| |
| Term |
Definition |
| A |
| Adverse
event |
General definition: unwanted effect(s) (i.e.
physical and/or psychological symptoms and signs) resulting from
treatment; any undesirable effect or problem that is present during
the period of treatment.
In contact lens practice, common categories:
- Serious adverse reaction = symptomatic adverse reaction of
sufficient clinical concern to warrant permanently discontinuing
lens wear and that produces or has the potential to produce
significant visual impairment.(eg MK)
- Significant adverse event = mostly symptomatic adverse reaction
of sufficient clinical concern to warrant temporary or permanent
discontinuation of lens wear.(eg CLPU, CLARE, IK, SEAL, CLPC,
Corneal erosion)
- Non-significant adverse events = asymptomatic adverse event
not of sufficient clinical concern; may not warrant discontinuation
of the patient from lens wear.(eg AIK, AI)
|
| Aftercare |
Regular examination of extended wear patients, consisting
of at least vision assessment, history and ocular examination with
and without the lenses in place using a biomicroscope slit-lamp;
recommended schedule for the first appointments after successful
lens fitting:
1. @ 24 hours
2. @ one week
3. @ one month
4. @ 3 months
Every three months thereafter, additional unscheduled appointments
whenever necessary. Also see Emergency
care. |
| Alcian blue |
A copper-staining dye that selectively stains mucus
and connective tissue. |
| Anoxia |
Complete deprivation of oxygen, suffocation. |
| Asymptomatic
infiltrate(s) |
Corneal condition including the presence of one or
more focal infiltrates (clusters of inflammatory cells),
less than 0.2mm in size. Asymptomatic infiltrates are commonly seen
in the periphery but may be observed anywhere in the cornea. The
infiltrates are limited to the anterior stroma and overlying epithelium
is intact. Bilateral events are common. The conjunctiva is normal.
No symptoms are present and therefore asymptomatic infiltrates are
usually only observed at routine aftercare visits. The condition
resolves rapidly with no sequelae. Asymptomatic infiltrates are
found in lens wearers and non-lens wearers. There is little variation
in the incidence with various modes of lens wear.
|
| B |
| Biphasic |
Having two phases or pathways for transmission
through the lens. In silicone hydrogel lenses, one phase allows
transmission of oxygen and the second phase allows transmission
of fluids and therefore ions, essential for good lens movement.
|
| C |
| CLARE |
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. Sometimes these
symptoms are not noticed until soon after waking. The condition
is usually observed unilaterally.
|
| CLPC |
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. |
| CLPU |
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. |
| Compliance |
The willingness to comply with instructions regarding
lens wear schedule, removals and care regimen. Compliance
with instructions is essential to maximize success with EW.
|
| Conjunctival
staining |
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. |
| Contact lens induced acute red
eye |
see CLARE. |
| Contact lens induced papillary
conjunctivitis |
see CLPC. |
| Contact lens induced peripheral
ulcer |
see CLPU. |
| Continuous
wear |
Wearing a contact lens constantly, safely and effectively
for up to 30 days and nights.
Also see Extended wear. |
| Corneal
distortion |
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.
|
| Corneal edema |
see Corneal oedema.
|
| Corneal neovascularization |
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. |
| Corneal
oedema |
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. |
| Corneal
scrape |
A sterile blade is commonly used to remove a small
amount of material from the edge/bed of a corneal lesion and placed
in various culture media to see if there is any growth of microbes.
If any growth occurs, this signals infection of the lesion, or microbial
keratitis (MK). Specific treatment can then be prescribed to prevent
escalation of the infection. |
| Corneal
staining |
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.
|
| Corneal swelling |
see Corneal oedema.
|
| Corneal
vascularization |
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.
|
| Corneal warpage |
see Corneal distortion. |
| CW |
see Continuous wear. |
| D |
| Daily disposables (DD) |
Single use lenses that are worn during the waking
hours and then discarded.
