Ординатура / Офтальмология / Английские материалы / Practical Ophthalmology A Manual for the Beginning Ophthalmology Residents 4th edition_Wilson_1996

* Or use light red or leave uncolored for attached retina.

t Or use purple for flat neovascularization and orange for elevated neovascularization.

Figure 13.20 The vitreoretina! drawing chart is inverted on the supine patient's chest so that the examiner can draw the image that is seen in the condensing lens onto the chart.

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takes practice. In examining a supine patient, the beginning resident should place the chart on die patient's chest so that the 12-o'clock chart meridian points toward the patient's feet, thereby preparing to make an inverted drawing of an inverted image (see Figure 13.21). Clinical Protocol 13.7 summarizes the steps of making the fundus drawing.

The retinal periphery is examined by moving around the patient, always standing directly opposite the meridian that is being examined. Because more peripheral details are seen at the bottom of the condensing lens, the image is drawn onto the part of the chart closest to the examiner (see Figure 13.21). After making many drawings, the experienced examiner will learn to correct mentally for the inverted image.

Drawing the Slit-Lamp Biomicroscopic View

In indirect biomicroscopy with the slit lamp, the image of the posterior pole seen in a face-to-face examination is drawn onto an inverted fundus chart beside the biomicroscope. For the examiner to draw the

r- equatorial and peripheral fundus with indirect slit-lamp biomicroscopy (or with a mirrored contact lens), the paper is turned as the patient's gaze direction changes (or as the contact lens is rotated) so that the meridian being drawn corresponds to the clock hour being examined.

For Hruby lens and contact lens biomicroscopy, the image is drawn as the examiner sees it.

Drawing the Direct Ophthalmoscopic View

An accurate drawing is made of the optic discs. The examiner should note the cup dimensions, the neuroretinal rim area, and other optic nerve and peripapillary changes. Because indirect ophthalmoscopy often underestimates the cup-disc ratio, stereoscopic examination with

,,i. a +78 D lens, the Hruby lens, or a fundus contact lens is also used to add this information to the drawing.

Imaging Studies

• ,r\. Many types of imaging studies are useful in evaluating and documenting vitreoretinal and choroidal findings. These include fundus photography, angiography, and ultrasonography, all discussed below. Radiography, computed tomography (CT), and magnetic resonance

imaging (MRI) also contribute information to the diagnosis of ocular abnormalities, but discussion of these techniques is beyond the scope of this manual.

Photography

Photographs help to document abnormalities of the fundus. Magnified photographs are taken of the optic disc and macula, and stereoscopic pairs can be useful. In addition to the standard 30° field, wide-angle cameras are also available. Clear instructions on the reasons for photography must be given to the ophthalmic photographer so the correct fields and magnifications are selected. Corresponding photographs are usually taken of both eyes for comparison.

Angiography

Fluorescein angiography is used to evaluate diseases of the retina, retinal pigment epithelium (RPE), and choroid. After obtaining informed consent, sodium fluorescein solution is injected intravenously, and fundus photographs are taken in rapid sequence. The dye is observed to circulate through the blood vessels of the retina and, although somewhat hidden by the RPE, the choroid. Normal retinal vessels and large choroidal vessels are impermeable to fluorescein, whereas the choriocapillaris normally leaks dye that permeates the choroid and is partly absorbed by the sclera. Fluorescein also passes into the optic nerve head from the peripapillary choriocapillaris and leaks into the aqueous and vitreous humors from the iris and ciliary body. Fluorescein also extends through Bruch's membrane, but the close approximation of normal RPE cells is a barrier to the further inward passage of dye and its fluorescence. Original negatives of the fluorescein angiogram are studied, because artifacts can develop during the printing process.

Indocyanine green (ICG) is a dye that absorbs and fluoresces in the near infrared range. Digital ICG angiography allows enhanced imaging of the choroid through overlying blood, lipid, and pigment and provides information that can supplement the fluorescein angiogram.

Ultrasonography

Diagnostic ultrasonography, or echography, is a useful technique when media opacification prevents adequate ophthalmoscopy of the posterior segment. Two formats are available: an A-scan is a one-dimensional display used to characterize tissues, and a B-scan is a two-dimensional display used for architectural information (Figure 13.22).

