In assessing internal eye structure, using ophthalmoscope the nurse should ___________________

Direct Ophthalmoscope

The entire retina, if spread out and flattened, is about the size of a large postage stamp. The important structures themselves are rather small. For example, the optic nerve is 1.5 mm in diameter, and the major blood vessels are only 0.1–0.2 mm in diameter. Significant papilledema, with an elevation of the nerve head of 3.00 D, is equivalent to only a 1 mm change in elevation. Most of the important red and yellow details, including blood vessels, hemorrhages, and exudates, are seen against the light red background of the blood-filled choroid. Subtle changes in the pinkish white backscattered light of the optic disc announce major glaucomatous or neuro-ophthalmic alterations. The presence of the corneal reflection and the usual backscattered light of the healthy cornea and lens make the evaluation of fundus changes even more difficult.

In the face of these obstacles, it seems almost miraculous that the examiner is able to make a significant number of diagnoses using the direct ophthalmoscope.Fig. 2.5.1 illustrates how the ophthalmoscope directs the light rays of illumination and observation coaxially, while the observation system is essentially a peephole.1 The lens and cornea of the patient's eye actually create the retinal image. Thus the observer does not really see the retina of the patient but an optical image of the retina.

To bring the red fundus reflex into sharp focus for the viewer, the modern ophthalmoscope has a disc of lenses. Because the compensating lens neutralizes the refractive error of both the physician and the patient and the accommodation of each, its total power provides only a rough estimate of the patient's refractive state. The magnitude of a large amount of astigmatism may actually be estimated if the lens is focused on a blood vessel that travels parallel to the foveal reflex and then refocused on a vessel that travels perpendicular to the first vessel.2

Probably the most important advance in direct ophthalmoscopy was the use of the halogen tungsten bulb,3 which has a number of advantages over the older tungsten bulb. A quartz jacket can withstand higher temperatures than can the glass jacket, thus the filament temperature may be raised higher than that in the conventional tungsten bulb to produce an increased lumen output.

The field of view of the modern direct ophthalmoscope averages about 10° and is limited by the most oblique pencil of rays that can pass from the outer edge of the observer's pupil to the opposite outer edge of the patient's pupil. To enlarge the field of view of the direct ophthalmoscope, the investigator's eye must be brought closer to the patient's eye with the patient's pupils dilated.

Because the enlargement capacity of any magnification lens usually is defined as one-fourth of the lens power, the retinal image in the typical emmetropic eye of 60 D may be considered to be magnified by 60/4, or ×15. In aphakic eyes, from which a 20 D natural lens has been removed, the magnification for the observer is reduced to about 40/4 or ×10.

Funduscopic Evaluation

A direct ophthalmoscope is invaluable for the primary care physician. The light source is bright enough to evaluate the pupils, a cobalt blue filter often is built into the instrument for use with fluorescein staining of the cornea, and the instrument allows an excellent evaluation of the fundus. If an abnormality in the posterior pole is suspected, the eyes may be dilated.

The physician should instill a weak mydriatic agent after vision assessment and pupillary exam. Tropicamide 0.5% or 1% and phenylephrine 2.5% are good choices; with both, effects are reversed in 4 to 6 hours. Atropine drops should not be used because they produce dilation for as long as 1 to 2 weeks. Pupillary dilation causing an attack of angle-closure glaucoma is extremely uncommon. A simple test to determine relative safety in dilation involves shining a penlight parallel to the iris at the temporal corneal limbus (see Fig. 11-5). If the anterior chamber is deep, the light reflex will be seen across the cornea to the nasal side. If the iris is bowed forward significantly, the light reflex will be obstructed by the “mound,” thus blocking the transmission of light to the nasal side of the cornea. In this instance, the patient should be referred to an ophthalmologist for pupillary dilation and examination when necessary. It is imperative that whenever dilating agents are instilled in the eyes, clear documentation in the patient's record, including the agent and the time of instillation, must be performed.

Documenting the time of dilation and the agents used for dilation in the chart is an important step. Even in undilated eyes, examination with the direct ophthalmoscope can give useful information pertaining to the clarity of the ocular media and refractive error. A diminished red reflex or irregularities in the red reflex may result from cloudy media (e.g., corneal or lens opacities, vitreous blood) and unusual refractive errors. The −3 to −4 diopter lens on the ophthalmoscope (the red 3 or 4) usually generates a comfortable view of the fundus. If the examiner has difficulty seeing the fundus, different lenses may be rotated into position until a clear image appears. The direct ophthalmoscope evaluates the optic nerve head, retinal vessels, and macula. For examination of the periphery, use of an indirect ophthalmoscope, necessitating the expertise of an ophthalmologist, is indicated (Fig. 1-17).

