|Year : 1987 | Volume
| Issue : 2 | Page : 95-97
Contact Lenses - A Review
VK Dada, Rajiv Sharma
Dr R.P.Centre for Opthalmic Science, A.I.I.M.S, New Delhi 110 029, India
V K Dada
Dr R.P.Centre for Opthalmic Science, A.I.I.M.S, New Delhi 110 029
Source of Support: None, Conflict of Interest: None
A review of recent literature on contact lenses shows increasingly more studies on soft contact lenses than PMMA hard lenses
The articles on contact lens wear and ulcerative keratitis have highlighted the increased risk of microbial keratitis in contact lens wearers compared to the general population, higher virulence of pathogens isolated and special association of fungi with EWSCL This high risk is due to multiple factors, organism survival in moist lens cases and cleaning solutions, microtrauma to the corneal epithelium by repeated insertion and removal, corneal hypoxia and lens deposits in soft lenses
Special problems of tonometry in eyes with bandage soft lenses and contact lens sterilization have been studied and useful suggestions have come forth from the authors
Keywords: 1) EWSCL - Extended wear soft contact lens 2) S.CL Soft contact lens 3) PMMA Polymethyl methyl acrylate.
|How to cite this article:|
Dada V K, Sharma R. Contact Lenses - A Review. Indian J Ophthalmol 1987;35:95-7
1. Ulcerative Keratitis, Associated with contact lens wear.
Alfonso, E, Mandelbaums, Fox, M, Forster, RK Am. J. OphthaL 101 : 429-433 1986.
A review of 573 cases of ulcerative keratitis cultured at Bascom Palmer Eye Institute from January 1977 to September 1982 showed 118 cultures (21 %) from eyes of contact lens wearers Positive microbial isolates were obtained in about 50% of cases cultured.
Of culture positive cases in contact lens users, 78% isolates were Gram negative (pseudomonas reported in 9 of 10 such isolates), Gram positive (staph aureus mainly) accounted for 14% and fungi were isolated in only two cultures
By contrast only45% of culture positive cases, not using contact lenses, were caused by Gram negative organisms Gram positive organisms and fungi were isolated in 28% respectively.
2. Association of fungi with extended wear soft contact lenses.
Wilson LA, Ahearn D.G: Am. J. OphthalmoL 101: 434-436 1986.
This paper describes the fungal isolates from eleven EWSCL cases Two of these eleven cases presented with fungal corneal ulcers 4 cases had signs of conjunctivitis and superficial epithelial keratitis and the remaining 5 cases presented with blurred vision and lens deposits which resisted cleaning. These lens deposits on slit lamp examination had mycelial character and on culture showed fungal growth. This can be prevented by adhering to the lens cleaning schedule.
3. The effects of hard & soft contact lenses on the corneal endothelium.
Mac. Rae. S.M, Matsuda, M, Shellan, Steve : Am. J. Ophthalmol 102: 50-57,1986.
Endothelial morphology was studied in different types of contact lens wearers.
There was a statistically significant change in the endothelial cell shape (polymegathism) and cell size (pleomorphism) in contact lens wearers irrespective of lens type compared to age related controls
Amongst the lens types, the morphological changes were more in PMMA hard lens wearers and more so if the lens had been worn for longer duration Daily wear SCL wearers also showed similar changes Hard contact lens wearers who had discontinued lens use for an average of 5 years continued to show endothelial changes suggesting that these changes were not completely reversible. These changes have been attributed to relative long term hypoxia and an anaerobic metabolic shift with build up of toxic byproducts.
4. Corneal deswelling response to
Hard and Hydrogel Extended wear lenses
Andrasko G.J. Invest Ophtha!moL and Vis Science, 27:.20-23, 1986.
The study on corneal endothelial pump function was noted in two eyes separately for 2 1 /z hours, with the lens on in one eye, and the lens in the other eye being removed.
The results showed that the swelling response corresponded to the gas transmissibility level of the contact lens This was more in PMMA hard lenses, and low transmissibility soft lenses, when compared to high transmissibility soft lenses The deswelling rate of the cornea was faster if the contact lens after overnight use was removed than if left in the eye. The maximum deswelling of the cornea was in the first fifteen minutes for all types of lenses But this rate was faster for hard lenses in these first 15 minutes After this period the deswelling rates were nearly the same for both types , of lenses.
5. The effects of extended wear Hydrophillic contact lenses on the human corneal epithelium
Lamp MA Gold J.B. Am. J. Ophthalmol 101 274-277 1986.
Using wide field specular microscopy of the corneal surface authors have demonstrated a shift in superficial cell population to medium and large sized cells compared to age related controls.
Other abnormalities noted were white dessicated cells, retained mucus, coarse mucus plaques and cellular debris
These epithelial changes are attributed to delay in normal corneal exfoliative process by the bandage effect of soft contact lenses This increases the residence time of epithelial cells in the cornea enabling the cells to increase in size and become flatter.
The significance of these changes may be in reducing the resistance of surface corneal epithelium, and in the pathogenesis of corneal complications reported with EWSCL
6. Use of tear enzyme activities to assess the corneal response to contact lens wear
Fullard RJ. Camey LG. Acta OphthalmoL 64: 216-220 1986.
Another study based on biochemical changes in corneal epithelium under hypoxic stress has been assessed for the first time in viva Corneal epithelial metabolism is mainly aerobic but with lens fitting there is a shift towards the anaerobic metabolic pathway. This leads to corresponding shift in enzymatic activities in epithelial cells These enzymes can be assessed in human tear film. With lens fitting the workers at University of Melbourne, Australia have shown a rise in Lactate dehydrogenase (LDH) corresponding to Maleate dehydrogenase (MDH). The parameter of rise in ratio of LDH/MDH is an indicator of corneal epithelial hypoxia It has been demonstrated that hard contact lenses, steeper fitting lenses, lenses worn for long durations and overnight, increase this ratio. This technique also has the potential of assessing in vivo, various lens designs, materials and environmental factors
7. Deep Stromal Vascularization associated with cosmetic, daily wear contact lens
Nirankari V.S. Karesh J, Lakhanpal V: Ophthalmol 101 :46-47,1983.
Deep stromal opacities and vascularization have been reported in three cases.
8. Circinate pattern interstitial keratopathy in daily wear soft contact lens wearers
Braude LS., Sugar J : Arch. Ophthalmol 103 1662-1663, 1985.
These authors reported 5 cases which developed deep stromal comeal vascularization and circinate pattern lipid exudation resembling interstitia keratitis, after the use of daily wear soft lenses The cause of these changes at presents needs to be investigated
9. Microwave sterilization of hydrophillic contact lenses
RohrerMD., TerryM.A Bulsad RA Graves D.C Taylor EM. Am J. Ophthalmol 101 : 43-57,1986.
The desire for a better method of sterilization prompted the workers at University of Okhahama, to investigate the feasibility of 2,450 MHZ microwave irradiation. This method does not alter the refractive properties of SCL or damage the soft lens matrix
10. Pneumotonometry through Bandage contact lenses
Rubenstein J. B., Dentsch T.A : Arch Ophthalmol 103: 1660-1661,1985. This study from St Lukes Medical Centre has demonstrated that pneumotonometry is an accurate method of assessing intraocular pressure in such cases and has eliminated the need of lens removal for this purpose.