timed test #1 Flashcards
Which organism represents the MOST common etiology for acute bacterial conjunctivitis in adults?
Staphylococcus aureus Haemophilus influenza Chlamydia trachomatis Streptococcus pneumoniae Moraxella catarrhalis
Staphylococcus aureus
Explanation
Acute bacterial conjunctivitis in adults is primarily due to Staphylococcus aureus, Streptococcus pneumoniae, and Haemophilus influenza, with Staphylococcus aureus representing the most common etiology.
In children, the most common causes of acute bacterial conjunctivitis are Haemophilus influenza, Streptococcus pneumoniae, and Moraxella catarrhalis (with Haemophilus representing the most common etiology).
Hyperacute conjunctivitis is primarily due to Neisseria gonorrhoeae, and chronic conjunctivitis is primarily caused by Chlamydia trachomatis.
The measure of how tightly a drug binds to its receptor is known as which of the following?
Potency
Affinity
Efficacy
Reliability
Affinity
Explanation
The affinity of a drug for a receptor is a measure of how tightly and how able the drug in question binds to the receptor. Affinity is typically determined by the chemical structure of the drug.
The efficacy of a drug is a measure of the drug’s ability to produce a biological effect or initiate a biological change once it is bound to the receptor. Efficacy is used to characterize the level of maximal response by a drug.
It is important to note that drug affinity and efficacy do not go hand-in-hand. A drug may have a high affinity to a receptor but have minimal efficacy and vice versa.
The potency of a drug refers to the amount of a drug that is required to achieve a desired biological effect. A drug that requires a lower dose is considered more potent than a drug that requires a higher dosage to have the same effect.
You wish to perform a visual field on a patient with advanced glaucoma using a Humphrey Field Analyzer. Which of the following visual field programs will BEST allow for monitoring of changes to or progression of visual field loss?
40 point screener
30-2
24-2
10-2
10-2 Correct Answer
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.
How will over-correction of myopia change the observed near phoria?
Increase exophoria and increase the esophoria measured
Decrease esophoria or increase the exophoria measured
The resultant phoria will not change
Increase esophoria or reduce the exophoria measured
Increase esophoria or reduce the exophoria measured
Explanation
Over-correction of myopia stimulates accommodation. As the viewing distance decreases, the eyes will converge reflexively (accommodative convergence). In addition to the expected accommodative convergence, there will be increased convergence as the eye accommodates to bring the target in focus compensating for the distance over-correction. This over-convergence will either cause increased esophoria or reduce the amount of exophoria present.
The circulatory system of the retina is capable of autoregulation. This property is attributable to which cell?
Glial cell
Pericyte
Astrocyte
Schwann cell
Pericyte
Explanation
Pericytes are smooth muscle cells that are generally adhered to small blood vessels. They are found at the junction between arterioles and capillaries. Their muscle action alters the flow of blood through the retina’s microcirculation. Pericytes are not found in the choroid.
In poorly controlled diabetics, the pericytes become damaged causing leakage through the microvasculature as seen in diabetic retinopathy.
Glial cells are non-neuronal cells that serve several functions, depending on the type of glial cell. On the whole, glial cells are responsible for structural and nutritional support as well as insulating and protecting neurons.
Astrocytes are a type of glial cell that serve many functions including the potential to regulate blood flow, metabolic support, structural support of the neural cells and formation of the blood-brain barrier.
Schwann cells are also a type of glial cell. These cells are primarily responsible for the production of the myelin sheath in the peripheral nervous system.
A colored filter is placed in front of an illuminated Tungsten light bulb, resulting in emergent light that appears red. Which of the following wavelengths is LEAST likely to be absorbed by the filter?
592 nm 648 nm 401 nm 518 nm 471 nm
648 nm
Explanation
Colored filters are used to block (absorb) some wavelengths while transmitting others, resulting in the perception of transmitted light that is a different color than the light that was incident upon the filter. A red filter that is placed in front of a white light source will strongly absorb the majority of the wavelengths, except for those in the red region (roughly 620 to 700 nm).
