|Year : 1983 | Volume
| Issue : 6 | Page : 785-787
Extended wear contact lenses for myopia
Gullapalli N Rao
The Corneal Research Laboratory, Dept. of Opthalmology and the Centre for Brain Research, University of Rochester Medical Centre, Rochester, New York, USA
Gullapalli N Rao
The Corneal Research Laboratory, Dept. of Opthalmology and the Centre for Brain Research, University of Rochester Medical Centre, Rochester, New York
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Rao GN. Extended wear contact lenses for myopia. Indian J Ophthalmol 1983;31:785-7
Extended wear of contact lenses is a concept which is based on the premise that the basic physiological requirements of the cornea are met in the presence of the contact lens in the eye. By definition, the waring time should be more than 24 hours. The concept has originated with the application of hydrophilic lenses for therapeutic purposes of later on was extended for the correction of aphakia. A number of contact lenses have been developed for the correction of myopia to be used on an extended wear basis. In additioin, the proliferation of surgical procedures for myopia has added to the importance of the availability of a non-surgical alternative to these patients.
The basic criterion for an extended wear of contact lens is the oxygen transmissibility. For the normal metabolism of the cornea, an optimal oxygen tension is required With the usage of contact lenses, this is compromised. All the contact lenses that are available now allow enough oxygen to pass to the cornea which is far below the physiological requirements of the normal human cornea. The tolerance of the cornea has been very good, however. In order to address the problem of oxygen transmissibility several basic approaches have been identified in the manufacture of lenses. Making the contact lenses very thin or increasing the water content of the lenses, will serve this purpose. A number of lenses have become available for extended wear of myopia and the Food and Drug Administration in the United States has approved some lenses such as Hydrocurve-55, as well as the Permalens with the former lens having water content of 55% while the latter has a water content of about 71 %. In addition, there are other lenses such as Bauisch & Lomb lens (Polymacon) which has a water content of 30%, and CS-1 lens with a water content of 40%. Studies are underway to prove the efficacy of these lenses. In addition, a number of other lenses are presently under investigation.
The requirements of extended wear of contact lenses is prompted to a considerable extent by the increasing popularity of surgical techniques for the correction of myopia such as radial keratotomy and keratomeleusis. The availability of extended wear contact lenses for myopes has become an important alternative to offer to these patients. The important indications for extended wear of contact lens in myopia are:
1. As an alternative to surgery for myopia
2. Any myope who is capable of wearing daily wear contact lenses can be fitted with extended wear contact lenses provided there are no contra-indications in their ocular structure.This would be advantageous for those people who are in professions which demand longer working hours and their lenses may have to be left in the eye for prolonged periods of time.
3. These contact lenses may provide adequate vision in those high myopes who cannot see without the myopic correction and, yet, do not have the dexterity to handle the daily wear contact lenses.
Of paramounmt importance in patient selection is the proper evaluation of the patient's ocular status prior to the fitting of extended wear lenses. The basic physiological needs of the eye should be considered for this procedure. A detailed, routine eye examination is mandatory with special emphasis on the structure of the anterior segment of the eye. One has to look especially for problems such as blepharitis, meibomitis and lid defects. Other significant factor in relation to eyelids is the blink mechanism. People who have poor blinking may not be able to wear extended wear lenses as successfully, mainly because of the relative drying of the lens that may occur from maldistribution of the pre-corneal tear film.
The other important consideration is the examination to determine the status of the pre-corneal tear film is important to have a good lens pump mechanism for proper circulation of oxygen around the lens, as well as to keep the lens moist. The pre-corneal tear film also provides a flushing effect on the lens surface, thereby minimizing the tendency for deposit formation in these patients. One has to assess the status of the conjunctiva for any evidence conjuntivitis which should be considered as a contra-indication for extended war contact lenses. In addition, one has to especially look for any alternations in the upper tarsal conjunctiva for future monitoring of these patients for changes such as giant papillary conjunctivitis.
