Ординатура / Офтальмология / Английские материалы / Medical Contact Lens Practice_Millis_2005

A full ophthalmic examination should be carried out annually, including intraocular pressure (IOP) and fundus examination.

A careful, detailed history and examination are essential for the proper diagnosis and management of any patient. Modern technology has

increased the information that can be acquired and has improved record keeping. Some instru mentation is expensive, but may reduce errors i diagnosis and fitting, and the time taken to fit con tact lenses, and patients are keen to attend a prac tice that is obviously up to date.

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4.Nakada S, Tanaka M, Nakajuna A. A comparison of automated and conventional keratometers. Am J Ophthalmol 1984;97:776–778.

5.Dave T. Current developments in measurement of corneal topography. Contact Lens and Anterior Eye 1998; 21(Suppl. 1): S13–S30.

6.Hubbe RE, Foulks GN. The effect of poor fixation on computer assisted topographic corneal analysis. Pseudokeratoconus. Ophthalmology 1994;10: 1745–1748.

7.Szczotka LL, Thomas J. Comparison of axial and instantaneous videokeratographic data in keratoconus and utility in contact lens curvature prediction. CLAO J 1998;24:22–28.

8.Seitz B, Behrens A, Langenbucher A. Corneal topography. Curr Opin Ophthalmol 1997;IV:8–24.

9.Bogan SJ, Waring III GO, Ibrahim O, et al. Classification of normal corneal topography based o computer-assisted videokeratography. Arch Ophthalmol 1990;108:945–949.

10.El Hage SG, Leach NE. Tangential or sagittal dioptric plots: is there a difference? Int Contact Lens Clin 1999;26:39–45.

11.Caroline PJ, Andre MP, Norman CW. Corneal topography and computerised lens-fitting modules. Int Contact Lens Clin 1994;21:185–195.

12.Chan JS, Mandell RB. Contact lens base curve prediction from videokeratography. OptomVis Sci 1998;75:445–449.

13.Cox I. Digital imaging in contact lens practice. Int Contact Lens Clin 1995;22:62–66.

14.Meyler J, Burnett Hodd N. The use of digital image capture in contact lens practice. Contact Lens and Anterior Eye 1998;21(Suppl. 1):S3–S11.

Binder PS. Videokeratography CLAO J 1995;21:133–144. Corbett M, Rosen E, O’Brart D. Corneal Topography.

London: BMJ Books; 1999.

Maguire L. Keratometry, photokeratoscopy and computer-assisted topographic analysis. In: Cornea: Fundamentals of Cornea and External Disease, eds Krachmer JH, Mannis MJ, Holland EJ, pp 223–235. 1997. New York: Mosby; 1997.

Dave T. Current developments in measurement of corneal topography. Contact Lens and Anterior Eye 1998;21(Suppl. 1):S13–S30.

Martonyi CL, Bahn CF, Meyer RF. Clinical Slit-Lamp Biomicroscopy and Photo Slit Lamp Biomicrography, 2nd Edition. 1985. Ann Arbor, Michigan: Time One Ink.

Martonyi, CL. Photography of the cornea and external eye. In: Cornea: Fundamentals of Cornea and Externa Disease, eds Krachmer JH, Mannis MJ, Holland EJ, pp 283–304. New York: Mosby; 1997.

Seitz B, Beherens A, Langenbucher A. Corneal topography. Curr Opin Ophthalmol 1997;8:8–24.

Veys J, Davies I. Basic contact lens practice: assessment o corneal contour. Optician 1995;209:22–29.

lower late in the morning, and at the end of the day. Bron2 suggests that the secretory pressure in the ducts increases overnight to a critical level, which ensures delivery, the excess oil being discharged as blinking recommences.

As not all meibomian glands function simultaneously patients with meibomian gland obstruction should be advised to use heat and eyelid massage shortly after waking.

Aqueous layer

The aqueous layer of the tear film is formed from the main and palpebral parts of the lacrimal gland in the superolateral orbit, and smaller accessory lacrimal glands in the conjunctival fornices. Production is affected by the reflex responses of the gland.

Mucus layer

The mucus layer of the tear film contains many chemicals, some of which are mucins. Originally believed to be formed entirely by the goblet cells of the conjunctiva, recent studies4 have shown that surface epithelial cells of the cornea and conjunctiva also express a variety of mucins. The classical view that mucin lowers surface tension and improves wettability of the ocular surface has now been challenged,5,6 but it may improve the wettability of a damaged surface.

Figure 2.1 Unstable tear film stained with fluorescein, showing some epithelial staining.

