The formed visual hallucinations associated with vision loss.

BACKGROUND: Patients with acquired visual impairment, but without mental illness, may experience repetitive episodes of vividly detailed, clearly focused, formed visual hallucinations. Yet these may not be shared voluntarily with clinicians. We wanted to learn: (1) the prevalence of formed visual hallucinations and (2) the nature of any changes in the hallucinations after more than two years. METHODS: Part I--Eighty-eight visually impaired adult patients at the Massachusetts Eye and Ear Infirmary were surveyed during 1995. Age, gender, ocular diagnoses, visual acuities, and hallucination descriptions were recorded. Part II--Those subjects reporting hallucinations in 1995 were selected to participate in a second survey--more than two years later-to ascertain changes. RESULTS: Part I--Nine of 88 subjects (10.2% prevalence) reported formed visual hallucinations, frequently human faces or figures. Five additional subjects (5.6%) reported a history of formed hallucinations-beginning after their vision loss--that had either disappeared or changed to unformed hallucinations (lights and colors) before this survey. Part II--Seven of the eligible nine subjects were surveyed more than two years later. Hallucinations persisted for six. Five reported reduced frequency of hallucinations, despite failing acuity among four of these five. CONCLUSIONS: Formed visual hallucinations are not uncommon among patents with significant acquired losses in visual acuity and/or visual field (homonymous hemianopsia). Although formed hallucinations may persist for years, there appears to be a tendency toward reduced frequency of episodes over time. Silent isolated visual hallucinations, in the absence of psychopathology, imply an organic etiology. Eliciting these phenomena through an appropriate clinical history provides a valuable opportunity for referral, or patient education and reassurance.

Study of luminance effects on pinhole test results for visually impaired patients.

PURPOSE: The visual acuity of visually impaired patients has been reported to improve after a refraction, despite pinhole test results that show a decline or no change in acuity. Our aim was to investigate whether the pinhole-induced reduction in retinal illuminance accounted for these unreliable predictions of best-corrected acuity. METHODS: Participants were 64 adult patients referred for low-vision rehabilitation. Neutral density filters reproduced the pinhole-induced luminance loss, allowing pinhole test and postrefraction acuities to be measured at essentially equivalent levels of retinal illuminance. The following data were collected in random order from each subject's better eye: (1) habitual visual acuity, (2) habitual visual acuity with filter, (3) habitual visual acuity with pinhole, (4) best-corrected/postrefraction visual acuity, (5) postrefraction visual acuity with filter. RESULTS: On average, the pinhole test under-estimated postrefraction visual acuity by six letters (95% confidence limits = +/- 20). The pinhole test underestimated postrefraction visual acuity with the filter by two letters (95% confidence limits = +/- 16). Among subjects whose acuity improved with the pinhole test (N = 24), 83% experienced better postrefraction visual acuity. Among subjects whose acuity declined or remained unchanged with the pinhole test (N = 40), 50% achieved better postrefraction visual acuity. CONCLUSIONS: The pinhole-induced luminance loss contributed to inadequate predictions of postrefraction visual acuity. Pinhole test results were enormously variable, underestimating and overestimating postrefraction visual acuity. The pinhole test was less reliable when improvements in postrefraction visual acuity were small. Visually impaired patients deserve periodic refractions, and the pinhole test result should not be used as a dichotomizer for clinical decisions regarding the need for a refraction.

In vivo metabolic activity of the suprachiasmatic nuclei: a comparative study.

In vivo glucose utilization was measured in the suprachiasmatic nuclei (SCN) of the rat, monkey, and cat using the 14C-labeled deoxyglucose technique. SCN metabolic activity in all species was endogenously rhythmic with high levels during the subjective daylight portion of the 24 h day. Such phase conservation across night-, day-, and randomly-active species is in agreement with formal analyses of the properties of entrainable circadian oscillators, and our data suggest that the biochemical processes which underlie the activity of this circadian clock are similar in mammals with differing patterns of expressed circadian rhythmicity.