One of the most significant complications associated' with contact lenses is the development of corneal edema and proper monitoring of corneal thickness is very important tc delineate the early changes in corneal thickness which mighteventually lead to the production of corneal edema. Corneal sensitivity is an important parameter since contact lenses in patients with hyposthetic or anesthetic cornea require closer follow-up because of the lack of appreciation of these patients for early subjective symptoms secondary to contact lens related complications. The next important thing is the patient's environment and his ability to at least remove the lens should some complications occur. In these cases, when the patients cannot handle the lenses, somebody within the patient's environment such as a nurse, relatives or fiends should be trained to at least remove the lenses.
The fitting procedure that is adopted for extended wear of myopia is basically the same procedure that is adopted for soft contact lenses. Experience has shown that fitting these lenses flat gives more reliable results in terms of improvement in visual acuity. In addition, the most popular way of fitting these lenses, clinically, is by trial and error. One can start with one lens and gradually adjust to a different diameter and fit depending on the condition of the original lens on the eye.
Once the lens is fitted, the patient has to be re-evaluated after one hour. Our follow-up instruction for this extended wear of patients include re-evaluation after one day, one week, one month and every three months during the first year following which the patient is examined every six months.
Patient instruction is very important for the success of extended wear of contact lenses. Patient should be taught how to handle the lenses, particularly because most of them are young, healthy patients or are in a situation where they have enough dexterity to be able to handle these lenses. The patients have to be evaluated closely and the signs such as lid reaction, conjunctival reaction, corneal thickness, as well as any changes in the corneal surface should be looked for. In addition, one has to be aware of the possible alterations that may occur in the corneal endothelium. The patient has to be instructed for the possibility of the development of Steep lens Syndrome which usually occurs within the first 24 - 48 hours after the fitting of the lens. This is, however, more common in aphakic patients and very rarely seen in myopic population.
| Results|| |
Over 3,500 myopes have been fitted so far in Canada and the US with extended wear contact lenses. The overall consensus is that the extended wear of contact lenses has been far more successful in myopic patients compared to the aphakic population. The success rate is well over 90% with the range from 88 - 95%. The success rate appeared to be within the same range with different kinds of lenses. Lenses that have been used by these different investigators included are Bausch' & Lomb (Polymacon Lens), CSI Lens, Sauflon-70 lens, Permalens, and Hydrourve-55 lens. The vision in over 90% of these patients was better than 20/25 with the best correction.
The problem of replacement of the lenses continues and the lens life is still a factor although to a much less degree compared to the aphakic patients. The average rate of replacement was 1.4 lenses per year.
Deposit formation is found to be much less of a problem with the myopic extended wear lenses. This may partly be due to the better lid hygiene as well as the better lid hygiene as well as the better structure of the pre-corneal tear film in the myopic population.
The complications that have been described with the usage of aphakic extended wear lenses have been found with myopic extended wear lenses also, although to a much less degree. The complications included conjunctival as well as corneal changes.
The conjunctival complications included the development of mild allergic conjunctivitis to the most severe form of contact lens related allergy such as giant-papillary conjunctivitis. In addition, several other forms of conjunctivitis of allergic nature were also noted.
Potential for infection continues to exist with this population of patients. Any red eye associated with contact lenses should be considered to be of infective etiology unless otherwise proven.
A number of corneal complications that are of concern have occurred in patients with myopic extended wear lenses. These included corneal edema, corneal ulcers, and corneal neovascularization. Although the incidence of infected ulcers is less, one has to be aware of this possibility. The incidence of all these complications, fortunately, is far lower compared to the aphakic patient population.
One of the important things to remember about the microbial ulcers secondary to contact lenses is the development of rare forms of corneal infections which assume different morphological patterns. The most notable example of this is Serratia mersecens.
| Conclusions|| |
In summary, the extended wear of contact lenses in myopia is a very effective alternative for refractive corneal surgery. It is safe, cost effective, and good alternative to spectacles and daily wear contact lenses. Like in all forms of extended wear contact lenses, patient selection, patient instruction, and prompt recognition and management of complications is the key to the ultimate success for this modality of myopic correction.