Table 2.1 Factors contributing to the diagnosis of a dry eye

Symptomatic

Corneal or conjunctival damage in interpalpebral area Unstable tear film

Reduced secretion Increased evaporation

An unstable tear film is pathognomonic of a dry eye (Fig. 2.1) and may be due to alterations in the composition, volume or the hydrodynamics of the fluid.

A deficiency in one or more tear film layers and increased tear evaporation will cause a dry eye (Table 2.1).

BLINKING

The act of blinking spreads the tear film over the surface of the eye. This is mainly due to the action of the upper eyelid, which spreads the tear film from the superiorly-sited lacrimal and accessory lacrimal glands. In addition, as the eyelid closes, it dips into the tear reservoir formed at the margin of the lower eyelid, and spreads this over the ocular surface as the eyelids open.

The mainly horizontal movement of the lower eyelid assists in the expulsion of tear film from the eye via the nasolacrimal duct. The movement of the globe also aids distribution of the tears. Inadequate and incomplete blinking is a common cause of symptoms in the contact lens wearer.

DEFINITION OF DRY EYE

A dry eye was defined by the National Eye Institute/Industry workshop in 1993/1994. “Dry eye is a disorder of the tear film due to tear deficiency or excessive tear evaporation that causes damage to the interpalpebral ocular surface and is associated with symptoms of ocular discomfort.” 7

Lemp7 points out that some modification of this definition may be necessary in certain circumstances. He cites ocular surface damage that may extend beyond the interpalpebral area, patients who are asymptomatic but meet all other criteria for dry eye, and patients who have symptoms, but in whom signs, as demonstrated by current methods, may be absent.

Table 2.2 Symptoms of dry eye

Gritty irritation Foreign body sensation

Burning and/or stinging Photophobia

Symptoms usually worse as day progresses, but may be present on waking

Classification

The workshop7 classified dry eye disease as:

●tear-deficient dry eye, which includes Sjögren’s and non-Sjögren’s disease due to an aqueous deficiency

●evaporative dry eye, including contact lensrelated dry eye.

Symptoms

The ocular surface does not contain specific receptors for dryness and patients therefore complain of a wide variety of symptoms (Table 2.2).

It is thought that a diurnal variation of symptoms and exacerbation by certain activities are indicative of dry eye disease.8 Symptoms usually become worse during the day, but may be present on waking, which may reflect reduced aqueous production during sleep. Long periods of reduced blinking (e.g. during reading, VDU use, or driving), as well as air conditioning and the low humidity in aircraft cabins all exacerbate the condition. Iatrogenic causes of dry eye include systemic and topical drugs, and certain autoimmune diseases are associated with Sjögren’s disease.

Diagnosis

A questionnaire is useful in assessing symptoms,9,10 while vital staining identifies ocular surface disease. Measurement of the tear film break-up time (TBUT) provides an assessment of tear film stability. Ideally osmometry is also carried out to measure tear osmolarity.

Assessment of ocular surface damage

Fluorescein Fluorescein 1% or 2% is a nontoxic dye, and staining by it indicates increased epithelial

permeability of the cornea or conjunctiva. I will stain punctate and ulcerative lesions and, by coloring the tear film, will outline nonstaining raised lesions.

Fluorescein eyedrops should be applied in smal quantities either with a sterile disposable appli cator, or by using a fluorescein-impregnated strip The strip is wetted with a drop of sterile Minims saline, the excess is shaken off and the strip i touched to the lower fornix.

An improved view can be gained by using yellow barrier filter such as the Kodak Wratten 1 with the cobalt blue light of the slit lamp.

Fluorescein should be washed from the eye by irrigating with sterile normal saline before sof contact lenses are reinserted. If the stain does colo the lens the patient may be reassured that th color will be removed by cleaning the lens, partic ularly if a hydrogen peroxide system is used, bu that it may take 2–3 days to resolve if staining i severe.

Rose Bengal Rose Bengal stains dead and degen erating conjunctival cells and corneal epithelia filaments a dark pink. It is toxic to the epithe lium and causes pain on instillation so only very small amounts should be used and it may b necessary to use topical anesthesia to relieve th symptoms, but the effect of the topical anesthesi may wear off before that of the Rose Benga stain.

If Rose Bengal gains entry to a soft contact lens i cannot be removed. In the USA Rose Bengal i available as a strip, but in the UK only as Minims Rose Bengal. Rose Bengal staining is more sensitiv and more specific in detecting patients with dry eyes than either a reduced TBUT or Schirmer’ test,11 but causes considerable discomfort.

