Slit Lamp Examination

Slit lamp or slit lamp microscope examination (synonyms: slit lamp microscopy; slit lamp examination) is one of the most important diagnostic procedures in ophthalmology. It is non-invasive (does not penetrate the body), easy to perform, and has a high information gain. Since the human eye is largely composed of transparent tissue, it is possible to shine a light beam through the various layers of tissue to detect opacities or other defects. The fine structures are rather difficult to see with diffuse light, so for better visualization a slit-shaped beam of light (hence slit lamp) is used to make an optical slice through the transparent eye tissue. Both the angle of incidence and the width of the light slit can be varied to obtain optimal visualization of the relevant structures. Furthermore, slit lamp examination can be performed in combination with other aids/devices (e.g., contact lens), depending on the problem.

Indications (areas of application)

The slit lamp microscope is used to closely inspect (view) the eyeball under appropriate illumination and high magnification. The procedure is used both as a preventive (precautionary) measure during a routine examination and as a diagnostic tool for existing conditions. Various defects in the different tissue layers of the eye can be diagnosed.

  • Conjunctiva (conjunctiva): defects on the conjunctiva or eyelids can be detected under optimal illumination, magnification, and stabilization of the head. A slit-shaped light beam is not yet mandatory here.
  • Cornea (cornea): the cornea is ideal for examination with the slit lamp microscope. Magnifications of 10x to 40x can be selected, and the slit illumination allows optical sectioning. The location and extent of numerous lesions can be determined:
    • Injuries, chemical burns, burns
    • Erosio corneae (exfoliation of the corneal epithelium).
    • Keratitis (inflammation of the cornea of the eye).
    • Curvature and size abnormalities of the cornea.
    • Corneal degeneration (gradual tissue loss).
    • Corneal dystrophy (bilateral, progressive, hereditary disease manifesting exclusively in the cornea; corneal opacity caused by congenital disorder of corneal metabolism)
  • Sclera (cornea): the surface of the sclera can be well examined with a slit lamp. Deeper layers are also accessible to inspection in part by compressing superficial blood vessels with a glass spatula or administering vasoconstrictive (vasoconstrictive) eye drops. Possible lesions on the sclera include:
    • Injuries
    • Discolorations
    • Scleral atrophy (scleral regression; thinning due to tissue loss, often as a result of inflammation).
    • Scleral ectasia (thinning of the sclera due to stretching of the eyeball, e.g., in high-grade myopia).
    • Zones of degeneration and calcification (common in older people in the palpebral fissure area).
    • Episcleritis (inflammation of the stroma (supporting framework) between the sclera and conjunctiva can be diffuse, sectorial or nodular).
    • Scleritis (deep inflammation of the sclera; usually a general disease is causally present, e.g., rheumatoid arthritis)
  • Lens (lens): the lens can be well examined with the slit lamp when the pupil is dilated.
    • Cataract (lens opacity): lens opacities can be due to age as well as numerous diseases (inflammation, injury, medication, etc.). Slit lamp can be used to detect opacities and, in particular, to determine in which lens layer they are located. Depending on the localization, a distinction is made between cataracta corticalis (cortical cataract), cataracta subcapsularis posterior (posterior shell opacity), cataracta nuclearis (nuclear cataract), cataracta zonularis (layered cataract) or cataracta coronaria (coronary cataract).
    • Changes in the shape of the lens
    • Ectopia lentis (positional changes of the lens).
  • Iris (iris) and corpus ciliare (ray body): with the slit lamp one looks at the shape, color and drawing of the iris as well as the iris vessels. In addition, one pays attention to the transparency of the anterior chamber, which is often abolished in inflammation of the iris.Various defects of the iris can be detected:
    • Injuries
    • Iridocyclitis (inflammation of the iris and ciliary body, often associated with autoimmune diseases).
    • Rubeosis iridis (vascular neoplasm at the iris due to ischemia (reduced blood flow) of the retina, e.g., in diabetes mellitus).
    • Tumors: Iris melanoma, ciliary body melanoma, etc.
    • Malformations: Coloboma (congenital (partly genetic) or also acquired cleft formation of iris (iris), lens, eyelid or choroid), aniridia (absence of iris), albinism (congenital disorders in the biosynthesis of melanins; here: lack of pigmentation of the iris).
  • Corpus vitreum (vitreous body): the anterior segment of the vitreous body can be easily assessed with the slit lamp.
    • Vitreous opacities
    • Endophthalmitis (inflammation of the interior of the eye, always involving the vitreous body, emergency situation).

The slit lamp microscope also finds its use in combination with other tools, some of which require direct corneal contact. This allows, for example, deeper sections of the eye to be assessed or intraocular pressure to be measured.

