Estimate the "severity" of your vision prescription based on sphere and cylinder values.
Understanding Your Eye Prescription and Severity
Your eye prescription is a detailed record of the lenses needed to correct your vision. It typically includes Sphere (SPH), Cylinder (CYL), and Axis values, and sometimes ADD power for bifocals or progressive lenses.
What do Sphere (SPH) and Cylinder (CYL) mean?
Sphere (SPH): This indicates the main refractive error of your eye.
A negative (-) number corrects myopia (nearsightedness), meaning distant objects are blurry.
A positive (+) number corrects hyperopia (farsightedness), meaning close objects (and sometimes distant ones) can be blurry.
Cylinder (CYL): This corrects astigmatism, a condition where the cornea or lens has an irregular shape, causing blurred vision at all distances.
A negative (-) cylinder is most common.
A positive (+) cylinder is less common but achieves the same correction.
Axis: This number (from 1 to 180 degrees) indicates the orientation or direction of the astigmatism correction needed on your eye. It's crucial for fitting toric (astigmatism-correcting) contact lenses or eyeglasses.
How is "Prescription Severity" Calculated?
There isn't a single, universally defined "severity score" for eye prescriptions. However, we can create a meaningful metric by considering the magnitude of the refractive error. This calculator uses a simplified approach that combines the absolute values of your Sphere and Cylinder to provide an indicative severity score.
The formula used is:
Severity Score = |Sphere| + |Cylinder|
Where:
|Sphere| represents the absolute value of your sphere power (ignoring the minus or plus sign).
|Cylinder| represents the absolute value of your cylinder power (ignoring the minus or plus sign).
This calculation gives you a numerical representation of the overall lens power required. Higher numbers generally indicate a stronger prescription.
Interpreting the Severity Score:
Low Scores (e.g., 0.00 – 2.00): Typically represent mild vision correction needs. You might have slight blurriness or only need glasses for specific tasks like reading or driving.
Moderate Scores (e.g., 2.25 – 4.00): Indicate a moderate level of nearsightedness, farsightedness, or astigmatism. Vision correction is likely needed for most daily activities.
High Scores (e.g., 4.25+): Suggest significant vision impairment requiring strong corrective lenses. Without correction, vision can be substantially blurry.
Important Note: This calculator provides an estimate for informational purposes only. It does not replace a professional eye examination. The "severity" is a simplified metric; your actual visual experience and the impact of your prescription depend on many factors, including your age, eye health, and specific visual demands.
function calculatePrescriptionSeverity() {
var sphereInput = document.getElementById("sphere");
var cylinderInput = document.getElementById("cylinder");
var axisInput = document.getElementById("axis");
var resultDiv = document.getElementById("result");
var sphere = parseFloat(sphereInput.value);
var cylinder = parseFloat(cylinderInput.value);
var axis = parseFloat(axisInput.value); // Axis is not used in the severity score calculation itself
// Clear previous results and error messages
resultDiv.style.display = 'none';
resultDiv.innerHTML = ";
// Validate inputs
if (isNaN(sphere)) {
resultDiv.innerHTML = 'Please enter a valid number for Sphere.';
resultDiv.style.backgroundColor = '#dc3545'; // Error color
resultDiv.style.display = 'block';
return;
}
if (isNaN(cylinder)) {
resultDiv.innerHTML = 'Please enter a valid number for Cylinder.';
resultDiv.style.backgroundColor = '#dc3545'; // Error color
resultDiv.style.display = 'block';
return;
}
// Optional validation for Axis if it was entered
if (!isNaN(axis) && (axis 180)) {
resultDiv.innerHTML = 'Axis must be between 1 and 180 degrees.';
resultDiv.style.backgroundColor = '#dc3545'; // Error color
resultDiv.style.display = 'block';
return;
}
// Calculate severity score: Absolute value of Sphere + Absolute value of Cylinder
var severityScore = Math.abs(sphere) + Math.abs(cylinder);
// Determine descriptive severity level
var severityLevel = "";
if (severityScore <= 1.00) {
severityLevel = "Very Mild";
} else if (severityScore <= 2.00) {
severityLevel = "Mild";
} else if (severityScore <= 4.00) {
severityLevel = "Moderate";
} else if (severityScore <= 6.00) {
severityLevel = "Moderately High";
} else {
severityLevel = "High";
}
// Display the result
resultDiv.innerHTML = `Your Estimated Severity Score: ${severityScore.toFixed(2)}Level: ${severityLevel}`;
resultDiv.style.backgroundColor = 'var(–success-green)'; // Success color
resultDiv.style.display = 'block';
}