Biomedical subjects
L D Roe
Publications and source records attributed to L D Roe.
The red reflex from retinoscopy's point of view. Reflections on a small area.
The size of the area of retina that is involved in neutralization during retinoscopy is considerably smaller than intuition might suggest. Simple optical analysis reveals this area to be approximately 1/640 the area of the optic disc. This becomes important when retinoscoping high myopes with posterior staphylomas because even minimal misalignment with the visual axis may induce spherical error in the retinoscopic findings.
The light that leaks: Brückner and the red reflex.
The Brückner test utilizes the ophthalmoscope to assess symmetry of binocular fixation by qualitative comparison of the red reflexes. Accurate fixation by the patient's eye on the ophthalmoscope light causes darkening of the red reflex, previously believed due to macular pigmentation. By designing and experimenting with a beamsplitter ophthalmoscope, we have demonstrated that if the patient's fovea is not exactly conjugate to the light source, light from the retina spills past the light source at the ophthalmoscope mirror into the examiner's eye, creating the red reflex. Therefore, binocular asymmetry of this conjugate relationship, whether due to anisometropia or strabismus, creates asymmetrical red reflexes. Understanding this principle of conjugacy is critical to optimal utilization of the red reflex in routine clinical examination as well as in microsurgery.
An ophthalmoscope is not a retinoscope. The difference is in the red reflex.
Both the retinoscope and the ophthalmoscope allow observation of the fundus and of the "red reflex." Retinoscopy, however, requires an effective light source that may be quickly moved off the visual axis. The ophthalmoscope is unable to provide this type of illumination. On the other hand, the retinoscope is unable to provide sufficient illumination of the retina to make it useful for ophthalmoscopy . Ophthalmoscopy requires the examiner's retina to be conjugate to the retina being examined, whereas the examiner's retina becomes conjugate to the peephole of the retinoscope in retinoscopy. The "red reflex" seen with either the retinoscope or the ophthalmoscope may be clear or blurred. The clear red reflex is more useful for ophthalmoscopy , while the blurred red reflex is primarily used for retinoscopy.