Detailed evaluation: manual of ophthalmological procedure

/Rft?. WORLD HEALTH ORGANIZATION ORGANISATION MONDIALE DE LA SANTE ONCHOCERCIASIS CONTROL PROGRAMME IN WEST AFRICA PROGRAMME DE LUTTE CONTRE L'ONCHOCERCOSE EN AFRIQUE DE L'OUEST EPIDEMIOT,OGICAL EVALUATION UNIT UMTE D'EVALUATION EPIDEMIOLOGIQUE DETAILED EVALUATION rr rr * {. !r {. :r rr * * :r * {. tr * {. MANUAL OF OPHTHALMOLOGICAL PROCEDURE Compiled By K. Y. Dadzie .1,th. I October 16, 1992 Contents INTRODUCTION. OBJECTIVES. . . COMPOSITION AND RESPONSIBILITIES OF THE OPHTHALMOLOGICAL TEAM OPHTHALMOLOGICAL EQUIPMENT . . PREPARATION OF THE SURVEY ARRIVAL AT THE VILLAGE CENSUS PARASITOLOGY OPHTHALMOLOGICAL EXAMINATION DATA ORGANIZATION DEPARTURE FROM THE VILLAGE DATA ENTRY AND PROCESSING DATA ANALYSIS ANNEXES 2 2 4 4 5 't 7 7 l3 l3 r3 t4 l5 t -l- I I.INTRODUCTION The Epidemiological Evaluation Unit (EPI) of the Onchocerciasis Control Programme in West Africa (OCP) is responsible for the evaluation of: - the impact of vector control, - the effect of chemotherapy or - the effect of both vector control and chemotherapy on onchocerciasis in the human populations To carry out this function two levels of evaluations, viz simple and detailed evaluations, are employed. In the original Programme area, where the control of onchocerciasis was by larviciding only some 480 villages were examined at least once at the start of vector control and of these some 80 were surveyed in detail. However only 150 selected villages have been followed up longitudinally every 3-4 years, with some 30 of them in detailed evaluation. The majority of the villages are for epidemiological evaluation only but some of the villages serve simultaneously is entomological catching points. The activities which are carried out during detailed evaluation are: - population census on the basis of family units and the collection of demographic data. - parasitological test of skin snip. - general clinical examinationl. - visual acuity test - detailed ophthalmological examination. Only individuals aged 5 years and over undergo visual acuity test and detailed ophthalmological examination. These examinations enable the determination of the prevalence and intensity of infection and the prevalence of blindness as well as the distribution of systemic and ocular onchocerciasis in the community. The patient record form in use, 560lM (annex l), is a modification of and a replacement for the original EPI detailed evaluation form 5601. The ophthalmological section of the form 560lM has two parts. The first part records the results of obligatory examinations for signs of ocular onchocerciasis and eye diseases of public health importance and the second part records the results of facultative examination of less important or less interesting eye signs. The new form also allows the differentiation of the coding of 'the main cause of blindness' into oncho and non-oncho blindness. For detailed evaluation, an ophthalmological team works in conjunction with a parasitological team and 2 census clerks. To conduct a detailed evaluation of villages, all the teams travel together, arrive in the villages together and set up their working stands in such a way as to harmonize the work. The ophthalmological examination is time consuming and its turn-over is at most half that for the parasitological examination. It is therefore often ideal to utilize the time of the parasitological team better by having 2 ophthalmologists working together with one parasitologist. This manual of procedure describes only the ophthalmological activities to be carried out during detailed evaluation. Other activities, viz, census and demographical data collection and parasitological examinations are described in an appendix. The general clinical examination has been dropped of late because analysis carried out recently on the data collected on the basis of the protocol in use has shown that the resulting data are not useful for demonstrating the evolution of systemic and skin manifestations of onchocerciasis in the human population. I _)- t 2. OBJECTIVES. The objectives of ophthalmological examination during detailed evaluation are: To identiÿ the public health import4nce of onchocerciasis as a disease in endemic zones by mapping out the geographical distribution of different community patterns of ocular onchocerciasis. To monitor the impact of vector control or chemotherapy or the combination of both on ocular onchocerciasis in the human populations. 3. COMPOSITION AND RESPONSIBILITIES OF THE OPHTHALMOLOGICAL TEAM. 3.1. The ophthalmological team: The ophthalmological team of the EPI Unit is made up of the Ophthalmologist and 3 assistants consisting of an ophthalmic trained nurse, a registered nurse and an auxiliary nurse. ORGANIZATION OF THE OPHTHALMOLOGICAL TEAM OPHTHALMOLOGIST OPHTTIALMIC NURSE REGISTERED NURSE AUXILIARY NURSE 3.2. Division of responsibility. 3.2.1. The ophthalmologist: He is in charge of: - Planning and executing the survey - Taking up contact with government officials on the way to the village. - At the village, taking up contact with the village authorities. - He is also responsible for filing a report on the results of the survey. 3.2.2 Ophthelmic nurse, teem leeder: - He is responsible for the assistants in his team. - Check that all equipment, including the back up equipment are in good working condition before the start of the survey. I -3- Makes requisition for materials and drugs for the survey Oversees the movement of the team when the Ophthalmologist does not travel with the team in a convoy. In the field, he is responsible for assigning duties to the assistants under him and ensuring the smooth running of the survey. His principal duty in the field is conductine visual field test of patients as requested by the ophthalmologist. 