Table 2.

Definition of air puff-derived corneal response variables and comparison in Marfan syndrome and control groups

Group	Variable	Operational Definition	Control	Marfan syndrome
			Mean ± SD	Mean ± SD	P-value
1: Applanation Signal Intensity	A1	Peak intensity of 1st applanation event	705 ± 89	629 ± 146	0.1
	A2	Peak intensity of 2nd applanation event	649 ± 80	567 ± 161	0.1
	Applanation Peak Difference	A2 – A1	−56 ± 105	−62 ± 106	0.9
	Concavity Min	Minimum applanation intensity between A1 and A2	69 ± 14	48 ± 20	0.003*
	Concavity Mean	Mean applanation intensity between A1 and A2	173 ± 25	145 ± 31	0.01*
2: Pressure Signal	CRF (mmHg)	Corneal Resistance Factor (P1 – 0.7P2)	11.0 ± 1.7	9.5 ± 1.6	0.01*
	CH (mmHg)	Corneal Hysteresis (P2 – P1)	11.2 ± 1.2	9.8 ± 1.7	0.01*
	P1 (mmHg)	Pressure at 1st applanation event	55.6 ± 7.2	47.9 ± 7.8	0.007*
	P2 (mmHg)	Pressure at 2nd applanation event	44.3 ± 6.1	38.1 ± 6.3	0.008*
	P1P2Avg (mmHg)	(P1+P2)/2	49.9 ± 6.6	43.0 ± 7.0	0.008*
	Pmax (mmHg)	Peak value of pressure signal	488.6 ± 40.1	470.6 ± 34.1	0.2
3: Temporal Response Variables	Concavity Duration (msec)	Time lapse between A1 and A2	10.88 ± 0.64	10.93 ± 0.53	0.8
	Concavity Time (msec)	Time from onset of applied pressure to Concavity Min	13.62 ± 3.65	13.34 ± 4.48	0.9
	Lag Time	Time between Pmax and Concavity Min	2.58 ± 2.75	2.35 ± 4.06	0.9
4: Applanation Intensity and Response Time	Slope Down (msec−1)	Negative slope of the 1st applanation peak, from peak to inflection point	−7 ± 205	−71 ± 189	0.4
	Slope Up (msec−1)	Positive slope of the 1st applanation peak, from inflection point to peak	84.5 ± 31.5	73.6 ± 34.4	0.4
5: Pressure and Applanation Intensity	HLA	Area enclosed by pressure vs. applanation function	38863 ± 13668	26412 ± 15699	0.03*
6: Pressure and Time	Impulse	Area under pressure vs. time curve	10063 ± 3228	10170 ± 2812	0.9

Abbreviations: CRF = Corneal Resistance Factor; CH = Corneal Hysteresis; HLA = Hysteresis Loop Area;

^*= statistically significant P-value