|Year : 1975 | Volume
| Issue : 4 | Page : 5-13
Flexible contact lenses and our experience with 'Sauflon 70' lenses in aphakia
Reader in Ophthalmology, Ravinder Nath Tagore Medical College, Udaipur, India
M R Jain
Reader in Ophthalmology, Ravinder Nath Tagore Medical College, Udaipur
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Jain M R. Flexible contact lenses and our experience with 'Sauflon 70' lenses in aphakia. Indian J Ophthalmol 1975;23:5-13
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Jain M R. Flexible contact lenses and our experience with 'Sauflon 70' lenses in aphakia. Indian J Ophthalmol [serial online] 1975 [cited 2020 Sep 20];23:5-13. Available from: http://www.ijo.in/text.asp?1975/23/4/5/31431
In 1960, Otto Wichterle working in Parague, Czechoslovakia, announced the introduction of a new hydrophilic plastic materialhydroxyethylmethacrylate (HEMA) to manufacture soft contact lenses. These lenses were manufactured by a spin moulded technique with a back surface curvature of pseudoconiconoidal form and a central back optic portion of steep curvature. Hard lenses were not known in Czechoslovakia at that time and hence soft lenses became very popular. These lenses were tried in England but didn't meet with success and hence were abandoned.
In 1964, this HEMA polymer and the Czechoslovakian technique of manufacturing was carried to U.S.A. under a licence from Czechoslovakian Government. Bausch and Lomb started working on these lenses in 1966, but it took a long time for them to improve the material, the technique of manufacturing, clinical trials and their final acceptance by the F.D.A. and hence the lenses could finally be made commercially available by Bausch and Lomb in 1971.
At present there are four important basic types of flexible contact lenses being used in various countries.
1. Bausch and Lomb or `Softens' contact lens.
2. Griffin 'Naturalens' or Bionite contact lens.
3. Other soft lenses and 'Sauflon' lenses.
4. Mueller-Welt Silicon or Rubber Contact lens.
Plastics are members of materials known as polymers (taken from Greek roots, meaning 'many parts'). Polymers have a high molecular weight and fibre like shape of their molecules. Both these features are as a result of the joining of relatively small molecules in a polymerization process to form giant molecules that may contain thousands of their starting units, called 'monomers'. It is because of this molecular structure that plastics have the combination of strength, transparency, formability, inertness and the other properties that make them so suited to use them as contact lenses.
Polymethylmethacrylate is a hard and strong polymer used for the manufacturing of hard contact lenses. When Hydrogen atoms on alternate carbon atoms of this polymer are substituted by methyl groups (-CH 3 ), the material formed is Poly-Hydroxyethylmethacrylate, which is a soft and rubbery material.
Modifications of polymers-Polymers can be tailored to have specific properties by copolymerization. In this process, more than one monomer is polymerized or cross linked to obtain materials which have properties intermediate between the two.
1. Bausch and Lomb 'Softens' contact lens.
These lenses are made from a hydrophilic polymer (Poly-HEMA), which consists of a three dimensional network of hydroxyethylmethacrylate crosslinked with ethyleneglycol dimethacrylate (EDMA) molecules about once every two hundred monomer units. In spin cast method of manufacturing, the monomer and the solvent are mixed and pumped into moulds with a ground and polished surface, each mould being attached to a spindle upon which it is rotated. The polymerization takes place in a spinning mould in the presence of carbondioxide at a temperature of 65 degrees centigrade. Water at 80 degree centigrade is then pumped into, to replace the glycerol and to rehydrate the material which is removed manually from the mould. The hydraction of the lens is only 40 percent and this may account for its durability. When hydrated, the lenses are soft, pliant, transparent and elastic. When allowed to dehydrate by standing in air, they become brittle and - crenated and can be broken easily. Due to its low hydrophilic nature, the lens is impermeable at physiological levels to gases and has a slow flow rate of water across the material., The lenses transmit more than 97 per cent of light and have a refractive index of 1.43. The elasticity of the material is not sufficient to form good optical surfaces when these lens forms are used on non-spherical corneal surfaces.
