USE OF THE HAND-HELD OPHTHALMOSCOPE

INTRODUCTION

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Examination of the living human retina provides a unique opportunity for the direct study of nervous, vascular, and connective tissues. Many systemic disorders have retinal manifestations that are valuable for screening, diagnosis, and management of these conditions. Furthermore, retinal involvement in systemic disorders, such as diabetes mellitus, is a major cause of morbidity. Early recognition by ophthalmoscopic screening is a key factor in effective treatment. Ophthalmoscopy has the potential to be one of the most “high-yield” elements of the physical examination. Effective ophthalmoscopy requires a basic understanding of ocular structures and ophthalmoscopic techniques and recognition of abnormal findings.

OVERVIEW OF OCULAR STRUCTURES

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The eye consists of a shell (cornea and sclera), lens, iris diaphragm, ciliary body, choroid, and retina. The anterior chamber is the space between the cornea and the lens, and it is filled with aqueous humor. The space between the posterior aspect of the lens and the retina is filled by vitreous gel. The choroid and the retina cover the posterior two-thirds of the sclera internally. The cornea and the lens form the focusing system of the eye, while the retina functions as the photoreceptor system, translating light to neuronal signals that are in turn transmitted to the brain via the optic nerve and visual pathways. The choroid is a layer of highly vascularized tissue that nourishes the retina and is located between the sclera and the retina. The retinal pigment epithelium (RPE) layer is a monolayer of pigmented cells that are adherent to the overlying retinal photoreceptor cells. RPE plays a major role in retinal photoreceptor metabolism.

NORMAL FUNDUS

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The important areas that are visible by ophthalmoscopy include the macula, optic disc, retinal blood vessels, and retinal periphery (Fig. 26-1).

FIGURE 26-1

Diagram showing the landmarks of the normal fundus. The macula is bounded by the superior and inferior vascular arcades and extends for 5 disc diameters (DD) temporal to the optic disc (optic nerve head). The central part of the macula (fovea) is located 2.5 DD temporal to the optic disc. The peripheral fundus is arbitrarily defined as the area extending anteriorly from the opening of the vortex veins to the ora serrata (the juncture between the retina and ciliary body). (Drawing courtesy of Juan R. Garcia. Used with permission from Johns Hopkins University.)

THE MACULA

The macula is the central part of the retina and is responsible for detailed vision (acuity) and perception of color. The macula is defined clinically as the area of the retina centered on the posterior pole of the fundus, measuring about 5 disc diameters (DD) (7–8 mm) and bordered by the optic disc nasally and the temporal vascular arcades superiorly and inferiorly. Temporally, the macula extends for about 2.5 DD from its center. The fovea, in the central part of the macula, corresponds to the site of sharpest visual acuity. It is approximately 1 DD in size and appears darker in color than the surrounding area. The center of the fovea, the foveola, has a depressed pit-like configuration measuring about 350 μm.

THE OPTIC DISC

The optic disc measures about 1.5 mm and is located about 4 mm (2.5 DD) nasal to the fovea. It contains the central retinal artery and vein as they branch, a central excavation (cup), and a peripheral neural rim. Normally, the cup-to-disc ratio is less than 0.6. The cup is located temporal to the entry of the disc vessels. The normal optic disc is yellow/pink in color. It has clear and well-defined margins and is in the same plane as the retina (Fig. 26-2). Pathologic findings include pallor (atrophy), swelling, and enlarged cupping.

FIGURE 26-2

Photograph of a normal left optic disc illustrating branching of the central retinal vein and artery, a physiologic cup, surface capillaries, and distinct margin. The cup is located temporal to the entry of the disc vessels. (From H Tabandeh, MF Goldberg: Retina in Systemic Disease: A Color Manual of Ophthalmoscopy. New York, Thieme, 2009.)

THE EQUATOR AND PERIPHERAL RETINA

The equator of the fundus is clinically defined as the area that includes the internal opening of the vortex veins. The peripheral retina extends from the equator anteriorly to the ora serrata.

