Astigmatism: an eye condition that usually results from a problem in the curvature of the cornea, preventing good vision at both far and near distances, resulting in a blurred and distorted image. Learn more about this eye disease.

Ablation: the removal of any organ or body part by an operation or surgical excision.

Accommodation: ability of the eye to change its refractive power so that rays of light are always focused on the retina, meaning it can see at various distances.

Visual acuity: the ability of the visual system to perceive, detect and identify objects under good lighting conditions.

Amblyopia or lazy eye: the partial loss of vision even with the best possible aids. It usually affects one eye, but it can be bilateral due to significant refractive errors in both eyes.

Aphakia: lack of a lens, due to congenital or acquired causes.

Ametropia: Refractive error (myopia, astigmatism, hyperoia, presbyopia…) The intensity of the defect is measured in dioptres.

Aberrations: optical defect due to which light from one point do not form a perfect image of that point passing through the optical system of the eye.

Blepharitis: is, as its name suggests, inflammation of the tissue that forms the eyelid. This is often due to a malfunction of the small glands on the edge of the eyelid.

Biometrics: the determination of the dimensions and dioptric power of the eye using ultrasound.

Cataract: the total or partial opacification of the lens. There are basically two types:

• congenital cataract: produced by the existence of a hereditary injury or a blow to the embryo during development.
• acquired cataract: the most common type and the leading cause of vision loss among people over 55, caused by the accumulation of dead cells in the lens. More information about cataracts

Cornea: a major anatomical portion of the eye. It is a transparent hemispherical structure located in front of the body of the eye. It allows the passage of light to the inner areas of the eye and protects the iris and lens.

Lens: a biconvex part of the eye lens located behind the iris and in front of the vitreous humour. Its main purpose is to allow the eye to focus on objects at different distances. This is achieved by an increase in curvature and thickness, a process called accommodation.

Topical eyedrops: a pharmaceutical treatment consisting of sterile solutions of one or more medicinal substances intended for instillation into the conjunctival sac.

Visual field: the space in which an object can be seen while the eye remains fixed in position.

Conjunctiva: a transparent mucous membrane lining the eyeball from the limbus to the conjunctival fornices. It helps to lubricate the eyeball, producing mucus and tears. Due to its exposure to external factors, it is particularly susceptible to trauma, infections and allergic reactions which may become inflamed and lead to conjunctivitis.

Dioptre: a unit expressed in positive or negative values ​​showing the refractive power of a lens.

Emmetropia: the perfect eye condition. Without any effort or the aid of lenses, the eye transmits a clear picture through the optic nerve to the brain.

Refractive Error: the dioptric power necessary to achieve emmetropia.

Epithelium: the fabric formed by one or several layers of juxtaposed cells which line all surfaces of the eye.

Strabismus: the deviation of the alignment of an eye relative to the other. It implies a lack of coordination between the eye muscles.

Glaucoma: an eye disease that defined as degenerative neuropathy of the optic nerve fibres.

Hyperopia or hypermetropia: a refractive eye disorder with impaired vision, producing convergence of light at a point behind the retina. An affected person has problems seeing at short distances and can see more clearly over long distances. Learn more about eye deficiencies such as hyperopia.

Vitreous humour: a gelatinous, transparent liquid that fills the space between the retina and the lens. It serves to dampen any possible traumas.

Iris: the coloured circular membrane in the eye, separating the anterior and posterior chambers. It has a central aperture of variable size that connects the two chambers: the pupil.

Intraocular lenses: lenses which are permanent surgically implanted inside the eye in place of the natural lens. They serve to aid with focusing after surgery such as for cataracts, for example. Learn more about intraocular lenses.

YAG laser: a laser which emits light near the infrared end of the spectrum (1064 nm) as high-energy pulses for very short periods of time. It is used mainly to destroy relatively transparent targets towards the back of the eye: posterior capsule, iris, anterior vitreous membranes.

Excimer laser: a laser that produces light at the ultraviolet end of the spectrum, allowing the surface of the corneal tissue to be modified in order to change its refractive parameters.

Tears: a liquid produced by the body’s lacrimation process to clean and lubricate the eye. They are primarily involved in ocular optics and normal functioning of the eye and structures. Any alteration of the tear influences visual acuity.

Myopia: the refractive state of the eye opposite of hyperopia in which the image is formed in front of the retina. It is considered one of the types of ametropia. A myopic person has difficulty focusing well on distant objects which can also lead to headaches and visual discomfort. Learn more about eye complaints such as myopia.

Macula: the part of the retina which specialises in fine detail, meaning we can read, see people’s faces, etc. It is located on the back of the retina and has an area of ​​approximately 5mm in diameter.

Floaters: these are an eye defect that occurs in vision as a set of spots, dots or filaments (often in the form of spiderweb) suspended in the visual field. These are opacities that form in the vitreous humour, the gelatinous fluid that fills the eyeball, which cast shadows on the retina.

Nystagmus: involuntary and uncontrollable eye movements. The movement may be horizontal, vertical, rotational, oblique or a combination of these. It is associated with a malfunction in areas of the brain responsible for controlling movement.

Dry eye: a reduction in the ability of the eyes to produce enough tears. Insufficient tear production can give the effect of turning the eye red, leading to pain and sensitivity to light.

Orbit: the bony socket containing the eyeball and its muscles, vessels and nerves.

Stye: an inflammation of the sebaceous glands of Zeis at the base of the lashes which may form inside or outside of the eyelid.

Presbyopia: often causing eye strain, this is a defect consisting of decreased focusing ability of the eye for objects are located at short distances, while long-distance vision is unaffected. More information on presbyopia.

Pupil: A black expandable and contractible opening at the centre of the iris which regulates the amount of light that reaches the retina.

Anterior pole of the eyeball: a point on the anterior surface of the eyeball in front of an imaginary frontal plane through the ora serrata.

Pachymetry: measurement of corneal thickness.

Retina: the innermost of the three layers of the eyeball which acts as the photoreceptor.

Intraocular tension: indirect measurement of intraocular pressure which also depends on the thickness and stiffness of the various layers of the eye. It is measured using a tonometer.

Tonometer: an instrument used for measuring intraocular pressure.