Palinopsia Peeking behind doors of visual perception, visual memory

Take-home message: Palinopsia can be broadly defined as the persistence or recurrence of an image after the stimulus has been removed. Formed, high-resolution afterimages are typically more alarming to patients than unformed, blurred afterimages.

The Neuro-Connection By David Gersztenkorn, MD, MS, and Andrew G. Lee, MD

The patient with palinopsia may be particularly challenging, because of the strange and sometimes bizarre descriptions that are reminiscent of what might be heard on a psychiatric ward.

In addition, the physical exam and work-up are usually negative. Illusory or hallucinatory visual symptoms can cause patients considerable mental distress, and these challenging encounters often result in a referral to neuro-ophthalmology.

In this article, we discuss the clinical considerations for a general ophthalmologist seeing a patient with palinopsia (Greek: opsia for “seeing”, palin for “again”).

Palinoptic afterimages are pathological and should be distinguished from physiological afterimages, common and benign phenomena that occur after viewing a bright stimulus such as seeing stars after a retinal exam.

Palinopsia thus describes a heterogeneous group of pathological symptoms, which we split into two categories: hallucinatory palinopsia and illusory palinopsia.¹Each group has similarities in symptom description, etiology, mechanism, prognosis, and treatment.

Hallucinatory palinopsia

A visual hallucination is the creation of an image or scene where none exists and can be simple/unformed (e.g., lights, colors, lines, geometric designs) or complex/formed (e.g., objects, animals, people, scenes). Hallucinatory palinopsia is similar to a complex hallucination but describes the persistence or recurrence of a previously-seen, formed, high-resolution image or scene (Figure 1a).

For example, after seeing a cat, an almost identical copy of the cat may remain fixed in the field of view. The hallucinatory afterimage usually is transitory and of short duration (e.g., lasting seconds to minutes) but may persist for hours.

A palinoptic scene consists of a short, stereotyped action sequence that continuously replays for several minutes (e.g., a patient views a person throwing a ball and then sees the same scene repeated many times). The palinoptic image or scene may occur immediately following the stimulus or may be delayed.

Hallucinatory palinopsia can also refer to seeing an object or physical feature which is superimposed onto other objects or people in the same context for a few minutes (Figure 1b).

For example, a patient sees a man with a beard and then observes the same beard on every subsequent person viewed. Another example might be seeing a person wearing distinctive shoes and then the same footwear is observed on every other person. Hallucinatory palinoptic afterimages are a dysfunction of visual memory and are caused by seizures or cortical lesions such as neoplasms, infarctions, and abscesses.

Illusory palinopsia

A visual illusion is the altered perception of a real external stimulus such as seeing distortions in shape, size, or color. Illusory palinopsia is similar to a visual illusion in that there is a dysfunction in the original perception of a stimulus, and the afterimages are unformed and indistinct.

For example, when viewing a light or other bright stimulus such as a computer screen and shifting visual focus, a prolonged, indiscrete afterimage remains for several minutes in the same location in the visual field. These illusory palinoptic afterimages are differentiated from physiological afterimages based on the afterimage intensity and duration.

Illusory palinopsia may also refer to an object or light in motion leaving a comet-like tail in its wake (Figure 1c).

The visual trails may be discontinuous such as in a film reel or may be blurred together such as in a long-exposure photograph. These movement-induced afterimages persist for several seconds before fading and are usually identical in color and shape to the original object or light, but may be vague or less intense. Illusory palinopsia occurs in migraineurs, after concussions, after hallucinogen use, and as a prescription drug side effect (e.g. trazodone, clomiphene, oral contraceptives, topiramate).

Illusory versus hallucinatory

Illusory palinopsia is due to an abnormality in the original perception of a stimulus, whereas hallucinatory palinopsia is due to an abnormality after a stimulus has been encoded in visual memory. External conditions such as stimulus intensity, background contrast, fixation time, and movement typically affect the generation and severity of illusory palinopsia but not hallucinatory palinopsia.

