The document describes a student's project to design a 4-mirror gonioscope to improve visualization of the eye compared to traditional 3-mirror models. The student first determined that adding a fourth mirror angled at 77 degrees would allow viewing farther back in the eye toward the retina. An initial prototype was 3D printed and mirrors were attached at angles of 59, 67, 73, and 77 degrees. However, challenges were encountered with thick mirrors that distorted the image and surfaces placed too high that reflected the cone instead of the eye. Future iterations will use thinner mirrors positioned lower and include a magnifying lens for clearer viewing.

1. RESEARCH POSTER PRESENTATION DESIGN © 2012
www.PosterPresentations.com
A gonioscope , or goniolens, is a medical device used by optometrists to
perform an opthalmoscopic examination of a patient’s eye. It is used to
examine the iridocorneal angle, which is the angle formed between the
patient’s cornea and iris.
There are many types of gonioscopes that have been designed, and the
model that I used was very similar to the Goldmann 3-mirror gonioscope.
What is a Gonioscope?
Objective
In order to achieve my goal of creating a 4-mirror gonioscope that would
allow a larger field of view inside a patient’s eye, I first had to determine
an angle that the fourth mirror should have. Because the goal is to get a
better view farther back into the eye, closer to the retina, I decided to
angle the fourth one at 77˚, just a few degrees more than the second
largest angle. After deciding this, I designed the part using CAD, making
the mirrors evenly spaced out and having the desired angles. Then, using a
3D printer, the design was created. The next step was to add mirrors to all
of the angles on the flat surfaces, and attach a meniscus lens at the bottom
for magnification so that the user can see the images more clearly. I cut
the mirrors to fit the shape of the 3D print out of the cone, and then glued
them onto the angled surfaces.
Design Method and Process
Above is a picture of the first prototype that I designed for this project.
There are four walls that are angled at 59, 67, 73, and 77 degrees. The
mirrors are attached with silica glue. The CAD design printed out very
well, with no weaknesses in the solid. The mirrors were difficult to cut,
and were also thicker than expected, so that created some unexpected
design flaws. Because the glass is thick, I was unable to get a good image
on the mirrors, especially the ones that have a greater angle. Another issue
that I ran into was placing the angled surfaces too high in the cone, so that
the mirrors were reflecting the image of the lower parts of the cone
instead of the subject’s eye.
Results & Challenges Conclusions & Future Design Ideas
This was the first prototype of my 4-mirror gonioscope design, and with
it, I learned much more about the design process and how gonioscopes
work.
For the next design, I plan to find thinner mirrors so that they will be
easier to cut and be less disruptive in trying to view the image. I will also
modify the CAD design of the cone solid so that the angled surfaces for
the mirrors will be farther lower. This will allow the mirror to reflect the
image of what is underneath the gonioscope instead of the lower part of
the cone. I also plan on attaching a lens to the bottom so that the user will
have a magnified and clearer image, so it will be more useful in medical
applications.
Further design objectives would be to design the cone that will have a
rotating part as well as a stationary part so that the user will no longer
have to rotate the entire gonioscope to change which mirror he wants to
look through. The part containing the mirrors will rotate while the part
that touches the eye will not, so that the patient will experience less
discomfort ad the user can use the device more easily.
Acknowledgements
Special Professor Israel Gannot and Sathappan Ramesh for all of their
guidance and help throughout this project.
References
Image of Iridocorneal Angle
http://en.wikipedia.org/wiki/Gonioscopy#/media/File:Gonio.png
Diagram of Mirrors
From Professor Gannot’s powerpoint about designing an optical device.
Volk 3-Mirror Gonioscope
http://www.opticalmarketplace.co.uk/img/fullsize/product1944.jpg
Top view of a Gonioscope
http://lombartinstrument.com/images/T/g6%20side.jpg
Image of Posterior Embryotoxin
http://www.reviewofoptometry.com/CMSImagesContent/2007/7/056_RO
707_F8_2.gif
Goldmann’s gonioscopes have three mirrors, each at a different set angle
that will allow the optometrist to look at a different part of the eye.
Because there are only three set angles, it is possible that the gonioscope
has limitations of how much of the eye the optometrist can see. There may
be spots in the eye that cannot be seen through the typical 3-mirror
gonioscope. By adding another mirror that is angled differently, the
gonioscope can see more parts of the eye that previously may have been
missed. In the traditional gonioscope, the three mirrors are angled at 59˚,
67˚, and 73˚, as shown in the image below. It is pretty clear that depending
on the size of the mirrors, there are areas inside the eye, especially near
the retina that the gonioscope cannot see. Adding a fourth mirror at 77˚
would allow the optometrist to see even further back into the eye, and
closer to the retina.
EN.520.483 · Bio-Photonics Laboratory · Spring 2015
Jason Jin
4-Mirror Gonioscope
Above, we see a professional crafted 3-mirror gonioscope. The exterior is
shaped like a cone, and below, we see an interior view of a different
gonioscope. Futher below, we see an image from a gonioscope that shows
the damage done to an eye.