Slit lamp examination

INTRODUCTION — The slit lamp is a binocular microscope that provides the examiner with a stereoscopic (ie, three dimensional) view of the eye (figure 1). It has changed little since its development by Goldman in 1937 [1]. However, there are alternate methods of examining the eye using portable digital photography and videography imaging devices [2,3]. These methods may afford some advantages but may not offer a stereoscopic view or magnification comparable to a slit lamp.

The slit lamp allows the eye to be examined with a beam or "slit" of light (versus diffuse light) whose height and width can be adjusted. The slit of light, when directed at an angle, accentuates the anatomic structures of the eye, allowing close inspection. The slit lamp provides greater magnification (10 to 25 times) and illumination than most handheld non-binocular devices (eg, Wood's lamp [4x] and Bluminator [7.5x]), which is necessary to diagnose a number of traumatic and nontraumatic disorders [4]. Portable handheld binocular slit lamp devices are readily available and allow bedside examination.

A useful, interactive teaching program on vision care is available free from the University of Michigan Kellogg Eye Center at kellogg.umich.edu/theeyeshaveit.

This topic review will focus on the steps involved in the examination of the anterior segment of the eye using the basic slit lamp found in most primary and emergency care settings as well as indications and contraindications for its use. Specific diseases and injuries of the eye are discussed elsewhere.

●(See "Approach to the adult with acute persistent visual loss".)

●(See "The red eye: Evaluation and management".)

●(See "Corneal abrasions and corneal foreign bodies: Clinical manifestations and diagnosis".)

●(See "Conjunctivitis".)

●(See "Cataract in adults".)

●(See "Retinal detachment".)

INDICATIONS — Indications for the use of a slit lamp in the nonophthalmology setting include any acute condition that requires magnification to inspect the anterior segment of the eye (ie, lids, lashes, conjunctiva, cornea, anterior chamber, iris, and lens) or to facilitate ocular foreign body removal. Thus, it is well suited for diagnosing conditions such as corneal epithelial defect, keratoconjunctivitis, hyphema, hypopyon, lens dislocation, herpetic infections, iritis, or evaluation of the red eye.

The slit lamp is less useful in diagnosing conditions of the posterior segment (ie, vitreous, fundus, optic disk) in the primary care office or emergency department. Such conditions include papilledema, vitreous hemorrhage, and retinal detachment. Diagnosis of such conditions with a slit lamp is feasible only if special attachments are available and the examiner has training and experience in their use.

CONTRAINDICATIONS AND PRECAUTIONS — There are no absolute contraindications for performing a slit lamp examination (SLE) [5]. However, the following points deserve emphasis:

●Patients with a possible open globe injury should be examined with extreme caution, and clinicians must avoid placing pressure on the globe (eg, with lid eversion or foreign body [FB] removal) until this injury is ruled out. (See "Open globe injuries: Emergency evaluation and initial management".)

●Patients with exposure to caustic substances should be thoroughly irrigated and a normal pH of the conjunctival fluid documented before initiating a SLE.

●Caution is necessary during FB removal to avoid injury from a sudden patient movement or loss of orientation with the tool being used to remove the FB (eg, needle or burr drill).

●Children may be examined with parental assistance, reassurance, and special positioning in the slit lamp. Using a portable handheld slit lamp may facilitate the examination.

PREPARATION — Patients undergoing a slit lamp examination (SLE) for an acute ocular condition are often uncomfortable or apprehensive. Use of a topical ophthalmic anesthetic agent (eg, proparacaine drops) reduces pain. Darkening the room and providing reassurance can also improve patient comfort.

Patient counseling — There are no specific risks inherent in a SLE that require informed consent. The purpose and methods of the SLE should be clearly explained to put the patient at ease and to maximize cooperation. Potential complications of foreign body (FB) removal, such as globe perforation, while possible, have not been reported. Corneal epithelial defect (ie, CED or corneal abrasion) is another potential complication of FB removal.

Materials — The SLE is typically performed in a room with control of lighting and necessary materials. Portable and handheld devices are readily available, which permits evaluation in bedbound or supine patients or where the standard slit lamp is not practicable, such as in austere environments [6]. Smart phone adapters for both stationary and handheld slit lamps allow digital photography and videography [7]. Materials needed for SLE may include anesthetic drops, cotton tipped applicator, cotton pledget, fluorescein strip, burr drill or 18 gauge needle, gauze or tissue, eye rinse solution, and contact lens removal device (table 1).