|
| Daily wear (DW) |
A lens wear schedule requiring daily or more
frequent removal for cleaning and other purposes. Lenses are not
worn during sleeping hours. |
| Debris |
Waste products located between the contact lens
and cornea. Post-lens tear debris has traditionally been considered
to have the appearance of amorphous cellular material. If substantial
amounts of debris are trapped under a lens, staining will be present
upon lens removal and fluorescein instillation. Post-lens tear debris
is a fairly common observation in patients who wear soft lenses
on an EW basis. It should not be confused with Mucin balls.
|
| Deposits |
An acquired protein and/or lipid film or haze on the anterior lens
surface. |
| Disposable
lenses |
Defined by the FDA as contact lenses worn for 1 week
of extended wear and those discarded daily (or after one-time
use). Defined clinically as contact lenses worn for 1 week of extended
wear and up to 2 weeks of daily wear. |
| Distortion |
see Corneal distortion.
|
| Dk |
Oxygen permeability of a contact lens material. Dk
usually depends on the water content of a hydrogel lens material
and the silicone content of a silicone hydrogel lens material.
Oxygen is more soluble in water than in PMMA, but far more soluble
in Silicone rubber than in water. Also known as P (permeability).
P = Dk = diffusion (D) * oxygen solubility (k)
Also see high Dk and low
Dk. |
| Dk/L |
see Dk/t |
| Dk/t |
Oxygen transmissibility of a contact lens material
with consideration of the thickness of the lens.
Dk/t = Dk / average thickness (L) of the contact lens. |
| DSCL |
Disposable soft contact lens.Also see Disposable
lenses. |
| E |
| Ectropionization |
see Lid eversion.
|
| Edge buckling |
see Edge lift. |
| Edge lift |
General definition in lens geometry: The distance between an extension
of the BCOR (back central optic radius) and the absolute edge of
the lens; when measured parallel to the optical axis, axial edge
lift (AEL); when measured along the radius, radial edge lift (REL).
The term is also used when the base curve of a lens is too flat
with the consequence that the edge of the lens is lifting excessively
so that lens alignment with the cornea is interrupted. Often the
lens will ride on the lower lid margin causing varying degrees of
discomfort. Edge lift does not reduce or settle with silicone hydrogel
lenses and the patient should not be fitted with lenses with this
appearance. If possible a steeper basecurve should be trial fitted
and assessed. Alternative expressions are lens fluting or lens buckling.
|
| Emergency
care |
The EW patient should have access to the practitioner
or a representative of the practitioner at all times in case of
an emergency such as CLPU or CLARE. 24-hour access
is considered as mandatory for undertaking EW practice. |
| Endothelial polymegethism |
Increase in size of corneal endothelial cells due
to structural damage of surrounding endothelial cells. The ratio
of the smallest to largest cells increases from 1:5 to 1:20. The
mosaic pattern of the endothelium becomes rather irregular with
cells of significantly differing sizes when viewed under specular
reflection. This irreversible condition is either age related (and
therefore physiological) or caused by long-term hypoxia (and
therefore pathological). |
| EW |
see Extended wear. |
| Extended
wear |
Originally referred to wear of contact lenses for
up to six nights and seven days without lens removal. The term EW
is now commonly used for continuous wear (CW). |
| F |
| Fluorescein |
Vital dye used to assess the integrity of cornea
and conjunctiva. Fluorescein stains the tear film and depending
on the tear film layer thickness, more or less green fluorescence
will be observed. A cobalt blue filter in the illumination system
of the slit lamp biomicroscope is necessary to excite the dye to
a green fluorescence. A yellow filter in or in front of the viewing
system of the slit lamp biomicroscope will enhance the visibility
of any fluorescent staining. |
| Fluorescein staining |
see Fluorescein, Corneal
staining, Conjunctival staining
and Staining |
| Flurexon |
High molecular weight fluorescein dye used to assess static and
dynamic lens fit of hydrogel lenses. A cobalt blue excitement filter
and a yellow enhancement filter are necessary in the illumination
and observation systems respectively. For optimal visibility, the
dye should be instilled on the back surface of the contact lens
before insertion of the lens. Minimal dosage is of importance because
higher amounts of the dye cause stinging and burning which results
in excessive tearing and therefore a false appearance of the lens
fit will be observed. |
| Fluting |
see Edge lift. |
| G |
| Gas plasma surfacing |
A technique employed in silicone hydrogel
contact lens manufacture to modify the lens surfaces in order to
improve the surface wettability and resistance to deposits. The
resulting surface treatment is an integral part of the lens and
cannot be easily "stripped" away from the base material.
|
| Ghost vessels |
see Corneal
neovascularization. |
| GPC |
Giant papillary conjunctivitis. See CLPC. |
| H |
| High Dk |
Term for contact lenses or contact lens materials
with Dk/t > 85 x 10-9 (cm x ml O2)/(s x ml x mmHg).
