DOCTORS VS MACHINES

Will advances in technology render ophthalmologists obsolete in the diagnosis and monitoring of glaucoma? Two noted glaucoma specialists debated the question during a session of the 11th Congress of the European Glaucoma Society in Nice.

Taking up the argument that machines will replace doctors, was Francisco Goni MD, PhD, Barcelona, Spain. “With the increasing number of patients in our healthcare systems we really need time-saving, effective, reliable, reproducible, and standardised methodology for disease diagnosis and follow-up,” he said.

He noted that although diagnosis by physicians remains the current gold standard, even experienced glaucoma specialists disagree on whether or not an eye has developed glaucomatous damage or if damage that is already present has worsened.

Dr Goni also noted that automated diagnosis is already in use by most glaucoma specialists in the form of computerised perimetry, with both diagnosis and progression analysis software. In fact, the European Glaucoma Society guidelines currently recommend the use of automated progression algorithms.

“Many doctors are making direct clinical decisions based on perimetric diagnostic indicators, like hemifield test or pattern standard deviation, statistical tools that help us separate patients as likely normal or abnormal. Similarly, progression algorithms allow us to detect and measure change in an objective manner. Clinical criteria developed from studies have shown a good sensitivity/specificity balance,” he said.

The automation of the detection of the structural abnormalities that characterise glaucoma has kept pace with functional testing. The past decade has seen rapid development in technologies such as scanning laser polarimetry, confocal scanning laser ophthalmoscopy and optical coherence tomography.

“These imaging devices have similar or even better diagnostic performance than clinical assessment by doctors. Their measurements are quantitative and show a high reproducibility, allowing the detection of change with strong confidence contrary to the qualitative, subjective evaluation of progression performed in a classic doctor's clinical examination. Thus nowadays an increasing number of doctors rely only on imaging devices to detect and measure structural progression,” he said.

Doctors still needed

Taking the opposing view, Anton Hommer MD, Vienna, Austria, agreed that computerised perimetry is here to stay, but without the supervision of a trained physician the automated tests are still prone to error because of fixation loss, and other diseases that can affect visual fields.

Furthermore, structural features detected by some of the newer imaging technologies can also be misleading, not only because changes similar to those that occur in glaucoma can also occur in other optic neuropathies, but also because there is so much variation in the optic nerve head and retinal nerve fibre layer among individuals without any disease at all.

For example, in the normal population the retinal nerve fibre layer thickness at the optic nerve head can vary by between 800,000 and 1.6 million nerve fibres. Similar differences exist in the normal population regarding the size of the optic nerve head and cup/disc ratios and the degree of asymmetry between the two eyes.

In addition, all of the current technologies have certain shortcomings. For example, the accuracy of early diagnosis with both the GDx-VCC scanning laser polarimeter (Carl Zeiss Meditec) and the HRT II confocal scanning laser ophthalmoscope (Heidelberg Engineering) is dependent on the disc size of the eye being examined. The GDx-VCC is more sensitive with small discs and the HRT II is more sensitive with large discs.

Spectral domain OCT with the Spectralis® system (Heidelberg Engineering), for its part, is limited by the size of its normative database, which includes only 246 eyes of 123 patients, all of whom were Caucasian and between the ages of 20 and 87 years. Normative database is limited in all machines/OCTs, Dr Hommer pointed out.

However the new imaging technologies have much to offer in the detection of progression, Dr Hommer said.

He suggested using a two-step approach.

“We know that with the available techniques nowadays structural changes are more likely to be detected at the early stage of glaucoma and functional examination is superior in advanced stages for detecting progression. Structural deviation from normal does not automatically mean that there is a disease.

“But if we have confirmed change in OHT or early glaucoma with the structural measurements (not only one follow-up picture) it may be justified to start or change treatment. If the visual field in the same patient stays normal it is probably justified to start medical therapy, but not to perform surgery, because of more potential severe complications for a patient that had no loss in QoL before. If we have on the other side confirmed visual field progression due to glaucoma, but structure stays unchanged, because of advanced damage yet and the measurements are not providing useful information, then the functional tests are more valuable,” he said.

“Therefore, all these high tech measurements are good for follow-up, but we always have to consider the patient individually as a whole, and this cannot be done by machines,” he said.

Francisco Goni: francisgoni@yahoo.com

Anton Hommer: a.hommer@aon.at