1. How to Model the Human Eye in Zemax

2. Introduction
Accurate simulation and modeling of the human eye can be tricky. Entire volumes have been written on the subject, and it is a subject that continues to spur new developments. In this study, we will create model of a human eye in Zemax using the Liou & Brennan 1997 eye model. 

3. Human Eye Model
set the System|General|Units Lens Units to “Millimeters”. Next you’ll want to set the Wavelengths (found in the System section) to “F, d, C (Visible)” as shown below: 

5. Next, go to System|General|Aperture and set the Aperture Type to “Float By Stop Size” and then go to System|General|Glass Catalogs and add the catalog “MISC” to your Glass Catalogs. Set just one Field, of Type “Angle(Deg)” with an X-Field value of 5: 

7. Now insert 3 surfaces before the STOP and insert another 3 surfaces after the STOP. Below is a step-by-step guide to setting up all the surfaces, one at a time. 

8. Surface 0  This surface is not actually labeled Surface 0 in the Zemax Lens Data Editor, it’s labeled “OBJ” and it’s the object surface. Below are the settings for Surface 0 (note that any settings not mentioned here should be left with their default values):  Surf:Type = Standard  Comment = Object  Radius = Infinity  Thickness = 1.00E+009 

9. Surface 1  The first surface (after the Object) is just a dummy plane, and we use it to make our layout drawings easier to understand. Below are the settings for Surface 1:  Surf:Type = Standard  Comment = Input Beam  Radius = Infinity  Thickness = 50.0 

10. Surface 2 This is the outer cornea surface
Surface 2  This is the outer cornea surface. Below are the settings for Surface 2:  Surf:Type = Standard  Comment = Cornea  Radius = 7.77  Thickness = 0.55  Glass = Model; 1.376, 50.23  Semi-Diameter = 5.00  Conic = -0.18  Note: to set these glass parameters you will need to right-click the Glass cell, select “Model” as the Solve Type from the drop down list, and then type in the values like this: 

12. Surface 3  This is the interface between the cornea and the aqueous humor. Below are the settings for Surface 3:  Surf:Type = Standard  Comment = Aqueous  Radius = 6.4  Thickness = 3.16  Glass = Model; 1.336, 50.23  Semi-Diameter = 5.00  Conic = -0.60 

13. Surface 4  This surface is not actually labeled Surface 4 in the Zemax Lens Data Editor, it’s labeled “STO” and it’s the aperture stop of the system. This is our eyemodel’s pupil plane. Below are the settings for Surface 4:  Surf:Type = Standard  Comment = Pupil  Radius = Infinity  Thickness = 0.00  Glass = Model; 1.336, 50.23  Semi-Diameter = 1.25 

14. Surface 5  This is the anterior (front) portion of our model’s crystalline lens. Below are the settings for Surface 5:  Surf:Type = Gradient 3  Comment = Lens-front  Radius = 12.4  Thickness = 1.59  Semi-Diameter = 5.00  n0 = 1.368  Nr2 = E-003  Nz1 =   Nz2 =  

15. Surface 6  This is the posterior (rear) portion of our model’s crystalline lens. Below are the settings for Surface 6:  Surf:Type = Gradient 3  Comment = Lens-back  Radius = Infinity  Thickness = 2.43  Semi-Diameter = 5.00  n0 = 1.407  Nr2 = E-003  Nz2 = E-003 

16. Surface 7  This is the rear surface of the crystalline lens (that is, it is the interface between the crystalline lens and the vitreous body of the eye). Below are the settings for: Surface 7:  Surf:Type = Standard  Comment = Vitreous  Radius = -8.1  Thickness =   Glass = Model; 1.336, 50.23  Semi-Diameter = 5.00  Conic = 0.96 

17. Surface 8  This surface is not actually labeled Surface 8 in the Zemax Lens Data Editor, it’s labeled “IMA” and it’s the image surface. This is the retina of our model. Below are the settings for Surface 8:  Surf:Type = Standard  Comment = Retina  Radius = -12.0  Semi-Diameter = 5.00 

19. This is the Liou & Brennan (1997) eye model
This is the Liou & Brennan (1997) eye model. At this point, your Lens Data Editor should look like this: 

20. Change the Settings on the 3D Layout so that Rotation Z = 90, and set it so that the First Surface is Surface 1 (input beam) and you’ll see the top-down view of the model, complete with offset pupil and off-axis field 

24. Here is the resulting Diffraction Image Analysis diagram:

25. You’ll see below that the thickness from the back of the eyeglass lens to the coordinate break (at the eyeball’s center) is 28mm (that’s 15mm from eyeglass to cornea plus 13mm from cornea to center of eyeball). Then, after the coordinate break, there is a thickness of negative 13mm, to get back to the cornea surface. 

26. Surface 2 This is the front surface of the eyeglass lens
Surface 2  This is the front surface of the eyeglass lens.  Surf:Type = Even Asphere  Comment = glasses-front  Radius = 100.0  Thickness = 3.0  Glass = POLYCARB  Semi-Diameter = 20.0 

27. Surface 3 This is the rear surface of the eyeglass lens
Surface 3  This is the rear surface of the eyeglass lens.  Surf:Type = Extended Polynomial  Comment = glasses-back  Radius = 100.0  Thickness = 28.0  Semi-Diameter = 20.0

28. Surface 4  This is the coordinate break located at the center of the eyeball.  Surf:Type = Coordinate Break  Comment = center of eye  Thickness = -13.0 

30. Here is a 3D Layout plot showing the system from a side view for the 3 configurations 

32. Prepare to Optimize

33. Insert two new operands at the beginning of the Merit Function
Insert two new operands at the beginning of the Merit Function. Below are the settings to use for these two new operands: 

34. First new operand  Type = XNEG  Surf1 = 2  Surf2 = 3  Zone = 0  Target = 1  Weight = 1 

35. Second new operand  Type = XXEG  Surf1 = 2  Surf2 = 3  Zone = 0  Target = 6  Weight = 1 

36. Optimizing The PAL 

38. Summary
We used Zemax to model a human eye using realistic parameters, including a gradient refractive-index crystalline lens, pupil, curved retina, and off-axis field angle. We then provided for a realistic rotation of this model and used this rotating eye model to design a progressive addition lens (PAL)