Modelling Human Eye for Illumination and Imaging

  • 10 May 2023
  • 5 replies
  • 249 views
Michaelkm8
Rank
Userlevel 1

Hello,

           I am hoping to get some guidance on how to model the human eye for an illumination application.  I am using a ring of LED’s to illuminate the eye and using the back reflection and a separate optical path to image it.

A Fundus camera with an internal illumination path is the specific design.

I downloaded the Eye_NSC file from the knowledge base article and made the Iris and Sclera Inner “mirror” surfaces so I could get a reflection from it.

I have empirical data that shows the illumination pattern from a real system that looks like elliptical rings, but I can’t seem to get the same pattern in NSC mode through the optical system.  I am focusing on the model eye being incorrect in some way, but I’m having a hard time figuring out how to change the model to suit this application.

Is there a better way to model the eye to get reflections from it?

5 replies

jwbeenakker
Userlevel 3

Hi Michael, 

Not having seen your experimental setup makes it a bit hard to fully grasp what is going own/what you have measured. The elliptical shape, however, feels to me that the eye has astigmatism (or isn’t properly aligned with the camera which will also introduce astigmatism). 

Not sure if that helps, but in the examples of the ZOSPy package we provided different eye-models based on clinical data. 

 
Csilla Timar-Fulep
Rank
Userlevel 5
Badge +2

Hi Michael,
Thanks for your question here on the Community Forum!
Such a fundus camera with an internal illumination path can be designed and analyzed in OpticStudio. For the first design part, you can separate the illumination and imaging systems, and optimize them separately in the sequential mode of OpticStudio. Then you can move to the NSC mode, where you can model the whole system together at once and analyze its performance, including the stray light in the system.
Your approach could be viable, for further guidance on the design, I would suggest to take a look at these articles:
Full article: Design of optical system for binocular fundus camera (tandfonline.com)
(PDF) Design, simulation and experimental analysis of an anti-stray-light illumination system of fundus camera (researchgate.net)
Without seeing your model and reference measurements, it would be hard to guess why the results don’t match. As part of the debugging, you could try to simplify your model, separate the parts, and see where it deviates from the expected behavior.
Best,
Csilla

Csilla Timar-Fulep
Michaelkm8
Rank
Userlevel 1

Hi Michael, 

Not having seen your experimental setup makes it a bit hard to fully grasp what is going own/what you have measured. The elliptical shape, however, feels to me that the eye has astigmatism (or isn’t properly aligned with the camera which will also introduce astigmatism). 

Not sure if that helps, but in the examples of the ZOSPy package we provided different eye-models based on clinical data. 

 

Thank you for the help.  I will check out the package to see if I can get the image to come into focus as I am seeing in the real images.

The elliptical pattern may be from the astigmatism, but let me be more clear about the issue.  Using the ring of LED’s in the real setup I am imaging the eye and in that image I see circular patterns from the LED’s.  However, when I model this in OpticStudio I cannot get the same intensity pattern.  The intensity pattern looks like even illumination which is not the case for the real system.

Thank you again for the help!

Michaelkm8
Rank
Userlevel 1

Hi Michael,
Thanks for your question here on the Community Forum!
Such a fundus camera with an internal illumination path can be designed and analyzed in OpticStudio. For the first design part, you can separate the illumination and imaging systems, and optimize them separately in the sequential mode of OpticStudio. Then you can move to the NSC mode, where you can model the whole system together at once and analyze its performance, including the stray light in the system.
Your approach could be viable, for further guidance on the design, I would suggest to take a look at these articles:
Full article: Design of optical system for binocular fundus camera (tandfonline.com)
(PDF) Design, simulation and experimental analysis of an anti-stray-light illumination system of fundus camera (researchgate.net)
Without seeing your model and reference measurements, it would be hard to guess why the results don’t match. As part of the debugging, you could try to simplify your model, separate the parts, and see where it deviates from the expected behavior.
Best,
Csilla

 

Hi Csilla,

                The sequential analysis has been done and validated by the real system.  The non-sequential system is valid up to the plane of the eye.  I can create the same intensity pattern in OpticStudio that I see if I put a piece of paper at the eye plane of the real system, so I know I have valid results up to there.  However, when I image the back reflections from the eye through the rest of the optical system I just get even illumination in OpticStudio when in the actual system I get bright rings in the center.  Hence why I think I’m doing something wrong with the eye model.

Unfortunately I cannot share the OpticStudio file, but I really appreciate the paper as that is very helpful!

jwbeenakker
Userlevel 3

The elliptical pattern may be from the astigmatism, but let me be more clear about the issue.  Using the ring of LED’s in the real setup I am imaging the eye and in that image I see circular patterns from the LED’s.  However, when I model this in OpticStudio I cannot get the same intensity pattern.  The intensity pattern looks like even illumination which is not the case for the real system.

 

The models proposed in the ZOSPy module, but also the Escudero-Sanz eye model (I. Escudero-Sanz, R. Navarro, “Off-axis aberrations of a wide-angle schematic eye model,” J. Opt. Soc. Am. A 16, 1881–1891 (1999).) have been  implemented in OpticStudy by many scientists and produced results that match those from in vivo data, so I would say that from an optics point of view those models are representative.

But, without seeing the setup and data/output it is kind of hard for me understand what is going on in your simulations.

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