Centre for Sensors, Instruments and Systems Development

Universitat Politècnica de Catalunya

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Development of a compact and low-cost double-pass system to evaluate the optical quality of the eye and the intraocular scattering

Next December 2nd, Ferran Sanabria will defend her doctoral thesis entitled "Development of a compact and low-cost double-pass system to evaluate the optical quality of the eye and the intraocular scattering" The thesis has been co-directed by Dr. Jaume Pujol and el Dr. Fernando Díaz.


The main objective of thesis is the design and validation of a compact and low cost implementation of a double-pass technique to obtain estimates of optical quality in general and diffuse light in particular, led to a possible future use in clinical practice. For this purpose, the double-pass scheme of the ophthalmologic instrument OQAS has been used and possible improvements, both in degree of integration and cost, have been studied and validated, which ensured the same or higher performance levels.

First we proceeded to the validation of an electro-optical lens as correction system of the spherical refraction. This device replaces the traditional Badal system composed of two lenses whose relative distance can be varied, allowing the correction of spherical refraction. We analyzed and demonstrated the validity of this new type of electro-optical lenses for correcting spherical refraction.

Secondly we proceeded to design and implement a double-pass system using the electro-optical lens to compensate spherical refraction. After verifying the electro-optical lens meet the optical quality requirements, we proceeded to implement the double-pass system substituting the Badal compensator by the mentioned electro-optical lens. It was verified and demonstrated that the use of the electro-optical lens yields similar or better performance than the classic double-pass system.

Third it was implemented and validated the lighting system based on a superluminescent LED source (SLED). An SLED was used as a light source in the double-pass system and the speckle noise in the obtained images is analyzed. The study found that the SLED used did not have enough low coherence to break the speckle noise by itself, but showed a good performance when combined with other methods for reducing speckle.

Fourth, we proceeded to implement and validate the acquisition system based on CMOS technology. A CMOS camera was used as a new device to record the double-pass system information. The study revealed a high correlation between the results obtained with both CMOS and CCD camera, that demonstrates the suitability of this type of sensor (CMOS) for its use in visual optics experimental setups and to implement instrumentation in this field.

And finally, the validation of the resulting double-pass system was performed. According to the previously obtained results, the final double-pass system was implemented based on simplicity and cost criteria. This system incorporates a spherical refraction compensator based on an electro-optical lens, a laser diode and a CMOS camera. To validate the results a commercial version of the OQAS clinical instrument was used as a reference. The results obtained in the study show a high correlation between the experimental system and OQAS instrument.

Therefore, according to the obtained results from this studies, we conclude that the double-pass system based on an electro-optical lens, a laser diode and a CMOS camera improves in size and cost a conventional double-pass system.
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