ARK (AutoRefractor & Keratometer) AutoRefraction & Keratometry

👁 What is ARK?

ARK (AutoRefractor & Keratometer)

• AutoRefraction: Measures refractive errors (myopia, hyperopia, astigmatism)
• Keratometry: Measures corneal curvature
  ➡️ Combined in a single automatic device

📌 Standard tool in eye clinics
📌 Fast, automated measurement: ~1 second × 3 trials → average result

 

---

⚠ Accuracy in Pediatrics: ARK vs Manual Refraction

• In children (especially <7 years old), ARK results can be inaccurate
• Greater discrepancy in:
  • Hyperopia
  • Amblyopia

📊 Korean study (2016, 388 children):

Refraction Parameter>0.5 D difference

Sphere	47.2%
Cylinder	37.1%
Axis	57.2%
Spherical Equivalent	52.6%

➡️ Nearly half showed clinically significant discrepancies

---

💡 Cycloplegic Refraction Helps

ParameterDifference (pre → post)

Sphere	47.2% → 29.4%
Cylinder	37.1% → 30.7%
Axis	57.2% → 51.0%
Sph. Eq.	52.6% → 32.5%

✅ After cycloplegia, ARK aligns better with manual results
✅ Still, retinoscopy remains gold standard in children

---

✅ Summary

• ARK = fast & useful, but less accurate in young children
• Significant error in <7 years old, especially with hyperopia/amblyopia
• Best practice:
  • Use cycloplegia before ARK in kids
  • Combine with manual retinoscopy & subjective tests for accurate Rx