Corneal Topographic versus Manifest Refractive Astigmatism in Patients with Keratoconus: A Retrospective Cross-Sectional Study

Figures & data

Table 1 Criteria of Studied Cases

	Mean ± SD	Range
Age (years)	27 ± 7.7	10 to 51
UCDVA (logMAR)	0.68 ± 0.5	0 to 2
CDVA (LogMAR)	0.19 ± 0.2	1 to 0
Spherical equivalent (D)	−2.47 ± 3	−17 to 2.25
MRC (D)	2.36 ± 1.75	0 to 9
TA (D)	3.02 ± 1.97	0 to 12.6
Km (D)	46.9 ± 4.2	40.3 to 64.5
K max (D)	53.7 ± 6.97	42.5 to 79
Thinnest location (um)	451 ± 45	325 to 578

Abbreviations: CDVA, corrected distance visual acuity; Km, mean keratometry readings; Kmax, maximum keratometric reading; MRC, manifest refractive cylinder; SD, standard deviation; TA, tomographic astigmatism; UCDVA, uncorrected distance visual acuity.

Figure 1 Correlation between power of topographic corneal astigmatism and manifest refractive astigmatism.

Figure 2 Correlation between axis of topographic corneal astigmatism (TA) and manifest refractive astigmatism (MRC).

Figure 3 Polar plot of astigmatism power and axis of studied cases; right eyes (OD) above and left eyes (OS) below.

Abbreviations: TA, topographic astigmatism (blue triangles); MRC, manifest refractive cylinder (red triangles) showing more vertical orientation of MRC in comparison of TA.

Table 2 Difference Between Axis of Tomographic Astigmatism (TA) and Manifest Refractive Cylinder (MRC) and Results of Vector Analysis

	OD	P-value*	OS	P-value*
TA axis (degrees)	62 ± 53	0.052	125 ± 48	<0.001
MRC axis (degrees)	66 ± 44		100 ± 48
X (Topographic)	0.71 ± 2.36	<0.001	0.97 ± 2.46	<0.001
X (MRC)	−0.94 ± 1.85		−0.82 ± 2.04
Y (Topographic)	1.92 ± 1.74	0.009	−1.93 ± 2.22	<0.001
Y (MRC)	1.26 ± 1.75		to1.2 ± 1.86
TA Mean vector (diopters)	1.80 axis 29	Difference vector	1.83 axis 150	Difference vector
MRC Mean vector (diopters)	1.25 axis 61	1.7 axis 98	1.29 axis 120	1.65 axis 352

Note: *Wilcoxon signed-rank test.

Abbreviations: OD, right eyes; OS, left eyes; MRC, manifest refractive cylinder; TA, tomographic astigmatism; X and Y, the horizontal and vertical components of astigmatism after vector analysis.

Figure 4 Correlation between Kmax (D) and vector difference between topographic and manifest astigmatism.