80 I: Principles

Anterior segment biomicroscopy

The cornea is usually clear in retinal detachment, but occasionally there is enough hypotony to create folds in Descemet’s membrane. Anterior uveitis is rarely sufficient to produce keratic precipitates. Mild flare and cells are frequently noted in the anterior chamber, and occasionally the reaction is marked. The depth of the anterior chamber should be noted. The angle of the chamber can be estimated with the slit-lamp beam near the limbus. If the peripheral anterior chamber seems unusually shallow, gonioscopy is indicated.

Any opacities of the lens should be noted. An objective assessment of the effect of opacities on visual acuity is more accurate with use of the direct ophthalmoscope. A posterior subcapsular cataract might interfere with visual acuity, but it often does not prevent a thorough examination of the fundus periphery. On the other hand, peripheral cortical opacities may not interfere with visual acuity, but they may seriously impair examination of the periphery and conceal the presence of peripheral retinal breaks. The vitreous should be examined for evidence of vitreous detachment, hemorrhage, inflammatory cells, or pigment.

If there has been no previous intraocular disturbance (such as uveitis, trauma, or intraocular surgery), the presence of pigment in the vitreous (“tobacco dust”) is very suggestive of a retinal break. Pigmented cells from the retinal pigment epithelium may pass through a retinal break into the vitreous cavity. Retinal breaks have been found in more than 70% of eyes with “tobacco dust” if there is no other obvious explanation for the presence of pigment in the vitreous.

The indirect ophthalmoscope can be used for examining the anterior segment when a slit lamp is not available. With the examiner’s eyes positioned just 8 to 10 inches from the patient, the condensing lens functions as a magnifying loupe that provides an erect real image.

Tonometry

The intraocular tension should be recorded for both eyes before the pressure is artificially lowered by the massage effect of scleral indentation (scleral depression). Usually, an eye with retinal detachment is relatively hypotonic, and the pressure may be as much as 10 mm Hg less than the unaffected eye. Occasionally, the hypotony is so profound that no tension can be recorded. Still rarer is the patient who has a paradoxically elevated intraocular pressure in the presence of retinal detachment (Schwartz syndrome). Either of these extremes is usually relieved by retinal reattachment.

RETINAL EXAMINATION

BINOCULAR INDIRECT OPHTHALMOSCOPY

Retinal surgeons rely primarily on the binocular indirect ophthalmoscope for diagnosing retinal detachment. Its main features are contrasted with those of the direct ophthalmoscope in Table 3–1. Despite its low magnification and inverted image, the binocular indirect ophthalmoscope is the instrument of choice due to its large

82 I: Principles

Figure 4–3. Diagram of fundus areas visible with Goldmann’s three-mirror lens. (Redrawn with permission from Havener WH, Gloeckner S: Atlas of Diagnostic Techniques and Treatment of Retinal Detachment. St Louis: CV Mosby Co; 1967.)

Vitreoretinal relationships in the periphery can be examined with mirrored lenses or with indirect lenses. Mirrored lenses have the advantage of a shallow depth of focus, which is valuable when a questionable retinal break cannot be clearly defined by ophthalmoscopy. By precise focus on the sensory retina, the presence of a break can be detected. With difficulty, scleral depression can be performed in combination with biomicroscopic evaluation of the peripheral retina (Figure 4–4).

Biomicroscopy is the best way to define the critical role of the detached vitreous cortex in proliferative diabetic retinopathy. The mechanism of elevation of previously flat neovascularization, avulsion of retinal vessels, and tractional retinal detachment can be clearly seen.

Biomicroscopy is also valuable for the preoperative evaluation of a patient with a giant retinal tear. The possible attachment of formed vitreous to the flap of the tear or the presence of formed vitreous behind the retina is a preoperative clue to the prognosis, and suggests the best technique of surgical management.

Binocular indirect ophthalmoscopy should be employed first to obtain a panoramic view of the entire posterior segment. Contact lens biomicroscopy can then be used to define specific details; that is, the indirect ophthalmoscope can be used to see the “forest,” and the slit lamp to see the individual “trees.” Exclusive reliance on slit lamp examination of the retina is not recommended.

Figure 4–4. Examination of a peripheral retinal lesion using slit lamp biomicroscope, mirrored contact lens, and scleral depression. Enables the determination of whether small retinal lesion represents a full-thickness retinal defect.

ANCILLARY TESTS

Perimetry

Most cases of retinal detachment can be evaluated adequately without perimetry, but there are certain instances in which it is helpful, and others in which it may be important. The visual fields should be examined by confrontation, and if there is any question about the correlation of the field defect with the detachment, formal perimetry may be helpful. Perimetry is particularly indicated if there is antecedent disease of the optic nerve, particularly glaucomatous cupping.

Perimetry may also be helpful in the differential diagnosis of retinoschisis. Relatively flat retinoschisis can be readily differentiated from shallow retinal detachment in that the former invariably causes an absolute field defect, while the latter causes only a relative defect. Perimetry is less specific for bullous detachment, because an absolute field defect could be found in either detachment or retinoschisis. Perimetry may be helpful with a miotic pupil. As previously mentioned, perimetry only discloses disease posterior to the equator.

Ultrasonography

When confronted with opaque media, the physician can obtain valuable information with ultrasonography—both A-scan and B-scan. The technique can reveal both rhegmatogenous and nonrhegmatogenous detachments, such as those secondary to malignant melanoma of the choroid (Figure 4–5). Retinal tears in the absence of retinal detachment can often be detected as well.

84 I: Principles

A

Lens

Vitreous

Retinal detachment

B

Vitreous

Orbital fat

Retinal Malignant detachment melanoma

Figure 4–5. Ultrasonograms. (A) Rhegmatogenous detachment. (B) Detachment secondary to malignant melanoma. (Reproduced with permission from Coleman DJ, Jack RL: B-scan ultrasonography in diagnosis and management of retinal detachments. Arch Ophthalmol 1973;90:29–34. Copyright 1973, American Medical Association.)

A detached retina always remains attached at the optic nerve. This feature of insertion at the shadow of the optic nerve is easily observable with B-scan and helps distinguish retinal detachment from posterior vitreous separation or vitreous hemorrhage (Figure 4–6). A standardized A-scan can also be helpful in making this distinction.

Laser test

The distinction between retinal detachment and retinoschisis can usually be made by retinal examination alone. However, at times this can be a difficult diagnosis to make; especially when retinal detachment and retinoschisis coexist, it can be difficult to tell the extent of each.

The laser test can be helpful in this instance. Laser intensity is adjusted to create a medium-intensity laser spot in normal retina. This same intensity is then applied to the area of the retina in question. Where retinoschisis is present, a white spot will result, but where retinal detachment is present, there will be no visible reaction to the laser.