Corneal Scraping Procedure: A Comprehensive Guide for Ophthalmologists

Introduction

Corneal scraping is a fundamental procedure in ophthalmology, serving both diagnostic and therapeutic purposes. This technique is essential for identifying pathogens in cases of microbial keratitis and for treating certain corneal conditions. As an experienced ophthalmologist, it's crucial to master this procedure to ensure accurate diagnosis and effective treatment of ocular surface diseases.

Indications for Corneal Scraping

Corneal scraping is primarily indicated in the following scenarios:

• Suspected microbial keratitis
• Large central corneal infiltrates with significant stromal involvement
• Chronic keratitis unresponsive to broad-spectrum antibiotics
• Atypical clinical features or multiple infiltrates
• History of corneal surgery or trauma

According to Gurnani and Kaur (2023), scraping is particularly important in cases with large central corneal infiltrates, chronic unresponsive keratitis, and atypical presentations.

Preparation and Technique

Proper preparation is key to a successful corneal scraping procedure:

1. Apply topical anesthesia (preservative-free 0.5% proparacaine or proxymetacaine)
2. Remove loose mucus and necrotic tissue from the ulcer surface
3. Use a sterile Kimura spatula, platinum spatula, or disposable blade
4. Obtain samples from the margin and base of the ulcer
5. Prepare slides for microscopic evaluation and culture media

Gurnani and Kaur (2023) emphasize the importance of using preservative-free anesthetics to avoid compromising bacterial viability for culture.

Sample Collection and Processing

Proper sample collection and processing are crucial for accurate diagnosis:

• Smear samples onto glass slides for Gram staining and microscopic evaluation
• Inoculate culture media (blood agar, chocolate agar, Sabouraud's agar)
• Use multiple C-shaped streaks when inoculating solid media
• Consider specialized media for suspected fungal or atypical infections

A study by Das et al. (2011) found that corneal scrapings were culture-positive in 76% of cases, highlighting the importance of proper sample collection and processing.

Interpretation of Results

Accurate interpretation of corneal scraping results is essential for guiding treatment:

• Gram stain results can provide immediate information on the type of pathogen
• Culture results typically take 24-48 hours for bacterial growth
• Fungal cultures may require up to 2 weeks for growth
• Consider the clinical picture alongside laboratory results

A comparative study by Martha et al. (2023) found that the scraping-microhomogenization technique yielded positive cultures in 72.2% of cases, compared to 50% with swab techniques.

Therapeutic Applications

Beyond diagnosis, corneal scraping has therapeutic applications:

• Removal of necrotic tissue in infectious keratitis
• Treatment of recurrent corneal erosions
• Management of band keratopathy
• Correction of post-refractive surgery complications

Cherry (1996) reported successful treatment of overcorrection after photorefractive keratectomy using corneal epithelial scraping, with mean refraction improving from +2.77D to +0.68D at 12 months post-scraping.

Complications and Precautions

While generally safe, corneal scraping can lead to complications if not performed correctly:

• Corneal thinning or perforation in cases of deep stromal involvement
• Iatrogenic infection if sterile technique is not maintained
• Delayed epithelial healing
• Induction of irregular astigmatism

To minimize risks, always use sterile instruments and exercise caution in cases of thin corneas or descemetoceles. Zhao et al. (2004) demonstrated that mechanical scraping can cause immediate damage to underlying keratocytes, emphasizing the need for gentle technique.

Conclusion

Corneal scraping is an indispensable skill for ophthalmologists, crucial for diagnosing and managing various corneal pathologies. By mastering the technique, understanding its applications, and interpreting results accurately, clinicians can provide timely and effective treatment for patients with ocular surface diseases. As research continues to refine this procedure, staying updated with the latest developments will ensure optimal patient care in ophthalmic practice.