All the colors, whether they are reds, blues, greens, or oranges, have exactly the same speed of light, which is 186,000 miles per second.
A wavelength is the distance from the top of one wave to the top of the next, whereas the frequency is the number of waves passing in 1 second. Red light may have a longer wavelength than blue but this indicates only its vertical vibration. All colors, white included, travel at the same speed.
The speed of light depends on frequency x wavelength. When the wavelength is shorter, its frequency is increased so that the speed of white versus colored light remains the same.
Obviously, the center of the lens remains where it is, regardless of how the lens is edged. However, high fashion dictates the shape of the frame and with radical lens designs the optical centers can be shifted in the frame itself and in relation to the eye.
Large frames that contain strong prescriptions, that is -5.00 diopters or more, frequently slide down the nose with reading. The effect of gravity drops the lens, and the vertex distance of the lens to the eye changed. With plus lenses it increases the prescription; with minus lenses it does the reverse. Also, unwanted base-up prism is added with plus lenses, with the opposite, or base-down, occurring with minus lenses.
The optical center and the mechanical center do not coincide. The optical center of a lens is that place of the lens that does not contain unwanted prism. It is the point detected on the lensmeter where the rays of light come into focus. The optical center should be in line with the eye. The mechanical center is the geographic center, and in a perfectly round lens it coincides with the optical center. The perfectly round center, not the mechanical center, concerns us.
The optical centers of the lenses always should be marked and compared with the interpupillary measurements - the distance from the center of one pupil to the other.
You will need the patient's full name and phone numbers, home and business. Ask if the patient has been to the office previously; if not, you should record the person's mailing address. This is needed if you have to change the appointment and the patient cannot be reached by phone.
It is also helpful to know the basic nature of the problem or the reason for the appointment; that is, a preoperative check, a complete eye examination for a driver's license, a minor surgical procedure, an ocular injury, a contact lens problem, and so on. This information will help you in the scheduling of time for the appointment and in your preparedness for the patient.
When scheduling a consultation appointment, you will need the referring physician's name, and preferably, the nature of the patient's problem. If the patient has undergone any tests related to this particular problem, request that copies be forwarded to you before the appointment date.
The key to a hysterical field is that the field loss is the same size regardless of the distance of the test object from the patient's eye, be it 1 or 2 meters. The tubular field is remarkably constant in size, shape, and steepness or margin. It is commonly found in military personnel attempting to escape duty or in children, where it is a device to avoid stress at home or school.
Hysteria should be separated from malingering, which is a conscious simulation of visual field loss and in which the field defect is used for monetary gain. The malingerer is often a person involved in litigation regarding a motor vehicle accident or an industrial mishap.
The hysterical patient is cooperative and reliable. The malingerer is snarly, hostile, and afraid to be uncovered. This individual will often not complete a test, complaining of lights, headaches, and watering of the eyes.
The discovery of a hysterical patient requires wit, shrewdness, and ingenuity. With the malingerer, the patient views the examiner with hostility and suspicion. The examiner must not only be creative in field testing but also be careful lest the patient turn against the perimetrist.
Drusen of the choroid are basically excrescences of Bruch's membrane of the choroid. They appear as yellow deposits in the posterior pole of the retina, sometimes surrounded by a collarette of retinal pigment. Unless associated with macular degenerative phenomena, these drusen usually are harmless.
Drusen of the optic nerve are another matter. They consist of hyalin or calcium, and these deposits take up and compress tissue in the optic nerve. Field defects are common and may be varied depending on the size of the drusen, their location, and their development.
In addition to causing visual field defects, drusen may stimulate the appearance of papilledema or swelling of the optic nerve head. Typically drusen are glistening pearl-like bodies, which, when visible, are seen in the surface of the optic disc. When they are buried, the disc is heaped up and its margins are blurred.
tubular or signet ring
Retinitis pigmentosa can cause tubular field defects. Such defects in the visual field also can be caused by syphilis, glaucoma, quinine poisoning, eclampsia, and, on occasion, hysteria. The diagnosis of this disease can be made by observing the bone spicule pigment deposits in the retina at the level of the midperiphery. Also, an ERG can reveal the flat electrical response of the rods, which is abolished under dim light.
There usually is a family history of the disease. This may not be obvious because the disease can be transmitted as dominant, recessive, or sex-linked type of hereditary pattern. Occasionally vitamin A deficiency can be uncovered, and this plus nutritional disorders, although rare in industrialized countries, may mimic retinitis pigmentosa. At present there is no cure for this disease. In many patients the evolution of this disease may be slow, thus blindness may not occur in all afflicted patients.
B) individuals between 25 and 50 years
Central serous retinopathy is a disease of young people. At times it may be related to stress or prolonged period of anxiety or to an allergic reaction to drugs, vapors, or chemicals, but commonly it has no antecedent of any kind. The person invariably is made aware of the problem because of blurred and distorted vision.
Lines appear curved, at times with missing pieces in the center, and color vision is depressed or darker in hue. The patient's symptoms are pathognomonic of this condition. However, support for the diagnosis can be made by the Amsler grid or by looking for the telltale macular blister, which usually is clinically evident. Often the condition improves without any drug or device. Angiography of the retinal and choroidal circulation should be done because stimulating conditions include a small macular melanoma, histoplasmosis, hematoma, and an effusion of a hemangioma.
D) None of the above.
The patient history is critical because it may reveal symptoms, exposures, or diagnoses that contribute to our understanding of the nature of the uveitis at hand.
There is no single laboratory workup for uveitis. Most uveitis is diagnosed on clinical grounds, with laboratory tests used to detect infectious diseases that cannot be identified by the clinical presentation, to detect systemic diseases with an effect on the patient's health, or to ensure the absence of unrelated underlying infectious diseases before initiating an immunosuppressive regimen.
Topical and systemic steroids are effective, but they may have dangerous side effects. In the eye they cause cataract and glaucoma. Systemically, there are many side effects including insomnia, blood glucose abnormalities, mood changes, and weight gain.
Although manufacturers provide preservatives such as chlorobutanol, thimerosal, ethylenediaminetetraacetic, and benzalkonium chloride to prevent the solutions from becoming contaminated, there is no fail-safe method. Once a bottle has been opened and used on any patient, organisms can enter the solution and not be destroyed by the preservative. The longer the bottle remains on the shelf of the ophthalmic office, the more likely this is to occur.
As a consequence, safeguards for ophthalmic drugs should be put into action once the bottle has been opened. These bottles should not remain on the shelf for any length of time. Second, when introducing drops into the eye, one should avoid contaminating the tip of the bottle or the tip of the eyedropper by touching the lashes or eyelid of the individual receiving the drops. If contamination is suspected, the solution should be discarded.
Most often the nurse, when employed by a hopsital or by an ophthalmologist, is the individual who assists in the care of eye patients.
A nurse is usually the individual in the operating room, who, by training and experience, can quickly learn the skills of assisting, aseptic technique, and microsurgery.
At the bedside, the nurse can follow the progress of a patient, identify abnormal signs and symptoms, and report progress to the ophthalmologist.
However, in many states someone who is not a nurse, but who is well trained in these functions, may accompany the ophthalmologist and assist with preoperative, operative, and postoperative care of the patients. In surgicenters, a trained layperson is taking on increasing importance in this role.