OPHTHALMOSCOPY

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There are a number of ways to visualize the retina, including direct ophthalmoscopy, binocular indirect ophthalmoscopy, and slit-lamp biomicroscopy. Most nonophthalmologists prefer direct ophthalmoscopy, performed with a hand-held ophthalmoscope, because the technique is simple to master and the device is very portable. Ophthalmologists often use slit-lamp biomicroscopy and indirect ophthalmoscopy to obtain a more extensive view of the fundus.

DIRECT OPHTHALMOSCOPE

Direct ophthalmoscopes are simple hand-held devices that include a small light source for illumination, a viewing aperture through which the examiner looks at the retina, and a lens dial used for correction of the examiner’s and the patient’s refractive errors. A more recent design, the PanOptic ophthalmoscope, provides a wider field of view.

How to use a direct ophthalmoscope

Good alignment is the key. The goal is to align the examiner’s eye with the viewing aperture of the ophthalmoscope, the patient’s pupil, and the area of interest on the retina. Both the patient and the examiner should be in a comfortable position (sitting or lying for the patient, sitting or standing for the examiner). Dilating the pupil and dimming the room lights make the examination easier. Steps for performing direct ophthalmoscopy are summarized in Table 26-1.

TABLE 26-1GUIDELINES FOR PERFORMING DIRECT OPHTHALMOSCOPY

Instruct the patient to remove glasses, keep the head straight, and to look steadily at a distant target straight in front. You may keep or remove your own glasses. Position your head at the same level as the patient’s head.
Use your right eye and right hand to examine the patient’s right eye, and use your left eye and left hand to examine the patient’s left eye.
Using the ophthalmoscope light as a pen light, briefly examine the external features of the eye, including lashes, lid margins, conjunctiva, sclera, iris, and pupil shape, size, and reactivity.
Shine the ophthalmoscope light into the patient’s pupil at arm’s length and observe the red reflex. Note abnormalities of the red reflex such as an opacity of the media.
Dialing up a +10 D lens in the lens wheel, while examining the eye from 10 cm, allows magnified viewing of the anterior segment of the eye.
Reduce the power of the lens in the wheel to zero, and move closer to the patient. Identify the optic disc by pointing the ophthalmoscope about 15° nasally or by following a blood vessel toward the apex of any branching. If the retina is out of focus, turn the lens dial either way, without moving your head. If the disc becomes clearer, keep turning until best focus is achieved; if it becomes more blurred, turn the dial the other way.
Once you visualize the optic nerve, note its shape, size, color, margins, and the cup. Also note the presence of any venous pulsation or surrounding pigment, such as a choroidal or scleral crescent.
Next, examine the macula. The macula is the area between the superior and inferior temporal vascular arcades, and its center is the fovea. You can examine the macula by pointing your ophthalmoscope about 15° temporal to the optic disc. Alternatively, ask the patient to look into the center of the light. Note the foveal reflex and the presence of any hemorrhage, exudate, abnormal blood vessels, scars, deposits, or other abnormalities.
Examine the retinal blood vessels by re-identifying the optic disc and following each of the four main branches away from the disc. The veins are dark red and relatively large. The arteries are narrower and bright red.
Ask the patient to look in the eight cardinal directions to allow you to view the peripheral fundus. In a patient with a well-dilated pupil, it is possible to visualize as far as the equator.

PANOPTIC OPHTHALMOSCOPE

The PanOptic ophthalmoscope is a type of direct ophthalmoscope that is designed to provide a wider view of the fundus and has slightly more magnification than the standard direct ophthalmoscope. Steps for using the PanOptic Ophthalmoscope are summarized in Table 26-2.

TABLE 26-2HOW TO USE A PANOPTIC OPHTHALMOSCOPE

Focus the ophthalmoscope: Look through the scope at an object that is at least 10 to 15 feet away. Sharpen the image of the object by using the focusing wheel. Set the aperture dial to “small” or home position.
Turn the scope on, and adjust the light intensity to “Maximum.”
Instruct the patient to look straight ahead. Move the ophthalmoscope close to the patient until the eyecup touches the patient’s brow. The eyecup should be compressed about half its length to optimize the view.
Visualize the optic disc.
Examine the fundus as described in Table 26-1.