ANATOMY — The examiner must be familiar with the anatomy of the eye's anterior chamber (figure 2 and figure 3). The tangential slit of light projected by the slit lamp allows a three-dimensional view of anatomic structures that are not normally appreciated with diffuse lighting even with magnification. These include the epithelium, stroma, and endothelium of the cornea; aqueous humor; and lens.

PROCEDURE

General considerations — Before performing a slit lamp examination (SLE), obtain a relevant history and perform an external ocular examination, including visual acuity and cranial nerve assessment. Document your findings, including the indication for SLE.

Patients undergoing a SLE may be sensitive to light (photophobia). Dim the ambient room light and use maximal illumination sparingly during the exam to alleviate discomfort. Allay patient fears by providing a concise introduction to the procedure. This is especially important with any maneuver that involves physical contact with the eye, whether it consists of instilling medications, rinsing the eye, using a paper strip to measure pH, or using a cotton swab or tool to remove a foreign body (FB). Give clear instructions about what the patient is to do (eg, eye movement, positioning, blinking) and what they are likely to feel. Position children in a family member's lap with the chin brace adjusted for their height. For children, patients with disability, or patients with class III obesity, consider using a portable slit lamp.

If the examiner wears corrective lenses, we recommend that these be worn during the exam. If not, pay careful attention to focusing (see 'Focusing the slit lamp' below). Inquire about the use of contact lenses before instilling any medication into the eye. Fluorescein will permanently stain contact lenses; remove contact lenses before applying fluorescein. If an intraocular FB (globe penetration) or open globe injury from penetrating or blunt trauma is suspected, protect the eye with a non-pressure shield and immediately consult an ophthalmologist.

Analgesia and sedation — Use a topical anesthetic to facilitate the SLE when eye pain or blepharospasm interfere. Before instilling the agent, inform the patient that all topical agents cause transient pain before they take effect. We suggest proparacaine be used for topical anesthesia during the procedure as it may cause less pain and longer anesthesia [8]. The use of topical anesthetics for corneal abrasions and other causes of eye pain is reviewed separately. (See "Corneal abrasions and corneal foreign bodies: Management", section on 'Pain control' and "Corneal abrasions and corneal foreign bodies: Management", section on 'Treatments to avoid'.)

Anesthetic agents typically degrade more quickly if left at room temperature for more than one week. Discard agents that turn from clear to light brown. Unit dose vials reduce the risk of infection.

Setup and patient positioning — The initial step in performing the SLE is to ensure that the slit lamp is configured correctly for the exam, the examiner, and the patient:

●Place adjunct material or equipment within reach (table 1).

●Adjust the examiner chair height for comfort.

●Loosen the locking nut on the slit lamp assembly to allow free movement (picture 1).

●Set each ocular lens to "0" (figure 4).

●Adjust interpupillary distance by grasping the binocular housing attached to the objective lens, and pull apart or push together the eyepieces to make the adjustment (figure 1).

●Set the magnification to low power.

●Position the patient in the chin rest and instruct the patient to keep his or her forehead in contact with the headrest at all times during the SLE.

●Adjust the height of the table for patient comfort.

●Adjust the chin rest height so that the pupils are aligned with the marker (picture 2). This places the eye within the range of the vertical height adjustment on the slit lamp.

●Patients may hold the slit lamp hand rest or rest their hands in their lap.

Focusing the slit lamp — This step is crucial for viewing subtleties such as cells in the anterior chamber or appreciating the depth of a corneal lesion. After preparing equipment and positioning the patient (see 'Setup and patient positioning' above), perform the following steps:

●Adjust the slit lamp beam for a tall, narrow vertical beam of white light. The slit width should be adjusted to make the beam as narrow as possible without causing illumination to decrease (picture 3A-B).

●Direct the beam onto the bridge of the patient's nose (not onto the eye) at an approximate angle of 45 degrees (focusing with the light directed at the eye is uncomfortable for the patient).

●Move the entire assembly (coarse focus) in and out along the axis of the light while watching the beam of light. Do not view the beam through the objective lenses yet rather, view directly by looking around the side of the objectives. The goal is to bring the slit of light into crisp sharp focus.

●Once a crisp focused beam is evident externally, look through the objective lenses and confirm that the microscope is on low power.

