Components/Devices Used: 

• Arduino Uno (or similar Arduino board) 

• Infrared (IR) Temperature Sensor (e.g. MLX90614) 

• DHT11 Temperature and Humidity Sensor 

• Breadboard 

• Jumper Wires 

• USB Cable for Arduino 

• Computer with Arduino IDE 

• Power Supply for Arduino 

Theory: 

DHT11 Sensor: The DHT11 sensor measures both temperature and humidity. It contains a thermistor for temperature measurement and a capacitive humidity sensor for humidity measurement. The sensor outputs a digital signal on the data pin. 

IR Temperature Sensor: The IR sensor, such as the MLX90614, is a non-contact thermometer that uses infrared radiation to measure temperature. It detects infrared energy emitted by objects and calculates their temperature based on the amount of IR energy emitted.

Arduino code for DHT11:

#include <dht.h>  // Include library

#define outPin 7  // Defines pin number to which the sensor is connected

dht DHT;      // Creates a DHT object

void setup() {

  Serial.begin(9600);

}

void loop() {

  int readData = DHT.read11(outPin);

  float t = DHT.temperature;  // Read temperature

  float h = DHT.humidity;   // Read humidity

  Serial.print("Temperature = ");

  Serial.print(t);

  Serial.print("°C | ");

  Serial.print((t*9.0)/5.0+32.0); // Convert celsius to fahrenheit

  Serial.println("°F ");

  Serial.print("Humidity = ");

  Serial.print(h);

  Serial.println("% ");

  Serial.println("");

  delay(2000); // wait two seconds

}

Arduino code for IR Sensor:

#include <Wire.h>

#include <Adafruit_MLX90614.h>

Adafruit_MLX90614 mlx = Adafruit_MLX90614();

void setup() {

  Serial.begin(9600);

  Serial.println("Adafruit MLX90614 test");  

  mlx.begin();  

}

void loop() {

  Serial.print("Ambient = "); Serial.print(mlx.readAmbientTempC()); 

  Serial.print("*C\tObject = "); Serial.print(mlx.readObjectTempC()); Serial.println("*C");

  Serial.print("Ambient = "); Serial.print(mlx.readAmbientTempF()); 

  Serial.print("*F\tObject = "); Serial.print(mlx.readObjectTempF()); Serial.println("*F");

  Serial.println();

  delay(500);

}

The Role of Corneal Curvature in Vision 

The cornea's curvature is pivotal in bending (refracting) light rays to focus them on the retina. The degree of curvature determines how effectively the eye can focus light. If the curvature is not ideal, it leads to refractive errors, meaning the light doesn't focus perfectly on the retina, affecting the clarity of vision. 

Common Refractive Errors Related to Corneal Shape 

• Myopia (Nearsightedness): Occurs when the cornea is too curved or the eyeball is too long, causing light rays to focus in front of the retina. This results in difficulty seeing distant objects clearly. 

• hypermetropia (Farsightedness): Happens when the cornea is too flat or the eyeball is too short, leading to light rays focusing behind the retina. This makes it hard to see close objects clearly. 

• Astigmatism: This is caused by an irregularly shaped cornea or lens. Instead of having a uniform curvature, the cornea or lens has different curvatures, causing light to focus on multiple points around the retina. This leads to blurred or distorted vision at all distances. 

Principles of Keratometry 

Keratometry is a technique used to measure the curvature of the anterior (front) surface of the cornea. 

• Light Reflection: The device projects a series of illuminated rings or mires onto the corneal surface. 

• Measuring Reflections: The keratometer measures the reflection of these rings from the cornea. Since the cornea acts like a convex mirror, the characteristics of the reflected image (like size and spacing) change based on the cornea's curvature. 

• Calculating Curvature: The keratometer uses the information from these reflections to calculate the radius of curvature of the cornea. The principle is based on the law of reflection and geometrical optics. 

• Output: The result is typically given in diopters, which is a unit of measurement that indicates the optical power of the cornea. The device may provide readings for different meridians of the cornea, especially useful in assessing and diagnosing astigmatism. 

Mathematically: 

In a simplified model, if you have the refractive power (D) of the cornea and the refractive index (n), you can use the formula,   

D= (n - 1)/r

where, r is the radius of curvature,  n is the refractive index of the cornea relative to air.

Discussion:

• SP (Spherical Power): This value reflects the overall refractive power of the cornea, assuming it has a spherical shape. It is typically given in diopters (D). The spherical power is primarily used to correct myopia (nearsightedness) or hyperopia (farsightedness) where the refractive error is evenly distributed across the cornea. 

• CY (Cylindrical Power): This represents the degree of astigmatism due to the difference in curvature between the flattest and steepest meridians of the cornea. It is also expressed in diopters. Astigmatism occurs when the cornea is not perfectly spherical (like a football) but has different curvatures (more like a rugby ball), leading to distorted or blurred vision. 

• AX (Axis): The axis indicates the orientation of the astigmatism in degrees, ranging from 0 to 180. It identifies the position of the flattest meridian of the cornea. For example, an axis of 90 degrees means the flattest meridian is vertical, and an axis of 180 degrees means it is horizontal. This information is crucial when prescribing cylindrical lenses to correct astigmatism. 

• R1 and R2: These are the measurements of the principal meridians of the cornea. Keratometers typically measure the two most different curvatures on the cornea, which are perpendicular to each other. R1 and R2 represent the radius of curvature for these meridians, usually given in millimeters. From these values, the keratometer calculates the corneal power in diopters for each meridian. The difference between R1 and R2 helps to determine the amount of corneal astigmatism. 

R1: Usually corresponds to the flatter (or least curved) meridian. 

R2: Usually corresponds to the steeper (or more curved) meridian.