3.2.3 The two other rssistants: They help the team leader in putting together the materials and equipments for the survey Their other duties are: Carrying out visual acuitv test (Sjôgren's hand test) according to laid down instructions and recording the results using laid down codes, see parag,raph 9.1 and annex 9. Assisting the ophthalmologist during his work in the ophthalmic mobile clinic where their duty consists of: Collecting the forms of patients who have had their visual acuity test done from the visual acuity test stand2. Calling out the patients in groups of 6 to 8 and seating them in the patients' waiting compartment of the ophthalmic vehicle with their heads bent down between their knees before slit lamp examination commences. Presenting the patients one after the other for slit lamp examination, after the first patient has bent down his head for at least 2 minutes. He thereby hands over the correctly identified record form allocated to the patient to the ophthalmologist. Instilling mydriatic drops in the patient's eyes after the slit lamp examination and asking the patient to wait outside the ophthalmic mobile clinic. Recalling the patients, after 4 groups of 24 - 32 persons have undergone slit lamp examination or after the lapse of about an hour of examination, for fundus examination. Dispensing eye drops or ointment to patients on the instructions of the ophthalmologist3. 4. OPHTHALMOLOGICAL EQUIPMENT Certain equipments are necessary for the proper execution of the ophthalmological examination: Ophthalmic mobile clinic: It has an air-conditioned dark room with 2 compartments, the examination compartment and the patients waiting compartment. It is fitted with basic furniture: In the examination compartment is a table for the ophthalmologist to record his findings, two chairs to seat the patient and the ophthalmologist, shelves to carry ophthalmic drops and other materials and a file cabinet to hold patient record forms. 2 These patients would have undergone parasitological examination at the parasitological stand previously, (see annex 5). 3 The details of the responsibilities of the assistant assigned to the ophthalmologist are described under 9. I -4- t The patient compartment has two benches to seat patients Ophthelmlc instruments: . a slit lamp with applanation tonometer . a direct and indirect ophthalmoscope . a fundus camera and accessories . 3-mirror fundus lens and gonioscope Diagnostic meterials: . eye drops . flourecein strips . disinfecting set (These are carried and used in the mobile clinic) Other ophthalmological equipments: . Sjôgren hand test optotypes for visual acuity test, . Bjerrum's screen and Freedman's analyser for visual field test None ophthalmic equlpment These are: generator for running the ophthalmic clinic and folded tables and chairs for various uses. A set of spare basic equipment is carried along as back-up equipment during surveys. 5. PREPARATION OF THE SURVEY Surveys are conducted in the dry season when the roads are motorable, the farming season is over and the villagers are available and are willing to spare their time for the examination. Before the survey, a plan or a timetable of villages to be examined is elaborated which takes into account the fact that the ophthalmologist can examine only up to 80 - 100 patients a day. Allowance is also made for travelling from one village to the other. A letter signed by the Programme Director is sent to the Minister of Health of the country concerned about 2 months in advance to announce the dates of the planned survey of the villages with an indication of their'sous-prefecture' and 'prefecture' or district or province or region, as the czrse may be. In the letter, the Minister is kindly asked to inform the local authorities concerned about the pending survey. The team leaves Ouagadougou after going through the check list of materials and equipment which are securely stacked in the vehicles to avoid any damage during travel. The journey to the village is planned in such a way that the team arrives there in the course of the afternoon. The 'village form' (annex 8) is to be carefully studied before setting out for the village. It contains all the details about the village, including its political set up as well as its access route4. A detailed map of the area where the village is situated is to be carried along to aid in finding the route to the village. In the event of the first evaluation of the village, the 'village form' should be filled in accordingly, (see annex 7 for guidelines for filling the form). 4 56. ARRIVAL AT THE VILLAGE. 6.1, Courtesy call on the vlllege chief: First, the chief of the village is sought for the u§ual salutation, to introduce the team, and to give a brief account of the purpose of the mission and to ask for a place to install the equipment. The chief is kindly asked to assemble the village population in the evening for a more detailed briefings. In some villages the political leader is the more influential personality. If that is the case, it is more effective to work through the political leader rather than the village chief. These facts are either noted on the 'village form' (annex 8) or can be enquired about discretely. 6.2. Instelletion of equlpments The team searches for a place of easy access to the villagers to park the ophthalmic mobile clinic. Preferably, it should be under the shade of a big tree or trees to avoid direct sunshine on the vehicle and provide shade for the patients waiting for their turn to be examined. - The Bjerrum screen is hung on the side of the vehicle for visual field test. It is necessary to conduct the test under the pleasant atmosphere of a shade. A place, preferably a shade under a tree for conducting visual acuity test is located6. The ophthalmic assistants arrange the ophthalmic mobile clinic. They set up the slit lamp and the fundus camera, arrange the eye drops and ointments in their proper places, test that the generator, the lighting system, as well as the air conditioner work and arrange all other equipment and materials in order for the consultation. The ophthalmic team leader then assigns one assistant to the ophthalmic vehicle and the other to the visual acuity stand for the duration of the survey in the village. 