Ординатура / Офтальмология / Английские материалы / Medical Contact Lens Practice_Millis_2005

CHAPTER CONTENTS

Scleral lenses 121

Indications 121

Advantages and disadvantages 122 Fitting scleral lenses 123 Ventilation 123

Checking a scleral lens 123 Lens care 124

Prosthetic lenses 125

Lens selection 125 Patient management 127 Lens care 127 Complications 127 References 128

SCLERAL LENSES

The earliest contact lenses were blown glass sclera lenses; then molded ground glass lenses becam available, and 50 years later, in the 1940s, lense were made from PMMA. All these lenses cause hypoxia and required ventilation, and even the all-day wear was not generally possible. Cornea lenses superseded them, and later hydrogel lenses which made longer wearing times possible.

More recently Ezekial1 and Pullum2 have use rigid gas permeable materials to reduce hypoxi complications, improve wearing time, and toler ance of scleral lenses.

Scleral lenses are very large lenses (ofte 22–24 mm) that fit over the cornea and bulbar con junctiva. Few clinicians now fit scleral lenses, bu they still have a place in the armamentarium o the contact lens fitter for special cases, and a understanding of the uses of such lenses, their fit ting characteristics, and complications are neces sary. When considered suitable for a scleral len the patient can be referred to a clinician who ha made scleral fitting a speciality.

INDICATIONS

To improve vision

A scleral lens, with the liquid lens that form behind it, provides a new, smooth corneal surfac for keratoconus and scarred, irregular corneas They avoid the decentration associated with high powered lenses and, if painted, can reduce glar

in aniridia and albinism. Because they are stable on the eye it is possible to incorporate horizontal or base-up prisms in these lenses. This is not possible with conventional rigid or soft lenses because the weight of the prism will cause these more mobile lenses to rotate inferiorly.

They have largely been superseded by prosthetic RGP and hydrogel lenses, but are particularly useful for phthisical eyes. The eye is too small and soft to support the shape of other types of contact lens, but a good cosmetic result can be obtained with a scleral lens.

Therapeutic uses

Scleral lenses can improve ocular surface conditions and reduce discomfort, but do not tend to alter the natural course of any disease. They are helpful in dry eye conditions, such as Stevens– Johnson syndrome and ocular cicatricial pemphigoid. Sealed lenses, or those with channels, create a tear reservoir, which aids corneal hydration. Scleral lenses also prevent dehydration in cases of exposure that may occur in association with eyelid deformities and exophthalmos. They should not be used for proptosis.

Inadequate eyelid closure, which may be caused by a facial nerve (cranial nerve VII) palsy, is an indication for scleral lenses. Deposit formation and increased eyelid sensation result from the lack of blinking, and the lens may need to be removed at regular intervals during the day for cleaning. Therefore these patients often prefer a tarsorrhaphy or the insertion of a weight in the upper eyelid.

Scleral lenses may be considered for some patients with anesthetic corneas. These require very careful and frequent supervision because of the risk of serious infection from unnoticed trauma.

Protection

Severe trichiasis may benefit from a scleral lens and the lens can prevent eyelid margin keratinization.

Scleral shells

Scleral shells are unpowered and unpainted scleral lenses that can be used to maintain the fornix after chemical burns.

Prosthetic scleral lenses

Prosthetic scleral lenses are painted lenses designed to cover unsightly, blind or scarred eyes.

Sport

RGP lenses are easily lost in contact sports and in activities such as high diving scleral lenses are often preferred.

