Eduard Jäger von Jaxtthal , a Vienna oculist, makes improvements to eye chart test types that were developed by Heinrich Kuechler.
A response plan that does not follow the specified format in appendix F to this part shall have an emergency response action plan as specified in paragraphs h 1 of this section and be supplemented with a cross-reference section to identify the location of the elements listed in paragraphs h 2 through h 10 of this section. To meet the requirements of this part, a response plan shall address the following elements, as further described in appendix F to this part:.
The response plan shall include an emergency response action plan in the format specified in paragraphs h 1 i through viii of this section that is maintained in the front of the response plan, or as a separate document accompanying the response plan, and that includes the following information:.
The response plan shall identify and discuss the location and type of the facility , the identity and tenure of the present owner and operator , and the identity of the qualified individual identified in paragraph h 1 of this section. The response plan shall include:. A Activate internal alarms and hazard communication systems to notify all facility personnel;.
B Notify all response personnel, as needed;. C Identify the character, exact source, amount, and extent of the release, as well as the other items needed for notification;. F Assess the possible hazards to human health and the environment due to the release.
This assessment must consider both the direct and indirect effects of the release i. G Assess and implement prompt removal actions to contain and remove the substance released;. H Coordinate rescue and response actions as previously arranged with all response personnel;. I Use authority to immediately access company funding to initiate cleanup activities; and. J Direct cleanup activities until properly relieved of this responsibility. The response plan shall discuss the facility 's known or reasonably identifiable history of discharges reportable under 40 CFR part for the entire life of the facility and shall identify areas within the facility where discharges could occur and what the potential effects of the discharges would be on the affected environment.
To assess the range of areas potentially affected, owners or operators shall, where appropriate, consider the distance calculated in paragraph f 1 ii of this section to determine whether a facility could, because of its location, reasonably be expected to cause substantial harm to the environment by discharging oil into or on the navigable waters or adjoining shorelines. The response plan shall include discussion of specific planning scenarios for:.
In cases where the Regional Administrator determines that the worst case discharge volume calculated by the facility is not appropriate, the Regional Administrator may specify the worst case discharge amount to be used for response planning at the facility. For complexes, the worst case planning quantity shall be the larger of the amounts calculated for each component of the facility ;.
For complexes, this planning quantity shall be the larger of the amounts calculated for each component of the facility ; and. For complexes, this planning quantity shall be the larger of the amounts calculated for each component of the facility. The response plan shall describe the procedures and equipment used to detect discharges. Meanwhile, in England, three A equipped Bombardment Groups were assigned to the 9th Air Force and became operational in They started using the same low-level tactics that had been so successful in the Pacific, but due to heavy German flak, losses were too high and the tactics were changed to medium-level raids.
After supporting advancing Allied forces into France until the end of , all units transitioned to the Douglas A Invader. Reconnaissance Havocs joined the 9th Air Force in Data from McDonnell Douglas Aircraft since . From Wikipedia, the free encyclopedia. This section needs expansion. You can help by adding to it. List of Douglas A Havoc operators. List of surviving A Havocs. US Attack Aircraft , , Retrieved: McDonnell Douglas Aircraft since Soviet Air Power in World War 2.
Hinkley UK, Midland Publishing, Green, William and Gordon Swanborough. WW2 Aircraft Fact Files: Macdonald and Jane's Publishers Ltd. Air Enthusiast , Thirty-six, May—August , pp. The Osprey Encyclopedia of Russian Aircraft — Mawer, Granville Alan Diary of a Spitfire Pilot. A Havoc in action. Cypress, California, Dana T. Douglas Havoc and Boston: The Crowood Press, Grange Books plc, Articles and topics related to the A Havoc.
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Views Read Edit View history. In other projects Wikimedia Commons. The RPE also has a vital function of recycling the chemicals used by the rods and cones in photon detection. If the RPE is damaged and does not clean up this "shed" blindness can result. As in a photographic lens , visual acuity is affected by the size of the pupil. If the optics of the eye were otherwise perfect, theoretically, acuity would be limited by pupil diffraction, which would be a diffraction-limited acuity of 0.
The smallest cone cells in the fovea have sizes corresponding to 0. The optimal acuity of 0. Laser interferometers are now used routinely in patients with optical problems, such as cataracts , to assess the health of the retina before subjecting them to surgery. The visual cortex is the part of the cerebral cortex in the posterior part of the brain responsible for processing visual stimuli, called the occipital lobe. Many of these neurons are believed to be involved directly in visual acuity processing.
Proper development of normal visual acuity depends on a human or an animal having normal visual input when it is very young. Any visual deprivation, that is, anything interfering with such input over a prolonged period of time, such as a cataract , severe eye turn or strabismus , anisometropia unequal refractive error between the two eyes , or covering or patching the eye during medical treatment, will usually result in a severe and permanent decrease in visual acuity and pattern recognition in the affected eye if not treated early in life, a condition known as amblyopia.
The decreased acuity is reflected in various abnormalities in cell properties in the visual cortex. These changes include a marked decrease in the number of cells connected to the affected eye as well as cells connected to both eyes in cortical area V1 , resulting in a loss of stereopsis , i. The period of time over which an animal is highly sensitive to such visual deprivation is referred to as the critical period.
The eye is connected to the visual cortex by the optic nerve coming out of the back of the eye. The two optic nerves come together behind the eyes at the optic chiasm , where about half of the fibers from each eye cross over to the opposite side and join fibers from the other eye representing the corresponding visual field, the combined nerve fibers from both eyes forming the optic tract.
This ultimately forms the physiological basis of binocular vision. The tracts project to a relay station in the midbrain called the lateral geniculate nucleus , part of the thalamus , and then to the visual cortex along a collection of nerve fibers called the optic radiation.
