Symptom Of Pelopsia

i-r1

Allesthesia

Fig. 13.3. Schematic diagram of the most common (pseudo) hallucinations. Upside down: inverted objects. Macropsia/microp-sia: objects seen as too large or small. Telopsia/pelopsia: objects seen as too far or near. Palinopsia: objects seen in "correct relation" to others (e.g., exclusively situated on horizontal planes) and thus in multiple locations (a subtype of polyopsia). Metamorphopsia: objects misshapen. Polyopsia: multiple images of a single object (a failure of the "extinguishing center"). Platyopsia: loss of spatial perception in which all objects appear flat. Allesthesia: objects appear to be floating

Visual (pseudo)hallucinations are much more common than visual agnosias or visual hemineglect. Specific questioning about pseudohallucinations will often elicit a positive response, especially in patients with migraine and visual aura. A particularly pronounced form of pseudohallucination occurs in the so-called Charles Bonnet syndrome, named after the Swiss naturalist who first described it. Patients with advanced visual loss, as in age-related macular degeneration, can experience hallucinations in the blind areas of their central visual field. Neural activity in higher visual centers becomes independent of input through the usual afferent pathways, and can lead to the recall of complex visual memories of past scenes and events that seem to fill in the missing areas of vision. History taking from these patients requires tact. Many are reluctant to describe their experiences, or fear that the images are a sign of impending madness. An explanation of the source of the problem can provide them with wonderful relief.

Visual Illusions r Definition

Visual illusions are deceptive perceptions for which visual stimuli are adequate, but are then misinterpreted (incorrectly processed).

■ Figure 13.4 gives a summary of the highly varied appearances that visual illusions can form.

An important feature is the temporal latency of several seconds or minutes, separating the illusion from the inciting event. This is an important differentiating criterion for illusions of retinal origin, as in the persistence of immediate afterimages following a dazzling light exposure.

A completely accurate differentiation of these perceptual disturbances is not always possible. For example, in patients with the metamorphopsias of migraine, one should not refer to pseudohallucinations, but rather to pseudoillusions, since these usually have an inciting visual stimulus.

Fig. 13.3. Schematic diagram of the most common (pseudo) hallucinations. Upside down: inverted objects. Macropsia/microp-sia: objects seen as too large or small. Telopsia/pelopsia: objects seen as too far or near. Palinopsia: objects seen in "correct relation" to others (e.g., exclusively situated on horizontal planes) and thus in multiple locations (a subtype of polyopsia). Metamorphopsia: objects misshapen. Polyopsia: multiple images of a single object (a failure of the "extinguishing center"). Platyopsia: loss of spatial perception in which all objects appear flat. Allesthesia: objects appear to be floating

Palinopsia

Palinopsia

Allesthesia

Fig. 13.4. Schematic diagram of the most common illusions (after Kolmel 1988). a Simple visual (pseudo)hallucinations/illusions are characterized by comparatively small but disruptive visual elements; these can appear unformed or alternatively as filigreed or finely structured objects. b Complex visual (pseudo)hallucinations/ illusions by contrast are marked by perceptions of faces, complex scenes, or sequences of events

Fig. 13.4. Schematic diagram of the most common illusions (after Kolmel 1988). a Simple visual (pseudo)hallucinations/illusions are characterized by comparatively small but disruptive visual elements; these can appear unformed or alternatively as filigreed or finely structured objects. b Complex visual (pseudo)hallucinations/ illusions by contrast are marked by perceptions of faces, complex scenes, or sequences of events

Diagnosis of Central Visual Disturbances

History/Techniques of Interview

Patients with acquired brain damage are often not able to provide a clear description of their visual problems. Often they report in general terms that they have poor vision or that they have lost vision in one eye. Not infrequently, they ascribe their problems (collisions, reading difficulties) entirely to their environment. They say, for example, "People are impolite and won't allow me to pass by", or "Everything is dark", or "I can't understand what I read". Their descriptions are often characterized by anxiety and fear: fear of public places, of getting lost, of being seen as demented. They are often aware that they can no longer properly read, and that they see colored spots, snakes, or animals when no such things are actually there. They may say that they are "imagining things" or they report that everything appears dull or dark. Through systematic questioning, useful information can be gleaned. The questions should be indirect in nature, focused not so much on the visual disturbances per se, but on their consequences, i.e., on the effects that they have on the patients' observations and experiences (■ Tables 13.1 and 13.3).

