Slit Lamp Examination

Purpose

The slit lamp examination serves as the primary method for evaluating the anterior segment of the eye under high magnification. It enables detection and characterization of corneal pathology, anterior chamber inflammation, lens opacities, and conjunctival/scleral disease. The examination is particularly valuable for differentiating between conditions such as episcleritis and scleritis, where medical history and slit lamp examination allow distinction between these entities.¹ With accessory lenses such as gonioscopy lenses and indirect ophthalmoscopy lenses, the examination extends to angle structures and posterior segment evaluation. The slit lamp provides the precision necessary for diagnosis, treatment planning, and monitoring of most anterior segment conditions encountered in clinical practice.

Equipment

Essential Components:

• Slit lamp biomicroscope with adjustable magnification (typically 6x to 40x)
• Variable width and height slit beam illumination system
• Adjustable chin rest and forehead rest for patient stabilization
• Joystick for examiner-controlled movement in multiple axes
• Blue cobalt filter for fluorescein evaluation
• Red-free (green) filter for vascular and nerve fiber layer assessment

Accessory Lenses:

• Gonioscopy lenses for angle evaluation (held directly on the patient's eye)
• Indirect ophthalmoscopy lenses for posterior segment visualization (positioned 5-10 cm from the patient's face)²
• Fundus contact lenses for detailed posterior pole examination

Infection Control Equipment:

Given that slit lamp examination occurs at a distance of 0.25 to 0.5 meters between examiner and patient, protective barriers are recommended.² Patient-sided breath shields attached to the chin rest have been shown to block 99.65% to 100% of forward-traveling droplets in simulated testing.³ These shields should be combined with standard precautionary measures including proper hand hygiene and disinfection of contact surfaces between patients.

Steps

Patient Preparation:

1. Explain the procedure to the patient
2. Position the patient comfortably with chin on chin rest and forehead against forehead rest
3. Adjust the height of the table and chin rest for optimal patient positioning
4. Ensure the patient keeps both eyes open and maintains steady gaze

Systematic Examination Sequence:

1. Initial Overview: Begin with low magnification (6x-10x) and diffuse illumination to survey both eyes and surrounding tissues

2. Eyelids and Lashes: Examine lid margins, meibomian gland orifices, and lash bases for inflammation, masses, or parasites

3. Conjunctiva and Sclera: Evaluate bulbar and palpebral conjunctiva for injection, chemosis, follicles, papillae, or lesions. Assess episcleral and scleral vessels for injection patterns

4. Cornea: Use medium-to-high magnification (16x-25x) with direct focal illumination

   • Examine epithelium for defects, irregularities, or foreign bodies
   • Assess stroma for infiltrates, edema, scars, or opacity
   • Evaluate endothelium for guttae or keratic precipitates
   • Use oblique or parallelepiped illumination to assess depth of pathology

5. Anterior Chamber: Evaluate depth, clarity, and presence of cells or flare using a narrow slit beam at 30-45 degrees

6. Iris: Assess color, pattern, transillumination defects, masses, or posterior synechiae

7. Lens: Examine for opacities, position, and pseudoexfoliation material using direct and retroillumination techniques

8. Anterior Vitreous: Assess for cells, hemorrhage, or debris when possible

Special Illumination Techniques:

• Diffuse illumination: General overview of structures
• Direct focal illumination: Detailed examination of specific areas
• Indirect illumination: Light scattered from adjacent tissues highlights subtle changes
• Retroillumination: Light reflected from iris or retina silhouettes anterior structures
• Specular reflection: Evaluates endothelial and epithelial surfaces
• Sclerotic scatter: Detects subtle corneal edema or infiltrates

Normal vs. Abnormal Findings

Normal Findings:

• Clear, smooth corneal epithelium with regular light reflex
• Transparent corneal stroma without opacities or vessels
• Deep, quiet anterior chamber without cells or flare
• Intact iris architecture with normal pupillary responses
• Clear crystalline lens without opacities
• White, quiet sclera without injection or nodules

Abnormal Findings:

Conjunctival/Episcleral:

• Sectoral or diffuse injection
• Follicles or papillae
• Hemorrhage, chemosis, or masses
• In episcleritis: superficial vascular injection that blanches with topical phenylephrine
• In scleritis: deep vascular injection with bluish hue that does not blanch¹

Corneal:

• Epithelial defects (demonstrated with fluorescein staining)
• Stromal infiltrates, edema, or scarring
• Neovascularization
• Keratic precipitates on endothelium
• Foreign bodies or rust rings

Anterior Chamber:

• Cells indicating inflammation (graded 0-4+)
• Flare indicating protein leakage
• Hypopyon or hyphema
• Shallow depth suggesting angle closure risk

Iris:

• Heterochromia
• Posterior synechiae
• Neovascularization
• Masses or nodules

Lens:

• Cortical, nuclear, or posterior subcapsular opacities
• Pseudoexfoliation material
• Subluxation or dislocation

Common Mistakes

• Inadequate patient positioning: Poor alignment leads to incomplete examination and patient discomfort. Ensure proper chin and forehead contact with appropriate height adjustment