These lenses are available in diameters of 13 and 13.5mm and earlier they were available in powers ranging from-1.00 to-9.00 diopters only but now aphakik lenses too are available. Low minus power are available in more than one back curve fitting, the high minus and aphakik series have one basic fitting for each power. The aphakik lenses have reduced front optics to give a central thickness of 0.4mm, a peripheral thickness of 0.14mm and an overall size of 13.50mm.
Sterilization-it is essential to sterilize the lens daily by boiling for 15 minutes in normal saline solution. The lens should be stored and sterilized in an isotonic saline solution.
2. Griffin 'Naturalens' or Bionite lens.
The lens is made up of bionite which is formed by polymerizing HEMA containing some EDMA (ethyleneglycol dimethacrylate) and about 20 percent P.V.P. (Poly N-Vinyl pyrolidone). The lens is a lathe cut and the front surface always has a lenticular cut to reduce edge thickness. The diameter of these lenses range from 13.5mm to 15.5mm. The inside curve is spherical with a small flat edge bevel, approximately 0.5 mm wide. There is a variety of inside curves available from 7.5mm to 8.7mm. The central thickness of average minus hydrated lens is between 0.35mm to 0.40mm. The lens rests on the eye in two areas; the central corneal region and a perilimbal area on the sclera. Thus the limbus is vaulted by the inside curve. The lens material is both hydrophilic and hygroscopic, which allows fluid to pass through it easily. It contains about 60 percent water by weight; however, there is no pore structure in the lens. In spite of the lens being quite soft, it has better elasticity than 'Softens' and hence gives better optical results due to stable optical surface at a relative thickness to that of polyHEMA.
The lens is poorly permeable to gases but almost twice as permeable to oxygen compared with polyHEMA. It is sufficiently rigid to allow formation of a tear layer underneath it and provide an adequate amount of oxygen to the cornea. It transmits 100 percent light and has a refractive index of 1.4 in a hydrated state.
Diameter-Usually 2 to 3mm larger than cornea. Commonly used diameters are 13.5mm and 14.5mm.
Curve-Inside curve is spherical with a flat narrow bevel at the edge, O.5mm wide. Most common radii used is 8.1mm, 8.4mm and 7.8mm and is available in a wide range of 7.2 to 8.7mm. These lenses are usually fitted 0.2 to 0.3mm flatter than the flattest meridian of the apex.
Thickness-Average central thickness of the minus lens ranges from 0.32 to 0.45mm and plus lens vary 0.45mm to 0.90mm.
Form-Both minus and plus lenses are made in lenticular form as a routine. The optical zone is 8.0mm in diameter in each case. The edge of the lens is thin and rounded.
Power-It is available in a wide power range from plus 20.00 D to minus 20.00 D.
Wearing Schedule-Can start wearing throughout the day from the beginning.
Sterilization-The lens is sterilized with hydrogen peroxide 3 percent U.S.P. The lenses are allowed to soak in peroxide for about 10 minutes. The perixode is then neutralized with bicarbonate which causes it to decompcse into water and oxygen. The lens is then kept in normal saline to eliminate any burning sensation created by bicarbonate
3. Other soft lenses and 'Sauflon' lenses
There are many other varieties of soft lenses manufactured from chemicals called physiological hydrophilic polymers (P.H.P. lenses). The chemicals used are of sparingly cross linked hydroxyethylmonomethacrylate. These lenses have about 70 percent water content when hydrated and refractive index of about 1.43. With little modifications, various chemical materials can be manufactured with varying water content and refractive index.
'Sauflon' soft contact lens used in our study is a copolymer of methylmethacrylate crosslinked with vinyl pyrolidine. Sauflon takes in a large amount of water, some free and some bound, until at saturation, the moisture content is 70 percent. It's refractive index is 1.43. The oxygen permeability of the 'Sauflon' lens is four tirries higher than HEMA and hence corneal oedema is rarely seen with this lens. Inspite of its being a high water content lens, its elasticity is adequate and provides good optical qualities. The lens is available in a wide range of powers, diameters and radii.
