Role of Signal Processing in Eye Care




Greater Copenhagen area

The treatment of several eye diseases requires proper patient management before, during and after surgery to prevent vision loss. For surgically treated eye diseases this means providing ideal physical and biomechanical conditions for the afflicted eye. To this aim patient positioning is prescribed in the treatment of corneal diseases in the front of the eye to retinal diseases in the back of the eye.

Visual loss or failed surgery is often attributed to poor adherence to recommended positioning (poor compliance) as positioning regimens are challenging3. In the following eye conditions, patient positioning plays a major role in the treatment regimen:

- Macular hole – an eye disease with a small break in the center of the eye's light-sensitive retina. It results in distorted and decreased central vision preventing reading, driving, and seeing fine detail, but can be treated by surgery (vitrectomy) and filling the eye with gas. Appropriate positioning for 3 days postoperatively ensures contact between the retina and the gas bubble necessary for hole
closure and visual improvement.

- Fuchs’ endothelial dystrophy - a condition causing blurred vision. An accumulation of focal outgrowths and thickening of inner corneal membrane (Descemet’s membrane) leads to corneal swelling and vision loss. Treated surgically with a partial-thickness cornea transplant procedure (Descemet membrane endothelial keratoplasty, DMEK). Postoperatively a gas bubble ensures fusion of the donor membrane and the recipient cornea facilitated by supine positioning for 3-5 days.

- Retinal detachment - disorder of the eye where the light-sensitive retina separates from the cell layer lining the wall of the eye. It often involves permanent vision loss in the affected area. Positioning is prescribed preoperatively (0-72 hours) to prevent further detachment of the retina and worsening of vision loss.

The purpose of this research is to improve patient’s vision in the treatment of macular holes and Fuchs’ corneal endothelial dystrophy and to prevent progression of retinal detachment through biomechanical knowledge of these conditions.

At the Department of Ophthalmology, Rigshospitalet – Glostrup we have studied the relationship between the actual performed positioning and surgical results in macular hole treatment (unpublished data, submitted for publication). Recently we have adopted DMEK for the treatment of Fuchs’ endothelial dystrophy. In both DMEK and macular hole treatments similar key principals are at play. They utilize the physical properties of gas with a high surface tension and low viscosity to create a biomechanical environment enabling visual gain. As positioning determines the location of the gas in the eye (through gravity), it directs the therapeutic effect of the gas bubble. In patients with a retinal detachment we have also studied the effects of positioning by assessing the retinal detachment progression rate in admitted paitents. Here, the vulnerable detached retina is subject to the effects of gravity, head motion and eye movements. Forces acting on the detached retina are thought to promote the progression of detachment. However, very little is known about forces and stresses in the eye before and after surgery. Knowledge and data on the role of the mechanics affecting the eye would likely allow us to improve patient care.

Objective recording is crucial for our understanding of the effects of gravity on gas in the eye. As there is often a large discrepancy between the positioning prescribed by surgeons and the actual positioning performed by patients it is not enough merely to rely on the surgeon prescribed positioning. At the Department of Ophthalmology, Rigshospitalet – Glostrup we have developed a novel device for monitoring the patient’s head position with small, low-power electronic sensors (accelerometer and gyroscope). With this ‘positioning device’ we have demonstrated a benefit of gas-macular-hole contact for achieving hole closure and have eliminated a previously standard unnecessarily arduous positioning regimen (face-down position). Furthermore, we have identified how to improve gas-macular hole contact which we wish to implement to improve the macular hole treatment regimen.
A significant limitation to the ‘positioning device’ is that it uses head pitch as a proxy to estimate eye position. Without knowledge of the eye position in relation to the head we are unable to precisely determine the location of the gas bubble postoperatively or determine whether head or eye
movement causes progression in a retinal detachment. The Technical University of Denmark collaboration provides a solution to this problem with electrooculography (EOG). EOG is a technique for measuring the corneo-retinal standing potential that exists between the front and the back of the human eye. The resulting signal (electrooculogram) allows for the recording of eye movements8. Long-term gaze recording is possible even at night with the eyes closed. It is, however, a difficult task analyzing the raw recordings and requires engineering expertise to remove artifacts from blinking, separate the EOG signal from drift and control for the variable corneo-retinal potential.

Fusing EOG with an updated positioning device represents a novel approach to gaining insights to treatments provided to patients. Although the use of positioning is routine, it is without a firm evidence base. By solidifying our understanding of the implications of poor adherence to positioning recommendations and ocular movements we believe we can give better patient care through better guidance and devices that actively assist patients to position better. Thus, the insights gained from looking at clinical outcomes as well as objective measurements will likely allow us to introduce improved treatment regimens that prevent unnecessary vision loss and enhance visual gain.

Research questions
(1) Can we improve macular hole treatment by assisting patients to better positioning?
(2) Does better gas-cornea transplant (graft) contact increase the surgical success rate in DMEK?
(3) What is the relative importance of positioning and eye movement prior to surgery for the progression of a retinal detachment?

Specific projects
Macular hole

In collaboration with

Department of Ophthalmology, Rigshospitalet, Glostrup

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DTU Sundhedsteknologi


Sadasivan Puthusserypady


Gruppeleder, Lektor


Supervisor info

BSc in Biomedical Engineering


Sadasivan Puthusserypady


BSc project, MSc thesis

MSc in Biomedical Engineering


Sadasivan Puthusserypady


BSc project, MSc thesis

Technical University of Denmark

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