  • Slit-lamp microscopy of the retina/choroid: By holding an additional magnifying glass (contact glass or magnifying glass) in front of the eye, the slit lamp can be used to examine the fundus (fundus of the eye) and posterior vitreous. Many changes in the fundus must be detected in time to prevent serious vision loss.
    • Ablatio retinae (retinal detachment) and retinoschisis (retinal detachment).
    • Diabetic retinopathy (retinal disease resulting from diabetes mellitus).
    • Hypertensive retinopathy (retinal disease resulting from hypertension / high blood pressure).
    • Retinal vascular occlusion (vascular occlusion of the retina).
    • Retinitis (inflammation of the retina)
    • Retinal vasculitis (inflammation of the retinal vessels).
    • Macular degeneration (group of diseases affecting the macula lutea (“the point of sharpest vision”) – also called the “yellow spot” – of the retina; the disease is associated with a gradual loss of function of the tissues located there)
    • Retinopathia pigmentosa (synonym: retinitis pigmentosa; abbreviation : RP) describes a retinal degeneration resulting from heredity or spontaneous mutation, in which the photoreceptors are destroyed)
    • Tumors of the retina: eg retinoblastoma, astrocytoma, hemangioma.
  • Tonometry (measurement of intraocular pressure): the slit lamp can be used to place the tonometer, so that subsequently the intraocular pressure (eg due toGlaucoma) can be measured.
  • Gonioscopy (viewing of the chamber angle): the slit lamp can be used to place the gonioscope, so that the chamber angle can be viewed.
  • Laser therapy: a slit lamp can be combined with a laser by making the light slit parallel to the laser beam, thereby facilitating laser guidance.
  • Fitting contact lenses: the correct fit and displaceability of contact lenses can be controlled by the magnification of the slit lamp microscope.

Contraindications

  • A mydriatic before a slit lamp examination is contraindicated in the presence of glaucoma (especially narrow-angle glaucoma).

Before the examination

Slit lamp examination of the anterior segments of the eye can be performed without special preparation of the patient. Inspection of the posterior segments of the eye (e.g., fundus) usually requires dilatation of the pupil, which is achieved with a mydriatic (pupil dilating drug) in the form of eye drops that is effective for a few hours. Local anesthesia (numbing) of the cornea is also performed before using devices that require direct corneal contact (e.g., tonometer, gonioscope).

The procedure

Nowadays, the slit lamp is a medical device consisting of several components, some of which are attached to swivel arms and thus can be moved against each other. There is an illumination device (slit lamp proper) and a binocular microscope that allows the physician to obtain a magnified view of the eye under examination. The patient’s head is stabilized by a chin and forehead support.

Examination of the anterior segment of the eye

The following structures of the anterior segment of the eye can be viewed with the slit lamp: Conjunctiva (conjunctiva), Cornea (cornea), Iris (iris), Lens (lens) and Camera anterior (anterior chamber). A variety of techniques are used:

  • Direct illumination: the physician passes the light beam over the entire cornea and creates its optical cross-section. The depth and thickness of corneal changes can be visualized.
  • Indirect illumination / scleral scattering: the light beam is decentered and adjusted so that it is incident laterally on the limbus corneae (corneal edge). If the cornea is intact and transparent, it is completely reflected from the inside and exits at the other limbus corneae. However, if the cornea is damaged and reduced in transparency, light scattering occurs in the area of the lesion.
  • Retrograde illumination: the light beam is directed vertically and reflected at the iris or fundus. This retrograde light is used to illuminate the cornea. With this, very fine changes such as epithelial cysts or small blood vessels can be depicted.
  • Special staining: For the assessment of superficial cell damage of the cornea, staining with fluorescein (followed by viewing under blue light) or bengal pink can be performed, so that, for example, erosions are better visualized.
  • Combination with indirect gonioscope: the slit lamp is used as a control instrument for correct placement of the gonioscope. A gonioscope is used to view the chamber angle.

Examination of the posterior segment of the eye

The slit lamp can also be used to view the corpus vitreum (vitreous body) and retina (retina) as structures of the posterior segment of the eye. This requires dilating the pupil and additional aids:

  • Three-mirror glass according to Goldmann: This is direct slit-lamp microscopy of the retina with a contact glass. After local anesthesia of the ocular surface, a three-mirror glass is placed directly so that the refractive power of the cornea is cancelled and inspection of the fundus of the eye is possible.
  • Panfundoscope / 78- or 90-dpt loupe: Holding a high-magnification loupe in front of the eye is an indirect method of retinal examination without direct corneal contact. An inverted, real image of the retina is obtained, which is magnified with the slit lamp microscope.

Other uses

  • Combination with a tonometer: The slit lamp is used as an aid for placing a tonometer. A tonometer can be used to measure intraocular pressure (for example, in glaucoma – glaucoma).
  • Combination with a laser: the laser beam is aligned parallel to the light beam of the slit lamp.

Possible complications

  • No complications are expected with slit lamp examination alone.