Ординатура / Офтальмология / Английские материалы / Contact Lenses in Ophthalmic Practice_Mannis, Zadnik. Coral-Ghanem, Kara-Jose_2003

9. Spherical Hydrophilic Soft Contact Lenses 81

astigmatism is present, the spherical equivalent should be used in the determination of lens power. If the refractive error is greater than 4.00 D, a table for correction of vertex distance should be used. The central posterior curve induces little alteration in the final power of the contact lens. The use of trial lenses is highly recommended. Place the trial lens on the eye and perform a spherical overrefraction.

1.High water content and ionic contact lenses should be avoided in people whose eyes tend to form deposits.

2.The trial contact lenses should have the same characteristics as the contact lenses to be fitted.

Biomicroscopy and Overrefraction

At the slit lamp, one way to facilitate assessment of the lens–cornea relationship is to ask the patient to blink while facing forward and while looking to the side. The evaluation of the movement and overrefraction should be performed approximately 15 minutes after insertion of the lens. One should consider adequate movement as 0.5 to 1 mm of lateral movement and 0.5 to 1 mm of vertical movement with blinking.

4.What are the characteristics of a well-fitted contact lens?

●Adequate lens centration with full limbal coverage: Adequate lens diameter selection will result in approximately 1 mm of limbal coverage around the circumference of the lens.

●Movement should be assessed using the following techniques: Straight gaze: With the patient viewing in primary gaze, the lens

should move 0.3 to 1.0 mm with the blink.

Upgaze: When the patient is asked to look up, the lens should move

0.3 to 0.7 mm with the blink.

Push-up test: With the patient viewing in primary gaze, gently manipulate the patient’s lower lid to push the contact lens superiorly. The lens should move freely.

5.What are the signs and symptoms of a loose contact lens?

●Discomfort, even after a short period of time

●Excessive movement and displacement of the contact lens, compromising the visual acuity immediately after a blink. (Note: the view with retinoscopy and keratometry will also be distorted immediately after the blink by a loose lens.)

●Worsening visual acuity with blinking

82R. Uras and M.J. Rah

6.What are the signs and symptoms of a tight contact lens?

●Discomfort after several hours of use

●The visual acuity, keratometric mires, and retinoscopic view in a tight-fitting contact lens may be distorted but improve immediately after the blink.

●Minimal or absent movement of the contact lens

●Perilimbal conjunctival hyperemia

●Microcystic edema

●Diffuse edema

●In severe cases of hypoxia, the following may also be noted: Deep corneal folds

Blurred vision and/or halos around lights, produced by corneal hypoxia as a result of decreased diffusion of oxygen into the tear film

7.How does one follow the hydrophilic lens wearer?

The following testing should be completed at the follow-up visit for hydrophilic soft lens wearers:

1.Visual acuity measurement

2.Overrefraction

3.Assessment of the patient’s contact lens–related comfort

4.Evaluation of the length of wear

5.Evaluation of lens maintenance

6.Biomicroscopy (examination for microcysts, fluorescein staining of the cornea, infiltrates, neovascularization, edema, and erosions)

The follow-up care should be ongoing. The follow-up schedule depends on the sensitivities and individual characteristics of each eye. First-time contact lens wearers should be examined 2 weeks after the initial dispensing visit and then at 3- to 6-month intervals during the first year, depending on the wearing schedule and lens type. In wearers who intend to sleep with their contact lenses, the clinician should verify that there are no contraindications to extended wear. After initial intensive follow-up care (1 day, 1 to 2 weeks), the patient should have an ocular examination every 3 to 6 months, with immediate discontinuation of use at the first signs of any adverse effects on the cornea. For those wearers who do not intend to sleep with their contact lenses, an annual examination is sufficient. In follow-up examinations, the clinician should always verify that the instructions for contact lens maintenance are being adhered to. The patient must be conscientious about mechanical cleaning, enzyme treatment and disinfection, and these must be correctly performed to minimize risks. Many eyes are very sensitive and show signs of hypoxia and overwear. In these cases, wearing time with a contact lens of low permeability should be reduced to 4 to 6 hours per day. In these circumstances, it is imperative to change the contact lens for one of higher permeability if wearing time is to be

9. Spherical Hydrophilic Soft Contact Lenses 83

increased. For patients wearing disposable lenses, the schedule for lens disposal should be reviewed.

8.What are the signs and symptoms of a poor fit?

