Learn More about Components of Phoropter

Here are the essential parts of a phoropter, the fundamental instrument in optometry for diagnosing and correcting vision. Below, we detail each component and its function.

Components of a Phoropter

Parts of Phoropter

Lenses and Dials

A phoropter is composed of various lenses and dials, each serving specific functions to aid in the accurate assessment of refractive errors and other visual conditions. But what is a phoropter exactly? It is an instrument used by eye care professionals to measure an individual's refractive error and determine their prescription for eyeglasses or contact lenses. Let's delve into the different types of lenses and their functions.

Different Types of Lenses

Spherical Lenses:

Understand the Difference between Concave and Convex lens
  • Description: Spherical lenses are uniform in curvature and have the same optical power across their entire surface. They can be either convex (positive power) or concave (negative power).
  • Function: Spherical lenses are used to correct myopia (nearsightedness) and hyperopia (farsightedness).
    • Convex Lenses: These lenses are thicker in the middle and thinner at the edges. They converge light rays and are used to correct hyperopia, helping the eye focus on close objects.
    • Concave Lenses: These lenses are thinner in the middle and thicker at the edges. They diverge light rays and are used to correct myopia, aiding the eye in focusing on distant objects.
Understanding Lens with Example
  • Vehicles and Headlamps:
    • S (Source Vehicle): The vehicle initiating communication, equipped with two headlamps, TX1 and TX2, separated by a distance dc.
    • D (Destination Vehicle): The vehicle receiving communication, equipped with an imaging receiver (RX) mounted at the back.
  • Diagrams (a), (b), and (c):
    • (a) Direct Line of Sight (LoS) Communication:
      • This diagram shows the source vehicle (S) directly behind the destination vehicle (D).
      • The headlamps TX1 and TX2 transmit optical signals to the imaging receiver RX on vehicle D.
      • Distances L1 and L2 represent the direct line-of-sight distances from TX1 and TX2 to RX.
    • (b) and (c) Off-Center Communication:
      • These diagrams show scenarios where vehicle S is not directly behind vehicle D but is offset by a horizontal distance dx and vertical distances dy1 and dy2.
      • (b) illustrates the scenario with an angle θ1 and an offset dh.
      • (c) shows another perspective with the same angle θ1, illustrating how the distance dxdxdx affects the line-of-sight paths L1 and L2.
Key Points:
  • Lane Width (W): The two-lane road has lanes of width W.
  • Headlamp Intensity Pattern: Vehicle headlamps (TX1 and TX2) have an asymmetrical intensity pattern designed to provide full illumination to the front and sides while minimizing glare.
  • Optical Power (P_t): The headlamps transmit information with an optical power denoted by Pt.
  • Imaging Receiver:
    • Vehicle D’s imaging receiver (RX) consists of photodetectors (PDs) and lenses mounted at the same height as the headlamps.
    • These receivers focus the light from the headlamps for effective communication.
  • Alternative Receivers: Instead of conventional PDs, a polar detector with a specific radius r and responsivity R can be used for receiving the optical signals.

    Cylindrical Lenses:

    Understanding Cylindrical Lens
    • Description: Cylindrical lenses have a curvature in only one direction, resembling a slice from a cylinder. They are used to correct astigmatism, a condition where the cornea or lens has an irregular shape.
    • Function: Cylindrical lenses correct astigmatism by compensating for the uneven curvature of the eye. They have two main powers: one for the meridian requiring correction and one for the axis perpendicular to it. The lens bends light differently along one axis than the other, addressing the specific distortion caused by astigmatism. The adjustments for cylindrical lenses are also measured in diopters, the units of refractive power.
    General guidelines for contact lens fitting in patients with astigmatism


      Prism Correction for Binocular Vision Disorder
      • Description: Prisms are transparent optical elements with flat, polished surfaces that refract light. Unlike lenses, prisms do not have a focal length but shift the image position.
      • Function: Prisms are used in phoropters to assess and correct binocular vision disorders, such as strabismus (misalignment of the eyes). They can also help diagnose issues with eye coordination and alignment. By displacing the image, prisms help in measuring how well the eyes work together and can assist in determining the necessary corrective measures.
      Understanding Binocular Vision Disorder

        This diagram shows how the visual system in mammals processes information from the eyes to the brain. Here’s a simplified explanation:

        • Eyes (Retina): The journey starts at the retina in both the right eye (RE) and the left eye (LE), which detect light and send visual information to the brain.
        • dLGN (Dorsal Lateral Geniculate Nucleus): The visual information travels from the retinas to a part of the brain called the dLGN. Think of the dLGN as a relay station that organizes and sends this information further into the brain.
        • V1 (Primary Visual Cortex): From the dLGN, the information moves to the primary visual cortex (V1). The V1 is crucial for processing visual details like shapes, colors, and movement.
        • Ocular Dominance Columns: Within the V1, there are specific areas called ocular dominance columns. These columns process information from either the right or left eye, helping the brain create a cohesive visual picture.
        • Layers (L1, L2/3, L4, L5/6): The V1 is organized into different layers, each responsible for different aspects of processing visual information.
        • Deprivation Patterns (BD and MD):
          • BD (Binocular Deprivation): When both eyes are deprived of normal visual experiences, for example, by raising an animal in the dark.
          • MD (Monocular Deprivation): When only one eye is deprived of normal visual experiences.