Also see Dk, Dk/t, Oxygen
demand and Oxygen supply.
|
| Hypoxia |
Reduced oxygenation of the corneal tissue causing
a variety of problems. The severity of the consequences depends
on the level and duration of hypoxia. Common signs of hypoxia are
corneal vascularization, corneal oedema and microcysts.
Any signs of hypoxia should be immediately addressed. In some cases
temporary or permanent discontinuation of lens wear is necessary
to prevent further damage. High Dk contact lenses should
be fitted to avoid hypoxic stress or to improve oxygen supply. |
| I |
| Infection |
Growth of microbes in or on one or more organs of
the body. Usually accompanied by inflammation. Corneal infection,
see Microbial Keratitis. |
| Infiltrates |
White or grey material in the normally transparent cornea, usually
composed of inflammatory leukocytes and/or invading microorganisms.
May be associated with symptoms.
See also Asymptomatic infiltrate(s)
|
| Infiltrative Keratitis (IK) |
Inflammation of the cornea characterised by focal
and/or diffuse sub-epithelial infiltrates with or without epithelial
involvement; some cases may slightly stain with fluorescein. Infiltrates
may occur anywhere in the cornea, but typically in the limbal area.
Patients with IK report mild to moderate irritation (foreign body
discomfort), mild hyperaemia and occasionally mild discharge. Lens
wear should be discontinued until full resolution occurs. The patient
should be monitored carefully over the first 24hours, but in many
cases no medication is required. In the long-term there may be a
small residual scar, depending upon the aetiology and depth of penetration
of the infiltrate. |
| Inflammation |
Non specific host response to tissue injury characterised
by swelling, pain, redness and heat. Tissue injury maybe due to
infection, toxins released by bacteria or mechanical trauma. |
| L |
| Lens adherence |
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. |
| Lens dehydration |
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.
|
| Lens fit |
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. |
| Lens fluting |
see Edge lift. |
| Lens movement |
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 |
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. |
| Lens wear modality |
see Lens wear schedule. |
| Lens
wear schedule |
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. Total wearing time
should not exceed 30 days.
DW: lenses are only worn
in waking hours, removed before sleep, cleaned and disinfected during
sleep and discarded after maximum 30 days. |
| Lens
wettability |
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). |
| Lid assessment |
see Lid eversion. |
| Lid eversion |
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. |
| Limbal vascularization |
see Corneal
neovascularization. |
| Lissamine green |
A vital stain that has a similar action to rose
bengal but does not sting on instillation. |
| Low Dk |
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. |
| Lubricating
drops |
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.
|
| M |
| Microbial
keratitis (MK) |
MK occurs as a result of infection of
the cornea by replicating microbes (bacterial, viral, fungal or
amoebae). In contact lens wear it is usually preceded by hypoxia
and/or an epithelial break. Contact lens wearers (particularly EW)
are more prone to develop MK. The most common microbe associated
with contact lens related MK, is a bacteria called Pseudomonas
aeruginosa. Symptoms include rapidly increasing pain, severe
redness, intense epiphora & photophobia. Paracentral or central
lesion(s) are observed with full thickness loss, raised edges and
an irregular appearance. Anterior chamber flare may also be present.
If the patient is wearing contact lenses, they must cease lens wear
and immediate medical management should be sought or instituted.
|
| Microcysts |
Small (15-50µm), irregular shaped inclusions
usually found in the paracentral to mid-peripheral zones of the
cornea. Observation is best with retro-illumination. Microcysts
show reversed illumination due to a suspected higher refractive
index than the surrounding tissue. A hypoxic mechanism has been
proposed for microcyst development involving a reduced epithelial
mitotic rate and a slower regeneration of the epithelium. Patients
refitted from low Dk lenses to high Dk silicone hydrogel
lenses may exhibit a temporary increase in microcysts. This "rebound"
effect is similar to that reported when patients discontinue low
Dk lens wear following a period of long term anoxia.
|
| Mucin balls |
Small discrete particles or plugs seen between contact lens and
corneal surface, composed mainly of mucin, tear proteins and lipids.
