with 481, 546, 656, 965, 985 nm \\ Focal Length & 10 mm \\ Magnification & 2.5x \\ F/\# & 2.0 \\ Overall Length & 20 mm \\ Optical Distortion & \textless{}3\% \\ MTF & \textgreater{}20–40\% (100 \text{lp/mm}) \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Right angle prism inverted fixed focal system specifications. Figure 2: Enclosed concept for the ophthalmoscope lens groups; 3D image-taking modules are rotated 270 degrees and enclosed in the sides of the glasses for use as ordinary glasses. Imaging Performance Assessment (Spots, Visual Field Diagrams, Aberrations, Modulation Transfer Function)  
We employ the optical software CODE V, a professional optical design software from the 1980s, to design the lens and implement the simulation. The CODE V is well-known for its accuracy of pupil grid function so that CODE V is able to predict pupil curve so precisely compared to other software. The important is that pupil curve directly reflect the aberrations of whole system except chromatic aberrations. Other software without precise description of CODE V might provide higher MTF because its pupil is close to perfect circle, which is simply a placebo. Besides, CODE V is very powerful with regard to optimization and extended optimization. LightTool is a non-image optimization software based on CODE V's optimization engine, which started from 2000. LightTool is different from traditional non-image optical software ASAP. LightTool is great for optimization but ASAP takes advantage of light tracking analysis. The imaging qualities of a right angle prism fixed focal optical design system are as shown in Figures 4-7. Images with Modulation Transfer Function (MTF) less than 20% at specific spatial frequencies will be no longer visible to the human eye if there is no electric noise available such as film camera. Image system with Complementary Metal-Oxide-Semiconductor (CMOS) or other electric sensor might require up to MTF 40% in order to guarantee that target at that specific spatial frequency is visible due to inherent electric noise. That's the reason why the 20% to 40% MTF is suggested, which depends on noise level of electric detector. Human eyes might detect higher frequencies in some cases. However, this kind of miniature lens employed in this case has its limitation up to 20% to 40% at 100 lp/mm according to some experiments. Their performance is limited due to chromatic aberrations, total length restriction, and actual front and rear size. The reason given is that very few plastic optical materials could be selected for this kind of optical design so that its MTF performance might be limited. Figure 3: Right angle prism inverted fixed focal lens simulation design. In Figure 4, we see that lateral color aberration, coma aberration, and astigmatism aberration play a role at the full field, although the diameter of spot diagram has been reduced to the minimum.