test 4 Flashcards
Which 2 of the following represent the main components of the vitreous body? (Select 2)
Chondroitin sulfate Keratin Hyaluronic acid Albumin Elastin Collagen
Which 2 of the following represent the main components of the vitreous body? (Select 2)
Hyaluronic acid
Collagen
Explanation Besides water (which comprises 98% of the vitreous), the two major components of the vitreous body are collagen and hyaluronic acid. The network of collagen fibrils (mostly type II) are stabilized by the hyaluronic acid due to its hydrophilic properties, keeping the collagen fibers separated by a distance that is far enough to minimize the scattering of light while also maintaining vitreous transparency.
The typical human contrast sensitivity function (CSF) for a young adult free of ocular pathology displays a high-spatial frequency cut-off of around 60 cycles per degree. What is the cause for this cut-off of high-frequency resolution?
Loss of visual information due to cross-over at the optic chiasm
Spacing of the photoreceptors
Limited cortical processing
Increased lateralization between the hemispheres
The typical human contrast sensitivity function (CSF) for a young adult free of ocular pathology displays a high-spatial frequency cut-off of around 60 cycles per degree. What is the cause for this cut-off of high-frequency resolution?
Spacing of the photoreceptors
Explanation
The human contrast sensitivity function (CSF) allows researchers to determine over what range of contrasts humans can detect various sine wave gratings. Essentially, a subject views a sine wave grating on a computer screen that is below threshold so that the screen appears blank. The contrast of the grating is increased until the subject reports that he/she is able to perceive it. This is repeated again with sine waves of various spatial frequencies. The threshold contrasts are plotted as a function of spatial frequency, resulting in the contrast sensitivity function. This graph demonstrates that humans are capable of detecting a grating of 4 cycles per degree at a much lower contrast than any other spatial frequency. The CSF typically shows a cut-off of 60 cycles per degree even at 100% contrast for high spatial frequencies. There are several reasons for this cut-off. One of them is the system’s inherent natural optical aberrations. Another is the retinal distribution of photoreceptors. Photoreceptors that are more tightly packed are able to discern a greater amount of detail than those that are loosely packed. Think of alternating light and dark bands. In order to properly appreciate these bands, one bright band must fall on one photoreceptor and an adjacent dark band must stimulate an adjacent receptor. If the receptors are too big or loosely packed, a light band may fall on half of one receptor and half of another; receptors then sum the information, causing a loss of visual information and the inability to properly discern the grating. The above is referred to as the Nyquist sampling theorem.
Your 67 year-old Asian female patient returns to your office for the third time in the past year with a bump in the same location on her left upper eyelid. You had previously diagnosed her with a chalazion; however, due to its recurrent nature, you send her out for a tissue biopsy. Which of the following eyelid lesion are you MOST concerned about?
Basal cell carcinoma Your Answer Sebaceous cell carcinoma Correct Answer Keratoacanthoma Squamous cell carcinoma Malignant melanoma
Your 67 year-old Asian female patient returns to your office for the third time in the past year with a bump in the same location on her left upper eyelid. You had previously diagnosed her with a chalazion; however, due to its recurrent nature, you send her out for a tissue biopsy. Which of the following eyelid lesion are you MOST concerned about?
Sebaceous cell carcinoma
Explanation
Sebaceous cell carcinoma of the eyelid often masquerades as a recurrent chalazion; therefore, it is very important to send patients out for tissue biopsies in cases of recurrent lesions. It is also for this reason that sebaceous cell carcinomas are one of the most dangerous eyelid tumors because correct diagnosis tends to be delayed until the tumor has metastasized.
This type of tumor is more common in Asian populations as compared to other races. In most cases, female patients outnumber males, and the mean age at diagnosis is in the mid-60s. Sebaceous cell carcinoma also tends to show a predilection for the upper eyelid (unlike basal cell carcinoma). It typically presents as a focal mass (pseudochalazion), but can also appear as a multi-centric tumor, or a diffuse lesion. It also does not usually ulcerate, as do basal and squamous cell carcinomatous lesions.
Excessive bleeding tendencies can result from a deficiency of what vitamin?
Vitamin E Vitamin A Vitamin B3 Vitamin K Vitamin B2
Excessive bleeding tendencies can result from a deficiency of what vitamin?
Vitamin K
Explanation
Avitaminosis K has been linked with increased bleeding time. Vitamin K plays an important role in mediating the synthesis of several clotting factors. Vitamin K can be found in green, leafy vegetables and in oils such as cottonseed, canola, and olive. There exist many causes of avitaminosis K, some of which include malnutrition, alcoholism, parenchymal liver disease, cystic fibrosis, and certain drugs (antibiotics such as cephalosporins, warfarin, and some sulfa drugs). Symptoms of vitamin K deficiency include hematomas (bruising), ecchymosis (swelling), and increased bleeding time at injury sites.
Which of the following best describes a symport?
An integral membrane protein that moves two compounds simultaneously across a cell membrane in the same direction, one compound being transported down its concentration gradient and the other against its gradient
An integral membrane protein that moves two compounds simultaneously across a cell membrane in the opposite direction, both being transported down their respective concentration gradients
an integral membrane protein that moves two compounds simultaneously across a cell membrane in the same direction, both moving against their respective gradients
An integral membrane protein that moves two compounds simultaneously across a cell membrane in opposite directions, both moving against their respective gradients
Which of the following best describes a symport?
An integral membrane protein that moves two compounds simultaneously across a cell membrane in the same direction, one compound being transported down its concentration gradient and the other against its gradient
Explanation
A symport is an integral membrane protein that moves two compounds simultaneously across a cell membrane in the same direction, one compound being transported down its concentration gradient and the other against its gradient. By contrast, an antiport moves two compounds simultaneously in opposite directions across a membrane.
Contraction of the ciliary muscle leads to which of the following?
The lens becomes more oblong and loses refractive power, bringing near objects into focus
The lens becomes more spherical and increases refractive power, bringing near objects into focus Your Answer
The lens becomes more oblong and loses refractive power, bringing distant objects into focus
The lens becomes more oblong and increases refractive power, bringing near objects into focus
The lens becomes more spherical and increases refractive power, bringing distant objects into focus
Contraction of the ciliary muscle leads to which of the following?
The lens becomes more spherical and increases refractive power, bringing near objects into focus r
Explanation
Contraction of the ciliary muscle decreases the diameter of the ring formed by the ciliary body. This releases tension on zonule fibers and allows the lens capsule to become more spherical. The anterior surface curve increases and the lens becomes thicker. This increases refractive power (a.k.a. accommodation) and brings near objects into focus on the retina. Another school of thought believes that ciliary body contraction causes an increase in the vitreal mass which causes the vitreous to push the lens forward allowing for clearer near acuity. When the ciliary muscle relaxes, the eye is considered at rest for distant vision.
Which of the following is TRUE in regards to the Y sutures found at the anterior and posterior zones of the fetal nucleus?
Both the anterior and posterior Y sutures are upright
An inverted Y suture is located at the anterior surface, and an upright Y is located posteriorly
An upright Y suture is located at the anterior surface, and an inverted Y is located posteriorly
Both the anterior and posterior Y sutures are inverted
Which of the following is TRUE in regards to the Y sutures found at the anterior and posterior zones of the fetal nucleus?
An upright Y suture is located at the anterior surface, and an inverted Y is located posteriorly
Explanation
During human fetal development, the elongated lens fiber cells meet at three planes forming an upright “Y” at the anterior zone of the fetal nucleus and an inverted “Y” at the posterior zone of the fetal nucleus (with respect to the superior-inferior axis of the eye).
