Practical Ophthalmology Flashcards
What is the shape of the cornea or lens that gives a patient astigmatism?
Spherocylindrical
What is the name of the shape the light rays take as they are focused by a spherocylindrical lens?
Conoid of Sturm
In patient’s with astigmatism, what is name given to the region of the Conoid of Sturm that provides the clearest image?
Circle of least confusion
The power of a prism to deviate light is expressed in what units?
Prism diopters
What is a prism diopter (PD)?
A measurement of the power of a prism to deviate light where 1 PD means a prism deviates parallel rays of light 1 cm when measured at a distance of 1 meter.
At what distance does a 1 prism diopter (PD) prism deviate parallel light 1 cm? 2 cm? 0.5cm? 0.33cm?
1 meter. 2 meters. 0.5 meters. 0.33 meters?
How far will a 3 prism diopter lens deviate parallel light at 1 meter? 3 meter? 4.33 meters?
3 cm. 9 cm. 13 cm.
Lens Prescription Transposition: \+1.00 + 1.00 x 90 Plano + 1.50 x 180 -0.75 + 0.50 x 150 -1.00 + -0.50 x 120
+1.00 + 1.00 x 90 = +2.00 - 1.00 x 180
Plano + 1.50 x 180 = +1.50 - 1.50 x 90
-0.75 + 0.50 x 150 = -0.25 - 0.50 x 60
-1.00 + 0.50 x 120 = -0.50 - 0.50 x 30
Lens Prescription Transposition:
-1.00 + 1.50 x 95
+3.00 + 2.00 x 20
-2.00 + 1.00 x 160
-1.00 + 1.50 x 95 = +0.50 - 1.50 x 05
+3.00 + 2.00 x 20 = +5.00 - 2.00 x 110
-2.00 + 1.00 x 160 = -1.00 - 1.00 x 70
What is vertex distance? What is used to measure it?
Vertex distance is distance between the patient’s eye and the back of the corrective lens. It is measured with a distometer.
What is consider the average vertex distance? In what patient’s is vertex distance especially critical in prescribing glasses?
13.5 mm. It is especially important in patients with more than 5.00 D of plus or minus sphere.
How do you correct for your working distance when doing retinoscopy?
Subtract the dioptric equivalent of your working distance.
What is the duochrome test?
The duochrome test is a quick method of determining if the patient has too much minus or plus in the spectacle correction during subjective refraction. Green light is refracted more than red light. If green is clearer, add plus. If red is clearer, add minus.
What are the systemic effects of atropine?
- Dryness of mouth and skin
- Fever
- Delirium
- Urinary retention
- Tachycardia
- Flushed face
- Respiratory depression
What are the systemic effects of cyclopentolate?
- CNS disturbance (particularly hypersensitivity) reported in infants, young children, and children with spastic paralysis or brain damage.
- Psychotic reaction (particularly with 2%), Ataxia, Incoherent speech, Restlessness, Seizures, Hallucinations, Hyperactivity
- Disorientation, failure to recognize familiar people
- Feeding intolerance (vomiting in neonates)
- Abdominal distention in infants from paralytic ileus
- Other reactions similar to atropine
What are the systemic effects of tropicamide?
Similar to cyclopentolate (less frequent and less severe)
- CNS disturbance (particularly hypersensitivity) reported in infants, young children, and children with spastic paralysis or brain damage.
- Psychotic reaction (particularly with 2%), Ataxia, Incoherent speech, Restlessness, Seizures, Hallucinations, Hyperactivity
- Disorientation, failure to recognize familiar people
- Feeding intolerance (vomiting in neonates)
- Abdominal distention in infants from paralytic ileus
- Other reactions similar to atropine
What are the systemic effects of phenylephrine?
- Do not use within 21 days of MAO inhibitors use due to potentiation
- Tachycardia
- Rebound miosis
- Hypertension, systemic vasopressor response (especially 10% solution)
What is the near point of accommodation?
The closest point at which a person can read fine print.
What is the accommodative amplitudes for different ages?
-Under 8 years old accommodative amplitude is 14.0 +/- 2D. Then loss 1.0D per 4 years until 40 where it is 6.0 +/- 2D. Loss 1.5D from 40 to 44 and 44 to 48 leaving 3.0 +/- 2D. Then loss 0.5D per 4 years till 68.
Define strabismus.
Misalignment of the eyes in which both eyes are not directed at the object of regard.
Define amblyopia.
Loss of vision due to abnormal visual input in childhood. In physiologic terms, it represents a failure of visual connections from disuses or inability to form a clearly focused retinal image during the first few years of life during the most critical period of visual pathway development.
In regards to strabismus, what constitutes a comitant (or concomitant) strabismus? When is a strabismus incomitant?
A strabismus is consider comitant (or concomitant) when the angle of misalignment is approximately equal (within 7 PD of each other) in all directions of gaze. A strabismus is otherwise incomitant.
Define a phoria (or heterophoria)?
A phoria (or heterophoria) is a latent tendency toward misalignment that occurs only when binocularity is interrupted.
Define a tropia (or heterotropia)? When is a tropia “intermittent” vs “constant”?
A tropia (or heterotropia), a manifest deviation that is present when both eyes are open. A intermittent tropia is present only part of the time (e.g. at the end of the day due to fatigue) vs a constant tropia which is present 24 hours a day, 7 days a week, 365 days a year.
Define esotropia? Define exotropia?
A esotropia, is a manifest strabismus in which the visual axis is deviated toward the nose. An exotropia is a manifest strabismus in which the visual axis is deviated outward toward the temple.
