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OPHTHALMIC IMAGES
Year : 2021  |  Volume : 59  |  Issue : 2  |  Page : 218-219

Accuracy of Scheimpflug Imaging (Sirius) in Detecting Subclinical Keratoconus ..Know Your Indices


1 Department of Glaucoma and Research, Mahathma Eye Hospital Private Limited, Tiruchirappalli, Tamil Nadu, India
2 Department of Cornea, Aravind Eye Care System, Puducherry, India
3 Department of Paediatric Ophthalmology, Aravind Eye Care System, Puducherry, India
4 Department of Cataract and Refractive Surgery, Mahathma Eye Hospital Private Limited, Tiruchirappalli, Tamil Nadu, India
5 Department of Paediatric Ophthalmology and Strabismus, Mahathma Eye Hospital Private Limited, Tiruchirappalli, Tamil Nadu, India

Date of Submission25-Sep-2020
Date of Acceptance05-Dec-2020
Date of Web Publication24-Jun-2021

Correspondence Address:
Dr. Prasanna Venkatesh Ramesh
167/1 Sarojini Street, Ram Nagar, Coimbatore - 641 009, Tamil Nadu
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/tjosr.tjosr_143_20

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How to cite this article:
Ramesh SV, Gurnani B, Kaur K, Ramesh PV, Ramesh MK, Rajasekaran R. Accuracy of Scheimpflug Imaging (Sirius) in Detecting Subclinical Keratoconus ..Know Your Indices. TNOA J Ophthalmic Sci Res 2021;59:218-9

How to cite this URL:
Ramesh SV, Gurnani B, Kaur K, Ramesh PV, Ramesh MK, Rajasekaran R. Accuracy of Scheimpflug Imaging (Sirius) in Detecting Subclinical Keratoconus ..Know Your Indices. TNOA J Ophthalmic Sci Res [serial online] 2021 [cited 2021 Jul 27];59:218-9. Available from: https://www.tnoajosr.com/text.asp?2021/59/2/218/319264



An 18-year-old young boy presented with defective vision OS for the past 2 years with a constant change of glasses. He had an uncorrected visual acuity of 20/20 OD and best-corrected visual acuity of 20/40 OS with a correction of −6.00D cylinder. On slit-lamp evaluation, keratoconus was noted in OS [Figure 1]. Scheimpflug imaging (Sirius, CSO, Italy) revealed subclinical keratoconus OD and advanced keratoconus OS [Table 1] and [Figure 2]. The patient was advised to undergo collagen cross-linkage in both eyes.
Figure 1: (a) Slit lamp imaging OD revealed normal anterior segment. (b) Slit lamp imaging OS revealed clinical keratoconus with central corneal thinning. (c) Keratoscopy imaging OD revealed normal Placido rings. (d) Keratoscopy imaging OS revealed crowding of Placido rings inferotemporally

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Table 1: Keratoconus summary

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Figure 2: The corneal topography maps of OD and OS. (a and b) Corneal pachymetry of OD and OS, respectively. (c and d). Tangential anterior map of OD and OS, respectively. (e and f) Tangential posterior map of OD and OS, respectively. (g and h) Posterior elevation map of OD and OS, respectively

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The classification algorithm in Sirius Scheimpflug analyzer has high accuracy, precision, sensitivity, and specificity, in discriminating among eyes with keratoconus or subclinical keratoconus from normal eyes.[1] It is of the essence to look through the indices on the topographic display after reading the map as it will give insight toward subclinical keratoconus. The first step would be to assess the quality of acquisition before interpretation. Both the anterior and posterior corneal surfaces have separate indices. Root mean square (RMS) represents the deviation of the surface being examined from the aspherotoric best-fit surface characterized by a flat radius, steep radius, asphericity, and axis. Low RMS indicates that the surface of the cornea in the area delimited by the given diameter is very regular; irregular corneal surfaces are associated with high RMS. RMS/A indicates RMS per unit of area.[2] The symmetry index of the curvature is defined as the difference of the mean tangential curvature of two circular zones centered on the vertical axis in the inferior and superior hemispheres. It measures the vertical asymmetry. A positive value indicates that the inferior hemisphere is steeper than the superior hemisphere, and a negative value indicates that the superior hemisphere is steeper than the inferior hemisphere. Baiocchi-Calossi-Versaci (BCV) index allows the evaluation of the presence of an ectasia through analysis of the coma and trefoil components of Zernike's decomposition of elevations in the zones where keratoconus statistically arises. The BCV index is the vectorial sum of the BCV front index and the BCV back index. It presumes that the ectasia statistically develops in a preferential direction, and it mainly manifests in the coma, trefoil, and spherical aberration. Another important index is the pachymetry indices which is interpolated as the thickness from the thinnest point.[3]

It is mandatory to identify the subtype of keratoconus as it plays a vital role in its timely management.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Arbelaez MC, Sekito MB. Screening for subclinical keratoconus. Oman J Ophthalmol 2013;6:1-2.  Back to cited text no. 1
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2.
Shetty R, Rao H, Khamar P, Sainani K, Vunnava K, Jayadev C, et al. Keratoconus screening indices and their diagnostic ability to distinguish normal from ectatic corneas. Am J Ophthalmol 2017;181:140-8.  Back to cited text no. 2
    
3.
Shetty R, Kaweri L, Ahuja P. SIRIUS Topographer - Map Reading Made Easy. Narayana Nethralaya; 2019.  Back to cited text no. 3
    


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