Mucin balls are round and vary in size and clarity. Smaller mucin
balls are generally 10-20µm in diameter and typically transparent.
Larger mucin balls, 20-50µm in diameter, tend to appear opalescent.
These 'deposits' may be either scattered or clumped. They do not
move as the lens moves, so they seem to be trapped against the corneal
surface. Lens removal and/or subsequent blinking causes them to
be dislodged leaving an indentation in the corneal surface which
resolves rapidly. |
| N |
| Necrosis |
The death of cells or tissues. |
| Neovascularization |
see Corneal
neovascularization. |
| O |
| Oxygen
demand |
The oxygen demands of the cornea are very high and
vary from individual to individual. Closed eye demands range from
as low as 1µl/cm²/h to as high as 10µl/cm²/h.
Demand increases with temperature. The epithelium is thought to
consume up to 95% of the oxygen available to the cornea. |
| Oxygen permeability (P) |
see Dk. |
| Oxygen supply |
In order to reduce the level of overnight corneal
oedema to a physiological level of 3.2% (the mean level of no
lens overnight oedema), the critical lens Dk/t would need
to be around 125 x 10-9 (cm x ml O2)/(s x ml x mmHg). |
| Oxygen transmissibility |
see Dk/t. |
| P |
| Patient history |
A careful history of the patient is necessary to
determine eligibility prior to fitting the patient with EW silicone
hydrogel contact lenses. Patients should provide detailed information
regarding their past ocular and general health. Motivational factors
and compliance with instructions need to be assessed and
addressed when the patient history is recorded.
EW
contra indications include:
- diabetes
- compromised immune system
- conditions that require steroid or other systemic medication
- severe seasonal allergies
- previous reactions to solutions or to hydrogel contact lenses.
Caution is advised with patients who have had previous episodes
of CLARE or CLPU. The risk of recurrence needs to
be taken in account in these cases. |
| Phase separation |
This is the term used to describe the situation where
the interconnections between chemically similar molecules in a material
are stronger than the adhesive connections between them and the
different molecules.
|
| Post-lens tear debris |
see Debris. |
| Post-lens tear
film (PoLTF) |
The PoLTF is the tear layer between ocular surface
and contact lens back surface. It is made up of a thin aqueous phase
(1µm) and of a compressed mucin phase (30-40µm). The
mucin phase is of unknown thickness but it is probably at least
marginally thinner than the pre-ocular tear film. The maintenance
of the integrity of the mucin layer is essential to safe contact
lens wear. The maintenance of the aqueous phase is essential to
controlling the viscosity of the PoLTF and facilitating the elimination
of back surface debris. The closed eye wearing period with it's
associated aqueous depletion and reduced lens movement produces
the most challenging phase in EW. The period immediately upon eye
opening is therefore the key recovery phase when PoLTF aqueous replenishment
takes place.
Regarding silicone hydrogels, the following clinical practice is
recommended:
Follow-up visits should take place in the morning and include the
evaluation of the PoLTF and the assessment of lens movement.
Patients should be instructed to carry out self-evaluation of lens
binding upon waking.
Non-viscous eye drops such as saline (preferably single dose eye
drops) should be dispensed for use upon waking.
Also see Lubricating drops.
|
| Pre-lens tear
film (PrLTF) |
The PrLTF is the tear layer on top of the contact
lens front surface. It is alternately in contact with the air and
tarsal conjunctiva. It is made up of an outer lipid layer and a
base aqueous layer. The aqueous layer is usually of reduced thickness
(3-4µm) compared to the pre-ocular aqueous layer (7µm).
|
| Push-up test |
The push-up test is a two-step assessment of
the lens dynamic performance to determine lens tightness:
1. The resistance to decentration is evaluated. For this the lens
is gently dislodged by digital upward manipulation of the lower
eyelid border against the lower edge of the contact lens.