Some of the signs and symptoms of a poor fit have already been mentioned. They include, but are not limited to:

●Discomfort

●Blurred vision and/or variable vision with blinking

●Burning at the time of contact lens removal

●Excessive movement or immobility

●Decentration

●Perilimbal hyperemia

Close attention should be paid to complaints of halos, foreign body sensation, or itching. This may signify the presence of corneal hypoxia, epithelial erosions, or giant papillary conjunctivitis. An asymptomatic complication is corneal neovascularization, which may be observed at the biomicroscope and is caused by either a poor fit or inappropriate use of the contact lens (i.e., extended wear of a daily wear lens).

9.What is the basic trial lens set for fitting hydrophilic contact lenses?

The trial lens set should include pairs ranging from low to moderate myopic powers through 4.00-D hyperopic corrections in all available base curves. Clinicians should have an appropriate fitting set for each type of contact lens they wish to fit. Fitting sets and fitting guides are available from many contact lens companies and should be utilized whenever possible. Exceptional cases include patients with ametropias greater than 15.00 D, which generally require special trial lenses.

References

1.Stone RP. Why contact lens groups? Contact Lens Spectrum 1988;3:38–41.

2.Bruce AS, Little SA. Soft lens design, fitting, and physiologic response. In: Hom MM, ed. Manual of Contact Lens Prescribing and Fitting with CD-ROM,

2nd ed. Boston: Butterworth-Heinemann, 2000:179–213.

Selected Readings

Mandell RB, ed. Contact Lens Practice, 2nd ed. Springfield, IL: Charles C. Thomas, 1974.

Ruben M, ed. Soft Contact Lenses Clinical and Applied Technology. London: John Wiley & Sons, 1978.

10

Disposable and Planned

Replacement Contact Lenses

Nilo Holzchuh, Cleusa Coral-Ghanem,

and Timothy B. Edrington

1. What is a disposable contact lens?

The disposable contact lens is the result of the development of moldingbased manufacturing methods that make possible the production of uniform lenses at low cost. Clinically, they are called ‘‘disposable’’ because the contact lens is made of a hydrogel (soft lens) material that can be replaced after 1 day, 1 week, or 2 weeks or of a silicone hydrogel developed for extended wear and discarded monthly. Hydrogel lenses exchanged at intervals of every 3 or 6 months are often referred to as ‘‘planned or frequent replacement.’’ Literally, all contact lenses are planned-replacement or disposable. The eye care practitioner and the patient simply choose the optimum interval at which to replace them.

2.What are the indications and contraindications for disposable contact lenses?

Disposable contact lenses are indicated for the correction of myopia, hyperopia, astigmatism, and presbyopia, as well as for cosmetic purposes. They are routinely prescribed for:

●Allergic individuals with sensitivity to chemical lens care system products

●Individuals who wish to use lenses on an extended wear basis because of difficulty with maintenance, the type of work they do, or convenience

●Patients who frequently lose contact lenses or need spare lenses

●Patients who play contact sports

●Wearers who are exposed to pollutants

●Individuals who suffer from giant papillary conjunctivitis (GPC)1

●Individuals with lacrimal deficiency or who form excessive deposits on the contact lenses

10. Disposable and Planned Replacement Contact Lenses 85

●Therapeutic use

●Pediatric use Contraindications include:

●Anterior segment inflammation or infection

●Significant changes in the tear film

●Environments with chemical pollution

3.What are the basic types of disposable contact lenses?

One-Day Disposable Contact Lenses

These lenses are discarded daily or after a single use. The principal indications are for individuals who are sensitive to chemicals in their contact lens care products, who are unwilling to keep up the maintenance of the lenses, or who use the lenses only occasionally (part-time wear). Lens cost is generally higher for daily disposable contact lenses. However, the patient does not need to disinfect the lenses, thereby saving money on lens care products.

When compared to conventional daily wear, daily disposable lens wear has been reported to provide the patient with better subjective vision and overall patient satisfaction. Also, fewer corneal complications, lens deposits, and unscheduled visits have been reported.2

Oneto Two-Week Disposable Lenses

This type of contact lens was approved by the U.S. Food and Drug Administration to be discarded after 7 days of extended wear or 14 days of daily wear. It is currently the most prescribed disposable lens option in the United States. Patients using their lenses on a daily wear basis need to disinfect their lenses between uses. It is generally not necessary to add enzyme cleaning to the lens care regimen for patients replacing their lenses every 1 to 2 weeks.

