Shape and radius of posterior corneal surface

Area of Science:

• Ophthalmology
• Corneal Biomechanics
• Refractive Surgery

Background:

• The posterior corneal surface's role in refractive surgery predictive models is often underestimated.
• Previous studies frequently assumed a spherical posterior surface, neglecting its asphericity.
• Limited research has adequately addressed the asphericity of the posterior cornea.

Purpose of the Study:

• To derive an algorithm for calculating the posterior corneal surface apical radius and asphericity.
• To investigate the characteristics of the posterior cornea in relation to the anterior cornea and corneal thickness.
• To quantify the asphericity of the posterior corneal surface.

Main Methods:

• Developed an algorithm integrating anterior corneal data and topographic corneal thickness variations.
• Measured anterior corneal asphericity using a photoelectric keratoscope.
• Employed ultrasonic pachometry with a marked contact lens for precise corneal thickness measurements.

Main Results:

• The average posterior corneal surface apical radius was approximately 5.8 mm in both vertical and horizontal meridians.
• Average posterior corneal asphericity (p) was 0.64 (vertical) and 0.52 (horizontal).
• Mean central corneal thickness was measured at 533 µm.

Conclusions:

• The posterior corneal surface exhibits an elliptical shape, characterized by an average asphericity below 1.
• The rate of flattening of the posterior corneal surface is more pronounced than that of the anterior corneal surface.
• These findings highlight the importance of considering posterior corneal geometry in refractive surgery planning.