|Year : 1990 | Volume
| Issue : 1 | Page : 27-29
Pitfalls in aphakic contact lens fitting
Vijay K Dada, Manoj R Mehta, Arun K Jain
R.P. Centre for Ophthalmic Sciences, AIIMS, New Delhi-110 029, India
Vijay K Dada
R.P. Centre for Ophthalmic Sciences, AIIMS, New Delhi-110 029
Source of Support: None, Conflict of Interest: None
We examined 23 consecutive cases of unilateral aphakia reporting to the contact lens office for endothelial count and morphology, corneal thickness and toricity. The fellow eye served as a control in all the cases. It was found that there is a significant drop in the central endothelial cell density, and change in the size and shape of the cells. These observations indicate a thermodynamically unstable state. The aphakic corneas were thicker than the controls but not to a significant extent. The cell count and pachymetry had no statistical correlation. Toricity of the aphakic corneas make successful fitting of a lens difficult. Since prolonged use of extended wear gas permeable as well as hydrogel lenses have a deleterious effect on the endothelium it is suggested that a careful case selection be made and strict monitoting carried out at follow up. These corneas are liable for decompensation with only mild noxious stimuli. This article is intended to acquaint the ophthalmologist with the pitfalls in aphakic contact lens fitting so that a cautious follow up may be planned.
|How to cite this article:|
Dada VK, Mehta MR, Jain AK. Pitfalls in aphakic contact lens fitting. Indian J Ophthalmol 1990;38:27-9
| Introduction|| |
Unilateral aphakia is an important indication for contact lens wherever a primary or secondary IOL is not considered appropriate. The anatomy as well as the physiology of the cornea in aphakia is altered to a significant extent. There are metabolic differences between the corneas of the normal and the aphakic eyes resulting in a differential response to the hypoxic stress. The present investigation was devised to highlight the pitfalls in fitting aphakic contact lenses, help the practitioner in a proper subject selection, and devise a follow up strategy. The normal fellow eye was used as a control.
| MATERIAL & METHODS|| |
23 consecutive patients with unilateral aphakia referred to the contact lens clinic were included in the study. Details of the surgical procedure carried out were recorded alongwith the time lapse since surgery. A complete slit lamp examination was carried out on both the eyes. Keratometry was performed using a Javal Schiotz keratometer. Pre-fit endothelial microscopy and digital pachymetry were obtained using a Nikon Endothelial Camera in the test as well as the control eye. The central endothelial cells were analysed. The [Table - 1],[Table - 2][Table - 3] give the relevant clinical data on the patients for the central endothelial cell count fixed frame analysis that was carried out. For pleomorphism and polymegathism the pictures were compared with the normal standard pictures for matched age and sex. The patients were prescribed `gas permeable' (XL 30) siliconeacrylate contact lenses after finalizing the base curve on the basis of flourescein pattern. All the lenses were lenticular.
| Results|| |
12 patients in our study were less than 20 years of age, 6 between 20 years to 40 years and 5 above 40 year of age. The patients were put into three groups for analysis. These groups were not statistically comparable in any way. In group I, 6 eyes had congenital cataract while the other 6 had traumatic cataract. Pars plana lensectomy was the preferred surgery in traumatic cases while needling and aspiration in the congenital cataract cases. Average central endothelial count in the control eyes was 2400mm 2±256 while in the aphakic eyes it was 1900 mm 2±417.8 which is statistically significant. The morphological changes observed were polymegathism and plemorphism predominently. The average pachymetry in the aphakic group was 0.52mm±0.047 in the control group. The average astigmatism found in aphakia was 2.2 Dioptres ± 2.2 with a range of, 1 to 7 dioptres. The control group had an astigmation of 1.1 D ± 0.54. This difference in astigmatism has only a weak statistical significance.
In group II the average central endothelial count was 2083 ± 147 in the controls and 1400 ± 502 in the aphakic eyes. The morphological changes were identical to those found in group 1. The average pachometry for the controls was 0.49 mm ± 0.03 and for aphakia 0.53mm ± 0.05 which had a slight statistical significance. Astigmatism in the aphakic group was 4.6 ± 4.2 with a range of 2 to 10 dioptres. The control group had an average of 1.5D.
In group III the average endothelial count was 2020 ± 491 in the control and 415 in the aphakes. The morphological changes were predominantly pleomorphism polymegathism and the presence of pigments. The average pachymetry was 0.50mm ± 0.02 and 0.52mm ± 0.01 respectively in the controls and aphakics. Astigmatism in aphakic eyes was of the order of 1.25D ± 0.64 and in the controls 0.66D + 0.28.
| Discussion|| |
The unilateral aphakes form a very diverse group. Each patient has to be tackled individually because of his or her unique problem. The aphakic cornea presents several peculiarities that may affect the successful wear of contact lenses, hydrogel as well as gas permeable hard lenses. The corneal endothelium which is normally a monolayer of hexagonal cells of uniform shape and size undergoes changes as a result of the surgical intervention or a preceding trauma that leads to a cataract. It has been observed that polymegathism  as well as pleomorphism ,, are sensitive indicators of the health of the corneal endothelium.
Pleomorphism is now given an equal importance as it indicates a stress condition. It is thermodynamically more unstable when compared to the normal hexagonal pattern. A number of clinical states are found to have an association with pelomorphism ,,,. Apart from the morphological changes a drop in the density of the endothelial cells is also observed ,.Both these changes have an effect on the deturgesence of corneal . A low count and a stressed functional state can lead to corneal decompensation in the form of bullous keratopathy. The aphakic corneas swell less as compared to the normal eyes when fitted with identical hydrogel lenses. Several hypotheses have been put forward to explain this phenomenon ,.The aphakic corneas respond better to hypoxic stimuli but it should be remembered that after surgery there is a gradual drop in the density of the endothelial cell. With the use of gas permeable hard as well as soft contact lenses a significant endothelial pleomorphism and polymegathism may occur which are not completely reversible, and are more profound, with the greater duration of use . The patients to start with have a compromised cornea, and therefore require a strict monitoring during follow up.
The corneal surface assumes toricity of varying degrees depending upon surgical technique and gauge of suture used ,,,.In our study the range of astigmatism varied widely. With hydrogel lenses it is important to prescribe a cylinder in a frame. With gas permeable hard lenses it is not possible to neutralize a cylinder of more than 3 dioptres. The cases with greater than 3 dioptres of astigmatism are not suitable for gas permeable hard lenses.
The aphakic corneas were thicker when compared to the controls but the difference was only slightly statistically significant. There was no correlation between the count and the thickness. This is in agreement with other authors.
The aphakic cornea is less sensitive and hence more prone to minor traumas and infections. Attention must be paid to the contact lens accessories used by the patients; lens cases, solutions etc. as they may be acting as a storehouse of infection for these devitalized corneas ,,25.
The aphakic contact lens fitting should be carried out under strict supervision. The patients should be followed up more frequently and examined thoroughly. Clear instructions should be issued to the patients regarding the handling of the lenses and aseptic methods. The challenge to develop a gas permeable polymer suited to the contact lens design in aphakia is very much open in the present state of technology. Till such times as the newer materials are introduced, a vigil must be kept during the follow up visit for any physiological decompensation.
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[Table - 1], [Table - 2], [Table - 3]