ADVANTAGES AND DISADVANTAGES

Because of their large size scleral lenses are not easily lost from the eye and there is less eyelid sensation because the edges rest in the fornices (Table 12.1). These lenses permit the formation of a preocular tear film behind the lens, which forms a liquid lens that minimizes the effect of corneal irregularity, and preserves moisture. They are longlasting and, because they are larger and thicker, and therefore more robust, they are easier to handle, particularly for the elderly. Topical medication is not contraindicated with these

Table 12.1 Advantages and disadvantages of scleral lenses

Advantages

Stable on the eye and are not easily lost

Less eyelid sensation than with smaller rigid lenses Possible to fit very irregular corneal topography Lens permits the formation of a precorneal tear film,

which preserves moisture

Longlasting and easier to handle for the elderly Topical medication does not pose a problem with these

lenses

Disadvantages

Lenses are very large and some patients find this unacceptable

Lens awareness may be caused by the mass of the lens Hypoxic change is common, particularly with PMMA PMMA lenses need ventilation that results in an air

bubble, which may occlude the visual axis

Fenestrated lenses may “settle back” and cause a tight fit

lenses, but high ocular concentrations may not be achieved.

FITTING SCLERAL LENSES

Scleral lenses may be fitted with preformed lenses, or by the impression method. Preformed lenses consist of an optic portion and a scleral portion and these elements may be present in a single lens or fitted separately. A single lens more nearly resembles the final lens, but needs to be filled with saline for insertion.

The impression method involves taking an impression, from the anesthetized cornea, using dental alginate. From this a cast or “stone” is made. A square of plastic is then moulded over the cast to form a scleral shell. The lens is then ventilated (see below) and the back optic zone radius (BOZR) is ground onto the posterior surface and the power is applied to the anterior surface.

The aim is to fit a lens that is aligned over the sclera and has corneal clearance. For scleral lenses clearance is more important than BOZR. Detailed descriptions of scleral lens fitting are available in a number of texts.3,4

VENTILATION

PMMA scleral lenses all need to be ventilated to minimize hypoxic change and improve wearing times. Various methods are used to achieve this

Figure 12.1 Scleral contact lens showing limbal air bubble and fenestration.

including, fenestration, channels, slots an truncation.

Fenestrations are the most common form o ventilation (Fig. 12.1). A counter-sunk hole, 0.5 mm in diameter, is drilled into the lens at the opti coscleral junction on the horizontal axis, where th limbal clearance is greatest, usually temporally Occasionally lenses are seen that have more tha one fenestration hole. Channels are grooves forme in the back surface of the lens that connect the opti portion with the lens edge. A slot is a crescent shaped cleft at the upper limbus in the area o transition. Truncating the lens superiorly will per mit greater access for air.

Channelled lenses are inserted filled with salin to prevent persistent bubbles, but fenestrate and slotted lenses permit an air bubble to form behind the lens. This is satisfactory providing tha the bubble is crescent-shaped, mobile in all pos itions of gaze, and does not interfere with th visual axis. Improved corneal hydration may b more easily achieved with channelled lenses Lenses without ventilation are known as seale lenses.

The hypoxia that has been associated with scle ral lenses has, in part, been relieved by the adven of gas-permeable scleral lenses. These are fitte using preformed lenses, which is a simpler proces than taking impressions. It is not possible to us the impression method, which requires heat, fo RGP lens manufacture. It is not usually necessar to ventilate the lens, so there is no air bubble, an the improved oxygen transmission has meant tha sealed lens designs give satisfactory results. There is less corneal swelling with these lense and the more gas permeable the material the les the swelling.6. If the sclera is very asymmetric it i possible to fit an optical portion into an impres sion-made PMMA scleral portion. RGP lenses ar more difficult to fit, and are more fragile for th patient to handle.

CHECKING A SCLERAL LENS

Few practitioners now fit scleral lenses, but ever clinic may see patients who are scleral lens wear ers, and should recognize fitting problems an complications. Many of these patients will still b wearing PMMA lenses.

The duration of the wearing time, and the number of periods a day the lens can be worn should be ascertained and the patient should be encouraged to report any symptoms, signs or problems.

