A portable device used by optometrists and ophthalmologists may aid in diagnosing schizophrenia, as well as help, predict relapse, evaluate symptom severity, and assess treatment effectiveness, new research suggests

Investigators used flash electroretinography (fERG), a technique used to examine retinal function, to compare retinal electrical activity in patients with schizophrenia vs a group of healthy persons who acted as a control comparator.

Results showed abnormalities in several aspects of retinal function in the patients with schizophrenia, including differences in cellular activation and cone response time.

"What's novel about our study is the use of the ERG device as a clinical tool," lead author Docia Demmin, a doctoral candidate in the Department of Psychology, Rutgers University, New Brunswick, New Jersey, told Medscape Medical News.

"Although it's not yet ready for routine clinical use, with additional research it could be appropriate for clinicians and psychiatrists to supplement their diagnostic determinations that may be a little more objective than interview-style questions aimed at getting at patients' experiences," Demmin said.

Window to the Brain

fERG has "proven to be useful in identifying functional anomalies in neurological and psychiatric populations," write the investigators.

The technique "records electrical potentials generated by retinal cells in response to light stimuli," they explain. The study authors add that ERG recordings in photopic (light-adapted and rod-saturated) conditions indicate cone functioning, while data from scotopic (dark-adapted) conditions reflect rod functioning.

"We have long been interested in vision and eye functioning in schizophrenia and what the retina could potentially tell us about what's happening in the brain," said Demmin. She noted that the retina is part of the central nervous system and shares the same neurotransmitters as the brain.

"Since neurotransmitter disruption or dysregulation is thought to be present in psychiatric disorders, including schizophrenia, looking at the retina can provide a window" into the brain, she explained.

A growing body of research into the use of fERG to examine the retina of patients with schizophrenia has demonstrated multiple anomalies in retinal cell functioning, suggesting trait-related as well as state-related changes.

These data point to photoreceptor activity, as reflected in the a-wave response as a state marker for schizophrenia, and bipolar cell activity, shown by a b-wave response, as about trait or diathesis.

Promising" Device

The PANSS five-factor negative symptom dimension revealed "large, significant correlations" with a-wave amplitude during photopic conditions and b-wave amplitude during scotopic conditions, the researchers report. It also correlated with a-wave implicit time during scotopic conditions, although to a lesser extent.

Increased negative symptoms correlated with an attenuated minimum PhNR amplitude and PhNR amplitude when measured at 72 ms post-stimulus.

Moreover, the PANSS excitement symptom dimension was significantly correlated with b-wave implicit time during condition S2.

After FDR correction, the two correlations that remained significant were negative symptoms and a-wave amplitude during photopic conditions (PPhNR) and excitement symptoms and b-wave implicit time during scotopic conditions (S2).

No significant correlations were found between medication (chlorpromazine) equivalent dosage photopic or scotopic fERG amplitudes, or implicit times.

The researchers summarize that the fERG device demonstrated "the utility of a flicker stimulus for isolating cone-related activity, and the use of the PhNR for isolating retinal ganglion cell activity," with results that were independent of medication effects.

"Our study confirmed findings of prior studies that showed abnormalities in retinal cell functioning in schizophrenia using EFG and also found new abnormalities," Demmin reported.

The device has "promising features" for use in patients with schizophrenia, such as the speed with which assessments can be conducted with the device, as well as its noninvasiveness — for example, "there is no need to dilate the pupil or touch the retina," she said.