Epidemiology Of Eye Disease Part 3 Review

Chapter 16 Corneal And External Diseases has sub-sections on microbial keratitis, viral infections, keratoconjunctivitis, acanthamoeba --- ocular manifestations, vernal keratoconjunctivitis, Mooren’s ulcer, climatic droplet keratopathy, and pterygium.

In developing countries, where most corneal trauma is caused by vegetable or animal material, often no definite association is found to exist between injury with organic matter and the development of a fungal ulcer. However, in south Florida the opposite is the case. Fungal keratitis was found to occur predominantly in young males who had a previous history of ocular trauma that occurred outdoors or in association with agricultural occupations. I see a fair # of fungal corneal ulcers in the tropics and it was interesting to realize that the history of ocular trauma may well not be elicited unlike southern Fl. I have sometimes questioned if I have gotten the full story ( history ) with a severe corneal ulcer and no history of trauma but it makes more sense now. You might not elicit that connection because it's not there. Three fungal organisms account for the majority of corneal infections: Fusarium sp., Aspergillus sp. and Candida sp. Candida sp. which is rarely seen in warm humid climates or in a developing country setting, seems preferentially to infect comprised corneas in industrialized countries with temperate climates. Areas where the climate is warm and humid, especially near the equator, appear to have proportionately more cases of fungal keratitis. It appears that the prevalence of fungal corneal infections in a community is somehow influenced by altitude, temperature, and/or humidity with high, dry, cool climates being protective against developing fungal keratitis. In the industrialized world, overnight contact lens wear is a major risk factor for the development of corneal ulceration -- bacterial or fungal. In many developing countries the incidence of corneal ulceration is 10-70 times higher than the incidence in the USA. In some tropical countries such as southern India, half of all cases of microbial keratitis are fungal and half are bacterial. Sometimes the corneal ulcer can be both bacterial and fungal ( mixed ). It has been reported that some antibiotics, including chloramphenicol, have a modest anti-fungal effect in vitro against Fusarium and Aspergillus. This may explain reports that describe a positive therapeutic effect of antibiotics in patients with proven fungal keratitis. Oral anti-fungal agents ( itraconazole, ketoconazole, etc. ) should be given with Coke or Pepsi ( acid media ) to enhance absorption. Doxycycline orally 100 mg bid with food ( do not take with milk / dairy products ) may be a useful addition with some corneal ulcers. My personal experience, as I have written about previously on this blog, is initially rubbing ( massaging ) the ulcer bed with 10% povidone-iodine wet Q-tips and starting povidone-iodine 5% 8 x daily and whatever else can be helpful, at least in my hands.

Chapter 16d Ocular Manifestations Of Leprosy. Paul Courtright and Susan Lewallen discussed leprosy which is a chronic inflammatory disease caused by Mycobacterium leprae, an acid-fast bacillus related to Mycobacterium tuberculosis. The three major causes of visual disability and blindness in leprosy patients are corneal disease ( primarily a result of exposure secondary to lagophthalmos and hypoesthesia ), uveal disease ( in particular, chronic uveitis ) and cataract ( both complicated and age-related ). The worldwide leprosy prevalence has continued to decline. The majority of new cases come from India, Brazil, and Indonesia. It is generally recognized that the distribution of leprosy is linked to the socio-economic status. In 1982 the WHO recommended multidrug therapy ( MDT ) comprising dapsone, rifampicin, and clofazimine. Leprosy has many ocular manifestations. A fascinating disease for the ophthalmologist. One of the main reasons I ended up as an ophthalmologist as I spent two years in the early 1970’s as a general medical officer at the USPHS National Leprosarium ( Carville ). I was fortunate to observe Dr. Margaret Brand ( my mentor ) who had spent 30 years in southern India working with leprosy patients in the eye clinic.

Climatic droplet keratopathy ( CDK ) is a degenerative condition of the cornea. It is characterized by the accumulation of translucent protein material looking like small ' droplets ' in the superficial corneal stroma. It is confined initially to an exposed, interpalpebral horizontal strip of each cornea, beginning in the nasal and temporal periphery of both eyes and extending centrally with time ( no pannus / no corneal edema ). CDK occurs throughout the world. It is rare in temperate climates and mid-latitudes. Those geographical areas where CDK is both severe and has high prevalence are where snowfall persists late into the summer in the northern hemisphere ( Labrador, Greenland, Siberia, Mongolia, and the Tibetan plateau ). At lower latitudes CDK occurs in dry, sandy, or desert areas, as in the Arabian Peninsula, Iran, or Australia. CDK can be misunderstood or misdiagnosed by ophthalmologists unfamiliar with this condition.
A pterygium is a radially - arranged, triangular or wing - shaped fibrovascular growth extending over the corneal limbus onto the cornea. Pterygia are more common within 40 degrees latitude north or south of the equator with a general trend of higher prevalence closer to the equator. The problem, as we all know, is the recurrence rate can be excessive. In my hands, conjunctival grafts have greatly reduced my recurrence rate. Pterygium can cause decreased vision due to induced irregular astigmatism or involvement ( invasion ) of the visual axis. I have seen 'kissing' ( connected ) nasal and temporal pterygia in the developing world. Patients should be told that there is more pain, redness, tearing, etc. post-op with pterygium surgery than after cataract surgery. My experience is early pterygia are best left alone --- let that sleeping dog lie. Ocular sun ( UV ) exposure appears to be a high risk factor.