Table 13.8 Normal Degenerative Changes of the Aging Eye

Druser,

Narrowing

Increased light reflex

Drusen

Reticular pigmentary degeneration

Chorioretinal degeneration

Paving-stone degeneration

Liquefaction

Floaters

Posterior vitreous detachment

Normal disc measurements for people of European descent are as follows: disc area, 2.6 mm2; cup area, 0.7 mm2; and rim area, 1.9 mm2. Blacks have 10% larger disc and cup areas, while the optic discs of Asian ethnic groups tend to be somewhat smaller.

Scleral rim

A physiologic scleral rim is seen when the choroid and retinal pigment epithelium do not reach the optic nerve. Its outer border is formed by the edge of the RPE and the inner border by the scleral canal of the optic nerve. If either of these pigmented layers is thickened, a pigment arc (conus) is seen. A darkly pigmented area is caused by the RPE extending farther than usual, and a lightly pigmented area is seen if the RPE stops short and exposes the choroid. Other normal variants include slightly blurred disc borders, resulting from a narrowed scleral aperture in hyperopic eyes and from a tilted disc in myopic eyes.

Posterior Pole

The macula has a diameter of about 15°, and its central zone, the fovea, a diameter of 5°. The yellow color of the macula lutea is not visible with white light but can be seen with bright illumination through a red-free interference filter. A healthy nerve fiber layer is slightly

334 Chapter 13: Posterior Segment Examination

opaque with parallel striations in an arcuate pattern above and below the macula. The central point of the foveola often has a reflex that is an inverted image of the light source. Loss of the foveal light reflex is a common age-related change of the posterior pole, along with atrophic spots of the RPE and drusen, which are yellow-white dots between the RPE and Bruch's membrane.

Retinal Blood Vessels

Retinal blood vessels radiate from the optic disc, dividing dichotomously into a pattern of branches unique for each individual. Cilioretinal arteries are present in about 20% of all eyes. Congenital tortuosity of the retinal arterioles and venules is sometimes found. The width of the central retinal artery (or at least the visible blood column, because the vascular wall is normally transparent) is about 0.1 mm.

Vascular crossings

Retinal arteries generally remain at one level and the vein passes underneath; compression of the venule is then seen as nicking. When the vein passes over the artery, a humping effect is seen.

Fundus Background

Physiologic color variations are commonly encountered in the hackground of the normal fundus. In a lightly pigmented (blond or albinotic) fundus, retinal and choroidal blood vessels are seen on a virtually white background. The fundus of a darkly pigmented person has an even, dark color, especially at the posterior pole. Nonuniform distribution of choroidal melanin produces a streaked or tessellated fundus background. In an eye with minimal pigment, the choroidal vessels are visible.

The venous tributaries of the choroid drain into the vortex ampullae, of which there are usually four (at 1-, 5-, 7-, and 11-o'clock positions) but sometimes more. The long posterior ciliary nerves are broad, yellow lines along the horizontal meridians. The long posterior ciliary arteries are usually inferior to the temporal nerve and superior to the nasal nerve.

Drusen

Drusen are small yellowish excrescences at Bruch's membrane. Drusen are more common at the equator, especially nasally, than in the posterior pole. Macular drusen are more often found in the elderly and may be punctate or geographic.

Pigmentary changes and nevus

Congenital hypertrophy of the retinal pigment epithelium (CHRPE) appears as a densely black, flat spot; grouped lesions are sometimes called bear tracks. Reticular pigmentary degeneration is an age-related degeneration of the retinal pigment epithelium. Also called honeycomb degeneration, it forms a fishnet or honeycomb pattern that is most prominent along the nasal equator.

A choroidal nevus is a dark, flat lesion that may have drusen on it but does not distort the overlying retina.

Peripheral Fundus

The ora serrata is characterized by about 50 ora teeth that point anteriorly and by ora bays that are formed between the teeth. The serrations of the peripheral retina are generally most pronounced nasally, sometimes with meridional ridges or folds, and the ora is smoother temporally. The transition from the deep nasal ora bays to the shallow temporal bays occurs at approximately 5 o'clock and 11 o'clock in the right eye and at 1 o'clock and 7 o'clock in the left eye.