        These deprivation patterns are used in research to understand how sensory experiences (or lack thereof) affect the development and adaptability (plasticity) of the brain's visual processing circuits. Essentially, scientists manipulate visual input to study how it impacts brain development and function.

        Function of Each Lens Type

        Spherical Lenses:

        • Correction of Myopia and Hyperopia: Pherical lenses are essential in determining the basic prescription for eyeglasses or contact lenses by correcting simple refractive errors. They are key components in the phoropter eye exam.
        • Focus Adjustment: These lenses help the optometrist or ophthalmologist identify the lens power that allows the patient to see clearly at different distances.

        Cylindrical Lenses:

        • Astigmatism Correction: Cylindrical lenses are crucial for diagnosing and correcting astigmatism. They address the uneven curvature in the eye that causes blurred or distorted vision.
        • Axis Identification: These lenses help in determining the precise angle (axis) at which the astigmatic correction needs to be applied, ensuring a clear and sharp vision.


        • Binocular Vision Assessment: Prisms are used to evaluate how the eyes work together. They can help identify issues like double vision or misalignment by shifting the visual field and testing the eyes' ability to align images correctly.
        • Therapeutic Use: Prisms can also be prescribed as part of vision therapy to help patients with binocular vision problems, aiding in the training of the eyes to work better together.

        Dials and Controls

        The dials and controls on a phoropter machine are used to switch between different lenses and adjust their power. Here are the key phoropter parts and their functions:

        Lens Power Dials:

        • These dials adjust the spherical and cylindrical lens powers. They allow the optometrist to fine-tune the lens strength by small increments to achieve the clearest possible vision for the patient.

        Axis Control Dial:

        • This dial rotates the cylindrical lenses to the correct axis for astigmatism correction. It ensures that the cylindrical power is applied at the proper angle to counteract the specific irregular curvature of the patient's cornea or lens.

        Prism Control Dial:

        • This dial adjusts the prisms within the phoropter. It allows the optometrist to measure the degree of image displacement needed to correct binocular vision disorders.

        Cross Cylinder Dial:

        • Used primarily during the fine-tuning of astigmatism correction, this dial helps in determining the precise power and axis of cylindrical lenses by flipping between two slightly different lens powers.

        By understanding the functions of these components, one can appreciate how the phoropter integrates various optical elements to provide a comprehensive assessment of a patient's visual needs.

        Adjustment Knobs on a Phoropter

        Explanation of Each Knob and Its Use

        A phoropter is equipped with several adjustment knobs and dials, each designed to control specific aspects of the vision testing process. Understanding the function of these knobs is crucial for accurately measuring and correcting refractive errors. Here’s a detailed explanation of each major knob and its use:

        Spherical Power Adjustment Knobs

        • Use: These knobs adjust the spherical lenses to correct myopia (nearsightedness) or hyperopia (farsightedness).
        • Function: By turning these knobs, the optometrist can increase or decrease the spherical power in small increments, measured in diopters (D). This helps find the optimal lens strength that allows the patient to see clearly at various distances.

        Cylindrical Power Adjustment Knobs

        • Use: These knobs are used to adjust the cylindrical lenses for astigmatism correction.
        • Function: They allow the optometrist to modify the cylindrical power, which corrects the uneven curvature in the cornea or lens that causes astigmatism. The adjustments are also measured in diopters.

        Axis Control Knobs

        • Use: These knobs rotate the cylindrical lenses to align them correctly with the patient’s astigmatism axis.
        • Function: The axis control knobs are marked with degree measurements (0 to 180 degrees) to ensure precise alignment. Proper alignment is critical for effectively correcting astigmatism.

        Prism Control Knobs

        • Use: These knobs adjust the prisms within the phoropter to assess and correct binocular vision problems.
        • Function: By adjusting these knobs, the optometrist can measure the amount of prism needed to correct issues like double vision or eye misalignment. The prism power is measured in prism diopters (Δ).

        Cross Cylinder Dial

        • Use: This dial is used during the refinement of astigmatism correction.
        • Function: It allows the optometrist to flip between two lens powers quickly, helping to fine-tune both the power and axis of cylindrical lenses. This dial is essential for precise astigmatism correction.

        PD (Pupillary Distance) Adjustment Knob

        • Use: This knob adjusts the distance between the optical centers of the phoropter lenses to match the patient’s pupillary distance.
        • Function: Proper alignment with the patient’s eyes ensures accurate vision testing and comfortable viewing. The PD measurement is crucial for creating lenses that align correctly with the patient’s eyes.

        Vertex Distance Control

        • Use: This control adjusts the distance between the lenses and the patient’s eyes.
        • Function: Maintaining an appropriate vertex distance ensures that the prescription lenses will provide the same vision correction when placed in eyeglass frames. It’s particularly important for high prescriptions.