Chapter 21 ( Diabetic Retinopathy ). Although maintaining normal blood glucose level from the onset would be ideal, any improvement in glycaemic control at virtually any stage in the course of retinopathy seems to be associated with a decrease risk of progression of retinopathy. It has been estimated that diabetes will increase in prevalence to about 300 million persons worldwide by 2025. Insulin dependent ( type 1 ) diabetics have a higher ( quicker ) prevalence of retinopathy compared to non-insulin dependent diabetics. There are recent data to suggest, that the impact of diabetes ( mostly diabetic retinopathy ) on vision may be diminishing in some places. Recent declines in prevalence and incidence of diabetic retinopathy and macular edema suggest that despite an apparently growing burden of diabetes, previous ocular forecasts may need to be readjusted. Risk factors for diabetic retinopathy include duration of diabetes. In virtually every prevalence study, duration of diabetes is the most important characteristic associated with increased risk. Good glycaemic control was quite important in reducing the incidence and the risk of developing proliferative retinopathy. Blood pressure is an important contributing cause of diabetic retinopathy and controlling it is important in attempts to minimize the incidence and progression of retinopathy in diabetics. Several investigations have reported a positive association between serum lipids and diabetic retinopathy, but the findings have not been universal or consistent. Microalbuminuria was associated with proliferative diabetic retinopathy in type 1 diabetics and with any retinopathy in those with older - onset diabetes. From the time of diagnosis, emphasis is now placed on intensive glycaemic and blood pressure control to reduce incidence and progression of retinopathy. The role of the ophthalmologist is to communicate his / her clinical findings to the primary care physician and inform the patient of the benefits of such care ( control ). Referring patients, who are obviously out of control, to a nutritionist / dietitian is often helpful in the developing world. Unfortunate many of my patients can not afford the cost of the strips needed in the glucose meters. Handouts in the local languages may be useful. In Belize we have a single page handout for diabetes and another for glaucoma. One side is in English and the other side in Spanish. Quite simple, basic information put together by my friend Larry Schwab MD, myself, and the eye staff in Belize. Glaucoma, of at least two distinct types, is more frequent in people with diabetes ---- neovascular glaucoma and open - angle glaucoma which is probably found in an increased frequency among diabetic persons. In persons without diabetes, this is usually an age-related disorder, but it appears to occur earlier in people with diabetes.

Chapter 22 Age-Related Macular Degeneration stated this is the leading cause of blindness in older people in the USA, UK, and in many industrialized countries. O.C.T. has obviously greatly enhanced our diagnosis and monitoring ability of macular problems in the developed world over the last 20 years. This is usually not the case in the developing world, certainly not in low-income countries. In fact, I have been to many developing world eye clinics where there are 3, 4, 5, etc. broken eye machines ( OCT, phaco, A-scan, perimetry, etc. ) that are gathering dust in the corner / closet as no one knows how to repair them. If there really is no chance of ever repairing ( know how / spare parts unavailable ), my advice often is to throw them all away. This often ‘shocks’ my host but probably is the best course. Sometimes well meaning organizations / ophthalmic persons ship already broken eye equipment to developing- world eye clinics. This might be a good tax write off for hospitals, etc. but not helpful to an eye clinic in rural Tanzania, etc. Although data from black populations are relatively sparse, there is some evidence that the steep rise in prevalence with increasing age, seen in white populations, is not evident in black ones. With the association between AMD ( risk factors ) and cardiovascular disease, the data most consistent links smoking with increased AMD. Systemic markers of inflammation such as raised levels of white blood cell counts, plasma fibrinogen and C-reactive protein have been associated with AMD in a number of new studies. Further research is needed to clarify the exact role of inflammation in AMD pathogenesis. Whether or not exposure to sunlight or artificial light sources is an important etiological factor in the development of AMD in human populations is not clear. There is evidence, although not conclusion, that omega-3 fatty acids may play a role in the primary prevention of AMD. There is now considerable evidence to suggest that genetic factors play a role in the development of AMD, and it is likely that multiple genes interacting with environmental factors, such as smoking and inflammatory markers, are involved. Obviously there was some discuss about anti-VEGF treatment which has changed the paradigm of neovascular AMD management.

Section 4 Prevention Strategies. Chapter 23. From Epidemiology to Programme. Chapter 24 Global Initiative For The Elimination Of Avoidable Blindness. The History And Priorities For Vision 2020 The Right To Sight. The primary goal of Vision 2020, launched in 1999, is to eliminate avoidable blindness by the year 2020. The four essential components of the Vision 2020 programme were: #1. Cost-effective disease control interventions. #2. Human resource development ( training and motivation ) #3. Infrastructure development ( facilities, appropriate technology / consumables, funds. #4. Advocacy. Growing up in a developed country such as USA, it is easy not to fully understand that without infrastructure and human resource development not much will happen in the reduction of blindness in the developing world. All that ophthalmic support that has simply always ’been there’ in say, North America is often lacking in the developing world, certainly in low income countries --- no ophthalmic nurses, no techs, no slit lamps, no slit lamp bulbs, no operating microscope, no IOL's, no O.R., no drugs / drops, etc., etc. The necessary diagnostic, therapeutic, and surgical equipment and consumables must be in place and functioning if much is going to happen to reduce the blindness in a developing country. This sometimes is a hard concept to fully grasp if you have not lived and work for an extended period in a developing country. Initially vision 2020 focused on five 'priority' diseases : #1. Cataract #2. Refractive Error #3. Onchocerciasis #4. Childhood Blindness #5.Trachoma. Early on ( early 2000's ) there was some criticism that glaucoma had not been included. The priority has since been broadened to include important chronic eye diseases: diabetic retinopathy, glaucoma, and age-related macular degeneration.

Well this wraps up my three part review of The Epidemiology Of Eye Disease. Hope this was useful. I certainly learned a lot.
Peace, Baxter

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