Keratoconus With Low Keratometry: Topometric, Tomographic, and Biomechanical Characteristics

Lopes, Bernardo

Keratoconus With Low Keratometry: Topometric, Tomographic, and Biomechanical Characteristics

Saturday, April 26, 2014: 3:29 PM

Room 155 (Boston Convention and Exhibition Center)

Bernardo T. Lopes, MD, Rio de Janeiro Corneal Tomography and Biomechanical Study Group, Rio de Janeiro, Brazil

Isaac C. Ramos, MD, Hospital de Olhos Santa Luzia, Maceió-AL, Brazil

Allan Luz, MD, Hospital de Olhos de Sergipe, Aracaju, Brazil

Rosane Correa, MD, Rio de Janeiro Corneal Tomography and Biomechanical Study Group, Rio de Janeiro, Brazil

Bruno F. Valbon, MD, University of São Paulo, Niterói, Brazil

Marcella Salomão, MD, Barra Vision Center, Rio de Janeiro, Brazil

Rodrigo T. Santos, MD, Rio de Janeiro Corneal Tomograhyand Biomechanics Study Group, SAO JOSE DOS CAMPOS, Brazil

Renato Ambrósio Jr., MD, PhD, Inst. Olhos R. Ambrósio, Rio de Janeiro, Brazil

Narrative Responses:

Purpose
To report prevalence, keratometric, topometric, tomographic and biomechanis on clinical keratoconus cases (KC), but central steepest simulated keratometric (K2) < 46D and maximum front curvature (KMax) < 47 D – “Low K Keratoconus” (LKKC) and to compare with IOP and age matched normal corneas and KC (K2>46, KMax > 47D)

Methods
Patients underwent complete eye examination, topography(Keratograph, Oculus), tomography (Pentacam, Oculus) and biomechanical evaluation(ORA, Reichert). Kruskal-Wallis test was used to assess the difference between groups with post hocDunn’s test

Keratometric values(central simulated Ks and KMax), topometric indices(derived from the axial front curvature map), and tomographic indices(anterior and posterior elevation at the thinnest point [AETP, PETP], thinnest point pachymetry(TP), maximal and average pachymetric progression[PPI-Max, PPI-Ave], maximal and average Ambrósio's Relational Thickness[ART-Max, ART-Ave] and Belin-Ambrósio Deviation[BAD-D]). ORA biomechanical indices(corneal hysteresis[CH], corneal resistance factor[CRF], KC Score, p1area)

Results
Participants:177 patients with KC and 170 eyes randomly selected from 170 age- and IOP-matched controls.

Results:13 eyes from 13 patients were identified as LKKC among 177 patients, a 3,67% prevalence.

All indices were statistically different among the 3 groups (p<0.0001). Differences (p<0.05) were found in post hoctest for topometric indices and AETP, KC group presented higher values, LKKC group intermediate values and normal group lower values. Tomographic indices (TP, PETP, PPI, ART and BAD-D) and biomechanical indices (CH, CRF, p1area) had significant differences (p<0.05) between KC and normal, between LKKC and normal but not between the KC and LKKC.

Conclusion
Keratoconus may occur despite of relatively normal keratometric values. While there are significant differences among cases with LKKC from the keratoconus group on curvature derived indices, such differences were not present on tomographic and biomechanical indices.