●Adjust the joystick (fine focus) in and out to obtain a crisp slit. Close each eye and obtain a crisp image, one eye at a time, by adjusting the objective lenses (oculars). Only a slight adjustment should be needed for emmetropic eyes or those with corrected visual acuity. A larger adjustment will be needed for those who have uncorrected myopic or hyperopic eyes or elect not to wear their corrective lenses. Once focus is achieved, the SLE can be performed.

To obtain rapid consistent focus from one exam to the next on the same slit lamp, the examiner may wish to determine their individual refractive state with the use of the focusing rod (found with most slit lamps). To do this, perform the following steps:

●Insert the focusing rod in the pivot post in front of the microscope (picture 4).

●Direct the slit beam to the center of the flat face of the rod and set beam 1 to 2 mm in width.

●Focus the eyepieces individually on the slit beam, starting the eyepiece from the positive side of the scale and stopping at the point at which the image first appears sharply focused.

●Note the setting on the eyepiece scale, and always use this setting when using the slit lamp.

●Remove focusing rod.

Performing the exam — Examine the following areas: lids, lashes, conjunctiva, cornea, anterior chamber, and lens. The SLE can also be used to perform applanation tonometry (not discussed here). Once the patient is in position, equipment is set up, and the slit lamp is focused and set to low power. The exam is performed as follows:

●Confirm that the light angle is approximately 45 degrees projecting temporal to nasal, and that the light projects in a tall, narrow, focused beam.

●Before looking through the oculars, look at the eyelids with the naked eye while sliding the entire assembly forward and temporally towards the lids. Observe until you see a crisp light beam (slit) on the lids (similar to focusing on the bridge of the nose described above). An out-of-focus beam appears fuzzy.

●Now, look through the oculars and make adjustments with the joystick to maintain focus as you move the entire assembly across the eye.

Lower lid/lashes/conjunctiva

●Use the vertical height adjustment to view the lower lid. Use a cotton tipped applicator (CTA) to facilitate lid movement for this portion of the exam.

●Use subtle forward and back movements of the joystick to focus on the lower lid while sliding the entire assembly horizontally to view the lower lid and lashes.

●Use the CTA to visualize the palpebral conjunctiva by placing it horizontally beneath the lower lid and rolling it downward while instructing the patient to look up. This everts the lower lid and allows examination of the palpebral conjunctiva.

Upper lid/lashes/conjunctiva

●Instruct the patient to look down.

●Use the vertical height adjustment to center the beam of light on the upper lid and lashes.

●Use subtle forward and back movements of the joystick to focus on the upper lid while sliding the entire assembly horizontally to view the upper lid and lashes.

●If examination of the upper lid palpebral conjunctiva is indicated (FB suspected from mechanism of injury or from corneal fluorescein uptake pattern), eversion of the lid can be performed as follows:

•Place the CTA horizontally along the palpebral fold of the upper lid. Roll the CTA slightly to evert the eyelashes so that they may be more easily grasped. Grasp the upper eyelashes with your free hand, pull slightly away, then pull upward, using the CTA as a fulcrum. The upper lid must be pulled away from the patient before pulling up in order to evert the lid around the fulcrum of the CTA. Just pulling up on the lid without pulling away first is usually unsuccessful.

•Hold the upper lid in an everted position with your thumb while the slit lamp (is moved horizontally to pan across the now exposed palpebral conjunctiva. Use subtle in and out movements of the joystick for focus. When examination of this segment is complete, release the upper lid, and instruct the patient to look up and blink. This will return the lid to its normal position.

Cornea

●Use the vertical height adjustment to center the beam on the central cornea at either the nasal or temporal limbus (edge of the cornea).

●Ensure the magnification is set to low power.

●Use subtle forward and back movements of the joystick to focus on the corneal epithelium while sliding the entire assembly left and right horizontally to view the cornea. As the cornea is curved in two dimensions, multiple adjustments will need to be made in order to visualize the entire corneal surface. The examiner must not allow the focus to wander from the corneal epithelium. Often, a small corneal epithelial defect (ie, CED or corneal abrasion) can be seen prior to fluorescein staining.

●If a lesion is seen, switch to high power to examine the lesion more closely. Use subtle forward and back movements of the joystick to bring the lesion into focus and to appreciate its size and depth as well as any surrounding infiltrate or corneal edema. The angle of the slit lamp beam may be adjusted to bring the lesion into better view.

