Contact lens induced acute red eye. Sudden onset, corneal infiltrative event observed during EW of hydrogel lenses which is always found associated with sleep. Patient reports generally include waking from sleep with symptoms of irritation or pain, redness and watery eyes. No symptoms are present prior to sleep. Sometimes these symptoms are not noticed until soon after waking. The condition is usually observed unilaterally.
Contact lens induced papillary conjunctivitis. Signs may range from mild hyperemia of the upper tarsal conjunctiva with a few, small papillae to severe hyperemia with large, raised papillae, which have a cobblestone appearance. CLPC may present as a localized or generalized response. Symptoms include itching and a stringy or ropy mucous discharge. Excessive lens movement or decentration and blurred vision may also occur. Lens material, design or fitting characteristics may need to be modified to prevent reoccurrence of this condition.
Contact lens induced peripheral ulcer. A circular, well circumscribed, dense, yellowish-white, focal corneal infiltrate (0.2-2.0mm in diameter) located in the peripheral to mid-peripheral cornea. It is always located in the anterior stroma and has a complete loss of overlying epithelium. Symptoms can vary, but may include pain or soreness, irritation and watering. The condition is almost always unilateral, consisting of a single lesion. Prognosis for healing is good. Typically the CLPU resolves to a circular, anterior stromal scar which persists for more than 6 months after the event. Some patients may not present with an “active” CLPU and the only evidence of the event may be the presence of the resulting scar.
The willingness to comply with instructions regarding lens wear schedule, removals and care regimen. Compliance with instructions is essential to maximize success with EW.
Fluorescein, lissamine green or rose bengal staining of the bulbar conjunctiva. A normal finding at low grades in most contact lens wearers, but may also be observed as a result of dry-eye conditions and/or due to microtrauma from the lens edge. The integrity of the bulbar conjunctiva should be assessed carefully with fluorescein at each contact lens aftercare visit. Conjunctival staining of grade 1 or 2 is considered to be normal or acceptable.
Wearing a contact lens constantly, safely and effectively for up to 30 days and nights. Also see Extended wear.
Often referred to as the clear front part of the eye, this tissue serves to bend light and helps focus light rays onto the retina. The cornea accounts for approximately 60% of the refractive power of the eye (the lens accounts for approximately 30-40%) and contains several layers that functions to help maintain transparency to light. The outermost layer is called the corneal epithelium, it is a protective barrier against the outside elements and prevents entry of micro-organisms and serves a small role in dehydrating the corneal stroma. It also contains glycoproteins that interact with the tear film. The corneal stroma lies beneath the corneal epithelium and is constructed of collagen arranged in a highly regular fashion. Disruption of fibre regularity, either as a result of trauma or edema will result in decreased corneal transparency. The corneal endothelium is the inner most layer of the cornea and its main function is to remove water from the stromal layer. In young patients, endothelial cells are arranged in an organized hexagonal pattern, but with aging, the arrangement becomes irregular as the number of endothelial cells decrease and endothelial pump function begins to decline.
Alteration of the corneal shape due to chronic hypoxia or poor lens fit. Often seen in patients with significant corneal astigmatism fitted with spherical, low permeability rigid lenses and long-term PMMA wearers. Also referred to as corneal warpage syndrome. Observed by keratometry, retinoscopy and corneal topography.
Vessel penetration at the limbus into the cornea beyond the translucent zone. The vessels may empty (ghost vessels) but the condition is irreversible and they will refill with the return of stress, usually of hypoxic nature. Localized neovascularization may appear subsequent to trauma or inflammatory events. When fitting a patient with silicone hydrogel lenses on an EW schedule, baseline neovascularization should not exceed 0.5mm.
Also called corneal swelling. Fluid diffuses into the stroma and interrupts the regularity of the stromal fiber structure, causing an increase in thickness (swelling) and loss of transparency. Usually occurs as a consequence to hypoxia or anoxia. Clinical signs include microcysts, corneal striae and/or stromal folds.
Occurs when fluorescein penetrates damaged cell membranes or when it fills gaps in the epithelial cell surface. Gaps are created when cells are damaged or displaced. There are a large number of reasons for corneal staining caused by lens wear including hypoxia, deposits, care products, lens fit, lens surface or edge irregularities, foreign bodies, and tear film disruption. The integrity of the epithelium should be assessed carefully at each contact lens aftercare visit. Attention should be paid to the extent, depth and type of staining. Corneal staining of grade 2 or more in any area of the cornea is considered unacceptable.
The contour of the cornea can be visualized using corneal topography. This is accomplished in a few ways. One method is to determine the radius of curvature for all regions on the surface of the cornea. Another method projects an imaginary spherical surface onto the anterior and posterior cornea, and the position of the surface of the cornea is expressed as a distance relative from the imaginary surface.
The normal existence of vascular capillaries at the limbus encroaching no more than 0.2 mm into the cornea from the limbus. Also see Corneal neovascularization.