The following are wavelengths and their associated color: Red= 650nm Orange= 600nm Yellow= 570nm Green= 520nm Blue= 470nm Violet= 400nm
Diurnal refractive fluctuations are MOST likely to be experienced by a patient who has undergone which of the following procedures?
Photorefractive keratectomy (PRK) Radial keratotomy (RK) Laser-assisted in situ keratomileusis (LASIK) Conductive keratoplasty (CK)
Radial keratotomy (RK)
Explanation
Radial keratotomy is performed by creating corneal incisions in a radial fashion, which serves to flatten the cornea, thereby decreasing the amount of myopia. However, many post-RK patients experience irregular astigmatism, dry eyes, and diurnal refractive error fluctuation. Studies have suggested that post RK patients suffer from unstable refractive errors secondary to normal variations in intraocular pressure (IOP) that typically occur throughout the day. Because the structure of the cornea has been surgically weakened, it is more susceptible to refractive instability due to an inability to compensate for IOP fluctuations. Treatment options include hard and soft contact lenses, hybrid lenses, several pairs of glasses with different prescriptions depending on refractive error and time of day, and suturing of RK incisions and lasso suture (circular suture that parallels the limbus to help stabilize the cornea). Other treatment options include the pharmaceutical use of brimonidine (off-label), which causes pupil miosis and helps to relieve glare and haloes, corneal cross-linking to help stabilize the cornea, and controlling IOP fluctuations via the use of topical prostaglandins (off-label).
Patients who have undergone LASIK, PRK and CK are much less likely to experience refractive variability throughout the day.
While attempting to determine the amplitude of accommodation via the push up method on your patient, she reports that the target is blurry at a distance of 14 cm for the right eye and at 13 cm for the left eye. What is her amplitude of accommodation in diopters for the right eye and the left eye respectively (to the nearest 0.25 D)?
- 14 D and 7.69 D
- 25 D and 7.75 D
- 725 D and 0.775 D
- 714 D and 0.769 D
7.25 D and 7.75 D
Explanation
In order to determine the amplitude of accommodation, one must take the reciprocal of the blur point in meters. For the above example, 1/0.14 = 7.14 and 1/0.13 = 7.69. Do not forget to convert to meters!! Also, the question asked that the answer be rounded to the nearest 0.25 D. Be sure to read questions carefully to avoid careless mistakes. Clinically, one always rounds to the nearest 0.25 D.
Which 2 of the following alterations to the cornea commonly occur after several years of contact lens wear? (Select 2)
The cornea becomes less sensitive to touch
The cornea becomes more sensitive to touch
The cornea epithelium thins
The corneal epithelium thickens
The cornea becomes less sensitive to touch
The cornea epithelium thins
Explanation
Long-term extended wear of contact lenses has been shown to lead to thinning of the corneal epithelium. Additionally, the corneal nerves exhibit a decrease in sensitivity over time.
Which of the following properly describes the movement of sodium and potassium ions in one cycle of the Na-K ATPase pump?
3 sodium out, 2 potassium in
2 sodium out, 3 potassium in
2 sodium in, 3 potassium out
3 sodium in, 2 potassium out
3 sodium out, 2 potassium in Correct Answer
Explanation
The sodium potassium ATPase pump, an integral membrane protein, is central to the functioning of most transporting epithelia. It is normally open to the cytoplasmic side with three Na binding sites. When those three are occupied, ATP phosphorylates the protein, prompting a change in configuration that now opens the protein’s binding sites to the outside, where the Na ions exit. The protein remains in its configuration until its two K binding sites are occupied. This causes dephosphorylation of the protein and reversal of the protein configuration so that it is again open to the inside of the cell. The 2 K ions enter the cytoplasm, completing one pump cycle.
What is the correct mechanism of action employed by fluoroquinolones that enables them to be strong antimicrobial agents?
Inhibition of cell wall synthesis
Inhibition of bacterial DNA gyrase and topoisomerase IV
Blocks elongation of peptidoglycan
Interruption of protein synthesis
Inhibition of bacterial DNA gyrase and topoisomerase IV
Explanation
Fluoroquinolones, such as Vigamox® and Zymar®, are effective antibacterial agents because they inhibit DNA gyrase and topoisomerase, and therefore ultimately inhibit bacterial DNA synthesis. Penicillin-based drugs inhibit cell wall synthesis.
