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Pre-Optometry Professional Society

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Pre-Optometry Professional Society

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Optometry Related News

Optometry Related News

Optometry Today

LAS VEGAS – RightEye, a company that currently markets three tests for concussion and other neurological issues, four aspects of vision such as convergence and depth perception, and vision combined with motor skills, is introducing two new tests for autism and Parkinson’s disease. The GeoPref Autism Test can assist optometrists with early diagnosis in toddlers, RightEye President Barbara Barclay said, and the POM (Parkinson’s and Other Movement) Disorders Test evaluates various eye movement problems associated with saccades and fixation to help determine a disorder such as Parkinson’s disease or essential tremor.

(To watch video, click the blue title above)

Optometry Today

LAS VEGAS – RightEye, a company that currently markets three tests for concussion and other neurological issues, four aspects of vision such as convergence and depth perception, and vision combined with motor skills, is introducing two new tests for autism and Parkinson’s disease. The GeoPref Autism Test can assist optometrists with early diagnosis in toddlers, RightEye President Barbara Barclay said, and the POM (Parkinson’s and Other Movement) Disorders Test evaluates various eye movement problems associated with saccades and fixation to help determine a disorder such as Parkinson’s disease or essential tremor.

(To watch video, click the blue title above)

OAT Quiz of the Week

(If you get a 100 on one of the quizzes for every month, you'll earn member points! Points will be added during the end of the month.)

OAT Quiz of the Week

(If you get a 100 on one of the quizzes for every month, you'll earn member points! Points will be added during the end of the month.)

Welcome to your OAT Practice Quiz

1) Which of the following would be the best solvent for an SN2 reaction?
2) Concerns about the likely occurrence of an influenza pandemic in the near future are increasing. The highly pathogenic strains of the H5N1 virus circulating in Asia, Europe, and Africa have become the most feared candidates for giving rise to a pandemic strain. Understanding the method of transmission of influenza from one host to another will become critical in the near future.

By definition, aerosols are suspensions in air of solid or liquid particles, small enough that they remain airborne for prolonged periods because of their low settling velocity. The median diameters at which particles exhibit aerosol behavior also correspond to the sizes at which they are efficiently deposited in the lower respiratory tract when inhaled. Particles of >6μm diameter are trapped increasingly in the upper respiratory tract, while no substantial deposition in the lower respiratory tract occurs at larger sizes. Many authors adopt a size cutoff of <5 μm for aerosols. This convenient convention is, however, somewhat arbitrary, because the long settling time and the efficient deposition in the lower respiratory tract are properties that do not appear abruptly at a specific diameter value. Certainly, particles in the micron or submicron range will behave as aerosols, and larger particles will settle rapidly, will not be deposited in the lower respiratory tract, and are referred to as large droplets.

Coughing or sneezing generates a substantial quantity of particles, a large number of which are large droplets. In addition, particles expelled by coughing or sneezing rapidly shrink in size by evaporation, thereby increasing the number of particles that behave as aerosols. Particles shrunken by evaporation are referred to as droplet nuclei. This phenomenon affects large droplets, and complete desiccation would decrease the diameter to a little less than half the initial diameter. When desiccated droplet nuclei are exposed to humid air, such as in the lungs, they will swell back to normal size. This is said to be a hygroscopic property of droplet nuclei. One would expect that inhaled hygroscopic particles would be retained in the lower respiratory tract with greater efficiency, and this hypothesis has been confirmed experimentally. Because aerosols remain airborne, they can be carried over large distances, which may create a potential for long-range infections. The occurrence of long-range infections is affected by several other factors. These include dilution, the infectious dose, the amount of infectious particles produced, the duration of shedding of the infectious agent, and the persistence of the agent in the environment. Inferring an absence of aerosols because long-range infections are not frequently observed is incorrect.

Humans acutely infected with influenza virus have a high virus titer in their respiratory secretions, which will be aerosolized when the patient sneezes or coughs. The viral titer measured in nasopharyngeal washes culminates on approximately day 2 or 3 after infection. The persistence of the infectivity of influenza virus in aerosols has been studied in the laboratory. In experiments that used homogeneous aerosolized influenza virus suspensions, virus infectivity at a fixed relative humidity undergoes an exponential decay. This decay is characterized by very low death rate constants, provided that a low relative humidity was given. These results are consistent with those of an older study in which infectious influenza viruses in an aerosol could be demonstrated for up to 24 hours by using infection in mice as a detection method, provided that the relative humidity was low. In all these studies, the decay of virus infectivity increased rapidly at a higher relative humidity. The increased survival of influenza virus in aerosols at low relative humidity has been suggested as a factor that accounts for the seasonality of influenza. The sharply increased decay of infectivity at high humidity has also been observed for other enveloped viruses, such as measles. In contrast, exactly the opposite relationship has been shown for some nonenveloped viruses, such as poliovirus.

