L9 Flashcards
(25 cards)
What are the main factors that affect magnification, field of view, and field of illumination in ophthalmoscopy?
Pupil diameter, sighthole size, distance between pupil and sighthole, working distance, and the subject’s refractive error (ametropia).
How does direct ophthalmoscopy work in terms of magnification?
The patient’s eye acts as a simple magnifier, making the retina appear larger than when viewed with the naked eye.
How does magnification differ between emmetropes, myopes, and hyperopes in direct ophthalmoscopy?
For emmetropes, magnification is around 15x; for myopes, it is greater than 15x; for hyperopes, it is less than 15x.
What is the field of view in direct ophthalmoscopy?
It is the amount of retina that can be seen through the ophthalmoscope, typically up to 10 degrees for maximum field, 6.5 degrees for useful field, and 3.3 degrees for full illumination.
How does the field of view change with pupil size and working distance?
A larger pupil and shorter working distance increase the field of view; a smaller pupil and longer working distance decrease it.
What happens to the field of view in hyperopia and myopia?
Field of view increases in hyperopia and decreases in myopia.
What is the ‘blur circle’ in ophthalmoscopy?
A blur circle is formed on the retina because the ophthalmoscope light does not focus on the retina but behind it.
What are the requirements of a good ophthalmoscope?
Clear, uniform light patch, field of view coincident with light patch, minimal corneal reflections, absence of sighthole flare, range of target apertures, and extra targets.
What are the main ophthalmoscopy techniques?
Direct ophthalmoscopy, indirect ophthalmoscopy, binocular indirect ophthalmoscopy (BIO), monocular indirect ophthalmoscopy, slit lamp BIO, head-mounted BIO, modified direct, Panoptic, Keeler wide-angle, AO monocular.
What is binocular indirect ophthalmoscopy (BIO)?
A technique where both eyes view the fundus for stereoscopic examination, using a hand-held condensing lens to form a real, inverted, and laterally reversed aerial image.
How does the field of view and magnification vary with BIO?
Field of view is greater in BIO, especially with higher power condensing lenses; magnification is lower than with direct ophthalmoscopy.
What are the advantages of BIO over direct ophthalmoscopy?
Wider field of view, stereoscopic (3D) view, less affected by media opacities, magnification not affected by refractive error, increased working distance, useful for uncooperative patients, and can be inexpensive if a slit lamp is already available.
What is monocular indirect ophthalmoscopy?
Uses a condensing lens to form a real, inverted aerial image, viewed through a direct ophthalmoscope; provides a larger field of view at lower magnification and increased working distance, but no stereopsis.
What are some monocular indirect ophthalmoscopes?
AO Monocular, Welch Allyn PanOptic, Keeler Wide-Angle.
What are the features of the AO Monocular indirect ophthalmoscope?
5x magnification, 15° field of view, good with small pupils, independent of patient’s refractive error, no stereoscopic view.
What are the features of the PanOptic indirect ophthalmoscope?
Provides a larger field of view than direct ophthalmoscopy, allows viewing of a real image, increased working distance, and an upright image due to inverting lens system.
What is direct biomicroscopy?
Direct view of the fundus with a slit lamp, using a high-power negative lens (e.g., Hruby lens) or contact lens to neutralize corneal power; image is not inverted.
What is the Hruby lens and how is it used?
A -55D plano-concave lens (concave side to patient), often mounted on a slit lamp; provides a binocular, erect image with a smaller field than Volk lenses.
What is the purpose of contact lenses in direct biomicroscopy?
Used with or without mirrors and viscous gel to view the peripheral retina.
What is a fundus camera?
A large instrument combining a low-power microscope and camera to photograph the fundus; based on the optical design of the indirect ophthalmoscope.
What is a scanning laser ophthalmoscope?
A video fundus camera using a laser to illuminate small sections of the fundus, allowing imaging at lower light levels and used for nerve head and retinal imaging.
What is the Optos Panoramic 200?
A scanning laser ophthalmoscope that uses red and green lasers to capture wide-field images of the retina, including the retinal pigment epithelium and neurosensory retina.
What is Heidelberg Retinal Tomography?
A confocal scanning laser ophthalmoscope using a 670 nm diode laser to create pseudo 3D images of the optic nerve head.
What is GDxVCC?
A scanning laser ophthalmoscope for glaucoma diagnosis, imaging the retinal nerve fiber layer using a 780 nm laser.
