Dissertation committee:
Χρυσάνθη Κουτσανδρέα, Καθηγήτρια, Ιατρική Σχολή, Ε.Κ.Π.Α.
Δημήτριος Μπρούζας, Καθηγητής, Ιατρική Σχολή, Ε.Κ.Π.Α.
Δημήτριος Παπακωνσταντίνου, Καθηγητής, Ιατρική Σχολή, Ε.Κ.Π.Α.
Γεωργάλας Ηλίας, Αν. Καθηγητής, Ιατρική Σχολή, Ε.Κ.Π.Α.
Χατζηστεφάνου Κλειώ, Επ. Καθηγήτρια, Ιατρική Σχολή, Ε.Κ.Π.Α.
Δρούτσας Κωνσταντίνος, Επ. Καθηγητής, Ιατρική Σχολή, Ε.Κ.Π.Α.
Χατζηράλλη Ειρήνη, Επ. Καθηγήτρια, Ιατρική Σχολή, Ε.Κ.Π.Α.
Summary:
Glaucoma represents a diverse group of disorders that have common characteristic changes in the optic nerve neuroretinal rim tissue and is a major cause of blindness. It is estimated that half of glaucoma cases are undiagnosed. The prevalence of glaucoma in the general US population 40 years of age and older is 2.1%, and ~2.4 million people in the US have undetected and untreated glaucoma.
Visual field testing is one of the most important exams for determining the stage of glaucoma, the efficacy of medical or surgical treatment, and the prognosis, as well as for assessing the patient’s quality of life and his/her ability to perform the activities of daily living. Increasing the frequency of visual field testing leads to earlier detection of glaucoma progression.
The most widely used method to assess visual field deficits in glaucoma is automated perimetry. Automated perimeters are objective and accurate devices but despite their advantages, there are a few disadvantages. Automated perimeters are built for physicians’ offices or hospitals. They are bulky and heavy devices and they are neither portable nor available for home use or at bedside. Often, it is tiring and difficult for patients to concentrate throughout the test and a large majority of the patients who have visual field test examination belong to the age group over 50.
On the other hand, smartphones are found everywhere, and they are inexpensive. Virtual reality (VR) glasses have some advantages in visual field testing. They are lightweight, portable, comfortable, and affordable, and there is no need for an eye patch.
Online visual field testing is interesting for its potential to be used as a low-cost method for glaucoma screening. The potential benefits of an effective online telemedicine system are plentiful, especially in countries with high prevalence of glaucoma or in developing countries, and may save costs to patients and costs to the health care system as a whole.
In this thesis the possibility of using VR glasses for glaucoma/visual field testing is examined. Virtual reality glasses, an android smartphone with a 6 inch display, and software that implements a: 1) FASTPAC 3 dB step staircase algorithm and 2) a Supra-Threshold algorithm, at three threshold levels: 1) -4 db, 2) -8 db, and 3) -12 db, from the age-expected sensitivity, for the central 24° (52 points) of visual field, was used for the purpose of testing. The software uses the web camera as a “virtual photometer” in order to detect room luminosity and allows self-testing using either a computer monitor or virtual reality glasses using an Android smartphone with a 6-inch display. The software includes an expert system to analyze the visual field image and validate the reliability of the results. It allows the user to email the test results to his/her doctor and also allows the physician to combine the results from two or more tests into a single test in order to achieve higher statistical accuracy of the final result:
1) A total of ten patients, were tested, as they appeared randomly and consecutively, using the VR-FASTPAC algorithm and the results were compared point to point to those obtained using the Humphrey perimeter for the same patients (20 eyes tested×52 points per eye=1,040 visual field test points). The result’s values were continuous ranging from 0 to 40 dB. High correlation coefficient (r=0.808, P<0.0001) was found between the virtual reality visual field test and the Humphrey perimeter visual field.
2) A total of ten patients, were tested, as they appeared randomly and consecutively, using the VR-Supra-Threshold algorithm and the results were compared point to point to those obtained using the Humphrey perimeter for the same patients (20 eyes tested×52 points per eye=1,040 visual field test points). The results were binary, seen/not seen. ROC curves were used because they have the ability to assess the performance of a binary classifier over its entire operating range using a graphical approach. The most desirable property of ROC analysis is that the accuracy indices derived from this technique are not distorted by fluctuations caused by the use of arbitrarily chosen decision criteria or cut-offs. In other words, the indices of accuracy are not influenced by the decision criterion. Using this as a measure of a diagnostic performance, one can compare individual tests or judge whether the various combination of tests can improve diagnostic accuracy. The ROC curves for each threshold level as well as the generalized Youden Index and the optimal cut points were computed using easyROC, an interactive, open-source web tool for ROC curve analysis using R Language Environment. Good receiver operating characteristic/area under the curve coefficient was found, ranging from 0.762 to 0.837 (P<0.001). Sensitivity ranged from 0.637 to 0.942, and specificity ranged from 0.735 to 0.497. In summary, it was found that as the threshold tested gets lower, the sensitivity increases while the specificity decreases and vice versa. The optimal cut-off point for Humphrey data was 28 dB for the high threshold, 25 dB for the medium threshold, and 16 dB for the low threshold. Black/gray stimuli on white background were also tested with similar results, but they are not included in this paper. In practice, when a single test is used repeatedly in routine screening, the same screening threshold is typically used at each screening visit. One possible alternative is to adjust the threshold at successive visits according to individual-specific characteristics. The test results can be combined in series or in parallel. Parallel testing is recommended for ruling in diagnoses, while series testing is recommended for ruling out diagnoses. The software allows the user to select and combine the results from two or more tests into a single test. The sum of positive responses at each point merged is shown.
Virtual reality glasses perimetry has many similarities to classical bowl perimetry.
The most important advantages of the virtual reality glasses method is the ease of use and the comfortable patient position, in fact it has been found that the patients tolerated the test well and fixation losses occurred rarely. The patients can move their heads freely.
VR visual field testing is simple, easy and does not require specialized equipment. It takes approx 2 minutes per eye using the supra-threshold algorithm and 8 mins per eye using the FASTPAC. The high correlation coefficient/ROC curves results between the virtual reality glasses and the Humphrey perimeter shows that the method is reliable at least when compared to Humphrey perimeter. The test may be useful for for glaucoma screening/monitoring.
Keywords:
Glaucoma, Visual field, Telemedicine, Teleophthalmology, Virtual reality glasses, VR, Smartphone, Android, Internet, Perimeter, Humphrey