The examiner's right eye is used to assess the patient's right eye, and the examiner's left eye assesses the patient's left eye. The optic nerve head is most easily seen by having the patient look straight ahead and approaching with the ophthalmoscope from a slightly temporal angle. The examiner looks for abnormalities in shape and color. The margins should be sharp and vessels crisp as they cross the edge of the disc. If this is not seen, the disc may be edematous. The examiner notes any hemorrhages or infarctions of the nerve fiber layer (“cotton-wool spots”) near the nerve head. Pallor of the nerves (resulting from optic atrophy) may indicate an old optic neuropathy and should be evaluated by an ophthalmologist. Increased intracranial pressure (papilledema) is one cause of disc edema. Marked or asymmetrical cupping of the nerve is a possible sign of glaucoma.

The best view of the macula is obtained when the patient looks directly at the examining light. (The macula is examined last because of the patient's light sensitivity.) A small reflex of light seen hovering directly over the fovea (the foveal light reflex) is one indicator of normal foveal anatomy. Hemorrhage, exudates, microaneurysms, and areas of edema are findings in microvascular disease. The examiner should note whether these signs are localized to one area of the retina (as in a vascular occlusion), are diffusely scattered throughout one retina (as in ocular ischemia or radiation retinopathy), or constitute generalized findings in both eyes (as in systemic diseases such as diabetes and hypertension). The depth of hemorrhage is difficult to determine; however, deep hemorrhages tend to be small and irregular (“dot and blot” hemorrhages), whereas superficial hemorrhages follow the nerve fiber layer and are flame shaped. Retinal edema gives the retina a grayish appearance and also is present in areas of vascular occlusion. In central retinal artery occlusions and conditions in which the nerve fiber layer is thickened, a red spot (the cherry-red spot) usually is present in the central macular region. This phenomenon occurs as the normal choroidal blood flow is viewed through the fovea centralis, the only area of the retina lacking ganglion cells and a nerve fiber layer. Cherry-red spots also occur in metabolic storage diseases (e.g., Tay-Sachs disease) as a result of accumulation in the retina of the products of abnormal enzyme pathways.

Evaluation of the retinal circulation is difficult with the direct ophthalmoscope, but dilation of the pupil facilitates observation of the vessels. Venous occlusions have associated retinal hemorrhages, exudates, and retinal thickening from edema. Arteriovenous nicking is present in hypertensive retinopathy. In atherosclerotic disease (especially carotid disease), cholesterol emboli may lodge in the retinal arterioles at their bifurcations and are therefore noticeable on ophthalmoscopic examination. These small, sometimes white or refractile bodies in the lumen of the vessels are known as Hollenhorst plaques.

Smartphone Ophthalmoscopy – Replacing the Direct Ophthalmoscope?

Screening

Diabetic retinopathy can progress significantly without the patient being aware of any problems. The primary aim of screening is the detection of potentially sight-threatening retinopathy in asymptomatic people so that treatment, where required, can be performed before visual impairment occurs.

Retinal screening is defined as the ongoing assessment of fundi with no diabetic retinopathy or non-sight-threatening diabetic retinopathy. Once sight-threatening eye disease develops, treatment is usually required. Diabetic retinopathy screening does not remove the need for a regular general eye examination to monitor changes in refraction and to detect other eye disease.

In patients with type 1 diabetes it takes 5–6 years for retinopathy to progress. In type 1 patients aged 11 years or older, it can take 1–2 years for retinopathy to progress. A population-based study demonstrated the prevalence of retinopathy to be 14.5% for any retinopathy and 2.3% for proliferative and pre-proliferative retinopathy in children and adolescents with insulin-dependent diabetes mellitus diagnosed before the age of 15 years and who were older than 9 years at the time of examination. Pre-proliferative retinopathy has been identified as early as 3.5 years after diagnosis in patients postpuberty, and within 2 months of onset of puberty.

Direct ophthalmoscope

The ophthalmoscope was invented more than 100 years ago by Hermann von Helmholtz. Von Helmholtz’s work was based on the observations of Ernest Brücke, a well-known Viennese physiologist, who 4 years earlier had reported noticing a red light in the pupil of a young man standing in the auditorium of the university as the chandelier light reflected from the student’s eye in a direction corresponding to that of his own visual axis. With the popularization of the ophthalmoscope, a wealth of blinding diseases could be understood, and investigation of their cause and treatment began.

