DRYEYE Project

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An increasing number of people spend most of their working time in front of a computer screen. As a result, more and more people complain about "itchy eyes", "dry eyes", and "problems with their eyes". The clinical problem underlying these symptoms is a lack of corneal tear liquid covering the surface of the eyes.

We are developing a new measurement device which should allow an automatic, non-invasive quantification of the tear film covering the cornea of the subject.

Project Leader: Thomas Haslwanter
Co-workers: Michael Platz, Michael Ring
Funded by: INVERSIA (EU & Upper Austria), Paracelsus Institut Bad Hall
Duration: June 2010 - Oct 2012

 

 


Introduction

Dry eye disease (keratoconjunctivitis sicca) is one of the most common diseases in the western world. It is caused by a disruption of the pre-corneal tear film. The effects of this disease can range from discomfort up to chronic damage of the cornea, going hand in hand with poor optical performance and insecurity in daily life. Risk factors include wearing contact lenses, air conditioned environments,computer work and metabolic parameters.
This individual multi-etiology and the complex multi-layered structure of the tear film make both the diagnosis and the therapy very challenging.
We have developed a low-budget device which allows us to track the dynamics of the tear film both with the conventional method using the dye fluorescine, and non-invasively using a pattern projected on the cornea.
Additionally the movement of the lipid layer can be made visible underlying the principle of white-light interferometry.
The main benefit from acquiring such videos is the availability for image processing. We hope to find significant parameters which reliably allow us to distinguish not just between healthy subjects and patients, but also allow us to classify the patient group into different subgroups. This should help ophthalmologists to provide more efficient therapy.

Invasive Method for Assessing the Tear Film

This method is a routine procedure performed by both ophthalmologists and optometrists. The principle is to apply the dye fluorescene to the eye and instruct the subject to blink a couple of times to mix the dye with the tear film. The eye is then illuminated with blue light, the stain is excited and emits green light.

Non Invasive Method for Assessing the Tear Film

It has been shown that it is also possible to detect the tear film break up through a pattern projected on the cornea (4): a local distortion of the grid indicates a rupture.

Tear Film Movement

A kinetic analysis of the lipid layer also contains information about the stability of the tear film (1,2). The direction of the propagation of the tear film immediately after a blink as well as the velocity profile is distinct for certain subtypes of the dry eye disease(3).

Image Processing

The USB Camera delivers frames with a resolution of 1280 by 1024 pixels at 8 frames per second.
Due to the movement of either the eye or the device, the first step is to discard blurred frames and align the remaining images to compensate for small eye movements. The next step is then to reliably find parts of the iris contour, which is achieved with the previously developed MSER algorithm (5). With these iris pixels, an ellipse can be fit and an affine transformation is performed so that the images can be finally aligned and analyzed.

Summary

A portable, cost-efficient device has been manufactured and tested on a small group of patients. At the moment a risk analysis according to ISO 14971 is performed and an evaluation study will be conducted.
Due the large number of parameters we expect to extract from the videos ( Invasive + Non- Invasive TBUT, Area of Break Up, Area- Growth- Rate, Localization of Break Up, Velocity and Direction of Tear Film Movement), we hope to provide information to distuinguish between the subtypes of dry eye to evaluate different therapies (artificial tears, lipid spray, lubricant eye gel, iontophoresis ... ). It is also planned to use this device to provide information for improved fitting of contact lenses.