Low Central Corneal Thickness (<500 µm): The Misleading Nature Of Pachymetry Before Cataract Surgery

To emphasize that Fuchs Endothelial Corneal Dystrophy (FECD) and visually significant subclinical edema can exist even when central corneal thickness (CCT) is measured at less than 500 µm, and to demonstrate the superior diagnostic value of Scheimpflug tomographic over biometric thickness measurements in preoperative cataract evaluation.

University of Health Sciences, Diskapi Yildirim Beyazit Training and Research Hospital, Department of Ophthalmology, Ankara, Turkiye.

An 83-year-old woman with pseudoexfoliative glaucoma, managed with latanoprost for six years, presented with reduced vision. Examination revealed bilateral corneal guttata, nuclear cataracts, and pseudoexfoliative material. Despite CCT measurements of 490 µm (OD) and 498 µm (OS)—values typically considered ''thin''—Scheimpflug tomography identified three definitive markers of subclinical edema: displacement of the thinnest point, loss of parallel isopachs, and focal posterior surface depression. Specular microscopy confirmed low endothelial cell density (908 cells/mm² OD). This case illustrates how chronic prostaglandin use and naturally thin baseline corneas can mask underlying endothelial dysfunction by keeping absolute CCT values deceptively low. After providing information of the risks of corneal decompansation, corneal edema and possibility of Descement Membrane Endothelial Keratoplasty (DMEK), an uneventful phacoemulsification and intraocular lens implantation was performed.

Diagnostic and surgical decisions should not rely solely on absolute CCT values. Long-term use of prostaglandin analogues is known to reduce corneal thickness, which may mask the stromal swelling characteristic of FECD and lead to an underestimation of disease severity. In patients scheduled for cataract surgery, a "thin" cornea does not guarantee a healthy endothelium.