Perception

Dysmegalopsia

Dysmegalopsia is a distortion in the perceived size or shape of a real object in view, so that it looks larger, smaller, further away, or oddly misshapen compared with its true form, even though the object itself has not changed. Unlike a hallucination, the object being looked at is entirely real; only its apparent size or shape is affected.

This has traditionally been treated as a distortion of spatial form rather than of intensity or quality, and has been linked most classically to disturbances of visual accommodation and convergence, retinal changes, and lesions of the temporal and parietal lobes.

Also known as

Micropsia

Objects are perceived as smaller than they actually are.

Macropsia

Objects are perceived as larger than they actually are; also called megalopsia.

Porropsia

Objects appear to recede into the distance without any actual change in their size.

Metamorphopsia

Objects appear irregular or distorted in shape rather than simply larger or smaller.

Recognition features

• A real object is correctly identified but its apparent size, distance, or shape is distorted
• Micropsia and macropsia describe opposite distortions of felt size; porropsia describes a distorted sense of distance; metamorphopsia describes irregular distortion of shape
• May occur transiently, for example during a seizure aura, or more persistently in connection with an eye or brain condition
• The person usually recognises that what they are seeing does not match how the object actually looks or measures

Eliciting it at interview

• Ask specifically about the visual quality involved: "Have things around you seemed to look bigger or smaller than they really are, or oddly shaped, or further away than they should be?"
• Establish timing and triggers, such as whether the distortion accompanies headaches, seizures, or occurs only in one part of the visual field
• Coordinate with an eye examination where indicated, since retinal and accommodation-related causes are well recognised alongside brain-based ones

Distinguishing features

• Differs from a hallucination in that the object being distorted genuinely exists and is being looked at; nothing is being perceived that is not actually present
• Differs from the Lilliputian hallucination described under visual hallucination, in which tiny figures are seen where nothing real is present, rather than a real object being misjudged in size
• The named sub-types differ from one another according to exactly which spatial dimension — size, distance, or shape — is affected

Common misconceptions

• That dysmegalopsia is always a sign of psychiatric illness; it is, in fact, more commonly linked to eye conditions or temporal and parietal lobe disturbance than to primary mental illness
• That micropsia and macropsia are rare curiosities without clinical relevance; they are well documented in association with specific, identifiable causes and are worth asking about directly

Related phenomena

Sensory Intensity Distortion · Chromatopsia

Practice this

A patient looks at a real chair across the room and reports that it appears tiny, as though seen from a great distance, though she knows perfectly well it is an ordinary-sized chair nearby. What is this? · A patient reports seeing a tiny, fully formed group of people walking across her empty living room floor, with no real object or person actually present. Before revealing the answer: is this dysmegalopsia? · A patient describes a distorted visual experience. Before revealing the answer, decide what distinguishes dysmegalopsia from a visual hallucination. · You suspect dysmegalopsia in a patient. Before revealing the answer, decide how you would assess for this. · Explain why dysmegalopsia is described as covering several differently-named sub-types rather than a single uniform experience.

Illustration

In the minutes before a seizure, a 33-year-old woman reports that the furniture in her sitting room briefly seems to shrink to a fraction of its true size while appearing to drift far away toward the opposite wall, an experience she finds strange but is quickly able to describe accurately once it has passed.

References

• Casey, P. & Kelly, B. (2019). Fish's Clinical Psychopathology, 4th ed. Ch. 3, 'Disorders of Perception'.