over-refraction is a vision test done **over** an existing optical correction. It measures how your prescription changes when you are wearing glasses, contact lenses, or an implanted lens. It is commonly used during contact lens checks and after eye surgery. It helps clinicians understand what “extra” power is still needed for clear vision.

A landing zone is the part of an eye device or design that “lands” or rests on a specific eye surface. In eye care, the term is most commonly used in specialty contact lenses, especially scleral lenses. It describes how the lens edge or haptic aligns with the conjunctiva and sclera (the white of the eye). The goal is stable positioning with acceptable comfort and ocular surface health.

haptic most commonly means “related to touch” or tactile sensation. In eye care, haptic often refers to the supporting arms or structures on an intraocular lens (IOL) that help hold the lens in position inside the eye. The term is also used when discussing “haptic feedback” in surgical tools and training simulators, where touch-like force feedback helps guide fine movements. You may encounter haptic in cataract surgery discussions, lens implant design, and surgical education.

limbal clearance describes the space between a contact lens and the limbal area of the eye. It is most commonly discussed when fitting scleral and other specialty rigid contact lenses. In plain terms, it means “the lens is vaulting over the limbus instead of touching it.” Clinicians assess limbal clearance to balance comfort, eye health, and optical performance.

vault is a clinical term that describes the “clearance” or space between an eye structure and a lens or device. In eye care, it is most commonly discussed when fitting scleral contact lenses and implantable lenses. Clinicians use vault to judge whether a lens sits at a safe and effective distance from sensitive tissues. It is typically assessed during an eye exam using specialized imaging or microscope-based evaluation.

sagittal depth is a measurement that describes how “deep” a curved surface is relative to a chosen diameter. In eye care, it most often describes the shape of the cornea and front surface of the eye. It is commonly used in specialty contact lens fitting, especially scleral lenses. It can also be referenced in corneal imaging and anterior segment evaluation.

diameter is the straight-line distance across a circle, passing through its center. In eye care, diameter is used to describe the size of round or near-round structures in and around the eye. It is commonly recorded in millimeters during eye exams, imaging, contact lens fitting, and surgical planning.

base curve is a measurement that describes the curvature of a lens surface. It is most commonly discussed in contact lenses and relates to how the lens aligns with the front of the eye. It is usually recorded in millimeters and appears on contact lens packaging and prescribing information. In simple terms, it helps determine how a lens “fits” on the cornea.

fitting is the clinical process of matching an eye-related device to a person’s eyes and visual needs. It commonly applies to contact lenses, glasses, and specialty lenses used in eye disease. It can also refer to sizing and aligning ocular prostheses or visual aids for comfort and function. The goal is a device that works well optically and is tolerated by the eye and surrounding tissues.

corneal staining (contact lens) refers to a visible staining pattern on the cornea seen during an eye exam in someone who wears contact lenses. It usually appears after a dye is placed on the eye and the surface is viewed under a blue light. It is commonly used to evaluate the health of the corneal surface and how the contact lens is interacting with it. It is a clinical sign, not a diagnosis by itself.

tight lens syndrome is a contact lens–related fitting problem where a lens sits too tightly on the eye. It is most often discussed with soft contact lenses, but similar “tight fit” patterns can occur with other lens types. It can reduce normal tear exchange under the lens and limit lens movement with blinking. Clinicians use the term to describe a recognizable set of symptoms and exam findings linked to an overly tight lens fit.

corneal neovascularization (contact lens) refers to the growth of new blood vessels from the edge of the cornea toward its center in the setting of contact lens wear. The cornea is normally clear and does not contain blood vessels. When vessels grow into the cornea, it can signal long-term stress such as low oxygen exposure or inflammation. This term is commonly used in optometry and ophthalmology when evaluating contact lens fit, wear habits, and corneal health.

corneal hypoxia means the cornea is not getting enough oxygen. It most often comes up in eye care when discussing contact lens wear, eyelid closure during sleep, or corneal swelling. Clinicians use the term to explain certain symptoms and exam findings, such as blurred vision after lens wear or corneal edema. It is also used in teaching and research to describe how oxygen affects corneal health and healing.

peripheral ulcerative keratitis (PUK) is an inflammatory condition that causes a corneal ulcer near the edge of the cornea. It can lead to thinning (“corneal melt”) and, in severe cases, risk of perforation. PUK is commonly discussed in urgent eye care and in autoimmune or vasculitic systemic disease workups. Clinicians use the term to describe a specific pattern of peripheral corneal damage that needs prompt evaluation.

microbial keratitis is an infection of the cornea, the clear front “window” of the eye. It can cause pain, redness, light sensitivity, and blurred vision. It is commonly discussed in eye clinics and emergency eye care because it can progress quickly. The term is used by ophthalmologists and optometrists to describe corneal infection caused by microorganisms.

A corneal infiltrate is a localized area of inflammatory cells within the cornea. It often appears as a white or gray spot in otherwise clear corneal tissue. The term is commonly used during eye exams to describe a clinical finding, not a final diagnosis. It can be associated with infection, immune reactions, trauma, or contact lens wear.

giant papillary conjunctivitis (GPC) is an inflammatory condition of the inner eyelid surface that causes enlarged “papillae” (raised bumps). It is most commonly associated with contact lens wear, ocular prostheses, or exposed sutures. People often notice itch, mucus, lens intolerance, and a feeling of something in the eye. The term is used in eye clinics to describe a specific pattern seen on exam when the upper eyelid is gently everted.

contact lens-associated keratitis is inflammation of the cornea (the clear front “window” of the eye) linked to contact lens wear. It can range from mild irritation with small inflammatory spots to serious infection that threatens vision. The term is commonly used in eye clinics and emergency settings when a contact lens wearer develops a painful red eye. It is a clinical label that helps clinicians evaluate risk, choose tests, and plan follow-up.

contact lens overwear is wearing contact lenses longer or more continuously than intended for the specific lens type and the individual eye. It is a common, preventable contributor to contact lens–related irritation and complications. Clinicians use the term when evaluating symptoms like redness, pain, dryness, or blurred vision in contact lens wearers. It is discussed in optometry and ophthalmology as both a behavior pattern and a risk factor.

lens intolerance is a term used when a person cannot comfortably wear contact lenses for the desired amount of time. It commonly describes symptoms such as dryness, burning, redness, blurred vision, or a “foreign body” sensation while wearing lenses. The phrase is used in optometry and ophthalmology to summarize a pattern of symptoms and signs related to contact lens wear. It can be temporary (triggered by a short-term issue) or persistent (linked to ongoing ocular surface or eyelid conditions).