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Value of Two Horizontal Prisms

One prism held over either eye

  • Prisms are assumed to be in the opposite directions over each eye (e.g. both base in or base out)
  • Prisms are in the Frontal Plane position

Calculator

<html> <head> 

  <title>Horizontal Prism Value Lookup</title>
  <style>
      #header {
          display: none; 
      }
      body {
          font-family: Arial, sans-serif;
          margin: 20px;
          padding: 20px;
      }
      h2 {
          color: #333;
      }
      label {
          font-weight: bold;
      }
      input, button {
          margin-top: 5px;
          padding: 8px;
          font-size: 16px;
      }
      p {
          font-size: 18px;
          font-weight: bold;
          color: blue;
          margin-top: 10px;
      }
  </style>
  <script>
      const prismTable = {
          10: {10: 20, 12: 22, 14: 24, 16: 26, 18: 29, 20: 31, 25: 36, 30: 41, 35: 47, 40: 52, 45: 58, 50: 63},
          12: {10: 22, 12: 24, 14: 26, 16: 29, 18: 31, 20: 33, 25: 38, 30: 44, 35: 49, 40: 55, 45: 60, 50: 66},
          14: {10: 24, 12: 26, 14: 29, 16: 31, 18: 33, 20: 35, 25: 40, 30: 46, 35: 52, 40: 57, 45: 63, 50: 69},
          16: {10: 26, 12: 29, 14: 31, 16: 33, 18: 35, 20: 37, 25: 43, 30: 48, 35: 54, 40: 60, 45: 66, 50: 72}, 
          18: {10: 29, 12: 31, 14: 33, 16: 35, 18: 37, 20: 39, 25: 45, 30: 51, 35: 57, 40: 63, 45: 69, 50: 75},
          20: {10: 31, 12: 33, 14: 35, 16: 37, 18: 39, 20: 42, 25: 47, 30: 53, 35: 59, 40: 65, 45: 71, 50: 78},
          25: {10: 36, 12: 38, 14: 40, 16: 43, 18: 45, 20: 47, 25: 53, 30: 59, 35: 66, 40: 72, 45: 79, 50: 86},
          30: {10: 41, 12: 44, 14: 46, 16: 48, 18: 51, 20: 53, 25: 59, 30: 66, 35: 73, 40: 80, 45: 87, 50: 94},
          35: {10: 47, 12: 49, 14: 52, 16: 54, 18: 57, 20: 59, 25: 66, 30: 73, 35: 80, 40: 87, 45: 95, 50: 103},
          40: {10: 52, 12: 55, 14: 57, 16: 60, 18: 63, 20: 65, 25: 72, 30: 80, 35: 87, 40: 95, 45: 104, 50: 113},
          45: {10: 58, 12: 60, 14: 63, 16: 66, 18: 69, 20: 71, 25: 79, 30: 87, 35: 95, 40: 104, 45: 113, 50: 123},
          50: {10: 63, 12: 66, 14: 69, 16: 72, 18: 75, 20: 78, 25: 86, 30: 94, 35: 103, 40: 113, 45: 123, 50: 133}
      };
      function lookupValue() {
          let prism1 = document.querySelector('input[name="prism1"]:checked').value;
          let prism2 = document.querySelector('input[name="prism2"]:checked').value;
          
          prism1 = parseInt(prism1);
          prism2 = parseInt(prism2);
          
          if (prismTable[prism2] && prismTable[prism2][prism1] !== undefined) {
              document.getElementById("result").innerHTML = `Result: <strong>${prismTable[prism2][prism1]} Prism Diopters</strong>`;
          } else {
              document.getElementById("result").innerText = "Invalid input";
          }
      }
  </script>

</head> <body> 

  <h2 id="header">Prism Value of One Horizontal Prism Held Over Each Eye</h2>
  <label for="prism1">Select Prism 1 (PD): </label>
  <br>
  <input type="radio" name="prism1" value="10"> 10
  <input type="radio" name="prism1" value="12"> 12
  <input type="radio" name="prism1" value="14"> 14
  <input type="radio" name="prism1" value="16"> 16
  <input type="radio" name="prism1" value="18"> 18
  <input type="radio" name="prism1" value="20"> 20
  <input type="radio" name="prism1" value="25"> 25
  <input type="radio" name="prism1" value="30"> 30
  <input type="radio" name="prism1" value="35"> 35
  <input type="radio" name="prism1" value="40"> 40
  <input type="radio" name="prism1" value="45"> 45
  <input type="radio" name="prism1" value="50"> 50
  <br><br>
  <label>Select Prism 2 (PD):</label>
  <br>
  <input type="radio" name="prism2" value="10"> 10
  <input type="radio" name="prism2" value="12"> 12
  <input type="radio" name="prism2" value="14"> 14
  <input type="radio" name="prism2" value="16"> 16
  <input type="radio" name="prism2" value="18"> 18
  <input type="radio" name="prism2" value="20"> 20
  <input type="radio" name="prism2" value="25"> 25
  <input type="radio" name="prism2" value="30"> 30
  <input type="radio" name="prism2" value="35"> 35
  <input type="radio" name="prism2" value="40"> 40
  <input type="radio" name="prism2" value="45"> 45
  <input type="radio" name="prism2" value="50"> 50
  <br><br>
  <button onclick="lookupValue()">Lookup</button>
  <br>
  <br>
  <p id="result"></p>

</body> </html>

<button type=“primary” size=“sm”>Reset Calculator</button>

Table

Prism Value 10 12 14 16 18 20 25 30 35 40 45 50
10 20 22 24 26 29 31 36 41 47 52 58 63
12 22 24 26 29 31 33 38 44 49 55 60 66
14 24 26 29 31 33 35 40 46 52 57 63 69
16 26 29 31 33 35 37 43 48 54 60 66 72
18 29 31 33 35 37 39 45 51 57 63 69 75
20 31 33 35 37 39 42 47 53 59 65 71 78
25 36 38 40 43 45 47 53 59 66 72 79 86
30 41 44 46 48 51 53 59 66 73 80 87 94
35 47 49 52 54 57 59 66 73 80 87 95 103
40 52 55 57 60 63 65 72 80 87 95 104 113
45 58 60 63 66 69 71 79 87 95 104 113 123
50 63 66 69 72 75 78 86 94 103 113 123 133

<pane id=“references”>Adapted From: Thompson & Guyton. Ophthalmic Prisms: Measurement Errors and How to Minimize Them. Ophthalmology 1983;90:204-2010</pane>

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