As Alexander Pope wrote, The proper study of Mankind is Man. None of the known classifications of allergy in humans resembles the clinical and biochemical picture of giant papillary conjunctivitis. Howard Backman, L.Sc.O., O.D., (Emeritus) and Malcolm Baines, Ph.D., Department of Microbiology and Immunology, McGill University, Montreal, Quebec
GPC Debate is Over
We thought GPC: Dont Call It an Allergic Reaction, by Terry Chin, O.D., was an interesting article, but he has little to say about the different leukocytes present in the papules or their histopathology.
Dr. Chin did not cite our studies on GPC (giant papillary conjunctivitis) published in Investigative Ophthalmology and Current Eye Research. From the histology of the rabbits we studied, it was apparent that the GPC-like lesions were chronic lesions resulting from prolonged stimulation with antigen-coated lenses in highly immune rabbits. We observed masses of mononuclear cells that looked like lymphoid follicles contained in the sub-conjunctiva.
I agree with him in one sense: It is not a classical type-1 immediate hypersensitivity and may not even be type-2 or type-3. His statement that there are Th1 and Th2 cells present could be taken to indicate a type-4 hypersensitivity, which would agree with the long duration of such lesions. Presumably, the presence of Th2 cells would also agree with the presence of lymphoid follicles that may be responsible for the local production of antibodies to the inciting stimulus.
Interesting how the same old arguments re-emerge from time to time.
Dr. Chin responds:
I appreciate the comments from Drs. Backman and Baines, and I have reviewed their research. While their study can be found as one of the 2,000 references to GPC in the literature, it relates to GPC in rabbits, not in humans.
Human studies of GPC, thimerosal, allergies and contact lenses have been performed since the publication of Drs. Backman and Bainess 1991 article. There are major structural differences between the rabbit eye and the human eye; therefore, extrapolation of data from pre-clinical studies does not add anything to our current understanding of GPC.
As Alexander Pope wrote, The proper study of Mankind is Man. None of the known classifications of allergy in humans resembles the clinical and biochemical picture of GPC. GPC is clinically, histologically and biochemically related to chronic irritation.
Thimerosal atopy has been identified as having a completely different clinical manifestation than GPC. Thimerosal has been eliminated from ophthalmic solutions for twenty yearsyet GPC still persists in the human population.
Historically, thimerosal in ophthalmic solutions was found to cause allergic reactions, but only when concentrated by contact lenses. However, thimerosal alone was never found to cause GPC. It should be noted that the clinical manifestation of thimerosal hypersensitivity was never clinical GPC, but rather a superior limbal fibrovascular pannus.
Furthermore, there is no evidence to implicate allergy, including type-4 hypersensitivity, as the cause of GPC in humans; GPC does not have the histology, signs or symptoms of allergy. GPC occurs in non-atopic people, and is directly related to contact lens edge irritation. It has even occurred unilaterally in bilateral contact lens wearers, when one lens has a different edge or when one eye is highly myopic.
Modification of the lens edge has been standard and effective therapy for GPC for two decades. Thus, the debate over the etiology of GPC is (and has been) over.
First Aid for CRAO
This is in regard to Dr. Gurwoods Diagnostic Quiz column (Sudden Vision Loss is a Warning, December 2006). I have always enjoyed listening to your lectures and reading your articles. But I am not sure why, with what would appear to be an obvious central retinal artery occlusion (CRAO), you did not have the patient rebreathe or try to reduce pressure by digital massage of the globe. I have seen this work somewhat in the office and feel that, besides all the tests that are necessary, you forgot to administer first aid, which might have saved some of his vision.
Steven J. Leighton, O.D., Charlotte, N.C.
Dr. Gurwood responds:
Good questions, and thanks for your interest. I did think of both of those things you suggest. But, the retina cannot be saved after 70 minutes of oxygen deprivation. By the time I saw this patient, the amount of time that had passed was in the hours.
Later, I did ask a retinologist if I should have undertaken the measures you suggest. The retinologist replied that it would have made no difference, while putting the eye and/or central nervous system at risk of complications from the medications.
Howard Backman, L.Sc.O., O.D., (Emeritus) and Malcolm Baines, Ph.D., Department of Microbiology and Immunology, McGill University, Montreal, Quebec