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It is used by optometrists and vision therapists to diagnose and manage conditions like phoria deviations, helping to improve binocular vision
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| Topic | Discription |
| Purpose / Target Users | Purpose: Used for measuring and training ocular deviations, assessing phorias, tropias, vergence ranges, and for vision therapy exercises. The prisms displace the image seen by one eye, allowing practitioners to measure the degree of ocular misalignment or stimulate fusional vergence during therapy. “Reversible” means each prism can be oriented either base in/out or up/down, depending on the test requirements. Target Users: Optometrists / Ophthalmologists, Vision therapists and orthoptists, Optometry students for clinical training, Patients during binocular vision assessments or therapy sessions |
| Optotypes / Symbols | The prisms are used along with optotype charts (letters, symbols, or fixation targets). The optotypes themselves depend on the test being performed (e.g., Snellen chart, Maddox rod, Worth four-dot, etc.) The prisms simply shift or split the visual image, enabling the clinician to measure deviation angles or stimulate fusion and suppression control. |
| Scaling / Spacing | Scaling: The set includes a range of prism diopter (Δ) powers, typically from 1Δ to 40Δ, scaled in increasing increments for precision testing. Example: 1Δ, 2Δ, 3Δ, 4Δ, 5Δ, 6Δ, 8Δ, 10Δ, 12Δ, 14Δ, 16Δ, 18Δ, 20Δ, 22Δ, 25Δ, 30Δ, 35Δ, 40Δ, etc. Spacing: Each prism is individually housed and clearly marked for easy identification and accurate selection during sequential testing. |
| Range of Acuity / Line Sizes | The prisms themselves do not define acuity or line sizes, but they are compatible with any acuity chart or target. The optical clarity of the prisms ensures that test symbols (letters, dots, etc.) remain sharp and undistorted at all acuity levels, even with higher prism powers. |
| Testing Distance | Near testing: Typically performed at 40 cm (for convergence and near phorias). Distance testing: Conducted at 6 m (20 feet) for distance deviation measurement. The prisms function effectively at all standard optometric test distances. |
| Physical Size & Dimensions | Each prism is a rectangular or wedge-shaped optical glass block, about: Length: 30–35 mm Width: 20–25 mm Thickness (varies with prism power): 5–20 mm The set of 22 pieces is stored in a protective foam-lined case, typically measuring around: Case size: ~25–30 cm (L) × 20 cm (W) × 4–5 cm (H) |
| Mounting / Display Features | Loose prisms: Handheld, allowing flexible placement before either eye. Reversible orientation: The base direction can be flipped (e.g., base-in/base-out or base-up/base-down). Each prism is engraved or labeled with its power (in prism diopters) for easy identification. Some sets include metal or acrylic handles for convenient holding during testing. |
| Included Accessories / Extras | 22 individual prisms of increasing strengths. Protective wooden or hard-plastic case with velvet or foam lining to prevent scratching and maintain alignment. Printed prism power chart or reference guide (sometimes included). Optional calibration certificate (for professional-grade or ISO-certified sets). |
| Durability / Material Qualities | Material: High-quality optical glass or acrylic (PMMA) with precise wedge angles. Finish: Polished surfaces for distortion-free image transmission. Edges: Smoothly ground to prevent injury and chipping. Durability: Glass prisms are scratch-resistant and optically stable. Acrylic prisms are lighter, shatter-resistant, and safer for pediatric or field use. Storage: Case ensures protection from dust, moisture, and impact. |
| Usability / Marker of Quality | Usability : Easy to handle, reversible, and clearly marked for fast clinical use. Compact and portable for both in-clinic and academic settings. Compatible with most binocular testing devices (Maddox rods, synoptophore, fixation targets, etc.). Markers of Quality: ISO or CE certification for optical instruments. Accurate prism power calibration (within ±0.25Δ for low powers, ±0.5Δ for higher powers). High transparency and minimal chromatic aberration. Smooth, polished surfaces and durable case. Consistent labeling and reversible design ensure clinical reliability. |
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