Part 1 of this article, which appeared in the June 2008 issue of Clinician's Brief, described the normal appearance of the ocular fundus and discussed the first 2 steps in examination-pupillary light reflexes and the menace/dazzle responses.
The posterior segment of the ocular fundus (the internal structures of the eye behind the lens) is examined using indirect ophthalmoscopy followed by direct ophthalmoscopy. These 2 methods are complementary rather than exclusive, because the limitations of one are the advantages of the other.
Ophthalmoscopy identifies changes in the eye's normal appearance, detachment of the retina, chorioretinal hypoplasia or dysplasia, vascular patterns, attenuation, congestion, hemorrhage, colobomas, scars, alteration in coloration, changes in pigmentation, and foci of inflammation. The optic disc should be examined for the presence of masses, pits, or colobomas; its size, shape, and color should also be evaluated. Swelling and inflammation of the optic disc occurs with optic neuritis and glaucoma. Excessive myelination of the disc is a normal variation and must be differentiated from swelling of the disc.
Indirect ophthalmoscopy, the technique favored by ophthalmologists, is an efficient technique for screening the ocular fundus for lesions. A biconvex condensing lens is positioned between the patient's eye and light source, producing a low magnification, stereoptic virtual image that is reversed and inverted. Mydriasis and darkness are essential for detailed examination.
The indirect technique allows greater distance between the face of the clinician and the patient's face compared to direct ophthalmoscopy and provides some protection to the clinician in intractable patients. The main disadvantages with indirect ophthalmoscopy are the low magnification available for studying particular areas and the amount of practice necessary to learn this technique.
Direct ophthalmoscopy is used more frequently by general practitioners than indirect ophthalmoscopy; however, both techniques have advantages that complement each other. The method is termed "direct" because a condensing lens is not positioned between the ophthalmoscope and the patient's eye, and the examiner has a direct optical image. The fundus image is magnified, real, and upright.
Direct ophthalmoscopy has certain limitations. Penetration of cloudy or partially crystallized media is limited. Because of magnification, there is a small field of view. Examination of the peripheral fundus is difficult. There may be difficulty in compensating for refractive errors and eye movements. Stereopsis is absent and depth of focus is limited. In addition, the small working distance between examiner's face and patient may be hazardous to the clinician.
The Panoptic ophthalmoscope (Welch Allyn, www.welchallyn.com) provides an intermediate level of magnification to the direct and indirect techniques.
Step by Step FUNDIC EXAMINATION: INDIRECT & DIRECT OPHTHALMOSCOPY
What You Will Need
• Direct ophthalmoscope
• Transilluminator head or bright penlight
• Indirect lens of sizes 5.5, 14, 20 and/or 30 diopter
• Dilating drops (tropicamide)
• Binocular indirect ophthalmoscope
Once the pupillary light response has been evaluated (discussed in Part 1), a mydriatic should be applied to the eye.