Thirty-Day Disposable Silicone Hydrogel

Contact Lenses

A new generation of materials with oxygen permeability (Dk) values greater than 100 has been prescribed in parts of the world since 1999. These lenses are manufactured from a silicone hydrogel material with a treated surface that is more hydrophilic and more resistant to deposits. In this type of material, the aqueous phase functions to promote comfort and movement, while the silicone is responsible for the high permeability to oxygen. Even though these lenses were developed for continuous use over a 30-day period, many eye care practitioners prescribe them for daily wear use or recommend that the lenses be re-

86 N. Holzchuh et al.

moved once weekly for disinfection. Reduced lens handling should result in fewer torn and microbially contaminated lenses.

Planned Replacement Contact Lenses

Other replacement options exist for soft contact patients. Lenses marketed or prescribed for monthly and quarterly replacement are used generally to minimize lens cost for the patient. Enzymatic treatment should be added to the care regimens for patients replacing their lenses monthly or less frequently. Oneto 3-month planned replacement lenses have also been shown to reduce contact lens–induced complications and to increase patient satisfaction when compared to conventional lens replacement.3

Disposable and Planned Replacement Toric

Contact Lenses

This type of lens is an alternative for patients with significant refractive astigmatism.

Disposable Bifocal and Multifocal Lenses

Currently, aspheric and annular multifocal disposable soft contact lens designs are available. One of the advantages of fitting disposable multifocals is the availability of in-office lenses that the patient can try with minimal cost to both practitioner and patient. Before beginning the fitting, it is advisable to inform the patient that a bifocal/multifocal contact lens may not provide the same clarity as spectacles over the same range of distances and may be clearer at far than at near, or vice versa. Frequently, monovision provides better results. Monovision systems have been another factor in the development of disposable lenses because they allow trial fitting with the appropriate power for the patient and afford the opportunity to determine which eye is best corrected for near work.4

4.How does one fit a disposable contact lens?

The fitting of disposable contact lenses employs the same methodologies used with conventional hydrophilic lenses:

1.Perform a trial fitting with the appropriate lens for the patient. For this, it is recommended that practitioners stock different powers and curvatures that will facilitate fitting the largest number of patients.

2.Evaluate the fitting of the trial lens at the slit lamp after 15 minutes, the time usually necessary for stabilization of the contact lens on the eye. At this point, one should perform an overrefraction to determine the optimal lens power prior to dispensing the lens.

10. Disposable and Planned Replacement Contact Lenses 87

5.What are the advantages of using disposable contact lenses for therapeutic purposes?

●Frequent replacement with new, clean lenses

●Fewer lens surface deposits

●Simultaneous use with topical medication

●Reasonable cost

6.How should one follow disposable and planned replacement lens patients?

If the patient is planning extended wear, he/she should be examined:

●After overnight wear

●After 1 week of extended wear

●At the end of 1 month of extended wear

●Every 3 to 6 months

Patients who regularly sleep in their contact lenses should be examined every 6 months. In most instances, daily wearers can be examined on an annual basis. It is important to counsel a contact lens wearer about the necessity of complying with instructions regarding the length of time a contact lens is worn and its recommended disposal schedule in order to minimize complications. The responsibility of the eye care practitioner is to provide the patient with the appropriate lens and to provide appropriate follow-up care. It is extremely important that every contact lens patient with ocular complaints be reevaluated in order to avoid more serious ocular complications and the cessation of contact lens use. The patient should be counseled to regularly verify that his or her eyes are clear (not red), free from discomfort or pain, and that their lenses provide optimal vision.

7.What are the most frequent complications associated with disposable contact

lens wear?

Improper or neglected instructions concerning lens replacement schedules and lens care regimens may lead to unnecessary ocular complications. Poor compliance with lens replacement instructions was demonstrated in a survey of university students; 88.5% of disposable soft contact lens wearers did not adhere to their prescribed lens replacement schedule.5 Corneal infiltrates, contact lens–associated red eye, and giant papillary conjunctivitis are complications that may occur more frequently in patients who are not compliant with their wearing schedules, lens replacement schedules, or lens care systems.

