An S4 class to hold visual acuity data

A class to hold Visual Acuity data for the oculus sinister (OS; left eye) and oculus dexter (OD; right eye)

Usage

# S4 method for VAObject,ANY,ANY,ANY
[(x, i, j, ..., drop = TRUE)

# S4 method for VAObject
print(x, ...)

# S4 method for VAObject
show(object)

# S4 method for VAObject
summary(object, weightbest = TRUE, w = c(0.75, 0.25))

Arguments

x

the object to subset

i

the rows to subset (optional)

j

the columns to subset (optional)

...

Additional arguments passed to lower functions

drop

should be missing

object

A VAObject class object

weightbest

Logical whether to upweight the best seeing eye. Defaults to TRUE.

w

A numeric vector of the weights, first for the best seeing then the worst seeing eye. Defaults to c(.75, .25).

Methods (by generic)

• x[i: extract method

• print(VAObject): print method

• show(VAObject): show method

• summary(VAObject): summary method

Slots

originalOS

the original visual acuity data for the left (ocular sinister) eye

originalOD

the original visual acuity data for the right (ocular dexter) eye

logMAROS

Logarithm of the minimum angle of resolution data for OS

logMAROD

Logarithm of the minimum angle of resolution data for OD

chart.values

the snellen values for each line of the chart used to measure visual acuity. Used for the linear interpolation in the case of partially correct line readings.

chart.nletters

the number of letters on each line of the chart used to measure visual acuity. Used for the linear interpolation in the case of partially correct line readings (+2 is 2/4 of the way to the next line if there are four letters, but only 2/6 if there are six, etc.)

zero

the logMAR value chosen to represent "zero" visual acuity when creating the combined logMAR values for both eyes or taking the arithmetic mean.