We studied the development and maturation of the visual system by determining when zebrafish begin to see and to move their eyes. This information was correlated with the time courses of the development of the retina, the retinofugal projection, the retinal image, and the extraocular muscles, to obtain an integrated picture of early visual development. Two visual behaviors were monitored over 48-96 hr postfertilization (hpf). The startle response (body twitch) was evoked by an abrupt decrease in light intensity. The optokinetic response (tracking eye movements) was evoked by rotation of a striped drum. Visually evoked startle developed over 68-79 hpf, more than 20 hr after the onset of a touch-evoked startle. It was not seen in eyeless fish, excluding a role for nonretinal light senses. Tracking eye movements developed over 73-80 hpf. They were always in the direction of drum rotation, even when the fish had been light deprived from blastula stage, ruling out a "trial and error" period of learning to track the drum. The image formed by the ocular lens was examined in intact fish made transparent by suppressing the formation of melanin. The eye was initially far sighted and gradually improved, so that by 72 hpf the image plane coincided with the photoreceptor layer. The extraocular muscles assumed their adult configuration between 66 and 72 hpf. Thus, the retinal image and functional extraocular muscles appeared nearly simultaneously with the onset of tracking eye movements and probably represent the last events in the construction of this behavior.

We investigated the development of oculomotor activity in zebrafish embryos and larvae of ages postfertilization (hpf). The optokinetic response (OKR: smooth 48-96 hrs tracking movements evoked by a rotating striped drum) improved steadily after its onset at and by had a achieved a gain (eye velocity/drum velocity) of 0.9, comparable 73 hpf, 96 hpf to adult performance. Reset movements (the fast phase of optokinetic nystagmus) developed over The vestibuloocular reflex (VOR: compensatory eye movements evoked by 75-81 hpf. passive rotation of the head) developed over and the associated reset movements, 74-81 hpf, overThe VOR was qualitatively normal in dark-reared fish, which excludes an 76-81 hpf. essential role for visual experience in its early development. Spontaneous saccadic movements (the fast shift of eye position) appeared between 81 and and at had maximum 96 hpf, 96 hpf velocities that were comparable to adults.These results are compared to, and found to be incompatible with, two earlier ideas of motor development: behavioral "differentiation" and "encephalization."

The ACR recognizes that radiology practices are grappling with when and how to safely resume routine radiology care during the coronavirus disease 2019 (COVID-19) pandemic. Although it is unclear how long the pandemic will last, it may persist for many months. Throughout this time, it will be important to perform safe, comprehensive, and effective care for patients with and patients without COVID-19, recognizing that asymptomatic transmission is common with this disease. Local idiosyncrasies prevent a single prescriptive strategy. However, general considerations can be applied to most practice environments. A comprehensive strategy will include consideration of local COVID-19 statistics; availability of personal protective equipment; local, state, and federal government mandates; institutional regulatory guidance; local safety measures; health care worker availability; patient and health care worker risk factors; factors specific to the indication(s) for radiology care; and examination or procedure acuity. An accurate risk-benefit analysis of postponing versus performing a given routine radiology examination or procedure often is not possible because of many unknown and complex factors. However, this is the overriding principle: If the risk of illness or death to a health care worker or patient from health care-acquired COVID-19 is greater than the risk of illness or death from delaying radiology care, the care should be delayed; however, if the opposite is true, the radiology care should proceed in a timely fashion.

SUMMARY:In recent months, organized medicine has been consumed by the anticipated transition to the 10th iteration of the International Classification of Disease system. Implementation has come and gone without the disruptive effects predicted by many. Despite the fundamental role the International Classification of Disease system plays in health care delivery and payment policy, few neuroradiologists are familiar with the history of its implementation and implications beyond coding for diseases.