Lissamine green Lissamine green is similar t Rose Bengal in that it is seen best over the scler and least over the dark iris, but it is better toler ated. At the present time it is not commercially available in the UK.

Grading surface damage Surface damage o the cornea and conjunctiva is best recorded using a grading scheme in which each area is graded from 0 to 3 and the final score is the sum of al areas.12

Assessment of tear film stability

There are several methods to assess TBUT.

TBUT with fluorescein (FTBUT) This is carried out using a small quantity of fluorescein, which is instilled into the lower fornix using an applicator. The patient is asked to blink and then keep the eyes open. The time taken for the first defect in the stained tear film to appear is recorded as the FTBUT. The tear film is best viewed using a blue exciter and a yellow barrier filter. The use of fluorescein shortens the noninvasive break-up time (NIBUT) for 2 minutes after instilling the stain.13

NIBUT The NIBUT is the time taken between the last blink and the break-up of the reflected image of a target. A number of commercial instruments are available, such as the Keeler Tearscope, for making direct and indirect measurements.14 The videokeratoscope may also be used – the patient is asked to blink and the concentric, circular black and white mires are viewed on the screen and the time taken for the first distortion of the mires to appear is recorded.

Recording TBUT With the methods described above the TBUT is not affected by fluorescein or any reflex tearing due to its instillation, but Elliot et al.15 found considerable variability between:

●repeated trials of the same subject

●instruments

●subjects.

The method used should be recorded for each set of data and care must be taken in interpreting TBUT results from any source. Further work on the measurement is necessary to ensure accurate readings.

With either method any corneal irregularity will cause a break in the tear film at that site, but these localized areas are usually easy to identify clinically on the slit lamp.

A regular recording of an FTBUT or NIBUT of less than 10 seconds indicates a dry eye.

Aqueous tear flow

strip of filter paper is placed with its tip in the lower fornix, and the length that becomes wet in a given time is measured.

Schirmer I test – without anesthetic This measures the reflex tear secretion, but the result depends on temperature, humidity and evaporation, so these values need to be reasonably consistent for all tests. Avoid touching all but the end of the strip to prevent skin secretions affecting the result. The patient should blink normally during the test. A dry eye is present if less than 5.5 mm of strip is wetted in 5 minutes.

The Schirmer I test with anesthetic gives a lower value than without anesthetic. It was believed to measure basal secretion rate in the absence of a reflex component, but this is now in doubt.

Farris16 suggests that the Schirmer I test is useful to estimate the production of reflex tears in contact lens wearers.

Schirmer II test – with nasal stimulation This test assesses the accessibility of the lacrimal gland to reflex stimulation. The test involves rigorous nasal stimulation and is unpleasant to perform.

Phenol red thread test A thread impregnated with phenol red is inserted into the temporal side of the lower fornix for 15 seconds. The alkaline pH of the tears changes the color of the wetted length of the thread from yellow to orange. The wetted length is proportional to the aqueous tear production. Asbell et al.17 and Chiang et al.18 found this test to be more reproducible and more specific when compared to Schirmer’s test. Cho and Yap19 found that cotton thread tests were more accurate predictors of successful soft contact lens wear than NIBUT or BUT tests.

Tear film turnover

A Schirmer test lasting 1 minute is performed every 10 minutes after instilling 5 l of fluorescein. Persistent staining of the Schirmer strip indicates reduced tear turnover.

Aqueous flow is measured by Schirmer’s test, which may be performed with and without the use of a local anesthetic. For Schirmer’s tests a

Tear film meniscus

The tear film meniscus (Fig. 2.2) may be measured using the slit lamp with a graticule placed in

Figure 2.2 Shallow irregular tear prism.

an ocular, or by image analysis of the slit-profile meniscus.

Assessment of osmolality

The preocular tear film has a large surface area and greater evaporation and its molality is therefore greater than that of the tear film meniscus. Some believe20,21 that hyperosmolality of the tear film is the main factor in the symptoms and signs of all types of dry eye, but at the time of writing there is no simple method of testing available to clinicians.2

The multiplicity of tests available means that care should be taken to perform the tests to prevent one test interfering with another. If tear samples are to be taken these should be obtained first and the eye allowed to assume a basal secretion level before other tests are carried out. Tests not requiring topical anesthesia should be performed first. NIBUTs should be recorded, followed after an interval by FTBUT. The eye may then be examined for corneal or conjunctival staining. The fluorescein should be allowed to drain before a Schirmer test is carried out, and finally, if needed, Rose Bengal may be instilled.