Experimental infection studies permit the clear separation of the aerosol route of transmission from transmission by large droplets. Laboratory preparation of homogeneous small particle aerosols free of large droplets is readily achieved. Conversely, transmission by large droplets without accompanying aerosols can be achieved by intranasal drop inoculation.

Influenza infection has been documented by aerosol exposure in the mouse model, the squirrel monkey model, and human volunteers. Observations made during experimental infections with human volunteers are particularly interesting and relevant. In studies conducted by Alford and colleagues, volunteers were exposed to carefully titrated aerosolized influenza virus suspensions by inhaling 10 L of aerosol through a facemask. Demonstration of infection in participants in the study was achieved by recovery of infectious viruses from daily throat swabs. The use of carefully titrated viral stocks enabled the determination of the minimal infectious dose by aerosol inoculation. For volunteers who lacked detectable neutralizing antibodies at the onset, the 50% human infectious dose for the aerosol group was one tenth of the dose required when inoculation was performed by intranasal drops. Additional data from experiments conducted with aerosolized influenza virus showed that when a dose was inhaled, only a hundredth of the dose was deposited in the nose. Since the dose deposited in the nose is largely below the minimal dose required by intranasal inoculation, this would indicate that the preferred site of infection initiation during aerosol inoculation is the lower respiratory tract.

Another relevant observation is that whereas the clinical symptoms initiated by aerosol inoculation covered the spectrum of symptoms seen in natural infections, the disease observed in study participants infected experimentally by intranasal drops was milder, with a longer incubation time and usually no involvement of the lower respiratory tract. For safety reasons, this finding led to the adoption of intranasal drop inoculation as the standard procedure in human experimental infections with influenza virus.

Additional support for the view that the lower respiratory tract the preferred site of infection is provided by studies on the use of zanamivir for prophylaxis, or the prevention of disease. In experimental settings, intranasal zanamivir was protective against experimental inoculation with influenza virus in intranasal drops. However, in studies on prophylaxis of natural infection, intranasally applied zanamivir was not protective, whereas inhaled zanamivir was protective in one study and a protective effect approached statistical significance in another study. These experiments and observations strongly support the view that many, possibly most, natural influenza infections occur by the aerosol route and that the lower respiratory tract may be the preferred site of initiation of the infection.

In natural infections, the postulated modes of transmission have included aerosols, large droplets, and direct contact with secretions or fomites because the virus can remain infectious on nonporous dry surfaces for nearly two days. Because in practice completely ruling out contributions of a given mode of transmission is often difficult, the relative contribution of each mode is usually difficult to establish by epidemiologic studies alone.

However, a certain number of observations are consistent with and strongly suggestive of an important role for aerosol transmission in natural infections, for example the explosive nature and simultaneous onset of disease in many persons, including in hospital outbreaks. The often-cited outbreak described by one study on an airplane with a defective ventilation system is best accounted for by aerosol transmission.

Even more compelling were the observations made at the Livermore Veterans Administration Hospital during the 1957–58 pandemic. The study group consisted of 209 tuberculous patients confined during their hospitalization to a building with ceiling-mounted UV lights; 396 tuberculous patients hospitalized in other buildings that lacked these lights constituted the control group. Although the study group participants remained confined to the building, they were attended to by the same personnel as the control group, and there were no restrictions on visits from the community. Thus, it was unavoidable at some point that attending personnel and visitors would introduce influenza virus in both groups. During the second wave of the pandemic, the control group and the personnel sustained a robust outbreak of respiratory illness, whereas the group in the irradiated building remained symptom free.

Whereas UV irradiation is highly effective in inactivating viruses in small-particle aerosols, it is ineffective for surface decontamination because of poor surface penetrations. It is also ineffective for large droplets because the germicidal activity sharply decreases as the relative humidity increases. Furthermore, because the installation of UV lights was set up in such a way as to decontaminate the upper air of rooms only, large droplets would not have been exposed to UV, whereas aerosols, carried by thermal air mixing, would have been exposed. So in effect in this study only the aerosol route of infection was blocked, and this step alone achieved near complete protection.

