Immobility of a lens on the eye – often observed immediately on eye opening after sleep with silicone hydrogel lenses. Normal movement patterns are gradually established after eye opening so that binding is usually not observed at an aftercare visit. Binding might occur when the aqueous layer of the post-lens tear film is decreased over night, leaving the tear film viscous and adhesive. Lens adherence is also observed in poor fitting RGPs.
Evaporation of the pre-lens tear film, consequently causing the lens to lose moisture to the environment. More common with higher water content and ionic lenses. May be related to dryness/discomfort symptoms reported by the patient. Pervaporation of the post-lens tear film may result, which has been shown to be more dramatic in high water content (>50%), thin soft contact lenses. A possible sign may include corneal staining in the lower third of the cornea. May be reduced with silicone hydrogel materials due to their high Dk, low water content and unique surface treatments.
Optimal lens fit includes 0.2-0.5mm primary gaze movement with good corneal coverage in all directions of gaze. Slightly loose fit (45-50%) on push-up test and no edge lift. Lens settling is uncommon and therefore initial impression is important. Also see Lens tightness.
Due to the higher rigidity of the new silicone-based materials, most lenses exhibit approximately up to 0.5mm of movement in primary gaze compared with approximately 0.2mm for DSCL.
Lens tightness can be examined with the push-up test. Using a continuous scale from 0 to 100 per cent, lens tightness of 50% indicates optimal lens behavior at push-up, 100% would indicate the lens is too tight (almost impossible to dislodge) and 0% would be a lens which is too loose (slides from the cornea without lid support). Lens tightness of slightly less than 50% (rather looser than tighter) is seen as desirable for silicone hydrogel contact lenses.
The lens wear schedule determines how many days and nights in a row the silicone hydrogel lenses should be worn without removal. This has to be carefully developed, for each patient individually, usually during the initial aftercare visits. The range may be from DW to flexible wear up to 30N EW. The actual wearing time can be shorter than the lens wear schedule prescribes. It might be necessary to advise patients to remove the lenses from time to time to clean them and rinse them if they are likely to develop deposits. The lenses should be discarded 30 days after opening the blister pack, regardless of whether they have been worn every day. Typical lens wear schedules are: • 6N EW: 6 nights in a row, then one night without lenses (lenses will be cleaned after removal and disinfected over night). This will be repeated over a period of a maximum of 4 weeks with one set of lenses. • 14N EW: 14 nights in a row followed by one night without lenses (lenses will be cleaned after removal and disinfected over night). After a further 14 nights in a row, there is one night without lenses. The next day a new set of lenses will be inserted. • 30N EW: 30 nights in a row, then one night without lenses before inserting a new pair of lenses the next day. • Flexible wear: lenses are worn on DW basis most of the time, but can be worn over night for up to x days. … [ Read More ]
Subjective assessment made after observations with the slit lamp biomicroscope. Takes into consideration the pattern in which the tears break over the contact lens, the speed of break up, the stability of the tear film, the lipid layer appearance and the non-invasive break up time (NIBUT).
To assess redness and roughness of the upper palpebral conjunctiva. At every aftercare visit lids need to be everted. Instillation of fluorescein can be helpful in the assessment of palpebral roughness. With lens wear, levels of both redness and roughness increase to slight or moderate levels. Depending on subjective symptoms this would be considered as acceptable. A localized or general CLPC response has been observed with silicone hydrogel lens wear.
The limbus is the junction between the cornea and the sclera of the eye. This is a vital area because it contains stem cells that constantly differentiate to replace the surface epithelium of the cornea. Damage to the limbus will show a marked decrease in the cornea’s ability to regenerate the surface epithelium and can lead to scarring and opacification of the cornea.
A vital stain that has a similar action to rose bengal but does not sting on instillation.
Term for contact lenses or contact lens materials with Dk/t between 18 and 25 x 10-9 (cm x ml O2)/(s x ml x mmHg). Also see Dk, Dk/t, Oxygen demand and Oxygen supply.
Unit dose or multi-dose comfort drops formulated for use with contact lenses. Patients should be advised to use lubricating drops often and liberally, especially before bedtime and upon awaking.