Sterilization-A Sauflon lens is normally sterilized chemically or it can be boiled.
Method and principle of chemical sterilization: All hydrophilic polymers consist of a three dimensational array of hydrophilic and hydrophobic monomer units, though the geometry and method of interconnections vary from one material to another. It has been found that dirt or contaminants are far less likely to adhere to a soft lens if the lens meets the contaminating material while it is loosing moisture i.e. while supersaturated. Conversely, a lens which is absorbing moisture is vulnerable to contamination.
After the lenses are removed from the eye, they are cleaned with Steri-solv. (hypromellose + disodium edetate + thimersol and 2.5% sodium chloride) which removes some moisture, dissolves mucous and other deposits on the lens (d). Then preserve these lenses for at least 2 hours in Steri-Sal (thiomersolchlorhexidine polymer complex + 0.9 percent sodium chloride and sodium edetate) which will supersaturate (by 5 to 10 percent) the lenses and provide controlled tonicity and pH and has bactericidal quality sufficient to maintain safety of the lenses.
'Allergan' which is a rapid acting broad spectrum germicidal and fungicidal soaking solution-a formulation combining a new quarternary ammonium compound with a special detoxifying agent, is also very effective as nightly sterilizing, hydrating and cleaning solution.
The lenses can also be satisfactorily sterilized by 0.02% Nipastat (a mixture of methyl ethyl propyl and butyl esters of p-hydroxybenzoic acid) in a water soluble polymer cony plex. The solution has marked surfactant and antibacterial properties.
Chemical sterilization is quite safe and even better because it removes all the mucous deposits from the lens whereas simple boiling is unable to remove the deposits.
4. Mueller-Welt Silicon Contact Lens
Silicons are man made macromoleculessemi organic polymers. Commercially Silicons are made from sand or quartz. Using carbon with the sand or quartz in an electric arc furnace, one obtains a high yield of high purity elemental silicon, a non-metal. This is crushed and made to react with methylchloride to obtain `methyl chloro silanes' which are rectified and hydrolysed to produce polydimethysiloxane. This polymethyl group makes the substance physiological inert. This material is further modified to obtain `poly siloxane' which is an elastic or rubbery substance used to manufacture silicon contact lenses by the process of moulding. Silicon is extremely hydrophobic material. It took over 2 years to develop a process of treating this material to render it hydrophilic by use of a contact lens wetting solution. So these lenses are having different types of softness as compared to soft or gel lenses. The lens is soft and flexible and yet has a certain degree of innate rigidity like a rubber. The lens neither requires boiling nor chemical sterilization. Sterility is obtained by using a wetting agent as in cases of hard contact lenses.
The lens material is highly permeable to oxygen and carbondioxide and hence an adequate supply of oxygen to the cornea is maintained.
Lens description-At present the lens available is 10.5 mm. in diameter. Anterior and posterior surfaces and peripheral curves are moulded and the edges are mechanically fabricated. A coating process is necessary to create a hydrophilic surface i.e. use of titanate solution as the dipping solution. Silicon lens has clear to light straw colour. The refractive index is 1.43 and it transmits 91% of visible light when the lens is wet as on the eye. Lens's thickness usually varies from 0.25 to 0.40 mm.
Fitting technique-A silicon lens is fitted with as much accuracy as hard contact lens. It is mostly fitted on `K' as the lens is available in all radii to hundreth of mms. The lens is wetted by wetting solution and the fit is checked by observing the fluorescein pattern under the slit lamp.
The silicon lens is a low riding lens. Often the lens is supported by the lower lid. With hard lenses, the minus lenses usually ride high and have a thick edge that the upper lid grabs and plus power lenses ride low as they have thick centres and thin edges. With silicon lenses-minus lens with central thickness of 0.3 mm. but edge thickness is reduced by making a lenticular cut-so silicon lens rides low. Low riding lens creates no visual problems by having the top part of the optical zone encroach over the superior pupillary area.
