Extracorneal connective tissue alterations in keratoconus: ultrasonographic evaluation of tendon, plantar fascia, and cartilage.

Purpose: Structures such as the cornea, Achilles tendon (AT), plantar fascia (PF), and cartilage share the common feature of containing collagen and being associated with collagenous tissue disorders. However, the relationship between keratoconus and AT and PF thicknesses has not been investigated before. The importance of this study lies in the potential to identify a link between keratoconus and conditions such as Achilles tendinitis, plantar fasciitis, or osteoarthritis.

Methods: This prospective, comparative study includes 33 keratoconus patients and 33 age- and gender-matched controls. AT, PF, talar cartilage (TC), and distal femoral cartilage (DFC) thicknesses were obtained by ultrasound (US). US parameters of the study and control groups were compared.

Results: The mean AT and PF thicknesses were significantly higher in the study group (p = 0.002 and p < 0.001, respectively). On the other hand, the mean lateral femoral condyle (LFC), medial femoral condyle (MFC), DFC, and TC thicknesses were significantly lower in the study group (p < 0.001, for all). There was a significant correlation between corneal thickness and AT thickness (r = - 0.482, p = 0.005) and between corneal thickness and intercondylar area (IA) thickness (r = 0.367, p = 0.036). No significant relationship was found between maximum keratometry and US parameters, and BCV index and US parameters (p > 0.05, for all).

Conclusion: This study clearly demonstrates that patients with keratoconus have significant PF, tendon and cartilage thickness abnormalities. Keratoconus patients may have a tendency to develop conditions such as Achilles tendinitis, plantar fasciitis, or osteoarthritis.