Illusory palinopsia occurs immediately after seeing the original stimulus in the same location in the visual field, while hallucinatory palinopsia may appear anywhere in the visual field and can be delayed in time. Illusory palinopsia occurs continuously or predictably such as in the morning or during light adaptation, however hallucinatory palinopsia is unpredictable. Visual field deficits are often present with hallucinatory palinopsia but not with illusory palinopsia.

Illusory palinopsia may be caused by diffuse neuronal pathology such as global alterations in neurotransmitter receptors, while hallucinatory palinopsia is typically caused by focal cortical pathology.

The clinical characteristics that separate illusory from hallucinatory palinopsia also help differentiate and assess risk in visual illusions and hallucinations. Complex visual hallucinations are usually more worrisome to patients than simple visual hallucinations or visual illusions.²

Clinical encounter

The examiner should obtain the details of the palinopsia to determine if it is hallucinatory or illusory. A full neuro-ophthalmologic exam including automated visual fields should then be performed. Hallucinatory palinopsia, usually caused by a cortical lesion or seizure, can be the presenting symptom of a serious neurological disease and typically resolves after treating the underlying disturbance.

A patient reporting even one such episode should probably be offered an MRI and a possible referral to neurology or neuro-ophthalmology.

In contrast, illusory palinopsia is more common and usually less worrisome. Patients often have multiple types of illusory palinopsia, along with visual illusions and simple hallucinations like visual snow, Alice in Wonderland Syndrome, and entoptic phenomena. These illusory symptoms are generally benign and long standing, but are often refractory to treatment.

Diagnosing the etiology of illusory palinopsia is based on clinical history, with the physical exam and work-up usually being non-contributory. Illusory palinopsia can be attributed to prescription drugs, head trauma, migrainous neuronal dysfunction, hallucinogen ingestion, or symptoms may be idiopathic. There is occasional treatment success with pharmaceuticals that reduce cortical excitability such as gabapentin. Sunglasses or tinted lenses or filters may improve symptoms.

Many patients with illusory palinopsia have played referral pinball between neurologists and ophthalmologists and have already received extensive work-ups. Due to the subjective nature of the symptoms and the absence of physical findings, clinicians are sometimes dismissive or mention non-organic disease.

There is considerable evidence in the literature confirming the symptom legitimacy, so validating and explaining the patient’s symptoms can help ease anxiety and should be of primary concern. Illusory palinopsia is presumably due to a modified neural excitability state causing dysfunction in light and motion processing mechanisms, thus there is an exaggeration of normal phenomena such as physiological afterimages from bright lights and trails behind quickly-moving objects.

For more information on palinopsia, please refer to the review article.¹

References

1. Gersztenkorn D, Lee AG. Palinopsia revamped: A systematic review of the literature. Surv Ophthalmol. 2014.

2. Teeple RC, Caplan JP, Stern TA. Visual hallucinations: differential diagnosis and treatment. Prim Care Companion J Clin Psychiatry. 2009;11:26-32.

David Gersztenkorn, MD, MS, is affiliated with the Department of Ophthalmology, Houston Methodist Hospital, Houston, and UTMB Galveston, TX, and the UT M.D. Anderson Cancer Center, Houston. He did not indicate any proprietary interest in the subject matter.

Andrew G. Lee, MD, is editor of “The Neuro-Connection” column. Dr. Lee is chairman, Department of Ophthalmology, Houston Methodist Hospital, Houston; adjunct professor of ophthalmology, Baylor College of Medicine, Houston; professor of ophthalmology, neurology, and neurosurgery, Weill Cornell Medical College, Houston; clinical professor of ophthalmology, The University of Texas Medical Branch, Galveston, TX and The UT MD Anderson Cancer Center; and adjunct professor of ophthalmology, The University of Iowa Hospitals and Clinics, Iowa City, IA and the University of Buffalo, SUNY, Buffalo, NY. He did not indicate any proprietary interest in the subject matter.