Examination of the lens should ensure that:

●the limbal bubble, if present, moves freely, is crescent shaped, and does not intrude on the visual axis

●there is no evidence of blanching of the limbal or conjunctival vessels in any position of gaze

●there is adequate corneal clearance, as judged with the instillation of fluorescein, and a clear limbal transition zone

●the lens edges are smooth and intact

●the fenestration, if present, is patent

●when the lens is removed the cornea should be healthy with no evidence of staining, edema, infiltrates or vascularization – corneal touch may be unavoidable and is acceptable if it does not cause an abrasion.

improved by fenestrating the lens where the bubble is retained, or by refitting the lens.

Red eye

The cause of a red eye may or may not be lens related. If it is thought to be due to the lens, the lens should be either adjusted or refitted.

Hypoxic changes

In acute hypoxia epithelial and stromal edema may be seen. It is sometimes associated with a cellular reaction in the anterior chamber. Corneal hypoxia results in edema and neovascularization. The lens should be ventilated or changed for an RGP lens.

Corneal abrasion

The practitioner should check the method of insertion and removal and ensure there is no central touch.

LENS CARE

Lenses should be cleaned and disinfected using RGP solutions. PMMA lenses are best stored dry, but RGP lenses should be stored in solution.

Complications

Despite the problems associated with scleral lens wear many patients are very content to use them for short periods, for example sport, and they are the only method of obtaining satisfactory vision in a number of clinical conditions.

Mucus

As a short-term measure the lens can be removed and rinsed with saline. More importantly any clinical cause, such as allergy, should be identified and treated.

Frothing

Large bubbles may break up and cause a froth to form under the lens. The condition may be

Neovascularization

Neovascularization may be unrelated to the lens if it was present before the start of lens wear, or occurred as a complication of underlying disease. Alternatively the lens may be the cause or a contributory factor, due to hypoxia or the exacerbation of an underlying condition.

Ventilation should be reviewed or, if the lens is PMMA, a change to RGP should be considered.

Giant papillary conjunctivitis

Scleral lenses are worn for many years, often with long intervals between cleaning and polishing the lens. Therefore giant papillary conjunctivitis is not uncommon with this type of lens.

Exposure keratopathy

Exposure keratopathy can occur when there are static bubbles trapped beneath the lens. A localized area of dryness forms, which can be relieved by modifying the lens.

Table 12.2 Indications for prosthetic contact lenses

ACongenital defects Albinism

Aniridia

Cone dystrophies Congenital nystagmus Coloboma Microphthalmia

BAcquired defects Traumatic aniridia Anisocoria Heterochromia

Cataract/traumatic mydriasis Phthisical eye

Enophthalmos Diplopia Strabismus

PROSTHETIC LENSES

Prosthetic lenses are colored contact lenses used to camouflage a damaged or unsightly eye, to reduce light entering the eye, or to occlude the pupil. Clinical applications include congenital and acquired disease (Table 12.2). Most prosthetic lenses are soft lenses, but RGP and scleral lenses are also fitted.

Soft lenses may consist of:

●translucent tints

●black pupil with a clear periphery

●colored iris with a clear or black pupil.

These lenses may be iris print lenses or handpainted lenses and may have an opaque backing applied to exclude light.

Careful consideration of the individual case should determine whether the lens is needed for vision or for cosmetic reasons, or both.

LENS SELECTION

The simplest lenses are those that carry a translucent tint, which transmits light depending on the absorptive properties of the tint. High-water content lenses absorb greater amounts of dye and are best for dark eyes. Tints must be stable, nontoxic

and able to be disinfected by standard care sys tems. Clear lenses transmit 98% of light whil translucent lenses transmit 80%.7 Translucent tin lenses are available in a range of water contents They are surprisingly good at disguising leukoco ria and may improve the appearance in cases o bullous keratopathy where pupil definition is lost The color of the iris behind the lens must be take into consideration when the color is selected because it will influence the final result. Thes lenses are fitted in the same way as untinte lenses.

Laminated lenses

Laminated lenses may be printed or handpainted and may be made with or without an opaqu backing. The lens is formed from a layer o clear polymer on which the design is printed o painted, and a final layer of clear polymer is the applied. Printed lenses are available as standar designs, or designs can be made from template containing different elements of the design. Thes iris patterns can be superimposed on one another which permits a more individual lens to be made Opaque backing for handpainted lenses is mad from a barium salt and, in some cases, the qualit of the tears causes loss of the salt from the lens This can be reapplied at a small cost.