TEAR FILM DISORDERS

Tear film disorders can be classified as aqueous deficiency, altered tear film lipids, mucus deficiency, and evaporative (Table 2.3).

Aqueous deficiency

Sjögren’s disease

Sjögren’s disease (Fig. 2.3) is a disease of th exocrine glands affecting the lacrimal and salivar glands. It may be primary or secondary:

●primary Sjögren’s disease is characterized b dry eyes and a dry mouth, a deficiency of aque ous, and autoantibodies in the blood

●secondary Sjögren’s disease exhibits the sam characteristics as the primary disease, but ther are clinical signs of autoimmune connectiv tissue disease, most commonly rheumatoi arthritis, but also systemic lupus erythemato sus and polyarteritis nodosa.

Non-Sjögren’s disease

Primary non-Sjögren’s disease is a dry eye du to destruction of the lacrimal gland by cellula infiltration, resulting in reduced production o aqueous, but no signs of autoimmune disease Lacrimal gland infiltration resulting in secondar non-Sjögren’s disease may also be associated wit systemic diseases such as sarcoidosis, lymphoma AIDS or graft versus host disease (GVH).

Reduced stimulus or corneal sensitivity

Neurogenic dry eye may result from damage t the trigeminal nerve (cranial nerve V) or facia nerve (cranial nerve VII). Loss of corneal sensatio (normally provided by the ophthalmic division o the trigeminal nerve [cranial nerve V1]) results in reduction in reflex tear flow. Damage to the facia nerve, which provides secretomotor fibres to th lacrimal gland, reduces both basal and refle secretion.

Mucus deficiency

Conjunctival scarring conditions such as ery thema multiforme (Stevens–Johnson syndrome) cicatricial pemphigoid or thermal or chemica burns (Fig. 2.4) destroy the goblet cells and there fore reduce mucus production. This results i poor distribution and instability of the tear film across the ocular surface.

Altered tear film oil (or lipids)

Blepharoconjunctivitis (blepharitis)

The etiology of this common condition is unclear and its management is often difficult. There are three types of blepharitis, determined by the anatomy of the eyelids, namely anterior, posterior and mixed:

●the anterior affects the eyelid anterior to the gray line and may be staphylococcal, seborrheic (Fig. 2.5) or mixed

●posterior blepharitis affects the meibomian glands.

Anterior blepharitis

Staphylococcal blepharitis Staphylococcal blepharitis is caused by staphylococcal infection of the bases of the lashes. It is often associated with dry eyes and eczema. It causes itching and burning and is characterized by collarettes of hard scales surrounding the bases of the lashes. These often leave a bleeding ulcer when removed. In severe cases bacterial exotoxins enter the tear film, irritate the ocular surface, and can cause an epitheliopathy with punctate staining.

Seborrheic blepharitis Seborrheic blepharitis affects the glands of Zeis and the skin of the scalp and face. The scales may be greasy or dry and the lashes are greasy and stuck together (Fig. 2.6). It is a less severe condition than the staphylococcal form.

Posterior blepharitis (meibomian gland dysfunction)

Meibomian gland disease (MGD) In MGD ther is reduced or altered meibomian gland secretion with increased evaporation of tears. The ducts ar blocked, there is a thick, cloudy or granular secre tion, and there may be gland drop-out. Altered secretion can be responsible for irritated, red eye and reduced contact lens wearing time. The gland should be examined at each visit and the secretion should be expressed. Diagnosis and managemen are aided by clinical grading schemes.22

The flow of secretion may be improved by th use of warm compresses to the closed eyelids Eyelid hygiene should be improved to remov wax, debris and skin scales from the eyelid margin and lashes. In particular, the wearing of eye line and mascara, and the use of creams or moisturizer should be discouraged until the symptoms hav improved, and when recommenced must be care fully and completely removed. Wearers should b advised to keep brushes clean and to renew prod ucts frequently. MGD is a frequent cause of contac lens intolerance, but careful examination of the eye lids is often overlooked.

Association with dry eye

Blepharitis may be associated with a dry eye. It i believed that desquamating skin scales fall int the lower fornix and that skin lipid can break up normal tear film.

Figure 2.5 Blepharitis with blocked meibomian gland orifice and scales on the lashes.

Figure 2.6 Mild seborrheic blepharitis with blocked meibomian gland.

