Measurement of the visual axis through two different methods: quantification and differences for measuring chord μ.

Area of Science:

• Ophthalmology
• Optometry
• Corneal Imaging

Background:

• Accurate corneal measurements are crucial for refractive surgery and contact lens fitting.
• Understanding discrepancies between different measurement devices is essential for clinical decision-making.

Purpose of the Study:

• To compare apparent and actual chord μ measurements obtained from Pentacam and HD Analyzer.
• To evaluate the correlation and differences between these two devices in measuring corneal parameters.

Main Methods:

• A prospective, comparative study involving 116 eyes of 58 patients (aged 21-71) with myopia and mild astigmatism.
• Corneal imaging was performed using Pentacam and HD Analyzer under scotopic conditions.
• Exclusion criteria included contact lens wear, prior eye surgery, and corneal abnormalities.

Main Results:

• A moderate positive linear relationship (Pearson's r=0.647) was observed between apparent and actual chord μ.
• Mean differences of 52.45 μm were found between the devices (p=0.01).
• Mean pupillary diameters measured were 5.76 mm (HD Analyzer) and 3.31 mm (Pentacam).

Conclusions:

• A correlation exists between Pentacam and HD Analyzer for chord μ measurements.
• Significant differences were noted, indicating that both devices can be utilized in clinical practice.
• Clinicians should acknowledge and respect the unique characteristics of each measurement device.