The Dk/t of the majority of disposable contact lenses currently prescribed (excluding the silicone hydrogel lenses) is similar to that of conventional hydrophilic lenses. Therefore, hypoxia problems still exist

88 N. Holzchuh et al.

with nonsilicone hydrogel soft contact lenses. Extended wear with conventional hydrophilic lenses can cause corneal edema, increasing the risk of infectious keratitis 10to 15-fold when compared with daily use.6 Alterations of the epithelium, hypoxia, and the presence of bacteria on the contact lens form a triad that predisposes the eye to the development of infectious corneal ulceration. Some studies indicated that the introduction of disposable contact lenses increased the frequency of noninfectious keratitis and may also be associated with ulcerative ker- atitis.7–9 Other studies have concluded that disposable lenses worn on a daily or extended wear basis have the same or lower risk of keratitis when compared to conventional soft contact lenses worn on the same basis.10,11 Infectious keratitis associated with the use of a hydrogel disposable lens occurs more in the periphery than in the center of the cornea, and the responsible microorganisms with the greatest frequency are gram positive, not gram negative. Moreover, the keratitis associated with disposable lenses is generally less severe than that associated with conventional hydrophilic lenses.

The incidence of giant papillary conjunctivitis is significantly less in patients who exchange their contact lenses every 3 weeks or less.12 Continued exchange of the contact lens appears to benefit the ocular surface. There are a number of scientific studies that demonstrate that, when the contact lens material is new, there is less accumulation of deposits. Likewise, the type of material from which the disposable lens is made may influence the quantity of deposits that form on the lens.12–15 Disposable contact lenses used in a regimen of planned replacement under the supervision of an eye care practitioner may prove to be an excellent alternative for patients who have not had success with other types of contact lenses.

References

1.Marshall EC, Begley CG, Nguyen CHD. Frequency of complications among wearers of disposable and conventional soft contact lenses. ICLC. 1992;19:55–59.

2.Solomon O, Freeman M, Boshnick E, et al. A 3-year prospective study of the clinical performance of daily disposable contact lenses compared with frequent-replacement and conventional daily wear contact lenses. CLAO J. 1996;22:250–257.

3.Pritchard N, Fonn D, Weed K. Ocular and subjective responses to frequent replacement of daily wear soft contact lenses. CLAO J. 1996;22:53–59.

4.Holzchuh N, Alves MR, Kara-Jose´ N. Dominaˆncia ocular e correc¸a˜o de presbiopia com lentes de contato atrave´s da te´cnica de monovisa˜o. Arq Bras Oftalmol. 1997;60:184–186.

5.Coral-Ghanem C, Ghanem RC, Bortoli GW, Yamazaki ES. Comportamento e caracterı´sticas de usua´rios de lentes de contato entre estudantes universita´rios da ´rea de sau´de. Arq Bras Oftalmol. 2000;63:123–127.

6.Poggio EC, Glynn RJ, Schein OD, et al. The incidence of ulcerative keratitis among users of daily-wear and extended-wear soft contact lenses. N Engl J Med. 1989;321:779–783.

7.Ficker L, Hunter P, Seal D, Wright P. Acanthamoeba keratitis occurring with disposable contact lens wear. Am J Ophthalmol. 1990;108:453.

10. Disposable and Planned Replacement Contact Lenses 89

8.Kent HD, Sanders RJ, Arentsen JJ, Cohen EJ, Laibson PR. Pseudomonas corneal ulcer associated with disposable soft contact lenses. Contact Lens Assoc Ophthalmol J. 1989;15:264–265.

9.Rabinowitz SM, Pflugfelder SC, Goldberg M. Disposable extended-wear contact lens-related keratitis. Arch Ophthalmol. 1989;107:1121.

10.Guillon M, Guillon J-P, Bansal M, Maskell R, Rees P. Incidence of ulcers with conventional and disposable daily wear soft contact lenses. J Br Contact Lens Assoc. 1994;17:69–76.

11.Buehler PO, Schein OD, Stamler JF, Verdier DD, Ketz J. The increased risk of ulcerative keratitis among disposable soft contact lens users. Arch Ophthalmol. 1992;110:1555–1558.

12.Porazinski AD, Donshik PC. Giant papillary conjunctivitis in frequent replacement contact lens wearers: a retrospective study. CLAO J. 1999;25: 142–147.

13.Poggio EC, Abelson M. Complications and symptoms in disposable ex- tended-wear lenses compared with conventional soft daily-wear and soft extended-wear lenses. Contact Lens Assoc Ophthalmol J. 1993;19:31–39.

14.Boswall GJ, Ehlers WH, Luistro A, Worrall M, Donshik PC. A comparison of conventional and disposable extended wear contact lenses. CLAO J. 1993; 19:158–165.

15.Hamano HK, Watanabe K, Hamano T, et al. A study of the complications induced by conventional and disposable contact lenses. CLAO J. 1994;20: 103–108.