Chapter 10 Flashcards
B-scan ultrasonography can be used for what purpose
To characterize intraocular structures and abnormalities, such as tumors.
This is particularly relevant for patients with mature cataracts or other obstructions in the anterior segment
While doing an A-scan a patient looks to the side and the axial length is .30mm shorter than the patient’s true cornea to retina distance. How will this affect the IOL calculation?
The IOL calculation will be a 1.00 D more than the patient needs. If the AL is measured too short than the postoperative refractive error will be myopic and hyperopic if the AL is measured too long
What does pachymetry measure?
Thickness of the cornea.
Pachymetry can be used to evaluate Corneal dystrophies, estimate the cornea’s ability to withstand surgery, and ensure accurate IOP readings for OHT patients
The Ocular media includes what structures?
Cornea, vitreous, lens.
These are the transparent optical structures that transmit light. Media opacities are conditions that cloud or obscure these structures and are the most common causes of vision disruption
Fluoroscein Angiography is most valuable for evaluation what condition?
Abnormalities in Ocular blood vessels.
Fluorescent dye is injected intravenously and is quickly delivered to the Ocular blood vessels. The fundus camera is equipped with a special lens and takes images in rapid sequence, giving the appearance of vessels at recorded time intervals
What does Corneal Topography measure?
Curvature of the Cornea.
This can be used to evaluate astigmatism, Corneal disorders, and Corneal transplants
What test is used to count the endothelial cells of the Cornea?
Specular microscopy/photography.
It produces photographs of the cornea’s endothelial cells at great magnification, allowing them to be counted. The cells Pump to regulate the amount of fluid in the Corneal layers which maintains Corneal clarity for properly focusing light rays
What device measures the effect of media opacity on visual acuity and does not require a clearer zone within the media for assessment?
Interferometer.
It uses Laser or other special light beams that are able to determine visual acuity even in the presence of opacity
Compression of the Cornea during A-scan May result in what kind of measurement error and IOL outcome?
Short actual length measurement which leads to a myopic refractive error.
Small errors in AL measurement will lead to large errors in dioptric power of the implant
What does optical coherence tomography measure?
Ocular anatomy.
Tomography is using ultrasound to map and analyze the contours of translucent tissue: commonly the anterior chamber angle, Optic nerve, and retina
What can A-scan tomography be used for?
Measuring the axial length of the globe.
A-scan uses sound waves traveling in a straight line to reveal the position of and distances between structures within the eye and orbit
What is an acuity chart printed in faint gray rather than in sharp black use full for?
Contact sensitivity.
Contrast-sensitivity testing measures whether there is an alteration in the patient’s functional vision
Why should fluoroscein or indocyanine only be performed when a physician and emergency equipment are available?
Risk of anaphylaxis.
Fluoroscein can cause nausea or, rarely, a severe allergic reaction. Indocyanine is better tolerated but should be avoided in patient’s with iodine or shellfish allergies
What can produce an artificially high IOP?
An abnormally thick Cornea.
Think or thin Corneas can manipulate IOP readings and need to be converted using CCT chart
B-scan is useful for evaluating what condition?
Media opacities.
If media opacities obstruct view into the eye, B-scan can detect tumors and structure abnormalities that are otherwise invisible