Anton's Syndrome (Visual Anosognosia) Definition

The inability to recognize one's own illness is described as an anosognosia. When patients completely deny visual problems, though they have obviously and severely impaired vision (visual anosognosia), it is referred to as Anton's syndrome; this can be produced by a parietotemporal lesion in the right cerebral hemisphere.

Table 13.3. Catalog of questions for when a central disturbance of vision is suspected

Have you noticed any change in your vision since the time you became sick?

Is your vision not as clear as it used to be?

Are you having problems avoiding or bumping into people or obstacles? Do people or objects suddenly appear from out of nowhere?

Are you having problems with reading? When yes:

• Are letters missing at the beginnings or ends of words?

• Are you having problems with finding the beginnings or ends of lines of print?

• Are you having problems with losing the line that you are reading?

Are you being dazzled by bright lights more frequently than before?

Do you have the feeling that you need more light than before? Does everything appear to be too dark?

Do colors now appear to be washed out, brighter than usual, unusual, or strange?

Have you seen colored patterns, stars, spots of light, lines, fogging or other unusual images during or since the time you became sick?

When yes:

Symptom-Guided Diagnostic Tests

Using the information obtained from a carefully taken history, simple symptom-guided diagnostic tests can be used in the office to establish an initial differential diagnosis (■ Table 13.2).

J Pearl

When testing visual recognition, one should make certain that the patient does not touch the objects or use any nonvisual sense (e.g., hearing or smell). In addition, the visually determined naming of objects should be specific and not rely on circumlocutions, such as "It's used for writing", rather than "pencil".

Additional Tests

Specific Diagnostic Tests

A complete neuro-ophthalmic examination is first necessary to eliminate ocular sources of such problems as refractive polyopsia, metamorphopsia, impairment of contrast sensitivity, and photophobia (Chap. 2). The fundus appearance will give valuable clues to the presence of vascular, neoplastic, or inflammatory changes affecting the health of the retina and/or optic nerve.

^ Pearl

Any suspicion of a central visual disturbance makes careful visual field testing mandatory. In addition, reading fluency must be tested, as it is most likely to be impaired by parafoveal homonymous field defects

Widespread lesions affecting the occipitoparietotemporal boundary region - the transitional zone between the "where system" and the "what system" (flow diagram; ■ Fig. 13.1; ■ Table 13.1) - produce the clinical phenomenon of an asymmetry in optokinetic nystagmus (OKN). A patterned stimulus moving horizontally toward the diseased side of the brain will fail to produce a normal train of saccadic movements (counter to the direction of the pattern movement), when compared with the response to stimulus movement in the opposite direction. This asymmetry of OKN responses is best elicited by ensuring an equal rate of movement, when comparing OKN responses with right- versus left-moving patterns (Chap. 11).

T| Pearl

Since directional descriptions of OKN often lead to confusion, it is best to record the results of testing by noting the side of the patient toward which the moving stimulus has produced abnormal responses.

Modern neuroimaging procedures (CT and MRI) can often determine the location and the cause of disturbances of central vision (Chap. 20). Since other neurological deficits are frequently associated with central visual disturbances, a more complete neurological examination is always necessary (Chap. 21). Patients with posterior brain damage can also have impairment of visual attention, of visual and verbal memory, and/or of language (anomia, aphasia). Thus, disease located in this region is practically always an indication for referral to a neuropsychologist. Neuropsychology is primarily focused on the study of disturbances of higher visual functions (spatial perception, object perception, reading, visual recognition, maintenance of visual attention or retention of visual information in memory).

