OptoPrep Flashcards

Question

A ray of light is deviated by a crown glass prism with a power of 4.0 pd that is located 4.0 m away from a screen. Which of the following will CORRECTLY determine the amount of deviation experienced by the ray of light projected at the screen? A. 4.0 pd= (100)(400.0 cm/x) B. 400.0 cm= (4.0 pd)(x/100) C. 4.0 pd= (400cm)(100/x) D. 4.0 pd= (100)(x/400.0 cm)

Answer 1

D. Explanation - Using the equation P= (100)(x/d), where P= power of the prism (in prism diopters, pd), x=the total distance that a ray of light is deviated and d=the total distance from the prism to the location where the deviation is measured, we can determine the total deviation of a ray of light. For the above question, 4.0 pd= (100)(x cm/400.0 cm), solving for x yields 16.0 cm.

Answer 2

B. Explanation - The non-conventional outflow route of the aqueous humor passes through the iris root, uveal meshwork, and the anterior face of the ciliary muscle. The conventional outflow is also called the trabecular route and, although there is a debate as to how much the trabecular route contributes to the outflow facility, it is agreed that this route is the major component of outflow facility of aqueous humor. Both the conventional and unconventional outflow facilities decline with increasing age.

Answer 3

C. Explanation - When a stimulus is presented to the retina, it stimulates the photoreceptors, and the information is transmitted to the brain by either magno, parvo, or konio cellular pathway. A white stimulus on a white background will not isolate any particular pathway, and all mechanisms will be stimulated. A blue stimulus on a yellow background suppresses the mid-range and long-range cones and selectively stimulates the blue/yellow opponent pathway or konio cellular pathway. A flickering target like that of frequency doubling technology readily isolates the magno cells, as they are the most sensitive to flicker.

Answer 4

A. Explanation - Characteristic defects in glaucoma consist of damage to the optic nerve head, resulting in a retinal nerve fiber bundle defect. The configuration of nerve fibers served by the damaged bundle will correspond to a specific defect in the visual field. The earliest visual field changes that may suggest glaucomatous damage commonly consist of an increased variability of responses in an area that will eventually develop a defect. When a glaucomatous visual field defect does occur, it tends to initially present as a paracentral scotoma. Paracentral scotomas are typically small and relatively steep depressions that are most commonly observed just supero-nasal to the fovea. Approximately 70% of all early glaucomatous field defects can be characterized as a paracentral scotoma. This type of defect is due to damage of the papillomacular bundle, which will respect the horizontal midline. It is important to remember that a single visual field test cannot definitively prove that a visual field defect exists. For this reason, interpretation of visual fields should not be performed in isolation but rather in conjunction with other clinical findings (IOP, appearance of optic nerve, RNFL). According to Kanski's Clinical Ophthalmology, there is a set of minimal criteria for determining glaucomatous damage (also known as Anderson's criteria), summarized below: 1. Glaucoma hemifield test that is "outside normal limits" on at least 2 consecutive occasions. 2. A cluster of 3 or more non-edge points in a location typical for glaucoma, all of which are depressed on pattern standard deviation (PSD) at a P

Answer 5

D. Explanation - A patient with advanced glaucoma should be monitored using a threshold 10-2 test which tests 68 test points, 2 degrees apart in a central 10 degree area. Patients with advanced glaucoma possess a central island of vision, and therefore it is important to monitor for change within this region. A 40 point screener, 30-2 or 24-2 threshold visual field presents too many test points that lay outside of the patient's area of useable vision and therefore do not provide useful information. A 30-2 field tests 76 points, 6 degrees apart within a central 30 degree radius. A 24-2 field presents a total of 54 points within a central 24 degree region (except nasally where it extends out to 30 degrees). When treating patients with advanced glaucoma, the objective is to save the central acuity. If the glaucoma is not adequately controlled, progression will cause a splitting of fixation due to inward advancement of the superior nasal field defect followed by inferior field loss due to encroachment of the nasal defect

Answer 6

D. Explanation - Optic disc hemorrhages occurring at the margin of the optic nerve are most commonly associated with normal tension glaucoma. These hemorrhages appear at the edge of the optic disc and typically extend onto the nerve fiber layer (called Drance hemorrhages). Additionally, they are most often found at the infero-temporal quadrant of the optic nerve head. It is thought that patients who exhibit progressive optic neuropathy with intraocular pressures (IOPs) consistently within the normal range are likely to have some form of vascular insufficiency or low systemic blood pressure which can lead to a decrease in the ocular perfusion pressure. It is for this reason that optic disc hemorrhages are more commonly observed in individuals exhibiting normal IOPs. When an optic disc hemorrhage is present, it is common to eventually manifest a visual field defect in the region corresponding to the location of the previous hemorrhage (often several months later).

