Year : 1979 | Volume
: 27 | Issue : 4 | Page : 44--46
The soft intraocular implant lens
SN Sathe, KR Mehta, SD Keryakar
Eye Clinic, Seaside, 147, Colaba, Mumbai-400005, India
K R Mehta
Eye Clinic, Seaside, 747, Colaba, Mumbai-400005
|How to cite this article:|
Sathe S N, Mehta K R, Keryakar S D. The soft intraocular implant lens.Indian J Ophthalmol 1979;27:44-46
|How to cite this URL:|
Sathe S N, Mehta K R, Keryakar S D. The soft intraocular implant lens. Indian J Ophthalmol [serial online] 1979 [cited 2013 Jun 19 ];27:44-46
Available from: http://www.ijo.in/text.asp?1979/27/4/44/32571
The most successful lens implants are those designed by Binkhorst, Epstein and Federov who have used the concept of iris fixation.
The material used has been polymethyl methacrylate of a clinical quality from which all the monomer has been removed. The iris suspension devices or struts have most commonly been made of tantalum, titanium, Dacron and nylon 55.
It would seem strange that there has been no published report of use of a soft material implant in the eye.
Type of soft lens material
There are many lens materials available in the world market. The criteria of selection of the material for the soft lens implant thus developed into a few basic requirements.
(a) The material should have as high a water content as possible, consonant with adequate structure stability.
(b) It should stand machining easily with no future plastic recoil and should develop no distortions.
(c) It should stand autoclaving with no structural changes.
(d) There should be no tendency towards discolouration and degradation.
(e) It should be possible to make the lens very thin with no distortion of the visual optics.
Of the above criteria only the first requires some explanation. A high water content lens has greater permeability to electrolytes and oxygen, but conversely has poor structural stability.
A number of lenses of different hydrated materials were tried under a saline bath after suspending them in a wire loop to test for dimensional stability. We found the Wohlk material with a standard hydration of 38.8 in saline to be the ideal lens material.
The Wohlk material had also been available for regular soft contact lens use and follow up of over a year in clinical practice had demonstrated a fairly adequate tensile strength with minimal plastic recoil or distort.
Developmental patterns of the soft implant
A fair degree of initial work went into the trial stage. A pattern which would, on paper be thought ideal would prove difficult to machine up to the standard. We are presenting the gestational stages to the present type V implant with the view that future workers in this field would not repeat the mistakes that we made.
Type I-A dumbell shaped lens. The front and back of the lens-both carried the dioptric segment with a groove in a V pattern in the middle. This lens was far too heavy and rocked excessively on sharp head movements leading to visual field distortions.
Type II-The surface was flattened and the power of the back dioptric section was increased. Though it appeared more effective, the heavier back segment led to a tilt which proved disconcerting to the patient.
Type III-The lens was made smaller and to make the lens fit snugly, the opening between the lens face plate and dioptric carrier was diminished to 0.4 mm. Though an excellent snug fit resulted, it was technically very difficult to insert the iris in the groove and the face plate had to be lifted at each segment. This lens fitted well with no rocking.
Type I V-This was an attempt to maintain th, snug fit but to make insertion surgically easier. The face plate was notched in a propellar fashion so that the leaves could be lifted to facilitate insertion. This lens was a failure and subsequently was removed as notching the face plate completely spoiled the stability.
Type V-Our present series lens
Since we could not make the troove tighter and still permit easy surgical insertion and stability, the obvious answer was to I ighten the lens by reducing the size of the dioptric carrier. This technique, known in the optical trade as lenticularisation permits a much lighter lens. Again, to facilitate insertion, the edges of the face plate were designed with a curve outwards. This particular pattern proved to be the most successful.
The problem of sterilization of the lens was solved by the simple expedient of selecting a material which could be autoclaved safely. It is best to insert straight from the vial in which it was sterilised.
All cases were done under local anaesthesia with pre-operative diamox.