Printed lenses

Most printed lenses are only available in standar parameters, with pupils of 4.5 mm and are onl useful to cover localized scars. They are not gener ally available with a black pupil nor are they use ful as occlusive lenses.

Cantor and Nissel produce a high-water con tent lens (SCL-Match), which is opaqued and ca be obtained with either clear or black pupils. The are available in a standard range for pupil an total diameters. The iris pattern is selected b combining a series of patterns, which are superim posed on one another. The range is more limited i color, iris pattern, and lens parameters than hand painted lenses, but they are less expensive an useful in some cases.

Both printed and handpainted lenses are avail able as toric lenses.

Handpainted lenses

Handpainted lenses are generally high-water content lenses and there is a loss of 10% in oxygen permeability as a result of painting the lens. Following a full ophthalmic examination, including K-readings, a high-water content lens, of the same type as will eventually be fitted, is used as a trial lens. If the fit is satisfactory the pupil diameter is measured in a dim light and the horizontal visible iris diameter (HVID) noted. If only one eye is damaged these measurements should be taken on the other, normal, eye so that a good likeness should be achieved. If the lens is to be rendered opaque the lens parameters are supplied to the laboratory and a trial lens obtained, which is opaqued and of the correct power, but without iris details and with a clear pupil. This allows the fit, which may be altered with the opaque backing, to be reassessed and avoids expensive mistakes. Finally the color is matched (see below) and the definitive lens ordered (Fig. 12.2).

Handpainted lenses are available up to 22 mm in diameter, and pupils can be of any diameter. There may be some glare with very small pupils because the opaquing is present throughout the lens thickness. This may be improved by applying a black annulus around the pupil.

adequate occlusion or an opaqued iris patch can be painted round a smaller pupil to achieve occlusion. The opaque salt is slightly translucent and the final color obtained will depend on that of the underlying iris.

Offset lenses

Offset lenses may be used to mask a convergent or divergent squint (Fig. 12.3). A large, opaque, stabilized lens, with thin zones above and below, is used. The top and the geometric center is marked on a trial lens. The required position of the black pupil center, from the lens center is measured with the lens on the eye. The lens is then painted with an iris and scleral veins.

It is also possible to obtain a lens in which only a segment of iris is painted and this can be used for a localized defect. These are stabilized by dynamic stabilization.

Color matching painted lenses

To obtain a satisfactory color match takes time and patience, particularly if only one eye is to be

Occlusive black pupils

Occlusive black pupils may be any diameter, but it is often best to order larger diameter pupils to get

(A)

(B)

Figure 12.2 Effect of a painted soft contact lens.

(A)

(B)

Figure 12.3 Offset lens to correct appearance of strabismus.

fitted and it is necessary to match the other eye. The preferred method is to take digital photographs of both eyes. The laboratory supplies “color correction strips”, which consist of an “iris” without any detail, that can be sent, with the photographs to aid the artist in color selection. The lenses are then handpainted under daylight lights because tungsten lights alter color.

Details of the underlying defects are included in the information sent to the laboratory. These lenses are expensive, the delivery times are longer and they are not always easy to reproduce and the patient needs to be informed of these facts.

RGP lenses

Lenses need to be 11–13 mm in diameter to cover the iris (Figs 12.4 and 12.5). This reduces lens movement, but improves the cosmetic effect, and minimizes the risk of exposure of the patient’s iris

Figure 12.4 Aniridia.

with ocular movement and blinking, but reduce the tear pump effect. Painting the lens also dimin ishes the oxygen transmission. Handpainted RGP lenses may be color matched in the same way a soft lenses.

Scleral shell

Handpainted scleral lenses can replace missing volume and are useful in cases of microphthalmos enophthalmos and phthisical eyes. Shells ar also useful in strabismus, and for those with damaged eyelids, but they are not suitable fo proptosis.