        Auxiliary Components

        In addition to the primary lenses and adjustment knobs, parts of the phoropter include several auxiliary components that enhance its functionality. These features are used for specialized tests and measurements, helping to diagnose a wide range of vision issues. Here’s a detailed look at some of the key auxiliary components and their uses:


        • Description: Occluders are opaque paddles or plates that can be inserted in front of one eye to block vision completely.
        • Function:
          • Monocular Testing: Occluders are used to cover one eye during tests that need to be conducted on each eye separately. This helps in assessing the individual visual function of each eye.
          • Binocular Vision Tests: By alternating the occlusion between eyes, the optometrist can evaluate how well the eyes work together. This is crucial for diagnosing issues like amblyopia (lazy eye) and binocular vision problems.

        Maddox Rods

        • Description: A Maddox rod consists of a series of parallel cylindrical lenses or grooves mounted in a disc or paddle. When a patient looks through it, a point light source appears as a line.
        • Function:
          • Phoria Testing: Maddox rods are primarily used to diagnose phorias, which are latent misalignments of the eyes. During the test, the patient looks at a point light source, and the Maddox rod creates a line image. The optometrist assesses the position and orientation of this line relative to the light source to determine the presence and degree of phoria.
          • Binocular Vision Assessment: The Maddox rod test helps in evaluating the alignment of the eyes and their ability to maintain proper focus on a single object. It’s an important tool for understanding binocular vision and diagnosing strabismus (misaligned eyes).

        Rotary Prisms (Risley Prisms)

        • Description: These are adjustable prisms that can rotate and change their power. They are mounted on a dial that allows for smooth and precise adjustment.
        • Function:
          • Measuring Deviation: Rotary prisms are used to measure the degree of eye deviation in conditions like strabismus. By rotating the prism, the optometrist can quantify the angle of deviation and determine the necessary corrective measures.
          • Fusion and Suppression Tests: These prisms help in assessing how well the eyes work together (fusion) and identifying any suppression of vision in one eye.

        Jackson Cross Cylinder (JCC)

        • Description: The JCC is a lens with two different powers and orientations, mounted in a holder that can be flipped to switch between the two powers quickly.
        • Function:
          • Astigmatism Refinement: The JCC is used during the fine-tuning of cylindrical power and axis in astigmatism correction. The optometrist flips the JCC while the patient focuses on an eye chart, helping to pinpoint the most accurate correction for astigmatism.

        Red-Green (Duochrome) Filters

        • Description: These filters divide the visual field into red and green halves using colored filters.
        • Function:
          • Chromatic Aberration Test: The red-green test helps in refining spherical power. The optometrist asks the patient to compare the clarity of letters on red and green backgrounds. Based on which side appears clearer, adjustments are made to achieve the best possible correction.

        Polarizing Filters

        • Description: These filters can polarize light in specific orientations.
        • Function:
          • Stereopsis (Depth Perception) Testing: Polarizing filters are used in tests that evaluate depth perception and binocular vision. They help determine how well the eyes work together to perceive three-dimensional objects.

        These auxiliary components significantly enhance the diagnostic capabilities of the phoropter, allowing for a comprehensive assessment of various visual functions and conditions.

        The detailed components of phoropters are essential for precise eye care diagnostics. Phoropter by AngelUS enhances traditional tools with innovative technology and design, leading the way in the optical industry. For superior accuracy and patient comfort, explore more about their unique features on our blog about the Phoropter by AngelUS. This additional resource provides an in-depth look at how their phoropters stand out in vision testing.

        Frequently Asked Questions

        What are the lenses in the phoropter used for?

        The lenses in a phoropter are used to test your vision. By switching between different lenses, the eye doctor can determine which ones help you see most clearly and prescribe the right glasses or contacts for you.

        What does the "dial" on the phoropter do?

        The dials on a phoropter are used to adjust the lenses. They change the strength and position of the lenses so the doctor can find the best combination for your vision.

        What is the purpose of the "prism" in a phoropter?

        The prisms in a phoropter are used to check how well your eyes work together. They can help identify issues with alignment and coordination between your eyes.

        How does the "astigmatism dial" work?

        The astigmatism dial rotates cylindrical lenses to measure and correct astigmatism, which is when your eye isn’t perfectly round, causing blurred vision.

        What are the "cross cylinders" in the phoropter for?

        Cross cylinders are special lenses that help fine-tune the correction for astigmatism. They are used in a specific test where the doctor asks you to compare different lens orientations.

        Why does the phoropter have "PD adjustment"?

        PD adjustment stands for Pupillary Distance adjustment. It ensures that the lenses are properly aligned with the center of your pupils, which is crucial for accurate measurement of your vision.

        What is the "phoropter arm" and why is it important?

        The phoropter arm holds the device in front of your face. It can be moved up, down, and sideways to position the phoropter correctly, ensuring you are comfortable and that the measurements are accurate.