Archived posting to the Leica Users Group, 2006/05/24
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Hello, Sorry if I jump too late on this topic and if the following is too technical and OT, I'll be glad to continue conversations offlist. Absolute colour blindness (ie not being able to see any colour at all, a B&W vision) is very very rare. In general, it is preferred not to denomine these conditions as 'colour blindness', but as dyschromatopsia, ie colour vision abnormalities. Colour blindness is a 'legacy' term for what was also called daltonism, a generally inherited congenital condition transmitted from mother to son first described by Dalton who suffered it and who was, if I recall correctly, the same who enunciated the Atomic theory. The Daltons instead were not daltonic, as far as I know :-). It is very (very) rare to find a daltonic woman. As Allen noted, there are lots of drugs that induce changes in colour perception. Most anti-malarian drugs (also used to treat severe types of reumatic diseases) do, as also some cardiologic drugs (ie digitalis). Once upon a time, digitalis was used to treat seizures (epilepsia), and it is a commonly accepted medical theory that Van Gogh suffered from dischromatopsia caused by this drug administration, leading to the hyper saturated colours he used (was he perhaps more realist than we choose to believe?). Ethambutol, usually useful in a combined drug therapy against tuberculosis, is neurotoxic at a cellular level, acting against the retinal cones, responsible for our colour vision. Intoxication depends on both dosis (amount of drug) and duration of therapy, and can produce from just subtle colour vision abnormalities to a more serious condition called optic neuropathy. I do not recall any antibiotics (ethambutol is not technically one) causing acquired dyschromatopsia. Frequency of the inherited form is very high (1 out of every 10 males of all humankind), and this frequency tends to be explained through evolution as it implies a better ability to discover predators with mimetic colours and patterns. Best Ed Albesi PS: I use every week two Leica operating microscopes, an independent M500 and another embedded into an excimer laser system, and have photographed them extensively with my M6s, as to give some On Topic luster... :-) El 24/05/2006, a las 11:09, Steve Barbour escribi?: > > On May 24, 2006, at 4:56 AM, Allen Graves wrote: > >> Chloroquine (used for treating malaria) and its cousin, Plaquenil >> (hydroxychloroquine)-used for treating rheumatologic disorders >> like lupus- can also cause color blindness. >> >> When I use ethambutol the normal screening for retinal toxicity >> is to check color vision IF the drug is going to be used for more >> than 2 or 3 months. It takes several months for toxicity to >> develop and it is usually reversible if detected early. Screening >> is usually every month or two after the first 3 months. If is >> continued too long after toxicity develops it can cause macular >> degeneration. We usually use ethambutol for 2 months and then >> discontinue it. >> >> The risk of toxicity from ethambutol is quite small compared to >> the risk of dying from untreated drug-resistant tuberculosis. >> >> I've never used chloroquine for long enough to have to bother with >> vision screening. Patients on Plaquenil are usually screened every >> 6 months or so. >> >> As far as I know, the mechanism of ethamutol toxicity is direct >> toxicity to the retinal receptor cells. The cones, which detect >> color, seem to be more sensitive and develop problems earlier (if >> problems are going to develop-I've only seen this once), allowing >> color vision to be used as a screening tool. >> >> I am unable to find any problems with color blindness caused by >> the sort of antibiotics used for sepsis. > > > nice summary Allen, thank you. We check kids that are on ethambutol > (which is rare) but I have never seen toxicity documented. > > As far as all the antibiotics used for bacterial infections/sepsis, > not aware of any problems...Steve >> >> Allen >> >>> hi Greg, a fascinating question, yours... I will tell you what I >>> have found so far, and I'll share it with the LUG list... >>> >>> ethambutol, a drug which is part of multidrug TB therapy, can >>> sometimes affect vision and especially color vision. >>> >>> this seems to be generally what is referred to, when we google... >>> >>> (I am not sure what the mechanism is...) >>> >>> I am also checking to see if any of the customary antibiotics >>> that are used to treat bacterial sepsis, may also cause >>> risk...though of this I don't know, but I'm further searching the >>> medical literature...and if I find something I'll let you know. >>> >>> It's a provocative question... one that I have never seen >>> investigated in questions of antibiotic toxicity, with the >>> exception of the drug ethambutol... >>> the LUG sure can be an amazing source of information, >>> >>> Steve >>> >>> >>> >>> >>> >>> >>> _______________________________________________ >>> Leica Users Group. >>> See http://leica-users.org/mailman/listinfo/lug for more information >> >> _______________________________________________ >> Leica Users Group. >> See http://leica-users.org/mailman/listinfo/lug for more information > > > _______________________________________________ > Leica Users Group. > See http://leica-users.org/mailman/listinfo/lug for more information >