Standard Graefe corneoscleral knife incision with peripheral iridectomy and extracapsular cataract extraction. The lens is held in a smooth tipped forceps. It is best to hold the lens from the hub which is the strongest place. Once the inferior pole is inserted, the lip can then be gently held to support the lens and the iris at the superior pole lifted with a forceps and allowed to flow between the lens. It must be realised that the lip is extremely thin and fragile and must be handled with great delicacy.
After inserting the lens the wound is closed by multiple virgin silk sutures. It is better to fill the anterior chamber with saline. Air tends to dehydrate the lens surface resulting in an irregular curved margin. It is thought permissible to utilise air to seat a lens properly but as far as possible, should be replaced by saline prior to sealing the anterior chamber.
Post-operative care consisted of oral and local steroids. The latter was continued for 1 month. Except for a drop instilled at the table, no further pilocarpine was required.
The type V series has been implanted in 10 patients with gratifying results. The eyes were quiet fairly early and the reaction can be favourably compared to the Binkhorst type hard lens. The eye becomes quiet within five days and remains quiet.
We have had to remove one lens because of severe iritis which settled down after the lens was removed. All the other cases are doing well.
Visual acuity with the soft implant
We commenced with an implant of 18 dioptres but found that we needed an average of 3 dioptres to achieve emmetropiazation. It is possible that we need a higher power as compared to the average of + 17.62 dioptres for the Binkhorst and +18 for the Copeland lens as our soft implant is fitted more posteriorly.
It would have been fortunate if we could do preoperative power assessments by ultrasonoscopy. At present we go by the patients record of clear distant vision without glasses prior to commencement of the cataract.
We did pre-operative and post-operative corneal astigmatism assessment with the keratometer. The residual astigmatism matched the corneal astigmatism thus displaying that the lens did not induce any astia matism.
We have achieved a vision of 6/6 in two patients without any correction but in all cases achieved a vision of 6/12 to 6/9 with additional spectacle correction.
Uveal response to a soft implant
As mentioned earlier one lens had to be removed because of severe iritis. The eye returned to normal on removal of the lens. Examination of the aqueous showed large collections of lymphocytes and giant cells showing that it was perhaps a foreign body reaction.
Nine cases showed no reaction. The eyes quietened rapidly and there was no conjunctival injection.
The soft implants showed a much less reaction as compared to the hard Binkhorst type implants. In no case was pigment splattering on the lens or cornea noticed and except for one case the gonioscopic evaluation showed no excess reaction. The work is really still in its infancy and a great deal of analysis still needs to be done.
There has been no leakage of the wound in the immediate post-operative period. There was no late complications in a follow up period of 4 months.
The ten cases of the Type V implant demonstrate that:
(a) The soft implant is acceptable to the eye
(b) Minimal reaction of the eye to the implant as followed up for over four months
(c) The design is acceptable with good results
(d) Good visual results accrued from the implants.
It is still early to say as to what direction the implants will take. Preliminary work indicates that it is a good possibility that all future implants may shift over to the soft material if the long term anyalysis works out well.
The Type V/G (G for glazed)
A soft implant is so clear that at times it becomes difficult to see the face plate of the lens during surgery and follow up. Hence the face plate has been made glazed to permit easy visibility, keeping the optical part clear.
The Type V/N (N for notched)
The implant has a narrow deep notch in the dioptric portion. We have not yet implanted this series, but this has been devised to permit discission of an after cataract if required at a later date. This facility is not possible in the present series.
Note: The soft implants have been conceived and designed by one of us (K. R. M.) and have been made at the Soflex contact lens laboratory at Bombay. Special mention is made of Sh. D. Panthaky, the head technician who made the implants.
|1||Binkhorst. C.D., 1959, Trans. Ophthal. Society. U.K., 79, 569.|
|2||Epstein, E. 1959, Brit. Jour. Ophthal., 43, 29-33.|