PATIENT MANAGEMENT

The aims and expectations of the patient should b discussed at the initial consultation and the pos sibilities explained. Is the lens needed for vision or cosmesis? Are one or both eyes to be fitted? It i obviously much easier to obtain a good match i both eyes are fitted. Nevertheless consideration should be given to the risks of fitting an “only eye”. If an opaque back is needed the patient mus understand that there is likely to be a restriction o the visual field, which many find difficult.8

The potential number of visits should be dis cussed because several visits are necessary t obtain a good result.

When patients attend for fitting with thei lenses they tend to peer closely into a mirror and try to identify minor discrepancies in color or pat tern. They should be dissuaded from looking to closely, and the final result should be viewed a about a distance of 1 m, because this is how th lenses will appear to others.

LENS CARE

Surfactant cleaners and enzymes do not affec tints, but chlorine solutions will reduce the tint Hydrogen peroxide is the preferred care system for handpainted lenses.

COMPLICATIONS

glare with handpainted lenses that can be due to light scatter by the acrylic paint on the front surface or the opaque back.9 Bucci et al.10 noted a ring-shaped pattern of astigmatism with annular tinted lenses associated with a reduced visual acuity. It often occurs after lenses have been worn for months, or even years. A circular shadow may be seen on retinoscopy or using retroillumination on the slit lamp. They observed concentric rings of steepening and flattening on topographic difference maps that they believed was due to deformation of the cornea at the junction of the clear pupil and the inner margin of the tint. The greater the amount of pigment, the greater the distortion. The eye recovers if the annular tint is not worn and does not occur with a fully tinted lens.

Despite the opaque back, glare from above may still be a problem. A black annulus can be added to a handpainted lens to relieve the symptoms, or the patient can be encouraged to wear a hat with a brim or peak.

Patients who wear a lens with an opaque black pupil for intractable diplopia often find that it does not totally exclude the image. It may help to use a lens with an opaque iris and pupil with a high correction to further blur the image.

Abadi et al.11 found tinted lenses without an opaque back gave the best results in a small series of albinos.

The best cosmetic effect in a blind eye is often achieved using a plus powered lens, which increases the bulk of the lens.

1.Ezekiel D. Gas permeable haptic lenses. J Br Contact Lens Assoc 1983;6:158.

2.Pullum KW. Feasibility study for the production of gas permeable scleral lenses using ocular impression techniques. Trans Br Contact Lens Assoc 1987;4:35–39.

3.Mackie IA. Fitting Scleral Lenses in Medical Contact Lens Practice: A Systematic Approach, pp 7–17. Oxford: Butterworth Heinemann; 1993.

4.Buckley RJ, Pullum KW. Scleral Contact Lenses in Contact Lenses: The CLAO Guide to Basic Science and Clinical Practice, ed. Kastl PR. Iowa:

Kendall/Hunt Publishing Co; 1995.

5.Pullum KW. The unique role of scleral lenses in contact lens practice. Contact Lens and Anterior Eye 1999;22(Suppl.):S26–34.

6.Pullum KW,Hobley AJ, Parker JN. Hypoxic corneal changes following sealed gas permeable impression scleral lens wear. J Br Contact Lens Assoc 1990;13:83–87.

7.Stechler J. Fitting cosmetic contact lenses. J Br Contact Lens Assoc Trans Scientific Meetings 1991;14:81–83.

8.Spraul CW, Roth HJG, Gackle H, et al. Influence of special-effects contact lenses (Crazy-Lenses®) on visual function. CLAO J 1998;24:29–32.

9.Cox ND, Jenkins C, Lohmann C, et al. Pigmented contact lenses can contribute to glare in traumatic aniridia. J Br Contact Lens Assoc Transactions of Scientific Meetings 1992;15:151–153.

10.Bucci FA, Evans RE, Moody KJ, et al. The annular tinted contact lens syndrome: corneal topographic analysis of ring-shaped irregular astigmatism caused by annular tinted contact lenses. CLAO J 1997;23:161–167.