The ophthalmoscope consists fundamentally of a light source, a viewing device, and a reflecting device to channel light into the patient’s eye. The reflecting device can be a mirror or a reflecting prism. If the patient and examiner are both emmetropic, then light from the patient’s retina will be in focus for the examiner. If, however, either the patient or the examiner is hyperopic or myopic, the spherical lenses must be used to overcome their refractive error. Because the ophthalmoscope contains no cylindric lenses, astigmatic errors of refraction cannot be compensated for. Thus if a patient has a large amount of astigmatism, a crystal-clear view of the fundus cannot be obtained. The direct ophthalmoscope enables the examiner to use the power of the subject’s eye as a magnifying system to see the retina. Although the field of vision is somewhat restricted compared with that seen with the indirect ophthalmoscope, the magnification is greater, being approximately × 15 for the former and × 5 for the latter (Figure 10.22).

To facilitate pupillary dilation, ophthalmoscopy is best performed in a darkened room. For a better inspection of the fundus, however, the pupils should be dilated with a weak mydriatic agent, such as 2.5% phenylephrine. With heavily pigmented irides, a stronger mydriatic agent, such as 10% phenylephrine, should be used but withcaution. Because there have been deaths recorded from the application of a single drop, 10% phenylephrine shouldnot be routinely used. It shouldnever be used with patients who have hypertension or cardiovascular disease. If it is imperative to dilate the pupils of these patients, then cyclopentolate (Cyclogyl) or tropicamide (Mydriacyl) should be used. Pupillary dilation with drops usually is performed in all new patients and in those with extremely small pupils.

The examiner stands directly in front of the patient and examines the patient’s right eye with his or her own right eye and the left eye in similar fashion (Figure 10.23). The first structure in the fundus noted, for purposes of orientation, is the optic disc. The disc is an oval structure and represents the site of entrance of the optic nerve (Figure 10.24). It is usually pink and may have a central white depression, called thephysiologic cup. The margins of the disc are sharp and distinct except for the margins of the upper and lower poles, which may be slightly fuzzy. From the disc the retinal arterioles and veins emerge and bifurcate; they extend toward the four quadrants of the retina. The retinal vein, which usually is found lateral to the retinal artery, is larger and darker red.

Historical discovery of macular edema

One of the first reports, after the advent of the direct ophthalmoscope, on what would be described as diabetic macular edema today was published by Eduard Jaeger in 1856.5 In 1872, Edward Nettleship provided the first histopathological proof for a “cystoid degeneration of the macula” in patients with diabetes,6 while histological observations on a cystic degeneration unrelated to diabetes were further documented by the Russian ophthalmologist Iwanoff.7

The first description of macular edema with documented vitreomacular traction was published by Irvine in his classical paper on CME after intra- and extracapsular cataract extraction characterizing the vitreous tug syndrome after incarcerated vitreous in the corneal wound.8

Funduscopic Examination

The posterior pole of the eye can be viewed with a direct ophthalmoscope through an undilated pupil. Any media opacity due to corneal exposure, cataract, or vitritis, for instance, can create a hazy view. Posteriorly, the optic disc, retinal vasculature, macula, and peripapillary retina should be carefully examined (Fig. 8‐6). Important details of the optic disc that should be noted include its color and contour and cup‐to‐disc ratio. The retinal vasculature should be evaluated in detail, with particular attention to the caliber of arteries and veins, branching patterns, and, when suspected, possible emboli. The macula, best observed by asking the patient to look at the direct ophthalmoscope's light, is examined for evidence of degeneration, lipid deposition, detachment, edema, or change in pigment color. Thorough evaluation of the retinal periphery requires a pharmacologically dilated pupil and indirect ophthalmoscopy.

Optic disc swelling suggests an optic neuropathy or papilledema. Chronic optic nerve processes lead to disc atrophy. Macular disturbances are associated with central field loss and decrease in visual acuity. If large enough, other retinal abnormalities can also cause corresponding field loss. For instance, retinitis pigmentosa beginning peripherally causes field constriction, whereas an inferior branch retinal artery occlusion is associated with a superior altitudinal field defect.

Diagnosis

Large cataracts are obvious on inspection. Smaller cataracts distort the normal red reflex when the direct ophthalmoscope is at arm’s length distance from the eye and a +12 to +20 lens is used.

Genetic disorders and maternal drug exposure are important considerations when cataracts are the only abnormality. Intrauterine disturbances, such as maternal illness and fetal infection, are usually associated with growth retardation and other malformations. Dysmorphic features are always an indication for ordering chromosome analysis. Galactosemia is suspected in children with hepatomegaly and milk intolerance (see Chapter 5), but cataracts may be present even before the development of systemic features.

B Technique

Figures 20-3 and 20-4 summarize the initial approach to anisocoria. The most important initial questions follow.