CorPresDefl

Compute three transformed corneal net pressure–volume slopes over Initial–A1, A1–HC, and HC–A2.

Install

install.packages("pak")
pak::pak("GulumimiRen/CorPresDefl")

Requires R 4.1.0 or later.

Usage

library(CorPresDefl)

corpd(
  A1t = 7.5, HCt = 17, A2t = 22, bIOP = 14,
  x_a1 = 0.2, x_hc = 4, x_a2 = 0.4
)

# Data frame with the native pipe
df <- data.frame(
  id = c("example_1", "example_2"),
  A1t = c(7.5, 8), HCt = c(17, 17.5), A2t = c(22, 22.5),
  bIOP = c(14, 15),
  A1DeflVol = c(0.2, 0.25), HCDeflVol = c(4, 4.5),
  A2DeflVol = c(0.4, 0.5)
)
df |> corpd()

# Custom volume column names
custom <- data.frame(A1t = 7.5, HCt = 17, A2t = 22, bIOP = 14,
                     volume_a1 = 0.2, volume_hc = 4, volume_a2 = 0.4)
custom |> corpd(
  columns = c(x_a1 = "volume_a1", x_hc = "volume_hc", x_a2 = "volume_a2")
)

Inputs and outputs

Parameter	Description	Unit
A1t, HCt, A2t	Device times of first applanation, highest concavity, and second applanation	ms
bIOP	Biomechanically corrected IOP from the same examination	mmHg
x_a1, x_hc, x_a2	Calculated DeflVol at A1, HC, and A2	mm³ = μL

Data-frame defaults are A1t, HCt, A2t, bIOP, A1DeflVol, HCDeflVol, and A2DeflVol. Numeric inputs may be vectors of equal length or scalars. The measure argument accepts "Vol" (the default).

Output	Interval	Pressure transformation
k_initial_a1	Initial–A1	Exponential, scale 4 mmHg
k_a1_hc	A1–HC	Natural logarithm
k_hc_a2	HC–A2	Exponential, scale 20 mmHg

Numeric calls return these three columns and status. Data-frame calls preserve the input and append Vol_k_initial_a1, Vol_k_a1_hc, Vol_k_hc_a2, and Vol_status. Use columns for custom input names and prefix for custom output names. All three slopes have units mm⁻³.

Valid inputs satisfy 0 < A1t < HCt < A2t <= 30, positive bIOP and event volumes, HC volume greater than A1 and A2, and positive A1 and HC net pressures. Invalid inputs produce NA slopes and a reason in status. Use invalid = "warn", "quiet", or "error" to select validation handling.

Algorithm

Reference on-eye pressure is interpolated from the bundled pressure–time table using monotone cubic Hermite interpolation on the rising and falling branches. Net pressure is $P(t)=P_{\mathrm{on-eye}}(t)-\mathrm{bIOP}$. Write $V=\mathrm{DeflVol}$, with $V_0=0$ and $P_0=-\mathrm{bIOP}$. The three endpoint slopes are:

$$k_{\mathrm{Initial-A1}}= \frac{\exp[P(A1t)/c_1]-\exp[-\mathrm{bIOP}/c_1]}{V(A1t)}, \qquad c_1=4,\mathrm{mmHg}.$$

$$k_{\mathrm{A1-HC}}= \frac{\ln[P(HCt)/(1,\mathrm{mmHg})]-\ln[P(A1t)/(1,\mathrm{mmHg})]} {V(HCt)-V(A1t)}.$$

$$k_{\mathrm{HC-A2}}= \frac{\exp[P(A2t)/c_2]-\exp[P(HCt)/c_2]}{V(A2t)-V(HCt)}, \qquad c_2=20,\mathrm{mmHg}.$$

References

Joda AA, Shervin MMS, Kook D, Elsheikh A. Development and validation of a correction equation for Corvis tonometry. Computer Methods in Biomechanics and Biomedical Engineering. 2016;19(9):943–953. doi:10.1080/10255842.2015.1077515.

Ren Q, Deng Z, Chu Z, Pan Z, Wan P. DeflVol: a model-derived volumetric descriptor of corneal deflection at highest concavity under Corvis ST air-puff loading. Frontiers in Bioengineering and Biotechnology. 2026;14:1933733. doi:10.3389/fbioe.2026.1933733.

License

R code: MIT. Bundled reference data: CC BY 4.0; see NOTICE.