Any pathological process in the visual system, even in older humans beyond the critical period, will often cause decreases in visual acuity. Thus measuring visual acuity is a simple test in accessing the health of the eyes, the visual brain, or pathway to the brain. Any relatively sudden decrease in visual acuity is always a cause for concern. Common causes of decreases in visual acuity are cataracts and scarred corneas , which affect the optical path, diseases that affect the retina, such as macular degeneration and diabetes , diseases affecting the optic pathway to the brain such as tumors and multiple sclerosis , and diseases affecting the visual cortex such as tumors and strokes.
As determined from single-cell experiments on the cat and primate, different ganglion cells in the retina are tuned to different spatial frequencies , so some ganglion cells at each location have better acuity than others. Ultimately, however, it appears that the size of a patch of cortical tissue in visual area V1 that processes a given location in the visual field a concept known as cortical magnification is equally important in determining visual acuity.
Besides the neural connections of the receptors, the optical system is an equally key player in retinal resolution. In the ideal eye, the image of a diffraction grating can subtend 0. This is certainly not the case, however, and furthermore the pupil can cause diffraction of the light.
Thus, black lines on a grating will be mixed with the intervening white lines to make a gray appearance. Defective optical issues such as uncorrected myopia can render it worse, but suitable lenses can help. Images such as gratings can be sharpened by lateral inhibition, i. A similar reaction is in the case of chromatic aberrations, in which the color fringes around black-and-white objects are inhibited similarly. Visual acuity is often measured according to the size of letters viewed on a Snellen chart or the size of other symbols, such as Landolt Cs or the E Chart.
In some countries, acuity is expressed as a vulgar fraction , and in some as a decimal number. In the decimal system, acuity is defined as the reciprocal value of the size of the gap measured in arc minutes of the smallest Landolt C , the orientation of which can be reliably identified.
A value of 1. The LogMAR scale converts the geometric sequence of a traditional chart to a linear scale. It measures visual acuity loss: When visual acuity is below the largest optotype on the chart, the reading distance is reduced until the patient can read it.
Once the patient is able to read the chart, the letter size and test distance are noted. If the patient is unable to read the chart at any distance, he or she is tested as follows:.
For example, the recording CF 5' would mean the patient was able to count the examiner's fingers from a maximum distance of 5 feet directly in front of the examiner. The results of this test, on the same patient, may vary from examiner to examiner. This is due more so to the size differences of the various examiner's hands and fingers, than fluctuating vision.
The results of the Hand Motion test are often recorded without the testing distance. This is due to the fact that this test is performed after the patient cannot "pass" the Counting Fingers test. At this point, the examiner is usually directly in front of the patient, and it is assumed that the Hand Motion test is performed at a testing distance of 1 foot or less.
Various countries have defined statutory limits for poor visual acuity that qualifies as a disability. For example, in Australia, the Social Security Act defines blindness as:. In the USA, the relevant federal statute defines blindness as follows: A person's visual acuity is registered documenting the following: Visual acuity measurement involves more than being able to see the optotypes. The patient should be cooperative, understand the optotypes, be able to communicate with the physician, and many more factors.
If any of these factors is missing, then the measurement will not represent the patient's real visual acuity. Visual acuity is a subjective test meaning that if the patient is unwilling or unable to cooperate, the test cannot be done. A patient who is sleepy, intoxicated, or has any disease that can alter their consciousness or mental status, may not achieve their maximum possible acuity.
Some patients will not tell the examiner that they don't know the optotypes, unless asked directly about it. Brain damage can result in a patient not being able to recognize printed letters, or being unable to spell them. A motor inability can make a person respond incorrectly to the optotype shown and negatively affect the visual acuity measurement. The measurement of visual acuity in infants, pre-verbal children and special populations for instance, handicapped individuals is not always possible with a letter chart.
For these populations, specialised testing is necessary. As a basic examination step, one must check whether visual stimuli can be fixated, centered and followed.
More formal testing using preferential looking techniques use Teller acuity cards presented by a technician from behind a window in the wall to check whether the child is more visually attentive to a random presentation of vertical or horizontal gratings on one side compared with a blank page on the other side — the bars become progressively finer or closer together, and the endpoint is noted when the child in its adult carer's lap equally prefers the two sides.
Another popular technique is electro-physiologic testing using visual evoked cortical potentials VEPs or VECPs , which can be used to estimate visual acuity in doubtful cases and expected severe vision loss cases like Leber's congenital amaurosis.
VEP testing of acuity is somewhat similar to preferential looking in using a series of black and white stripes sine wave gratings or checkerboard patterns which produce larger responses than stripes. Behavioral responses are not required and brain waves created by the presentation of the patterns are recorded instead. The patterns become finer and finer until the evoked brain wave just disappears, which is considered to be the endpoint measure of visual acuity. In adults and older, verbal children capable of paying attention and following instructions, the endpoint provided by the VEP corresponds very well to the psychophysical measure in the standard measurement i.
There is an assumption that this correspondence also applies to much younger children and infants, though this does not necessarily have to be the case. Studies do show the evoked brain waves, as well as derived acuities, are very adult-like by one year of age. For reasons not totally understood, until a child is several years old, visual acuities from behavioral preferential looking techniques typically lag behind those determined using the VEP, a direct physiological measure of early visual processing in the brain.
Possibly it takes longer for more complex behavioral and attentional responses, involving brain areas not directly involved in processing vision, to mature. Thus the visual brain may detect the presence of a finer pattern reflected in the evoked brain wave , but the "behavioral brain" of a small child may not find it salient enough to pay special attention to. A simple but less-used technique is checking oculomotor responses with an optokinetic nystagmus drum, where the subject is placed inside the drum and surrounded by rotating black and white stripes.