Neurotrophic Keratitis - Causes, Symptoms, Diagnosis, and Management

What Is Neurotrophic Keratitis?

The corneal nerve plays an essential role in wound healing, proliferation, and epithelial integrity of the cornea. Besides, any damage to this nerve can lead to a myriad of corneal complications affecting overall eye structure.

Neurotrophic keratitis is a condition where corneal digestion is seen. Usually, this condition is associated with complications such as loss of corneal sensation, epithelial degeneration, delayed healing, or corneal ulceration leading to perforation. It is considered to be a rare condition with a prevalence of 5 in 10,000 documented cases. Moreover, patients with herpetic keratitis, herpes zoster, or trigeminal neuralgia recovery are more prone to this condition. Not very often, the patients with this condition complain about any significant symptoms. Loss of corneal sensation plays a major role in this. However, due to corneal edema or perforation, they might complain of redness and blurring of vision.

What Are the Stages of Neurotrophic Keratitis?

According to Mickie's classification of severity and progress, neurotrophic keratitis is classified into the following stages:

• Stage 1: During this stage, the epithelial tissue of the cornea shows significant changes, such as a dry and cloudy appearance of epithelium, corneal edema (swelling of cornea), and superficial keratopathy (a condition caused by cell death in the cornea). This stage of the condition is usually treated by topical artificial tears without added preservatives.

• Stage 2: During this stage, the epithelial defects are usually persistent, circular in shape, or localized to the superior half of the cornea. There is significant edema at the anterior chamber along with Descemet's fold seen at this stage.

• Stage 3: This stage is normally characterized by corneal ulcer leading to corneal perforation and stromal melting type of complications.

What Are the Causes of Neurotrophic Keratitis?

The following are the etiological factors associated with neurotrophic keratitis:

• Chemical or physical burns.

• Topical anesthetic abuse.

• Contact lens abuse.

• Drug toxicity.

• Adnexa: The terminology refers to an accessory organ or structure.

• Corneal surgery.

• Diabetes mellitus.

• Trigeminal impairment due to congenital hypoplasia.

• Aneurysms.

• Multiple sclerosis.

• Vitamin A deficiency.

• Leprosy.

• Extensive use of topical medication such as Benzalkonium chloride can cause an adverse effect on the eye by decreasing corneal sensation along with damage to corneal epithelial healing.

• Corneal procedures such as photorefractive keratectomy and LASIK (laser in situ keratomileusis) are the refractive procedures. These procedures are associated with complications such as transient nerve damage or neurotrophic keratitis.

What Are the Signs and Symptoms of Neurotrophic Keratitis?

Patients with this condition might not experience any significant changes or symptoms. However, with the progress of neurotrophic keratitis, the following signs and symptoms are seen:

• Blurring vision.

• Redness of the eye.

• The acuity of vision.

• Photophobia (the patient might be extremely sensitive to light).

• Poor wound healing.

• Recurrent corneal erosion.

• Irregular astigmatism.

• Corneal scarring.

• Permanent loss of vision.

• Loss of corneal sensation.

• Reduced blinking rate of eyes.

• Reduced tear production.

How to Diagnose Neurotrophic Keratitis?

There are the following diagnostic methods used for neurotrophic keratitis:

• Clinical Testing:

  • Usually, the blinking rate of the eyes is reduced with this condition, and doctors take note of this feature in neurotrophic keratitis.

  • Patients with this condition represent symptoms such as lid scarring, ectropion (it is the condition where the upper eyelid turns outwards by dropping away), or lagophthalmos (incomplete eyelid closure), and doctors do an eyelid examination for this.

• Quantitative Testing: Patients with corneal sensitivity issues are given eye drops, and then the corneal sensitivity is examined with a cotton swab or corneal anesthesia meter (Cochet-Bonnet).

• Corneal Staining: This procedure is done along with fluorescein to check for any epithelial changes. Vital dyes such as lissamine green or rose bengal are used in this procedure. These can also be used to check for tear break-up time or meniscus height.

• Schirmer Test: In patients with reduced corneal sensitivity, this diagnostic method is used to evaluate tear production.

• Slit-lamp Examination: This is the best procedure to check for corneal scarring along with underlying complications such as atrophy related to herpetic eye disease.

• Fundus Examination: This diagnostic method is used to check for retinopathy related to diabetes or panretinal photo-regulation scars.

• In-vivo Microscopy: This is the best diagnostic method to check for sub-basal nerve complications.

How to Manage Neurotrophic Keratitis?

Neurotrophic keratitis can be managed by directly addressing the symptoms of this condition. A multi-specialty team of health professionals is required to manage this condition. There are the following steps to manage the condition:

• Medication:

  • The patients should stop taking any topical eye drops, which are responsible for the progress of this condition.

  • In the year 2018, the U.S. Food and Drug Administration (FDA) successfully approved the medication named Cenegermin as a treatment option for complete corneal healing. It is documented that almost 70 percent of the cases show promising results within eight weeks of using these eye drops.

  • For all stages of keratitis, the continuous lubrication and application of artificial tears can reduce the redness and dryness of the cornea.

  • If the patient is facing any type of infection, topical antibiotic eye drops are used as a prophylactic treatment.

• Surgery:

  • Tarsorrhaphy: If the condition is extremely severe and cannot be corrected using any other treatment option, surgery is the only option. Total or partial tarsorrhaphy is a surgical method of sewing upper and lower eyelids together to reduce the space between them. This surgery can also prevent the cornea from any future wear and tear or trauma. Depending on the condition, these sutures are kept for either some time or permanently.

  • Surgical Implantation of Amniotic Membrane: These treatment options are used for corneal ulcers which cannot heal. There are two different approaches to this technique. In the first one, called Prokera, the amniotic membrane is sandwiched between two plastic rings and placed on the cornea. The second one is used for more advanced and severe cases where single or multiple layers of the amniotic membrane are transplanted on the cornea.

• Supportive Therapy:

  • Scleral or Corneal Contact Lenses: These types of contact lenses are used for mild to severe cases of neurotrophic keratitis, and the lubrication solution used in these lenses also advances with the condition. The dome-shaped contact lens rests over the cornea, which is wet with the solution. This solution ensures that the corneal is wet and promotes healing. However, with this supportive treatment method, the chances of getting an eye infection also increase.

What Are the Differential Diagnosis of Neurotrophic Keratitis?

The following are differential diagnoses associated with neurotrophic keratitis:

• Bacterial Keratitis: It is a condition caused by streptococcus, staphylococcus, and pseudomonas which causes eye problems.

• Sjogren Syndrome: It is a disorder that affects the immune system of the body causing symptoms such as dry eye or dry mouth.

• Herpes Zoster: It is a viral condition caused by the varicella-zoster virus. Due to this condition, patients have rashes and blisters all over their skin.

Conclusion:

Neurotrophic keratitis is a rare condition that shows no symptoms at the start. Due to these characteristics, it is very difficult to diagnose this condition. However, the condition can cause mild to severe complications related to the eye, which can also lead to permanent loss of vision. It is very important to diagnose this condition accurately on time and proceed with the treatment before it causes any permanent damage.