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.
distance vision is the ability to see objects clearly that are far away. It is commonly discussed in eye exams, glasses and contact lens prescriptions, and driving or safety vision standards. Clinically, it is often measured as distance visual acuity and documented with standardized charts. It is also a practical way to describe how well the eye focuses light for far viewing.
near vision is the ability to see clearly at close working distances. It is used for tasks like reading, writing, sewing, and using a smartphone. In clinics, it is measured to assess focusing ability and to prescribe glasses or contact lenses. It is also considered when planning cataract or refractive surgery.
visual acuity is a measure of how clearly a person can see fine detail. It is commonly checked in eye exams using letter or symbol charts. Clinicians use it to document baseline vision and monitor changes over time. Patients often recognize it from results like “20/20” or similar formats.
vision is the process of seeing and understanding what the eyes detect. vision is commonly discussed in eye exams to describe clarity, comfort, and function. vision is also used in daily life to describe tasks like reading, driving, and recognizing faces. vision can refer to more than sharpness, including color, contrast, depth, and peripheral awareness.
The parasympathetic pathway is the part of the autonomic nervous system that helps the eye “rest and focus.” It controls pupil constriction, near focusing (accommodation), and contributes to tear production. It is commonly referenced in eye exams, neurologic evaluations, and when using certain eye drops.
The sympathetic pathway is a nerve network that helps control automatic functions in and around the eye. In eye care, it is best known for widening the pupil in dim light and helping hold the upper eyelid slightly open. Clinicians use knowledge of this pathway to interpret symptoms like unequal pupils (anisocoria) or a mild droopy eyelid (ptosis). It is also discussed when evaluating certain neurologic conditions, such as Horner syndrome.
cranial nerve VII is the facial nerve, a major nerve that controls facial movement and several gland functions. It helps close the eyelids, support normal blinking, and contribute to tear production. In eye care, it is commonly discussed when facial weakness affects the cornea (the clear front window of the eye). It is also used in neuro-ophthalmology exams to help localize neurologic problems.