Therapeutic Options Pearl

Fortunately, many patients with posterior visual pathway disease show some spontaneous improvement in visual function within the first few months after onset.

For cases of homonymous visual field loss, which is the most frequent visual disturbance in this group of patients, there are neurorehabilitation or occupational therapy facilities associated with many neurology/neuropsychology departments. These facilities commonly have programs that include clinically tested methods for maximizing the prospects for recovery following brain damage. These include oculomotor compensation strategies for improvement of field of view, visual exploration, visual orientation, and reading. This can result in a significant reduction in functional visual impairment after 20 to 30 lessons over a period of just 2 to 3 weeks. Other methods, such as visual stimulation in the transitional zone between damaged and intact regions of the visual field, remain controversial. Unfortunately, well-intentioned efforts to instruct patients in methods that might compensate for visual field defects (by using head turning, or tilting the head to one side or the other) have not been clinically successful.

Counseling

There should be an initial counseling session immediately following the first office examination, to explain to the patient as clearly as possible the cause for his or her visual difficulties. At the same time, there should be a discussion of the realistic chances for spontaneous improvement in visual function, and the physician should also use this opportunity to clarify the reasons for referral to other specialists and the anticipated diagnostic testing that will like ly follow. More complete explanation and counseling should follow completion of all relevant diagnostic examinations. A systematic discussion of all available options for management will reduce the patient's sense of insecurity without raising false or exaggerated expectations.

Pearl

Where possible, the patient's closest relatives should be included in these discussions, as they too need to understand the potential risks to the patient (e.g., in driving) associated with visual field loss or hemineglect.

It is especially important for patients with paracen-tral loss of visual field caused by posterior pathway disease to be warned in the presence of others (preferably close family members) that this type of visual loss makes safe driving impossible.

If the visual loss persists for a period of 3 months, discussions with the patient and relatives or close advisers should be directed toward a long-term plan for appropriate changes in occupational and social aspects of daily living. In this regard, referral to an occupational rehabilitation program may be most helpful.

Conclusion

Due to their unusual disturbances of vision, many patients with central visual damage will first seek the care of an ophthalmologist. This chapter is meant to provide a basis for systematic investigation and characterization of such visual disorders. Appropriate diagnostic and therapeutic care of such patients requires a multidisciplinary approach, including participation by neurologists, neuroradiologists, neuropsychologists, and neuro-ophthalmologists. Whenever a central disturbance of vision is associated with progressive symptoms (which may include sensory loss, oculomotor paralysis, or altered levels of consciousness), an immediate investigation should begin, including neuroim-aging and neurological examination.

Further Reading

Damasio AR, Damasio H, van Hoesen GW (1982) Prosopagnosia: anatomic basis and behavioral mechanisms. Neurology 32: 331-341

Fahle M, Greenlee M (eds) (2003) The neuropsychology of vision. Oxford University Press, Oxford

Hartje W, Poeck K (2002) Klinische Neuropsychologie. Thieme, Stuttgart

Huber A, Kömpf D (1998) Klinische Neuroophthalmologie. Thieme, Stuttgart

Karnath H-O, Thier P (eds) (2006) Neuropsychologie. Springer, Berlin Heidelberg New York

Kerkhoff G, Schaub J, Zihl J (1990) Die Anamnese zerebral bedingter

Sehstörungen. Nervenarzt 61: 711-718 Kölmel HW (1988) Die homonymen Hemianopsien. Springer, Berlin

Heidelberg New York Sacks O (1985) The man who mistook his wife for a hat. Simon & Schuster, New York

Zihl J, von Cramon D (1986) Zerebrale Sehstörungen. Kohlhammer, Stuttgart

Zihl J (2000) Rehabilitation of visual disorders after brain injury. Hove, UK: Psychology Press

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