1. Silicon lens is a moulded lens and hence exact repeatability may require making 6 to 10 lenses. Edge reconstruction is still more difficult.
2. Astigmatism of minor degrees can only be corrected.
3. Mucous collects on the silicon lenses and hence must be cleaned more frequently than hard lenses.
4. The lenses cannot be modified as there can neither be any cut down in size, nor bevelling or blending, or any change in power or polishing.
5. They are not as comfortable as soft lenses and over wearing symptoms, spectacle blur and intolerance may be there as in hard contact lenses.
They have neither too hard nor too soft and hence if their qualities are further improved, they may be more acceptable. Longivity of these lenses are more than soft contact lenses.
CLINICAL USES OF SOFT CONTACT LENSES
a. Refractive error specially of minor to moderate degree is adequately corrected by these lenses. Astigmatism up to 1.5 D can be corrected to give satisfactory vision.
b. High myopia-Mypoes up to-12.00 diopters are very well corrected. Myopes higher than this are better corrected with hard lenses.
c. Aphakia-Continuous comfortable wear is possible and reduced optic lenses and high water content lenses are very well tolerated. Because of central thickness of these lenses, astigmatism of about 1.5 diopters can be corrected.,
d. Keratoconus-Soft lens should only be tried where hard lenses have failed. A special technique of `piggy back' lenses provide considerable improvement of vision. In this technique, a hard lens rides over the soft lens and hence neutralizes the corneal astigmatism to a considerable extent and provides good and comfortable vision.
e. Post keratoplasty-Soft lenses may be used after removal of the sutures for corneal protection and better visual acuity.
a. Bullous keratopathy-Adequately flat and larger diameter (14 to 15mm) lens usually gives good result. If the patient can tolerate the lens for the first 20-30 minutes, he usually tolerates it well. 5 per cent hypertonic saline and/or methylcellulose is frequently instilled. Patients usually feel considerable relief of pain and improvement of vision with this therapy.
In advanced cases, the pathological epithelium and underlying connective tissue is scraped and then soft lenses are applied and followed by the use of hypertonic saline and mydriatics.
b. Dry eyes-Sjogren's Syndrome, rheumatoid keratitis, Steven's Johnson syndrome, essential mucous membrane atrophy (Ocular pemphigoid), limbal keratitis (Theodore), anaesthetic cornea due to complete Vth and with partial VIth nerve lesions and radiation exposure keratitis respond favourably to the continuous wear of soft contact lenses. Normal saline or half normal saline are frequently instilled. Instillation of caster oil drops may give a considerable soothing effect, (and it does not require any preservative and cannot be easily contaminated). Methylcellulose is good but can be contaminated easily.
C. Medication with Soft Lenses
Soft contact lenses act as an excellent vehicle for certain drugs to treat some ocular conditions. Contact lenses saturated with pilocarpine when applied to the glaucomatous eyes, provide a sustained and prolonged hypotensive effect with much less concentration of the drug than used otherwise.,, The lenses can also be used as a vehicle for antibiotics and steroids in certain ocular conditions., The drugs used must, however, be free of any preservative.
Soft lens may be used to relieve pain and discomfort in conjunctival vernal catarrh, sclerokeratitis, trachoma, entropion, trichiasis and perforated cornea. It is preferable to apply soft contact lens to the eye during ptosis surgery to prevent any corneal abrasion due to prolonged rubbing of ptosis clamp against the cornea.