●Under high power, the corneal stroma and endothelium is visualized for infiltrate, edema, or keratic precipitates (collections of red or white blood cells on the endothelial surface). Wrinkling of the corneal endothelium is evidence of corneal edema. The focal point of the beam must be placed precisely on the endothelium for these findings to be appreciated.

Fluorescein examination for corneal abrasion — A fluorescein examination is commonly performed when a corneal abrasion (or corneal epithelial defect [CED]) is suspected. It is performed as follows:

●Wet a fluorescein strip with a single drop of liquid (eg, saline or topical anesthetic).

●Pull the lower lid down while instructing the patient to look up.

●Touch the tip of the strip to the lower conjunctival fornix, taking care to avoid abrading the cornea. Topical anesthesia is not required if done gently.

●Have the patient blink. A greenish hue overlying the cornea indicates adequate fluorescein instillation. This is best appreciated while watching the slit lamp beam directed on the cornea with the naked eye. If no green hue is seen, repeat the application. The goal is to apply the minimum needed amount of fluorescein; too much will obscure subtle CEDs. If too much is applied, rinse the eye and continue with the next step of the exam.

●Select the cobalt blue filter and widen the slit beam by turning the width adjustment.

●Position the patient properly in the slit lamp and observe the cornea under low power as described above.

●Use high power as needed to identify subtle (punctate) or dendritic (herpetic) lesions (picture 5) that fluoresce. The appearance of a CED often gives the examiner a clue to its etiology (picture 6 and picture 7). Infiltrates that are seen under white light but not seen with the cobalt blue filter are typically subepithelial and are not CEDs. However, CEDs from minor trauma can rapidly re-epithelialize and thus may not fluoresce.

Seidel's test — This test uses fluorescein to examine for suspected microperforation of the globe.

●Apply topical anesthetic agent.

●Select the cobalt blue filter and widen the slit beam maximally by turning the width adjustment.

●Wet a fluorescein strip with several drops of liquid (eg, saline or topical anesthetic).

●Touch the end of the strip to the eye in a painting motion to maximize contact between the eye and the strip.

●Ensure proper positioning of the patient in the slit lamp and observe the cornea under low power as described above. A small perforation will cause a clearing of the dense fluorescein, which will appear to be streaming away from the perforation site (picture 8). This is a positive Seidel's test indicating perforation of the globe.

●If the Seidel's test is positive, protect the eye with a shield, and consult an ophthalmologist immediately.

Cells and flare

●Darken the room completely to reduce ambient light.

●Adjust the beam height and width to short and slightly wide.

●Use the vertical height adjustment to center the beam on the central cornea, using the pupil as a black background.

●Move the joystick forward to focus on the iris then backward to focus on the corneal epithelium. Repeat this several times to get a feel for the range of movement required between these two focus points.

●Use about one half of the movement needed above to place the focal point in the middle of the anterior chamber.

●Observe for the presence of flare (like the headlight beam in the fog (picture 9)) or cells (tiny "sparkles" of light (picture 10)) floating through the currents of the anterior chamber. White blood cells (WBCs) have white reflections, while red blood cells (RBCs) in the anterior chamber have a reddish brown reflection. Flare is better appreciated with a higher light intensity.

Foreign body removal

●Apply adequate topical anesthesia.

●Emphasize to the patient the need for maximal compliance with positioning during the procedure.

●Reassure the patient (complications and perforation are extremely unlikely).

●Grasp the removal device (burr drill or needle with syringe or CTA attached) with the hand on the same side as the foreign body (eg, use right hand for left FB). If using a needle, remove the cap by carefully pushing it off the needle, rather than pulling it off by grasping the cap in one hand and the needle-syringe in the other (which can cause a needlestick injury).

●Rest your hand on the patient's cheek to stabilize the hand during the procedure but ensure that the removal device is held well away from the eye.

●While directly observing the removal device, position it in the light beam and move slowly toward the eye, stopping about 3 to 5 mm in front of the eye.

●Observe the device through the objective lenses of the slit lamp and slowly advance it under magnification until the removal device and area of the FB is clear and in focus.

●Use the removal device to scrape the FB tangential to the cornea for removal (figure 5) [9]. Remove only what is easily scraped away. There is no need to aggressively scrape or use a puncture motion on the cornea. Residual material, such as a rust ring (picture 11), can easily be removed in 24 hours as the small area of surrounding tissue becomes necrotic. If using a needle, keep the needle tip in view at all times to avoid unintentional injury.

