Seidel Test

Anatomy and Physiology

The eye is an incredibly complex organ; multiple components and intricate mechanisms must collaborate for the eye to function correctly. The Seidel test assesses for disruption of the cornea, sclera, or a combination of both. The sclera is a fibrous, opaque, “white of the eye,” which provides support and protection to the deep structures of the eye. Anteriorly, at the limbus, the sclera is continuous with the cornea.[4] The cornea, the clear outermost part of the eye, sits anterior to the pupil, iris, and lens. Light enters the eye through this construct and accounts for a large portion of the eye's focusing power. The cornea comprises 5 layers from superficial to deep: the corneal epithelium, Bowman’s layer, corneal stroma, Descemet’s membrane, and corneal endothelium.

All 5 layers combined are approximately 550 microns or just over half a millimeter thick. The epithelium is about 5 to 7 cells thick, which provides the eye with a smooth surface for the tears to form a film. This film spreads across, keeps the eye moist and healthy, and allows for clear vision. The epithelium has a high turnover rate and is replaced over 7 days. The Bowman layer is the next layer, a dense fibrous sheet that protects the deeper layers. Once a scratch passes Bowman’s layer, the probability of scaring increases significantly. The following layer is the stromal layer, about 90% of the cornea and composed of connective tissue called collagen fibrils. They are uniform in size and are stacked parallel to one another in bundles called lamellae. Their arrangement makes them a transparent layer. The next layer is Descemet’s membrane, another extremely thin layer separating the stroma from the endothelial layer. The final layer is the endothelium, which is also 1 cell layer thick and directly communicates with the anterior chamber's aqueous humor. The anterior chamber is behind the cornea and in front of the Iris and pupil. Behind the iris and pupil lies the posterior chamber, which includes multiple structures out of the scope of this discussion.[5]

Indications

The Seidel test is indicated anytime one suspects orbital trauma with concern for an ocular leak. Conditions that should raise suspicion for potential trauma and ocular leak include but are not limited to:

• Pupillary defect
• Laceration through eyelid
• Shallow anterior chamber
• Blood in the anterior chamber
• Bullous subconjunctival hemorrhage
• Post-surgical with concern for ocular leak
• Evaluation of corneal laceration to evaluate if it is sealed or not
• Corneal perforation secondary to degeneration

Contraindications

Contraindications to the Seidel test include several conditions, such as:

• Obvious globe rupture
• Full-thickness eye laceration
• Obvious corneal perforation
• Hypersensitivity to fluorescein dye

Equipment

The Seidel test does not require significant resources, but specific components are required to obtain an accurate analysis, including:

• Fluorescein strip
• Topical ophthalmic anesthetic
• Slit-lamp with cobalt blue light

Personnel

The Seidel test can be performed by any medical provider who can instill the dye and interpret the results. It is usually performed by physicians and physician extenders and does not require additional support personnel.

Preparation

Prepare the room for evaluation and obtain all necessary equipment and medications. The cornea is very sensitive, and any lesion can cause severe photophobia, limiting the exam. Dim the lights in the room as much as possible to ensure patient comfort and improve the evaluation.

Technique or Treatment

The following steps are generally required to complete the Seidel test:

1. Prepare the room and obtain all equipment.
2. Prepare the slit lamp.
3. Explain the procedure to the patient.
4. Apply topical anesthetic.
5. Moisten fluorescein dye strip with normal saline.
6. Apply fluorescein above the lesion or the superior conjunctival fornix.
7. Ask the patient to blink to help spread the stain.
8. Visualize the injured site under cobalt blue light.[6]

Interpretation

Fluorescein, when concentrated, is an orange to red color. When it becomes diluted, it turns green under cobalt blue light. When instilled into the eye, defects in the cornea, such as abrasions or lacerations, take up the dye. Seidel test is positive when the fluorescein dilutes in the aqueous humor and causes it to fluoresce bright green and stream down the eye with gravity. Some sometimes describe the streaming as a waterfall with more brisk leaks. There may be a focal area or dilution if the leak is not brisk. The fluorescent green color is located above the lesion and along the sides of the leaked aqueous. The center of the waterfall does not have fluorescein present, as it is just aqueous humor. A positive test indicates a full-thickness corneal or scleral injury.[3]

Possible false negatives:

• A small defect that has self-sealed
• A large laceration that has plugged
• Retrobulbar rupture

Suppose there is a strong suspicion of a globe rupture, and the Seidel test is negative. In that case, the next step in evaluation is to obtain an orbital CT scan, which can evaluate for a flat anterior chamber and may demonstrate an intraocular foreign body.[7]

Complications

The patient must remove contact lenses before staining the eye as the fluorescein permanently stains them. The eye should be flushed with saline, and contacts should be left out about 1 hour after staining if no injury is identified. Staining of the skin around the eye fades over a few hours. Another possible complication occurs as a missed ruptured globe due to the laceration or perforation being already sealed or in a location unable to be tested by the Seidel test (posterior globe rupture).[7]

Clinical Significance

A positive test indicates leakage of aqueous humor for the anterior chamber, which is an ocular emergency (see Image. Positive Seidel Test).

• Management of positive Seidel test
  • Consult ophthalmology immediately for surgical repair
  • Prevent further Injury 
    • Do not manipulate the eye
    • Do not check intraocular pressure or perform an ocular ultrasound
    • Cover the eye with a metal shield (Fox Shield) or a cover that does not touch or apply pressure to the globe
      • Do not place a patch over the eye
• Minimize elevation of intraocular pressure
  • Bed rest; no Valsalva maneuvers, bending, or lifting
    • Consider anti-emetic and Foley catheter
• Pain control
• Tetanus prophylaxis
• IV antibiotics to prevent
  • No intra-ocular foreign body
    • 1line: Fluoroquinolone, OR
    • 2line: Vancomycin and ceftazidime
  • Intra-ocular foreign bodies present
    • Ceftazidime and vancomycin
    • Penicillin allergy: Cipro and vancomycin
  • No intravitreal antibiotics [8]

Enhancing Healthcare Team Outcomes

Ocular injuries with a positive Seidel test require multiple healthcare workers and specialties in an interprofessional team approach. Most ocular traumas are present in the emergency department, where they likely first contact nursing staff to evaluate the patient. They may notice the injury and begin to protect the eye by covering it. They may also obtain medications and equipment needed for further patient evaluation. Usually, during triage, they also obtain a visual acuity that is 1 of the best prognostic indicators once there has been a definitive repair to the defect.[9]

Once triage is complete, the patient is evaluated and treated by a provider and possibly multiple providers, depending on if they have any other injuries. The entire staff coordinates care to ensure the patients get a fast, accurate exam. Once a positive Seidel test is found, an ophthalmologist is contacted immediately for definitive repair and continues to follow up with the patient on an outpatient basis once it is repaired. A pharmacist is also involved in care in acute and outpatient settings. Ocular injuries are real emergencies; it takes a team to ensure the patient receives the best care possible.