Analysis of Scheimpflug Tomography Parameters for Detecting Subclinical Keratoconus in the Fellow Eyes of Patients with Unilateral Keratoconus in the Eastern Province of Saudi Arabia

Abdulaziz Al Somali,1 Hatim Najmi,2 Hend Alsawadi,2 Hassan Alsawadi,3 Assaf AlMalki,2 Mustafa Alhamoud,2 Hatlan Alhatlan,4 Nada Alwohaibi5 1Department of Ophthalmology, King Faisal University, Alahsa, Saudi Arabia; 2Department of Ophthalmology, Dhahran Eye Specialist Hospital, Dhahran, Saudi Arabia; 3Department of Electrical and Computer Engineering, King Abdulaziz University, Jeddah, Saudi Arabia; 4Department of Ophthalmology, King Fahad Hospital, Hofuf, Saudi Arabia; 5Cornea, External Diseases, and Refractive Surgery Fellow, Dhahran Eye Specialist Hospital, Dhahran, Saudi ArabiaCorrespondence: Hatim Najmi, Department of Ophthalmology, Dhahran Eye Specialist Hospital, Dhahran, Al Ameen 6927, Khobar, Eastern Province, 34446, Saudi Arabia, Tel +966533677784, Fax +966133583898, Email [email protected]: We compared the characteristics of subtle morphological changes in subclinical keratoconus (KC) and normal corneas using Scheimpflug tomography (Pentacam®) and assessed the efficacy of these parameters for distinguishing KC or subclinical KC from normal eyes.Patients and Methods: In this multicenter comparative study at Dhahran Eye Specialist Hospital and Al Kahhal Medical Complex in the Eastern Province of Saudi Arabia, we analyzed the Scheimpflug tomography charts of patients with topographically normal eyes and those with unilateral KC. Patients were divided into the normal (NL: patients considered for refractive surgery and with normal topographic/tomographic features, 129 eyes), KC (30 patients with manifest KC in one eye based on biomicroscopy and topographical findings), and forme fruste KC (FFKC: fellow eyes of patients in the KC group that met the NL group criteria) groups. Corneal morphological parameters were analyzed using the area under the receiver operating characteristic (ROC) curves (AUCs).Results: For distinguishing NL and KC groups, all measured corneal morphological parameters, except for flat keratometry, maximum Ambrósio relational thickness index, and minimum sagittal curvature, had AUCs > 0.75. The surface variance index yielded the largest AUC (0.999). For distinguishing NL and FFKC groups, all corneal morphological parameters had AUCs < 0.8. Total higher-order aberrations (RMS HOA) yielded the highest AUC, followed by Belin/Ambrỏsio Enhanced Ectasia total deviation (BAD-D), back elevation at the thinnest location, average pachymetric progression index (PPIave), and deviation of Ambrỏsio relational thickness (Da) (AUC 0.74– 0.78).Conclusion: The diagnostic performance of all tested topographic and tomographic parameters measured using Scheimpflug tomography for discriminating subclinical KC was fair at best, with the top parameters being RMS HOA, BAD-D, back elevation at the thinnest location, PPIave, and Da. Distinguishing between subclinical KC and healthy eyes remains challenging. Multimodal imaging techniques may be required for optimal early detection of subtle morphological changes.Plain language summary: Normal fellow eyes in patients with unilateral keratoconus were found to exhibit the mildest form of subclinical keratoconus. The parameters of these eyes were compared with those of normal eyes in the Saudi population using Scheimpflug tomography to detect early, subtle morphological changes. Most of the evaluated parameters were unsatisfactory in terms of their ability to discriminate between subclinical keratoconus and normal eyes, implying the need for multimodal imaging techniques for the optimal early detection of subclinical keratoconus.Keywords: ectatic corneal disease, forme fruste keratoconus, keratoconu