Auxiliary Lenses for Slit-Lamp Examination of the Retina
The cornea and lens together provide so much convergence that ordinarily we cannot see the retina using a slit-lamp biomicroscope. At most, the slit lamp could view about half of the way back from the crystalline lens to the retina, and usually no more than one third of the way. Auxiliary lenses for slit-lamp examination of the retina can be placed in front of the eye to overcome this problem. Table 8-1 lists common auxiliary lenses for slit-lamp examination of the retina.
The Goldmann 3-mirror contact gonioscopy lens is a special viewing lens that is widely used for looking at the eye with the slit lamp. With a power of about –64 D, it essentially nullifies the power of the eye (recall that the eye itself has about 60 D of plus power) and provides an upright view of the posterior pole. The mirrors inside the contact lens enable alternative (left-right reversed) views of more and less peripheral portions of the eye, and even of the angle of the anterior chamber (Fig 8-14; gonioscopy). The main disadvantage of the Goldmann lens is its limited field of view requiring rotation of the lens to visualize more than a small patch of the fundus.
Table 8-1 Auxiliary Lenses for Slit-Lamp Examination of the Retina
Other examples of contact lenses for the slit-lamp biomicroscope are the fundus contact lenses from manufacturers such as Volk (Mentor, OH) or Ocular Instruments (Bellevue, WA). Examples include the Area Centralis lens for viewing the central fundus, and the QuadrAspheric and TransEquator lenses that enable peripheral wide-angle views of the retina.
Holding a high-power plus lens (eg, 60 D or 90 D fundus lenses) in front of the eye, produces an inverted aerial image of the retina, which can be viewed with the slit lamp in a manner similar to performing “indirect ophthalmoscopy” (Fig 8-15).
Excerpted from BCSC 2020-2021 series : Section 3 - Clinical Optics. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.