No abstract

PURPOSE: To investigate the corneal biomechanical responses of subclinical keratoconus with normal topographic, topometric, and tomographic findings. METHODS: In this prospective observational study, the study group was selected from patients with clinically evident keratoconus in one eye and subclinical keratoconus with normal topographic, topometric, and tomographic findings in the fellow eye. The control group was selected from candidates for contact lens use. The biomechanical analyses were performed using the Corvis ST (Oculus Optikgeräte, Wetzlar, Germany). The following parameters were analyzed: A1 velocity, A2 velocity, A1 length, A2 length, deformation amplitude ratio, stiffness parameter at the first applanation, Corvis Biomechanical Index, and Tomographic and Biomechanical Index (TBI). RESULTS: The study group consisted of 21 patients (10 men and 11 women; mean age: 27.7 ± 6.9 years), and the control group consisted of 35 patients (17 men and 18 women; mean age: 26.1 ± 5.8 years). No significant differences were found between the eyes with subclinical keratoconus and normal eyes in corrected distance visual acuity and the topographic, topometric, and tomographic parameters ( P > .05). Significant differences were found in the values of A2 length, A1 velocity, A2 velocity, and TBI between the subclinical keratoconus group and the control group ( P < .05). In distinguishing eyes with subclinical keratoconus from normal eyes, the TBI showed the highest area under the curve (0.790; cut-off: 0.29; sensitivity: 67%; specificity: 86%) in the receiver operating characteristic analysis. CONCLUSIONS: Biomechanical analysis with the Corvis ST may be used as a complementary diagnostic method in detecting subclinical keratoconus. [ J Refract Surg . 2019;35(4):247–252.]

The increase in densitometry in the central zone could be useful in detecting subclinical keratoconus.

PurposeTo evaluate the topographic, tomographic, and densitometric properties of patients with pellucid marginal degeneration (PMD) and inferior keratoconus.Patients and methodsRetrospective, comparative case series. Forty-seven eyes of 32 patients with crab claw patterns were identified from 2751 patients with corneal ectasia. They were divided into two groups, inferior keratoconus and PMD, based on clinical findings. The topographic, tomographic, and densitometric measurements were analyzed.ResultsPMD was detected in 11 eyes of eight patients (mean age 50.2±11.1 years), and inferior keratoconus was detected in 36 eyes of 24 patients (mean age 34.7±10.1 years). The control group consisted of 40 patients (33.1±4.6 years). The thinnest corneal point and maximum anterior and posterior elevation points were located lower in the PMD than in the inferior keratoconus (P<0.01). In the PMD, all deviation indices were higher than the controls (P<0.01), whereas the deviation indices, except Dt (P=0.960), were lower than the inferior keratoconus (P<0.01). The densitometry values of PMD were significantly higher than those of the controls in all zones and layers (P<0.01) and significantly higher than the densitometry values of inferior keratoconus in the 6-10 and 10-12 mm zones (P<0.05).ConclusionThere is a higher probability of a patient with crab claw pattern on the topography of having inferior keratoconus than having PMD. Therefore, analyzing only the anterior corneal surface is not sufficient in differential diagnosis. Tomographic and densitometric evaluations may facilitate the differential diagnosis.

Uncorrected IOP, corrected IOP, CCT, and CV values decreased after HD, whereas the anterior chamber morphometry values remained similar between the measurements performed before and after HD.

None of the authors has a financial or proprietary interest in any material or method mentioned.

The maximum K value, most topometric indices, and ectasia display indices were repeatable and reliable in normal eyes and keratoconic eyes.

Objectives: To evaluate the longitudinal tomographic changes and to compare the discriminatory potential of a novel progression display between progressive and nonprogressive keratoconic eyes. Methods: Retrospective evaluation was made of 81 eyes of 81 patients with keratoconus who had undergone Scheimpflug measurements at least twice with an interval of 12 months or longer between each measurement. The progressive group was defined as 36 eyes, which showed progression according to the definition of the global consensus on keratoconus and ectatic diseases when 2 of the 3 criteria were met, and the other 45 eyes were considered the nonprogressive group. The main outcome measures from progression display were “A” for anterior radius of curvature, “B” for posterior radius of curvature, “C” for thinnest pachymetry, “D” for distance visual acuity; Kmax; Q-value front and back; index of surface variance (ISV), vertical asymmetry, height asymmetry, and height decentration; overall deviation of normality (final D); average pachymetric progression index; and maximum Ambrósio relational thickness. Results: The rate of change per year of A, B, C, thinnest pachymetry, Kmax, final D, and ISV was significantly different between groups (P≤0.01 for all values). It was determined that yearly change rates greater than 0.12 for A, 0.14 for B, 10.04 μm for thinnest pachymetry, 0.68 D for Kmax, 0.15 for final D, and 2.11 for ISV might indicate progression in keratoconus management. Conclusions: Belin progression display parameters may be useful in discriminating progressive from nonprogressive keratoconic eyes.