Answer 7

A. Explanation - Starting with the iris and moving anteriorly, the anterior chamber angle structures are as follows: Ciliary body --> scleral spur --> posterior trabecular meshwork --> anterior trabecular meshwork --> Schwalbe's line When evaluating the anterior chamber angle using gonioscopy, it is best to orient oneself by beginning with the iris structure and following it out to the ciliary body. The ciliary body will vary in color, depending on the pigmentation of the iris, but is typically darker than the iris itself. Moving anteriorly, the next observable structure is the scleral spur, which will be bright white in color because it is a projection of the white sclera. This is a great landmark when assessing the angle because it does not vary much from person to person. Adjacent to the scleral spur is the trabecular meshwork. This can be greyish or pinkish in color (not as bright as the scleral spur). If there is pigment in the trabecular meshwork, one will be able to differentiate between the posterior and anterior trabecular meshwork; the posterior will be more pigmented than the anterior trabecular meshwork. The most anterior identifiable structure in the angle is Schwalbe's line, which is the termination of Descemet's membrane. It is a white ridge (which may be difficult to observe in some patients) that may occasionally have pigment lying on surface of the ridge. The area anterior to Schwalbe's line represents reflections from the surface of the cornea.

Answer 8

A. Explanation - Iridodialysis involves a detachment between the iris root and the ciliary body. Cyclodialysis cleft involves a detachment between the ciliary body and the scleral spur.

Answer 9

A. Explanation - Ptosis and cataracts will most likely present on this area of the printout (see figure 1A). The pattern deviation plot gives a more accurate rendering of whether or not a true defect exists by removing excess "noise" such as that seen with a cataract. By removing the effects of generalized depression, it is easier to determine the size, shape and depth of a visual field defect (see figure 1B). The VFI relates information pertaining to the overall amount of field loss. The VFI ranges from 100% (normal) to 0% (a blind eye). This index is purported to be less affected by cataracts than the other indices. The VFI can be used to monitor progression when compared to previous visual field results. The glaucoma hemifield test compares test points above the horizontal midline to those below the midline. Any asymmetry is considered suspect and appropriate action should be taken (see figure 1C). Cataracts, if they are advanced enough, may cause a generalized depression of the visual field because they will act like a filter and will also scatter light.

Answer 10

B and D. Explanation - Chorioretinal atrophy surrounding the optic nerve (also known as peripapillary atrophy) can be divided into two separate zones. The beta zone directly borders the margin of the optic disc, while the alpha zone is the outer region that concentrically surrounds the beta zone. Chorioretinal atrophy that occurs in the beta zone will present with increased visibility of the sclera and large choroidal blood vessels, in contrast to the appearance of alpha zone atrophy, which displays an irregular variation of both hyper and hypopigmentation of the retinal pigmented epithelium. Typically, when comparing peripapillary atrophy characteristics in normal and glaucomatous patients, the alpha zone is usually larger in patients with glaucoma; however, its frequency is similar in both groups. Conversely, both the size and frequency of beta zone atrophy is greater in patients with glaucoma, and the changes appear to be more pronounced in more severely affected eyes.

Answer 11

D. Explanation - Horizontal saccadic eye movements first emerge at birth and continue to develop until roughly 24 months. Vertical saccades require a longer time to mature and emerge at around 2 months of age and continue to develop until about 24 months. Pursuits may be seen as early as 2 months but are more commonly evident at 4 months of age. Stereopsis is absent at birth and does not become apparent until 3-5 months of age (some sources quote 4-6 months), reaching adult levels at 5-7 years of age.

