Human cornea before and after refractive surgery using a new device: VCH-1

Area of Science:

• Ophthalmology
• Biomedical Optics
• Corneal Physiology

Background:

• The refractive index (RI) and water content (%WC) of corneal layers are critical for ocular optics.
• Variations in these properties can impact visual outcomes and surgical procedures like photorefractive keratectomy and laser-assisted in situ keratomileusis (LASIK).

Purpose of the Study:

• To evaluate the repeatability and accuracy of the VCH-1 device for measuring corneal refractive index (RI) and estimating water content (%WC).
• To assess changes in RI and %WC in anterior corneal layers before and after excimer laser photoablation.

Main Methods:

• The VCH-1 device was used to measure RI in corneal epithelium, Bowman layer, and midstroma.
• Measurements were taken before and immediately after excimer laser photoablation in patients undergoing various refractive surgeries.
• Repeatability was assessed using hydrogel contact lenses.

Main Results:

• The VCH-1 demonstrated high repeatability for RI measurements (average +/-0.001).
• Significant increases in RI and decreases in %WC were observed in the Bowman layer and midstroma after photoablation (P = 0.005 and P < 0.0001, respectively).
• Pre-ablation RI of epithelium and Bowman layer was significantly higher than that of the midstroma (P < 0.001).

Conclusions:

• The VCH-1 is a reliable tool for measuring corneal RI with high precision.
• Corneal RI and %WC are non-uniform, with intersubject and intracorneal variations that must be considered.
• Excimer laser photoablation leads to tissue dehydration, increasing corneal RI.