Aminoglycosides, such as tobramycin, interfere with protein synthesis by binding to bacterial ribosomes. Vancomycin disrupts cell wall synthesis by binding to pentapeptides, thereby inhibiting elongation of peptidoglycan, which is necessary for cell wall synthesis.
Which 3 of the following represent common symptoms associated with hyperthyroidism? (Select 3)
Heart palpitations Hair loss Weight loss Dry skin Heat intolerance Elevated cholesterol
Heart palpitations
Weight loss
Heat intolerance
Explanation These are the most frequently-observed symptoms of hyperthyroidism: -Heart palpitations -Fatigue -Tremors -Anxiety -Disturbed sleep -Weight loss -Heat intolerance -Sweating -Polydipsia
Congenital cataracts can be caused by a viral infection of the mother with rubella virus (German measles) during development of the primary lens fibers. At which time period in embryonic development can infection cause congenital cataracts?
1st trimester Post-delivery 3rd trimester 2nd trimester Conception
1st trimester
Explanation
The developing lens is susceptible to rubella virus when the lens fibers are forming, which occurs around weeks 4-7 of gestation. Earlier infection will occur prior to lens fiber development, and the lens is resistant to later infection because the virus is unable to penetrate the lens capsule.
The fetus is most susceptible to lenticular damage during the first trimester. Contraction of the rubella virus will cause the greatest amount of damage during this time period. Congenital cataracts are usually detectable at birth but may be seen later because the virus can persist in the lens.
Which of the following 3 activities is associated with a decrease in intraocular pressure? (Select 3)
Coughing Blinking Alcohol consumption Lying down General anesthesia Exercise
Alcohol consumption
General anesthesia
Exercise
Explanation
Exercise, general anesthesia, alcohol consumption, and marijuana use cause a temporary decrease in intraocular pressure (IOP). Transitioning from sitting to a lying down position, blinking, coughing, blepharospasm and tobacco usage may cause an increase in IOP.
An 8-year old Hispanic male comes in with the following habitual prescription: +0.75-0.75 x 180 OU. His entering visual acuity with correction was 20/40 OD, OS, OU at both distance and near. After cycloplegic examination, you find the following on wet retinoscopy:
OD: +4.00-2.75 x 180 20/25 (Distance)
OS: +4.50-2.75 x 180 20/25 (Distance)
Which of the following would be the most appropriate treatment for this patient?
OD: +3.50-2.75x180
OS: +3.50-2.75x180
Return for follow-up appointment in 4-6 weeks
Continue with current habitual prescription; alternate patching therapy 3hrs/day 5 days/week. Return for follow-up appointment in 4-6 weeks.
OD: +0.75-2.75 x 180
OS: +0.75-2.75 x 180
Return for follow-up appointment in 1 year
Spectacle prescription
OD: +4.00-1.00 x 180
OS: +4.00-1.00 x 180
Return for follow up appointment in 4-6 weeks
Spectacle prescription:
OD: +3.25-2.75 x 180
OS: +3.75-2.75 x 180
Return for a follow-up appointment in 4-6 weeks
Spectacle prescription:
OD: +3.25-2.75 x 180
OS: +3.75-2.75 x 180
Return for a follow-up appointment in 4-6 weeks
Explanation
In this case, poor entering visual acuities were attributed to refractive amblyopia in both eyes. The patient was not wearing his full potential prescription. When deciding on the spectacle prescription, one should keep in mind that the prescription should have full cylinder and no less than half of the hyperopic prescription. For full visual acuity potential, the retinal images should be equal and balanced, hence keeping the +0.50 DS difference between the two eyes. It is important to follow up on these types of prescription changes in case the patient presents with more hyperopia after adapting to his/her new spectacle prescription. Part-time patching is not warranted at this initial visit as his visual acuity may improve drastically by correcting his refractive error alone, and his refractive error is relatively equal in both eyes.