Advantages of soft contact lenses
2. Rapid adaptation
3. No spectacle blur
4. Can be worn intermittently or continuously
5. Minimal overwearing reaction
6. Lack of glare and photophobia
7. Difficult to dislodge--specially Griffin and Sauflon lenses and hence can be worn during active sports
8. Protects the entire cornea
9. Good alternative for hard lens 'drop outs'
10. Birth control pills have no adverse effect
11. No serious corneal abrasion
12. Can be used for therapeutic purpose also
13. Continuous wear lenses are a great boon to children and very old patients
1. Does not usually correct astigmatism more than 1.5 D
2. Alteration in vision
3. Lack of durability
4. Faulty duplication specially with Griffin lenses
5. Eye drops with perservative cannot be employed
6. Precipitates tend to form on and within the lens
7. Modifications impossible
8. Sterilization costly and time consuming
9. Danger of infection
10. Fluorescein cannot be used to examine the fit as these lenses get stained with the dye
| 'Sauflon 70' lenses in aphakia|| |
The conventional hard contact lenses quite efficiently correct the invariably occuring corneal astigmatism in aphakiks by altering the effective corneal surface and rendering it essentially spherical but there are few inevitable problems which are frequently encountered in the aged persons with those lenses. Routine removal and insertion of the lenses is a big problem and for 60 to 70 per cent of these patients, this regime is rather impossible. Quite a good number of patients find difficulty in adaptation and few have no patience to continue with this initial discomfort.
Selection of cases-Out of the total 15 cases forty seven per cent were 'drop outs' of hard contact lens wearers as they felt some sort of difficulty with hard contact lenses. The rest of the cases were never put on hard contact lenses as 2 of them were having slightly ectatic cornea following penetrating corneal injury and one case was of bullous keratopathy. One case did not accept hard lenses during trial and 4 cases were thought unfit to use hard lenses due to physical reasons. The cases with 'Sauflon' lens wear have been followed for 1 to 3 years.
Method-Slit lamp examination, Ophthalmoscopy, refraction and keratometry was done in every case. Trial 'Sauflon' contact lens with a radius of 0.2 mm. flatter than the flatter meridian and of the power of about 12 to 13 diopter and diameter 1.5 mm. larger than cornea was chosen and applied on patient's cornea. After about 10 to 15 minutes, the eye was examined torch light and slit lamp. A good fitting lens should normally be centered over the iris and should have very slight movement when the eye is moved to its extreme. Excessive movements suggest too much apical touch and complete stability suggests too tight lens fit. If necessary, a lens more flat or steep was tried till satisfactory fit was obtained. Too steep or too small lens usually causes congestion near its edge. Slit lamp examination was done to confirm its fit: keratometry over the lens was also done to observe that after the blink, the anterior surface of contact lens does not remain distorted. Retinoscopy through the lens was done and proper correction applied in the trial frame. Final prescription specifying the diameter, radius and power of the lens was made as under
Power ± 16.0D
After the lens was obtained from the manufacturer, it was fitted to the patient's eye and the fit was consequently checked every week or fortnightly till we were satisfied about the fit. Consequent checkups were done every month. On these visits, the lenses were inspected and sterilized chemically and/or by boiling and reapplied.
| Observations and Discussion|| |
Out of the 15 eyes fitted with soft contact lenses, 7 were males and 8 females. The maximum age in our series was 78 years and the minimum 14 years, the average being 46.4 years [Table - 1]. Two younger cases of the group were having corneal ectasia following perforating corneal and lenticular injury.
Keratometric Measurements and soft contact lenses
Range of corneal radii in horizontal meridian was from 7.15 to 8.40mm. and in vertical meridian 7.40 to 8.60 mm. Average corneal radius in horizontal meridian was 7.81 mm. and vertical 8.19 mm., indicating a steeper corneal curvature in horizontal meridian as compared to vertical after the cataract surgery, which is in conformity with Lobascher et al. [Table - 2]. One case of corneal ectasia had extreme irregularity and hence corneal curvature could not be measured.
'Sauflon 70' contact lenses prescribed had average base curve, diameter and diopertic power of 8.27 mm., 13.60 mm. and 14.81 dioptre respectively [Table - 3]. Base curve finding indicates that the best tolerated soft contact lenses were flatter than the average corneal curvature (horizontal 7.81 mm. & vertical 8.19 mm). Diameter of lenses was 1 to 2 mm. larger than average corneal diameter and as expected dioptric power of the lenses was 3 to 4 dioptres more than average spectacle numbers.