• Insufficient magnification: Examining at too low magnification misses subtle pathology such as fine keratic precipitates or early corneal infiltrates

• Limited illumination techniques: Relying only on diffuse illumination without using oblique, indirect, or retroillumination techniques reduces diagnostic sensitivity

• Failure to examine systematically: Skipping structures or examining in random order increases likelihood of missing pathology

• Not adjusting slit width and height: Using improper beam dimensions prevents optimal visualization of anterior chamber depth and corneal pathology

• Inadequate fluorescein staining: Failing to use fluorescein with cobalt blue filter may miss epithelial defects

• Poor infection control: Neglecting to disinfect chin rest and forehead rest between patients. Not implementing protective barriers when appropriate, particularly given the close face-to-face proximity of 0.25 to 0.5 meters during examination²

• Rushing the examination: Insufficient time spent on systematic evaluation leads to missed findings

OSCE Script

Introduction (30 seconds):

"Hello, I'm [Name], and I'll be performing a slit lamp examination of your eyes today. This instrument will allow me to examine the front parts of your eyes under magnification. The examination is painless, but I'll need you to keep your eyes open and hold still. Do you have any questions?"

Patient Positioning (30 seconds):

"Please place your chin on this rest and lean your forehead against this bar. I'll adjust the height so you're comfortable. Try to keep both eyes open and look straight ahead at my ear unless I ask you to look in a different direction."

Examination (3-4 minutes):

"I'm going to bring this light close to examine your eyes. You'll see a bright light, which is normal. Please try not to pull back."

Conduct systematic examination as outlined in Steps section

Right Eye Examination:

• "Looking at your right eye now..."
• Examine lids, conjunctiva, sclera
• "Now I'm examining your cornea with higher magnification..."
• Assess anterior chamber, iris, lens

Left Eye Examination:

• Repeat systematic examination
• "Please look up... now down... now to the right... now to the left" (to examine peripheral cornea and conjunctiva)

Fluorescein Staining (if indicated):

"I'm going to place a small amount of orange dye on your eye to check the surface. You may feel the paper touch the inside of your lower lid briefly. Please blink a few times to spread the dye."

Closure (30 seconds):

"The examination is complete. You can sit back now. Based on what I've seen, [provide appropriate summary of findings]. Do you have any questions about the examination?"

Clinical Pearls

• Begin every examination with low magnification and diffuse illumination to avoid missing large or obvious pathology before focusing on details

• Use the "optic section" technique (very narrow slit beam at 30-60 degrees) to precisely localize the depth of corneal pathology or assess anterior chamber depth

• When differentiating episcleritis from scleritis on slit lamp examination, remember that episcleritis is typically benign and self-limiting with superficial vessel involvement, while scleritis shows deep vessel involvement and is often associated with systemic rheumatological disease requiring aggressive treatment¹

• The corneal nerves are best visualized using medium magnification with oblique illumination against a dark background

• Always examine the inferior fornix by having the patient look up while gently pulling down the lower lid—this area is frequently overlooked but may harbor foreign bodies or papillae

• Red-free filter enhances visualization of blood vessels, nerve fiber layer defects, and subtle hemorrhages

• When using accessory lenses for gonioscopy or indirect ophthalmoscopy, maintain awareness that these procedures position the examiner's hands very close to the patient's face (5-10 cm), increasing infection transmission risk²

• Patient-sided breath shields provide effective barrier protection during slit lamp examination and can be positioned at the chin rest level for optimal coverage³

• In patients with media opacity preventing clear visualization, retroillumination from the red reflex can reveal silhouettes of anterior segment structures

Common Pitfalls

• Misidentifying the anatomic location of pathology: Corneal vs. conjunctival lesions, or anterior vs. posterior chamber inflammation. Use optical sectioning with a narrow beam to determine precise depth

• Overlooking subtle angle abnormalities: Failing to perform gonioscopy when anterior chamber appears shallow or in patients at risk for angle closure

• Underestimating infection risk: The slit lamp examination occurs at 0.25 to 0.5 meters face-to-face distance, placing eye care professionals at high risk for respiratory droplet transmission, particularly from asymptomatic carriers². Always adhere to infection control measures

• Missing peripheral corneal pathology: Examining only the central cornea without asking the patient to look in different directions to bring peripheral areas into view

• Confusing artifacts for pathology: Reflecting light from dirty breath shields or condensation on lenses may simulate corneal pathology

• Inadequate pupillary dilation when indicated: Attempting to examine the lens fully without adequate dilation limits assessment of peripheral lens and anterior vitreous

• Not recognizing when specialty consultation is needed: Patients with scleritis require early and aggressive anti-inflammatory treatment in a stepwise approach¹, making prompt recognition and referral critical

• Forgetting to document slit lamp findings systematically: Poor documentation of location, size, and depth of pathology complicates follow-up care

• Neglecting to correlate slit lamp findings with symptoms: The examination should be interpreted in clinical context rather than in isolation