Abstract
BackgroundTo analyze mean corneal powers and astigmatisms on anterior, posterior, and total cornea in patients with keratoconus as calculated according to various keratometric measurements using a Scheimpflug camera.MethodsWe examined the left eyes of 64 patients (41 males and 23 females; mean age 29.94 ± 6.63 years) with keratoconus. We measured simulated K (Sim-K), posterior K, true net power (TNP) and four types of total corneal refractive powers (TCRP). We then used the obtained values to analyze mean K, and corneal astigmatism. TCRP were measured at 2.0 ~ 5.0 mm.ResultsMean corneal powers from Sim K, posterior K, and TNP were 49.12 ± 3.99, − 7.39 ± 0.79, and 47.78 ± 4.09 diopters, respectively. For TCRP centered on the pupil, mean K tended to decrease with measurement area (all p < 0.01). While, both mean K and astigmatism measured using TCRP centered on the apex decreased with measurement area (all p < 0.001). TCRP centered on the apex were greater than those centered on the pupil for mean K values calculated using TCRP (all p < 0.001). The proportion of WTR was greatest on the anterior and total cornea. As the measurement area moved to the periphery, the proportion of WTR increased.ConclusionsMean corneal powers and astigmatisms on total cornea with keratoconus change depending on calculation methods and measurement areas.
Highlights
To analyze mean corneal powers and astigmatisms on anterior, posterior, and total cornea in patients with keratoconus as calculated according to various keratometric measurements using a Scheimpflug camera
Significant difference was observed in mean keratometric value (mean K) values between measurements of anterior corneal power and true net power (p < 0.001)
No significant difference was observed between astigmatism derived from true net power and that derived from power of the anterior surface (p = 0.34)
Summary
To analyze mean corneal powers and astigmatisms on anterior, posterior, and total cornea in patients with keratoconus as calculated according to various keratometric measurements using a Scheimpflug camera. The Pentacam® is a rotating Scheimpflug camera used to evaluate the topography of the corneal surface and measure corneal thickness, which may be helpful in the diagnosis of keratoconus and identification of disease stage [2]. Kamiya et al [4] investigated eyes with keratoconus and concluded that 78.8% exhibit ATR astigmatism, while only 10.2 and 10.9% exhibit with-the-rule (WTR) and oblique astigmatism, respectively. The authors of the aforementioned study further reported a mean magnitude of posterior corneal astigmatism in keratoconus of 0.93 diopters. In contrast with mean magnitude of posterior corneal astigmatism, WTR astigmatism was more prevalent than oblique and ATR astigmatism in their study
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