Visual Acuity and Complications
Out of 15 cases, 3 cases required additional spectacle correction to attain maximum visual acuity. 76.36 per cent of cases improved vision up to 6/9, maximum cases (7 cases) attaining vision of 6/9 [Figure - 1]. Unsatisfactory improvement of vision was observed only in three cases; two of which had post traumatic ectatic cornea and one case suffered from bullous keratopathy. Normally these three cases were unfit for hard contact lenses and a trial with soft contact lenses was quite gratifying as far as visual improvement was concerned.
Out of 15 cases, only 10 cases used spectacles for sometime in the past. Improvement of vision with gel lenses could very favourably be compared with spectacles as 7 cases attained same vision, one case was even better and one slightly worse. Inherent advantages of soft contact lenses over spectacles, namely, the absence of tunnel vision, ring scotoma, `Jack in the box' phenomenon and magnification were great assets to the patient.
Acceptance of the soft lenses even in cases of hard contact lens `drop outs' was very satisfactory. 7 cases almost did not feel the presence of lenses in their eyes ˝ to 1 hour after the first insertion and 6 cases got acclimatized within 2-4 days after slight discomfort. Two cases of corneal ectasia produced some problems; in one case the lens used to slip over to sclera and produce considerable discomfort and hence the patient was switched on to spectacles. Another case developed epithelial erosion after wearing the lens for 3 months and the lens was discontinued [Table - 4]. None of the other cases developed any harmful effects on corneal epithelium or any conjunctival inflammation, though the lenses were worn continuously for 1 to 2 months.
| Conclusion|| |
'Sauflon 70' soft contact lenses are most suitable for aphakiks as a routine measure. `Continuous wear' in addition to good visual improvement without the inherent drawbacks of thick spectacle lenses appears to be a distinct advantage.
| Summary|| |
Presently available flexible contact lenses have been reviewed with respect to their merits and demerits. Experience with 'Sauflon 70' soft contact lenses in 15 cases of aphakia have been discussed with a followup period of 1 to 3 years, concluding their definite advantage in cases of hard contact lens 'drop outs'.
| Acknowledgement|| |
I am extremely thankful to Mr. N.L. Dallas and Mr. R. Warr of Bristol Eye Hospital for allowing me to examine their cases and inspect the records.
| References|| |
Wichterle, 0., and Lim. D., 1960, Nature,
185, 706, 117.
Gasset, A. and Kaufman, H.E., 1972, Soft Contact Lens, The C.V. Mosby Company, Saint Louis.
Bionite J.L., and Keates, R.H., 1972, Symposium on the flexible lenses, The C.V. Mosby Company, Saint Louis.
Hill, R.M., 1967, Am. Opt. Ass. Jour., 38,181.
Takahashi, G.H. et al., 1966, Brit. Med. Jour.
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Knoll, H A. and Williams, J., 1970, Am. J. Optom., 47,
Karageozian, H.L., 1973, Read before seventh contact lens seminar, Ohio State University.
Ganju S.N. and Thomson, R.M., 1975, Paper read at the International Contact lens Congress, Montreaux, Switzerland. Aug. 1974 and Published in Contact.
Vespar, G., Klin. fur. Augen.,
Sedlacck, J., 1966, 24,
Kaufman, H.E., Uotila, M.H., Gasset, A.R., Wood, T., and Varnell, E.D., 1972, Medical uses of soft contact lenses. The C.V. Mosby Company, Saint Louis.
Hillman, T.S., 1974, Brit. J, Ophthal., 58,
Jain, M.R., 1975, Read at the meeting of South Western Ophthalmological Society at Bristol, U.K.
Watson, S.R , and Kaufman, H.E., 1970, Investi. Ophthal., 9,
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[Figure - 1]
[Table - 1], [Table - 2], [Table - 3], [Table - 4]