Exercise for viewing anterior chamber cells

●Follow instructions for patient position, equipment set up, and slit lamp focus as listed above.

●Set slit lamp to high power with a tall narrow beam.

●Completely darken the room to reduce ambient light.

●Use the vertical height adjustment to center the beam on the nasal or temporal limbus (edge of the cornea). Look for a vessel in this area that shows some movement or shimmers with each systole.

●Use subtle forward and back movements of the joystick to focus on a segment of the vessel that allows visualization of the red blood cells (RBCs) in the vessel. RBCs may be seen in rouleaux (stacked like coins), or individually as they course through the vessel with each systole. This is usually the maximum resolution that can be obtained with a primary care slit lamp.

The examiner must have the skills to obtain this resolution in order to visualize important findings on SLE. This exercise provides practice at obtaining these skills. With instruction, most attentive students can perform this exercise during the first session using a slit lamp.

COMPLICATIONS — Serious complications during slit lamp examination are rare and include globe perforation during foreign body (FB) removal and allergic reaction to medication placed in the eye. Mild complications include iatrogenic corneal epithelial defect (ie, CED or corneal abrasion) when removing a FB or contact lens and minor irritation from medication.

FOLLOW-UP CARE — The slit lamp examination (SLE) does not require follow-up care, but acute eye conditions often do. The patient should be given appropriate and clear instructions that address the diagnosis and treatment of the condition. Any patient who has the eye manipulated (eg, foreign body or contact lens removal) should be given precautions to return for worsening pain, photophobia, eye redness, and decreased visual acuity. Medication for pain and possibly lubrication should be given until healing occurs. Follow-up is generally advised within 24 hours. It is common practice for many clinicians to place patients with a corneal epithelial defect (ie, CED or corneal abrasion) on topical antibiotics, though no randomized controlled studies exist to support this practice. (See "Corneal abrasions and corneal foreign bodies: Clinical manifestations and diagnosis".)

SUMMARY AND RECOMMENDATIONS

●Indications – In the non-ophthalmology setting, the slit lamp examination (SLE) is useful for diagnosing many acute conditions involving the anterior segment of the eye or to facilitate ocular foreign body removal. Such conditions may include corneal epithelial defect, keratoconjunctivitis, hyphema, hypopyon, lens dislocation, herpetic infections, iritis, or the red eye. The slit lamp is less useful for diagnosing conditions of the posterior segment. (See 'Indications' above.)

●Contraindications – There are no absolute contraindications for performing a SLE. However, patients with a possible open globe injury should be examined with extreme caution until such injury is ruled out, and patients with exposure to caustic substances should be thoroughly irrigated and a normal pH of the conjunctival fluid obtained before initiating a SLE. (See 'Contraindications and precautions' above.)

●Preparation and analgesia – Patients undergoing SLE for an acute ocular condition are often uncomfortable or apprehensive. Use of a topical ophthalmic anesthetic agent (eg, proparacaine drops) reduces pain. A list of materials needed for SLE is provided (table 1). (See 'Preparation' above and 'Analgesia and sedation' above.)

●Procedure – The steps involved in setting up the slit lamp and performing the examination are outlined below and described in detail in the text. (See 'Procedure' above.)

•Set up the slit lamp and ensure proper patient position. (See 'Setup and patient positioning' above.)

•Focus the slit lamp by adjusting for a tall, narrow, vertical beam of white light without causing illumination to decrease and directing the beam onto the bridge of the patient's nose at an approximate angle of 45 degrees (picture 3A-B). (See 'Focusing the slit lamp' above.)

•Examine the lids, lashes, conjunctiva, cornea, anterior chamber, and lens. (See 'Performing the exam' above.)

•A fluorescein exam to evaluate for corneal defect (picture 6) or keratitis (picture 5) or Seidel's test to rule out globe rupture (picture 8) can be performed. (See 'Fluorescein examination for corneal abrasion' above and 'Seidel's test' above.)

•Examine the anterior chamber for the presence of cells (picture 10) and flare (picture 9). (See 'Cells and flare' above.)

•The SLE can aid in removal of foreign body (figure 5) or rust ring (picture 11). (See 'Foreign body removal' above.)