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EXAMINATION OF THE VITREOUS

Slitlamp Examination

Normal vitreous is not visible by either direct or indirect ophthalmoscopy. The numerous ophthalmoscopically visible features are anomalies attributable either to structural changes, such as the floaters of syneresis and the ring-like form associated with posterior vitreous detachment (Figure 9-1), or to invasive elements, such as blood, white blood cell masses, or fibrovascular proliferations from adjacent tissues. Normal vitreous in situ and many important anomalies (eg, the retraction, condensation, and shrinkage of vitreous characteristic of diabetes or injury) can be viewed only with a slitlamp. The slitlamp (biomicroscope) is a microscope with a specialized illuminating system that make transparent and near-transparent ocular fluids and tissues visible. Although slitlamp examination of the vitreous is quite easy to learn and plays an important role in the management of vitreous disease, too few ophthalmologists make optimal use of this instrument.

Contact Lenses as Aid in Vitreous Examination

The anterior central vitreous is the only part of the inner eye (behind the lens) that can be seen with the slitlamp alone. In order to view other areas, special contact lenses must be placed on the patient's eye. A relatively thin contact lens with a flat front surface allows stereoscopic examination of tissues on and near the visual axis of the eye-the optic disk, the posterior retina and choroid, and the axial vitreous. Much thicker contact lenses with built-in mirrors and a flat front surface allow examination of the nonaxial retina and vitreous.

These special contact lenses are also used in therapeutic procedures. Fundus contact lenses with built-in mirrors are widely used in laser photocoagulation of the peripheral retina, such as in the management of retinal neovascularization due to diabetic retinopathy, retinal vein occlusion, or (more rarely) sickle cell anemia. The thinner contact lenses are used in ablation of macular lesions associated with diabetic retinopathy, age-related macular degeneration, and histoplasmosis.

Use of special contact lenses, whether for diagnostic or therapeutic procedures, requires maximum dilation of the pupil with a combination of mydriatic and cycloplegic solutions; use of a topical anesthetic to make the patient more comfortable; and use of a clear viscous solution of methylcellulose to prevent air from entering the lens-cornea interface.

B-Scan Ultrasonography

B-scan ultrasonography is an important diagnostic tool used in many posterior segment problems associated with gross vitreous opacification (Figure 9-2). Where light-dependent ophthalmoscopes and slitlamps provide insufficient information, skillful use of B-scan ultrasonography can provide much information about the vitreous and adjacent structures. For example, it is possible to identify and locate vitreous membranes (Figure 9-3), vitreoretinal relationships and retinal detachments greater than 1 mm in depth (Figures 9-3, 9-4 and 9-5), scleral ruptures, and intraocular foreign bodies (even nonlucent plastic and glass).

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