11.Abadi RV, Papas E. Visual performance with artificial iris lenses. J Br Contact Lens Assoc 1987; 10:10–15.

CHAPTER CONTENTS

Pain relief 129 Epithelial healing 130 Protection 131

Molding and splinting 132 Drug delivery 132

Lens selection 132

Fitting therapeutic contact lenses 133 Management of therapeutic contact

lens wear 133

Contraindications to therapeutic contact lens wear 134

Complications 134 Medication 134 References 134 Further reading 135

Therapeutic contact lenses (TCLs), often calle bandage lenses, are lenses used to treat specifi conditions, with the aim of relieving pain, enhan cing healing, improving hydration, providing pro tection and supporting or aiding the delivery o drugs. They are usually therapeutic soft contac lenses (TSCLs), but may be RGP lenses, or sclera lenses or made of silicone rubber. They may b used in a wide variety of conditions.

PAIN RELIEF

Pain relief is the most common reason for fitting TCL. Bullous keratopathy, filamentary keratiti and Thygeson’s superficial punctate keratitis al benefit from a high-water content lens fitted wit minimal movement and apical clearance.

Bullous keratopathy

Bullous keratopathy (Fig. 13.1) is a painful con dition that tends to occur in the elderly and pre dominantly in females. The cornea become waterlogged as a result of endothelial damage and blisterlike bullae form, which rupture an cause intense pain. A soft contact lens protects th exposed nerve endings and may flatten the bulla reducing them to epithelial edema. The pain i relieved almost immediately the lens is inserted but the course of the disease is unaltered and pai recurs when the lens is removed.1 Instilling hyper tonic (5%) saline drops may help to reduce th edema and improve vision.

Filamentary keratitis

Filamentary keratitis is common in very dry eyes (e.g. rheumatoid arthritis). Filaments consisting of desquamated epithelial cells and mucus threads are adherent to the cornea. Before fitting a contact lens, treatment with copious amounts of wetting drops should be tried. These should be aqueous rather than gel preparations. All filaments should be removed gently before the lens is applied and the lubrication should be maintained. Acetylcysteine eye drops, a mucolytic, may help to reduce the filaments.

Thygeson’s superficial punctate keratitis

In Thygeson’s superficial punctate keratitis, small, granular, white, nonstaining lesions occur in the cornea. The conjunctiva is unaffected and the patient complains of pain in a white eye. The disease is characterized by exacerbations and remissions, but eventually resolves spontaneously. Topical corticosteroids relieve the pain, as does closure of the eye or a soft contact lens.

Superior limbic keratoconjunctivitis

Superior limbic keratoconjunctivitis is an uncommon chronic inflammation that is typically seen in middle-aged women and may be associated with thyroid disease. The upper bulbar conjunctiva is

EPITHELIAL HEALING

Corneal epithelial dystrophies

In corneal epithelial dystrophies poor adherence of the epithelium to the stroma results in recurrent corneal erosions. Healing is promoted and pain relieved in Reis–Buckler’s, Meesman’s and Cogan’s dystrophies (Fig. 13.2).

Recurrent corneal erosions

Recurrent erosions are often caused by minor trauma from a baby’s fingernail or injury by a plant. They may recur over many months or even years. Meibomian gland disease has been associated with recurrent erosions2 because it alters the composition of the tear film. It should be treated before insertion of the lens. Any loose epithelium should be debrided before fitting the lens.

If the eye is dry a high-water content lens is preferred, but if tear supply is adequate, a thin lowwater content lens is fitted. It is necessary to leave the lens in place for two–three months for a new basement membrane to form. The patient must be warned that the erosion may recur after the lens is removed. To minimize this risk lubrication as drops or ointment should be continued for several months after cessation of wear. In particular ointment should be applied at night to prevent a dry eyelid sticking to the new epithelium during sleep because the eyelid may cause detachment of the epithelium as the eyes open on waking.