Treatment involves hot bathing to melt the wax at the gland orifices, and scrubbing the eyelid margins (e.g. with a flannel) to remove skin scales and debris from the bases of the lashes. Severe cases may require treatment three to four times a day initially, and this can be reduced when the condition is under control. Lubricating drops are useful if the eyes are dry.

For cases that do not resolve with simple measures, topical antibiotics such as chloramphenicol or sulphacetamide ointment can be rubbed into the clean eyelid margin when all the scales have been removed. Low-dose systemic tetracycline is helpful in cases of seborrheic disease.

In severe blepharitis peripheral vascularization and pannus formation may be seen in the cornea, and corneal thinning, with the possibility of perforation, and scarring may result.

Evaporative dry eye

In evaporative dry eye (Fig. 2.7) lacrimal gland function is normal, but evaporation of the tear film is greater than normal and the supply of fresh tear fluid does not meet the demand. It may be due to reduced oil production, eyelid distortion or contact lens wear.

Blinking

Inadequate blinking results in poor distribution of the lipid layer of the tear film and can be seen in:

●contact lens wearers, where it may result in three and nine o’clock staining if RGP lenses are worn

Figure 2.7 Corneal staining in evaporative dry eye.

●lagophthalmos

●those with systemic disorders affecting the eyelids, such as Parkinson’s disease.

Eyelid abnormalities

An inability to close the eyelid may result from injuries and scarring of the eyelids or from facial nerve injury. Exophthalmos due to thyroid disease, orbital tumor or aneurysm, may be sufficiently severe to prevent eyelid closure. Incomplete eyelid closure may also be seen during sleep (lagophthalmos).

Fitting patients with these eyelid abnormalities with a contact lens carries a high risk of infection. Treatment of the underlying condition may improve closure. Alternative treatments such as inserting a weight in the upper eyelid, or a lateral tarsorrhaphy, to reduce the palpebral aperture are often preferable. A lens may be fitted if adequate closure is obtained and the patient agrees to frequent supervision.

Contact lens wear

A reduced or altered tear film may affect contact lens wear. Soft contact lenses dehydrate on the eye and the higher the water content of the lens, the greater the evaporation which may take place over a prolonged period.23

Oxygen transmission (Dk/L) depends on the water content of a soft lens, so lenses with an adequate initial Dk/L may not provide sufficient oxygen at the end of the day, or during overnight wear. Dehydration has been found to be greatest in Group 4 lenses and least in Group 124 (Tables 2.4 and 2.5). The rate of dehydration is greater in thinner lenses than in thicker lenses, so minus lenses are likely to dehydrate more than plus lenses.

Soft lenses are always in a state of relative dehydration due to evaporation, and will replenish the fluid from the nearest available supply, namely the tear film. If this is already borderline or insufficient the eye may become clinically dry, with a reduced wearing time and sometimes lens loss.

Tomlinson and Cedarstaff25 found that evaporation in the non-contact lens wearing eye was least on waking and rose to a constant volume within 2 hours. They believed this to be due to

Table 2.5 Oxygen permeability. This part of the ISO code is a numerical designation, which categorizes the oxygen permeability in ISO Dk units at intervals considered significant in contact lens wear. For both lenses and materials the oxygen permeability is measured according to ISO 9913-1 or ISO 9913-2 and the Dk range is then denoted by one of the following numbers. Dk units are: (cm2/s) [ml O2/

(ml hPa)]. Derived from the ISO by the Association of Contact Lens Manufacturers and is reproduced by kind permission of the ACLM Contact Lens Yearbook

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low tear production during sleep or a thick lipid layer, which was present on waking. They thought that these factors were also responsible for lens adherence to the corneal epithelium, which is most common with overnight wear of lenses.

Studies have also shown a reduction in tear secre tion with age26 and this may lead to a deterior ation in lens tolerance (see Ch. 4).

Changes in the immunoglobulin content of th tear film have been reported with lens wear27 tha may be due to mechanical irritation.

MANAGEMENT OF DRY EYE IN

CONTACT LENS WEAR

Initially any meibomitis or blepharitis should b treated. Then medication should be stopped o reduced to a minimum and the condition of th eyes should be reviewed and the tear film com pared to the pre-treatment results. The idea tha the problems resulting from dry eye are due t increased tear osmolarity has resulted in new formulations of drops and their uses. Gilbard2 noted that dry eye disease evolved over time in sequence of four events (Table 2.6):

●Stage 1 – reduced tear production or increase evaporation

●Stage 2 – loss of conjunctival goblet cells

●Stage 3 – increased corneal epithelial desquamation

●Stage 4 – destabilization of the corneal–tea interface.