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Eric L Crowell, Alice Chuang, Lauren Blieden; AGREEMENT OF CENTRAL CORNEAL THICKNESS with the CASIA SS-1000 ASOCT and ULTRASOUND PACHYMETRY. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):1612.
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© ARVO (1962-2015); The Authors (2016-present)
Using a retrospective review, determine the agreement of central corneal thickness (CCT) measurements taken by the CASIA SS-1000 Anterior Segment Ocular Coherence Tomography (ASOCT; Tomey, Nagoya, Japan) with those taken by ultrasound pachymetry (USP), the current clinical gold-standard.
Patients who had undergone ASOCT imaging using the ‘Corneal Map Mode were reviewed. Participants were included if they had CCT measured by USP on the same date as ASOCT imaging. Patients were excluded if they had anterior segment abnormalities or media opacities that affected the cornea or measurements. If both eyes were eligible, one eye was randomly selected. Eyes were classified into 5 groups: refractive error, keratoconus (KCN)/bullous keratopathy (BK), corneal dystrophy, other corneal diseases, and non-corneal ocular diseases. Agreement was evaluated by the mean difference between ASOCT and USP and limits of agreement.
Seventy-eight eyes from 78 participants were included. The mean age of participants was 41.0 (± 19.0) years with 42 (53.8%) male, 32 (42.7%) white, and 34 (43.6%) right eyes. Mean IOP was15.0 (± 5.5) mm Hg. Thirty-seven (47.4%) eyes had refractive error, 18 (23.1%) KCN/BK, 8 (10.3%) corneal dystrophy, 6 (7.7%) other corneal disease, and 9 (11.5%) noncorneal ocular diseases. Previous surgeries included 5 (6.4%) partial thickness penetrating keratoplasty, 5 (6.4%) full thickness penetrating keratoplasty, 5 (5.1%) LASIK, 2 (2.6%) photorefractive keratectomy, and 2 (2.6%) filtration surgery. Sixty-five (82.3%) eyes were phakic, 13 (16.5%) pseudophakic, and one (1.3%) aphakic. On average the CASIA SS-1000 ASOCT underestimates CCT by -16µm (Figure 1). The magnitude of agreement between the 2 instruments did not vary according to corneal thickness The limits of agreement show a 95% variation within 38µm, with 5 eyes outside the limits of agreement. Four of these 5 consist of those eyes with KCN/BK, and one eye with myopia & regular astigmatism.
The CASIA SS-1000 is similar to other ASOCT machines in that it gives a CCT reading lower than the USP, the current gold standard. KCN eyes tend to have larger differences in CCT measurement between ASOCT and USP. This difference may indicate that one modality of CCT measurement is more appropriate in KCN eyes.
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