A cataract, which is the clouding of the eye's natural lens as a result of aging or injury,
is the leading cause of preventable blindness worldwide. As one of the of the most common
surgical procedures, cataract surgery is performed almost 22 million times worldwide each
year. The World Health Organisation estimates that by 2020 more than 32 million cataract
surgeries will take place globally per annum.
Phacoemulsification cataract surgery in topical anaesthesia has become the anaesthetic method
of choice since first described by Fichman in 1992. Although this procedure has proven to be
relatively painless, safe and effective, patients often report increased pain or discomfort
during surgery of the second eye. Several studies were performed to find out if there was any
proof to that common finding and some tried to find a correlation to fear and anxiety using
standardized questionnaires.
In one study of 65 patients there was a subtle increase in pain in the second surgery
relative to the first which appeared to be associated with decreased preoperative anxiety.
Another study found that previous cataract extraction correlated negatively, but weakly with
preoperative anxiety.
A study of 70 patients having first cataract extraction found no difference in mean pain
scores, fear and anxiety when compared with a second, independent population of 57 patients
having second cataract extraction. A similar outcome was found in 2 other studies where there
was no difference in perceived pain between the first and second cataract surgery.
Summarized, the results in the related literature are controversial concerning the assessment
of pain, fear and anxiety during cataract surgery performed in the second eye.
Emotional stress and anxiety in surgical patients lead to sympathetic stimulation with
tachycardia, hypertension and possible cardiac ischaemia which are haemodynamic stress
responses, triggered by endocrine regulatory mechanisms and the autonomic nervous system with
increased cortisol, adrenaline and noradrenaline blood levels. Furthermore palmar and plantar
sweat glands activity decreases skin resistance which is shown as a surge in electric skin
conductance in bio- feedback measurements.
For obtaining and processing the information about these physiological reactions a system
with the ability to measure and record various bio-signals is needed. These kind of systems
are used for biofeedback. Galvanic Skin response Sensors measure the above mentioned
electrical conductance of the skin. It is used as an indication of psychological and
physiological excitation and thus represents an indicator for the individual's stress
response.
Electromyograph (EMG) uses surface electrodes to measure the electrical activity of the
skeletal muscles when they are relaxed and contracted by detecting the combined electrical
potential generated by the muscle cells. The mean value of the rectified EMG signal of the
upper trapezius muscle increases during stressful conditions and decreases again during
relaxation periods.
Electrocardiogram (ECG) electrodes are used to measure the heart function and further
calculate the heart rate variability (HRV). HRV is defined as the beat-to-beat changes, the
interbeat interval, which is the time between two successive R waves. HRV is considered as a
measure of the interaction between sympathetic and parasympathetic influence on heart rate.
The activation of the sympathetic branch of the autonomic nervous system increases heart
rate, while the activation of the parasympathetic branch, primarily mediated by the vagus
nerve, slows it. These physiological signals provide a reliable measurement of agitation
(stress).