Analysis of total corneal astigmatism with a rotating Scheimpflug camera in keratoconus
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RESEARCH ARTICLE
Open Access
Analysis of total corneal astigmatism with a rotating Scheimpflug camera in keratoconus Jinho Kim1, Woong-Joo Whang2*
and Hyun-Seung Kim1
Abstract Background: 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. Methods: We 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. Results: Mean 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. Conclusions: Mean corneal powers and astigmatisms on total cornea with keratoconus change depending on calculation methods and measurement areas.
Background Keratoconus is a progressive non-inflammatory disease characterized by thinning and protrusion of the cornea, resulting in high degrees of irregular astigmatism and myopia that lead to impairment of visual quality and distorted vision [1]. 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]. Although corneal power has traditionally been assessed using instruments that measure anterior corneal * Correspondence: [email protected] 2 Department of Ophthalmology, Yeouido St. Mary’s Hospital, College of Medicine, The Catholic University of Korea Korea, Seoul, South Korea Full list of author information is available at the end of the article
power alone, a rotating Scheimpflug camera has made it possible to measure posterior corneal curvature as well [3]. Furthermore, keratometric and pachymetric measurements by a Scheimpflug rotating camera were repeatable than placido topographer combined with slitscanning technology [3]. 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. Naderan et al. [5] also reported a similar value for the magnitude of poster
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