2. When the pressure of the lower eyelid is removed type and speed
of the recentration movement are judged. |
| R |
| Red eye |
Increased volume of blood in the conjunctival
vessels results in an increased appearance of redness. Red eye
may be due to a number of different reasons.
Also see CLARE. |
| Removal frequency |
see Lens wear schedules. |
| Rose bengal |
An iodine derivative of fluorescein which
binds to mucus and cellular components. It is useful in the diagnosis
of dry eye, in which it is seen binding to degenerated cells on
the corneal surface. This dye often stings on insertion. |
| S |
| Scrape |
See Corneal scrape |
| SEAL |
Superior epithelial arcuate lesion. Thin arcuate white
lesion in the superior cornea; within 1-3mm of the superior limbus
between 10 and 2 o'clock. SEALs can be up to 0.5mm wide and from
1 to 5 mm in length, sometimes with heaped edges. Diffuse infiltration
underlying the lesion is possible. Unilateral or bilateral but usually
asymptomatic. Occurring symptoms may include edge awareness or irritation
and/or foreign body sensation. |
| Silicone hydrogel contact lens
material |
There are now two different materials of silicone
hydrogel lenses on the market: Balafilcon A (B&L PureVision)
and Lotrafilcon A (CIBA Focus Night&Day):
Balafilcon A is based on a homogeneous co-polymer of a vinyl carbamate
derivative of TRIS. TRIS is a monomer that has been successfully
used in the preparation of RGP lens materials. The water content
of Balafilcon A is 35% and the Dk/t is 110 x 10-9 (cm x ml
O2)/(s x ml x mmHg) at -3.00D.
Lotrafilcon A is based on a fluoroether macromer co-polymerized
with TRIS monomer and N,N-dimethyl acrylamide in the presence of
a diluent. It is a fluoroether-based silicone hydrogel having a
water content of 24% and a Dk/t of 175 x 10-9 (cm x ml O2)/(s
x ml x mmHg) at -3.00D.
|
| Sodium fluorescein |
see Fluorescein. |
| Staining |
The appearance of tissue disruption and other patho-physiological
changes in the front surface of the eye as revealed with the aid of one
or more of a number of dyes, such as fluorescein, rose bengal
or alcian blue. Also see Fluorescein,
Corneal staining and Conjunctival
staining. test |
| Superior epithelial arcuate lesion |
see SEAL. |
| Swab |
Sterile swabs (either cotton or calcium alginate)
are used to sample microbes on the tissue. The swab is removed from
its protective covering, slightly moistened with sterile saline
and passed along the tissue surface and then placed in a sterile
transport solution. On transport to the laboratory, the solution
is cultured onto various media to encourage growth of any microbes.
Common ocular sites for swabs include: upper bulbar conjunctiva,
lower lids, and fornix. |
| T |
| Tears |
see Post-lens tear film and Pre-lens tear film. |
| Tear layers |
see Post-lens tear film and Pre-lens tear film. |
| Tear exchange |
Outflow and inflow of tears at the lens periphery,
triggered by the movement of the lens upon blinking. Clinical guidelines
recommend that back surface debris accumulated during sleep must
be eliminated within two hours of waking.
Also see Post-lens tear film and Pre-lens
tear film. |
| U |
| Ulcer |
Pathological loss of substance of the surface of
the cornea, due to progressive erosion and necrosis of the tissue.
Also see CLPU and Microbial
Keratitis. |
| Undesirable side effects |
see Adverse event.
|
| V |
| Vacuoles |
Fluid filled vesicles (20-50µm). Almost circular,
intra-epithelial inclusions that show unreversed illumination indicating
a lower refractive index than the surrounding tissue. |
| Vascularization |
see Corneal vascularization. |
| W |
| Warpage |
see Corneal distortion.
|
| Wearing schedule |
see Lens wear schedule.
|
| Wearing time |
The number of consecutive days and nights that the
patient is able to wear the lenses before either a scheduled or
unscheduled removal.
Also see Lens wear schedule.
|
| Wettability |
see Lens wettability. |
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