The converse occurrence, blocking only the large droplet and fomites routes in natural infections, can be inferred from the studies on the use of zanamivir for prophylaxis described previously. In experimental settings, intranasally applied zanamivir was protective against an experimental challenge with influenza by intranasal drops. However, in studies on prophylaxis of natural disease, intranasal zanamivir was not protective, which leads to the conclusion that natural infection can occur efficiently by a route other than large droplets or fomites. As noted above, inhaled zanamivir was significantly protective.



How could scientists disprove that the lower respiratory tract is the preferred site of infection?
3) A weightlifter lifts a 275kg barbell from the ground to a height of 2.4 m

How much work has he done?
4) Which of the following lines has no point of intersection with the line y = 4x + 5?

Name

Email

 

Diagnosis of the Week

Diagnosis of the Week

Usher Syndrome

Photograph of the retina of a patient with Usher syndrome (left) compared to a normal retina (right). The optic nerve (arrow) looks very pale, the vessels (stars) are very thin and there is characteristic pigment, called bone spicules (double arrows).

Usher syndrome is the most common condition that affects both hearing and vision. The major symptoms of Usher syndrome are hearing loss and an eye disorder called retinitis pigmentosa, or RP. RP causes night-blindness and a loss of peripheral vision (side vision) through the progressive degeneration of the retina. 

As RP progresses, the field of vision narrows—a condition known as “tunnel vision”—until only central vision (the ability to see straight ahead) remains. Many people with Usher syndrome also have severe balance problems.

 

There are three clinical types of Usher syndrome: type 1, type 2, and type 3. In the United States, types 1 and 2 are the most common types. Together, they account for approximately 90 to 95 percent of all cases of children who have Usher syndrome.

 

Who is affected by Usher syndrome?

Approximately 3 to 6 percent of all children who are deaf and another 3 to 6 percent of children who are hard-of-hearing have Usher syndrome. In developed countries such as the United States, about four babies in every 100,000 births have Usher syndrome.

 

What causes Usher syndrome?

Usher syndrome is inherited, which means that it is passed from parents to their children through genes. Usher syndrome is inherited as an autosomal recessive trait.

 

How is Usher syndrome diagnosed?

Because Usher syndrome affects hearing, balance, and vision, diagnosis of the disorder usually includes the evaluation of all three senses. Evaluation of the eyes may include a visual field test to measure a person’s peripheral vision, an electroretinogram (ERG) to measure the electrical response of the eye’s light-sensitive cells, and a retinal examination to observe the retina and other structures in the back of the eye. A hearing (audiologic) evaluation measures how loud sounds at a range of frequencies need to be before a person can hear them. An electronystagmogram (ENG) measures involuntary eye movements that could signify a balance problem.

 

Usher Syndrome

Photograph of the retina of a patient with Usher syndrome (left) compared to a normal retina (right). The optic nerve (arrow) looks very pale, the vessels (stars) are very thin and there is characteristic pigment, called bone spicules (double arrows).

Usher syndrome is the most common condition that affects both hearing and vision. The major symptoms of Usher syndrome are hearing loss and an eye disorder called retinitis pigmentosa, or RP. RP causes night-blindness and a loss of peripheral vision (side vision) through the progressive degeneration of the retina. 

As RP progresses, the field of vision narrows—a condition known as “tunnel vision”—until only central vision (the ability to see straight ahead) remains. Many people with Usher syndrome also have severe balance problems.

 

There are three clinical types of Usher syndrome: type 1, type 2, and type 3. In the United States, types 1 and 2 are the most common types. Together, they account for approximately 90 to 95 percent of all cases of children who have Usher syndrome.

 

Who is affected by Usher syndrome?

Approximately 3 to 6 percent of all children who are deaf and another 3 to 6 percent of children who are hard-of-hearing have Usher syndrome. In developed countries such as the United States, about four babies in every 100,000 births have Usher syndrome.

 

What causes Usher syndrome?

Usher syndrome is inherited, which means that it is passed from parents to their children through genes. Usher syndrome is inherited as an autosomal recessive trait.

 

How is Usher syndrome diagnosed?

Because Usher syndrome affects hearing, balance, and vision, diagnosis of the disorder usually includes the evaluation of all three senses. Evaluation of the eyes may include a visual field test to measure a person’s peripheral vision, an electroretinogram (ERG) to measure the electrical response of the eye’s light-sensitive cells, and a retinal examination to observe the retina and other structures in the back of the eye. A hearing (audiologic) evaluation measures how loud sounds at a range of frequencies need to be before a person can hear them. An electronystagmogram (ENG) measures involuntary eye movements that could signify a balance problem.

 

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