A visual field is the full area you can see while looking straight ahead. It includes central vision and peripheral (side) vision in each eye. Clinicians use visual field assessment to understand how vision is functioning beyond a standard eye chart. It is commonly used in eye care, neurology, and driving- or work-related vision evaluations.

color vision is the ability to detect and interpret differences in light wavelength as different colors. It is a normal visual function mainly supported by cone cells in the retina. It helps people recognize objects, signals, and subtle visual patterns in daily life. It is also used in eye care to support diagnosis and monitoring of certain eye and nerve conditions.

contrast sensitivity is the ability to see differences between an object and its background when the contrast is low. It complements visual acuity, which measures how small a high-contrast letter you can read. It helps explain real-world vision problems like trouble seeing in fog, dim light, or glare. It is commonly assessed in eye clinics and research to evaluate visual function beyond the eye chart.

stereopsis is the brain’s ability to perceive depth by combining the two slightly different images from each eye. It is often described as “3D vision” or true binocular depth perception. Clinicians assess it to understand how well the eyes work together. It is commonly discussed in eye exams, strabismus care, and vision development in children.

binocular vision is the ability to use both eyes together as a coordinated system. It allows the brain to combine two slightly different images into one clear visual percept. It is commonly discussed in eye exams, strabismus (eye misalignment) care, and vision therapy. It also matters in everyday tasks like reading, driving, sports, and hand–eye coordination.

convergence is the coordinated inward movement of both eyes to look at a near object. It is a normal part of binocular vision, helping the brain combine two images into one. Clinicians assess convergence during eye exams when people report near-vision symptoms. convergence is also a key concept in strabismus care, prism prescribing, and vision therapy.

amplitude of accommodation is the eye’s focusing range from far to near. It describes how much the natural lens can change focus to keep near objects clear. Clinicians use it in eye exams to understand near-vision function and age-related changes. It is commonly discussed in presbyopia, eyestrain, and pediatric vision assessments.

accommodation is the eye’s natural ability to change focus from far to near. It happens mainly by changing the shape of the eye’s crystalline lens. It is commonly discussed in eye exams, reading vision, and presbyopia (age-related near blur). Clinicians also consider accommodation when evaluating eye strain, headaches, and binocular vision issues.

interpupillary distance is the distance between the centers of your pupils. It helps align lenses and optical devices with the way your eyes naturally look at the world. It is commonly used when making eyeglasses, fitting some contact lens setups, and adjusting binocular devices. Clinicians also document it as part of broader binocular vision and facial/ocular assessments.

pupillary distance (PD) is the distance between the centers of the two pupils. It is most commonly used to center eyeglass lenses so the optical zones align with the eyes. It can be measured for distance viewing and for near tasks like reading. It is a practical measurement used in optometry, ophthalmology, and optical dispensing.

A prism diopter is a unit used to describe how strongly a prism bends (deviates) light. It is commonly written as Δ and used in eye care to measure and prescribe prism. Prism is used in exams and in eyeglasses to help align images seen by the two eyes. You’ll encounter prism diopter in optometry and ophthalmology when discussing strabismus and double vision.

A diopter is a unit used to describe the focusing power of a lens or optical system. It is most commonly used in eyeglass prescriptions, contact lens prescriptions, and intraocular lens (IOL) calculations. It helps clinicians quantify how much a lens converges or diverges light to bring images into focus on the retina. You will usually see it written as “D” in clinic notes and prescriptions.

keratometry is a way to measure the curvature of the cornea, the clear front window of the eye. It produces “K readings,” which describe how steep or flat the central cornea is. Eye care clinicians use keratometry in routine eye exams and before many types of eye surgery. It is also a core measurement for fitting contact lenses and assessing astigmatism.

An autorefractor is a diagnostic device that estimates a person’s refractive error (focus) objectively. It helps determine whether the eye is more nearsighted, farsighted, or has astigmatism. It is commonly used in optometry and ophthalmology clinics, vision screening settings, and pre-testing areas. Its results often guide, but do not replace, a full eye exam and a final glasses or contact lens prescription.

retinoscopy is an eye examination technique used to estimate a person’s glasses prescription. It measures refractive error by observing how light reflects off the retina through the pupil. It is commonly used in optometry and ophthalmology clinics during routine vision exams. It is especially helpful when a patient cannot reliably read an eye chart or describe clarity.

subjective refraction is a vision test that finds the lens power that looks clearest to you. It relies on your answers to “Which is better, one or two?” while viewing letters or symbols. It is commonly performed during routine eye exams in optometry and ophthalmology clinics. The result is typically used to refine a glasses or contact lens prescription.

objective refraction is a way to measure refractive error without relying on a person’s answers. It estimates the lens power needed to focus light on the retina for clearer vision. It is commonly used in optometry and ophthalmology clinics, especially for children and patients who cannot give reliable responses. It is often paired with subjective refraction, where the patient fine-tunes the prescription by choosing which option looks clearer.

refraction is the process of measuring how the eye focuses light to produce clear vision. It is commonly used to determine a glasses or contact lens prescription. It is also used in eye clinics to document vision changes over time. In simple terms, it identifies whether the eye is “overpowered,” “underpowered,” or unevenly focused.

uncorrected visual acuity (UCVA) is a measure of how clearly a person can see without glasses or contact lenses. It describes “naked-eye” vision at a specific testing distance and under defined lighting conditions. Clinicians use it in routine eye exams, screening programs, and before/after comparisons in vision correction care. UCVA is recorded as a standardized value (such as Snellen or logMAR) so it can be tracked over time.

best corrected visual acuity (BCVA) is the sharpest vision a person can achieve with optimal optical correction. It is usually measured with glasses or contact lenses during an eye exam. Clinicians use it to separate blur from “needs a stronger prescription” versus blur from eye disease. It is commonly recorded in optometry and ophthalmology visits, pre-op evaluations, and clinical research.