Answer 12

B. Explanation - Pepsinogen and fibrinogen are categorized as zymogens. Zymogens, also called proenzymes, are synthesized as inactive proteins that later become activated via some type of transformation, for example, cleavage of a portion of the protein resulting in a functional enzyme. The enzymes cannot be reverted back to their inactive forms. Blood-clotting factors and digestive enzymes are common examples of zymogens. The zymogen pepsinogen is secreted from chief cells in the stomach and is converted to its active form, pepsin, via exposure to hydrochloric acid. The enzyme pepsin aids in the digestion of proteins. Allosteric enzymes are regulatory proteins that are controlled via modulators. The modulators activate or inhibit the enzyme function by binding to a location on the enzyme that is not the active site. Isoenzymes are enzymes that are molecularly different but catalyze the same reaction. Isozymes have different amino acid sequences than other enzymes, but both used for the same reaction. Sphingolipids are important for central nervous system (CNS) function. They are generally incorporated into CNS membranes.

Answer 13

Explanation - Sine wave gratings are specified by frequency, phase, orientation and contrast. Frequency denotes the number of cycles of alternating dark and light bands per degree. Contrast describes the luminance profile of the grating; this is basically the difference in luminance between the light and the dark bands. Mathematically, this can be calculated as contrast= the difference in luminance between the peak and trough/the total luminance of the peak and the trough. The phase of the sine wave grating is relative to another grating. Two gratings are in phase if their positions are the same (i.e., their peaks and troughs align) or 180 degrees out of phase (i.e., the trough of one grating is aligned with the peak of the other). The orientation refers to the angle of the grating in reference to horizontal or vertical.

Answer 14

B. Explanation - Drusenoid pigment epithelial detachments are a sign of dry ARMD, as there is no leakage involved. Instead, a detachment in the retinal pigment epithelium occurs due to the thickness of the soft confluent drusen. The drusen push and displace the retinal pigment epithelium.

Answer 15

A. Explanation - The atrial natriuretic hormone (ANH) is secreted by the atria in response to increased fluid volume signaled by atrial stretch. ANH causes the kidney to excrete greater quantities of sodium as well vasodilation of blood vessels, leading to a decrease in blood pressure. Calcitonin is released by the thyroid; it inhibits osteoclast activity in bones and absorption of calcium by the intestines, leading to diminished blood calcium levels. Melatonin is produced by the pineal gland in response to diminished light levels and causes the hypothalamus to ready the body for sleep. Erythropoietin is released by the kidneys and stimulates the production of red blood cells by the bone marrow.

Answer 16

B. Explanation - Removing the contact lens for several hours will typically allow for resolution of dimple veiling and any associated symptoms. Long-term treatment, however, will require modification of the contact lens parameters. Dimple veiling is a result of poor tear exchange under the gas permeable contact lens, which leads to the entrapment of bubbles of carbon dioxide under the central curvature of the lens. Decreasing the overall diameter of the contact lens and flattening the base curve of the lens may help prevent the formation of dimple veiling, but the treatment of choice is to decrease the diameter of the optic zone or in some manner reduce the vault of the lens. This allows for better tear flow that may have been impeded by a tight mid-peripheral junction of the optic zone and intermediate and peripheral curvatures of the contact lens

Answer 17

D. Explanation - When the patient presents with an anterior uveitis that has an initial presentation, occurs unilaterally, and the patient is otherwise healthy with no other systemic symptoms, no further laboratory testing is usually indicated. On the other hand, patients with recurrent, chronic, or bilateral presentations, or patients that have other symptoms possibly indicating the presence of an associated systemic condition, should undergo a thorough work-up to determine the underlying etiology. Typically, in conjunction with the patient's primary care provider, laboratory testing should be initiated in a patient where anterior uveitis recurs after cessation of treatment (2nd episode). In these cases, there is a much higher risk of being associated with a systemic disease, as compared to a patient with a single episode of intraocular inflammation. When indicated, minimal lab testing should include the following: - Complete blood cell count (CBC) - Urinalysis - Lyme titers - HLA-B27 test (spondylarthropathies) - Antinuclear antibody (ANA) test (juvenile arthritis) - Angiotensin converting enzyme (ACE) test (sarcoidosis) - Venereal disease research laboratory (VDRL) test (syphilis) - Fluorescent treponemal antibody absorption (FTA-ABS) test (syphilis)