6.3 Generel Assembly The assembly serves as a forum for public education and mobilization to ensure maximum participation and cooperation at the examination. As many villagers :§ possible are encouraged to attend. The chief, his elders, the political leader, notables of the village and the heads of all the families must be present. The ophthalmologist exposes briefly about the programme and states the aim of the survey. He then explains carefully the procedure of the survey and emphasizes on what the villagers are expected to do. He stresses on the benefit to be derived from the ophthalmological examination which is painless. He urges all to attend the examination and assures the population of treatment of all ailments at the end of the survey. It is explained that only a limited number of persons can be examined in a day (about 100 - 120 parasitologically of whom E0 - 100 aged 5 years and over can be examined by the ophthalmologist). It therefore follows that only a certain number of families can be asked to attend the examination each day but everybody will have his turn. s The timing of the assembly in the evening ensures maximum participation. This is the time when all the villagers would have returned home from their farms. In moslem communities, the meeting must be timed to take place after the last prayer of the day. 6 The places chosen for the above named tests should be located close to each other and to the parasitological and census stands to avoid the loss of patients when moving from one stand to the next. 7-6- At this time the names of the heads of families to be seen on the first day of the survey is announcedT. It is important to stress that all members of the family ihould attond the examination together and not singly. This ensures the smooth running of the census and eliminates unnecessary delays. It is proper to start the survey with the family of the village chief and the chief himself as the first patient. It is stated that the names of the heads of families to be seen the next day will be communicated to the village authorities on the preceding evening with the same instructions, until all families and therefore every body in the village has been examined. The selection of the number of families to be examined is done in consultation with the census clerk if there has been a previous "passage" (see appendix 3). In the event of a first survey, an attempt is made to estimate the sizes of the families to guide in the selection. It is necessary to have about 20 candidates carried over to the next day to ensure that the ophthalmologist can also start work at the same time as the others the next morning. t -7 - EVALUATION Detailed evaluation of a village starts as early as possible in the morning; not later than 08:00 hours). Cw ahrÈ ------È Vl,ruf, .@it:t C{È 5r tf,tra1È.l.ay hLÈllt Lrrndr ------------> fr t Èlrtt pGÈ Yt&rll1.ld È-È 7. CENSUS The villagers report first at the census stand (see annex 3) 8. PARASITOLOGY Skin snip is done after census (see annex 5) 9. OPHTHALMOLOGICAL EXAMINATION 9.1 Yisual ecuity Visual acuity test starts when at least l0 persons arrive at the visual acuity stand from the parasitological stand. The test employed is Sjôgren's illiterate Hand test. The examiner conducts the test at a distance of 5 metres from the patient who sits down comfortably and relaxed on a seat provided. A mark is also made at 3 metres from the patient to test those who see worse than 6/60 or 0.1. The visual acuity test is conducted with 4 single optotypes of the Sjôgren's Hand test. They are Y=5/4 corresponding to a visual acuity of 6/6 or 1.0; Y=5/5 being the visual acuity equivalent to 6/9 or 0.7; Y=5/10 equivalent to 6/18 or 0.3 and V= 5/30 tantamount to a visual acuity oî 6/60 or 0.1. The test is carried out on each eye separately and with the other eye occluded, after clearly explaining the procedure to the patient. The population is encouraged to look on in order to learn the procedure. The conduct of the test is shown by the flow chart. For details, see annex 9. oDàtàrls Db11. I 8OUTCOME Fail START Tesr. _V = 5 TEST OF VISUAL ACUTTY AND CODING TEST OUTCOME OUTCOME Fail Tesr. _ y =5/30 (at 3m Pass ;/30 (at 5m) v =5/70 (at 5m)_.--Fail Pass CODE 3 2 L 5 4 Test: Y = 5/5 (at 5m) _.-Fail Pass Test._ Y =5/4 (at5m)_Fail 0Pass I I Pass a -9- 9.t2. trxemlnetion in the ophthalmic vehicle. The ophthalmologist's work begins with the availability of the first lO- l5 or so patients arrivingfrom the visual acuity stand. Before this time the ophthalmologist would have ascertained thai all equipment and instruments to be used for the examination arè in working condition. He must also have acquainted himself previously with the form 560lM and its recoà description, annexI and 2 or he must have refreshed his memory in this regard. 9.2.1 Antcrlor segmcnt cxrmlnrtlon The assistant assigned to the mobile clinic calls in the first 6-E patients who get seated withtheir heads bent down between their knees. - He explains the procedure and the purpose of the examination to the patients directly orthrough an interpreter when he does not speak the local dialect. - The bending down of the heads between the knees by the patients causes microfilariae in the anterior chamber of the eye to fall by gravitÿ and aggregate at the l2 o'clock position, the topmost point of the anterioi chamber t"-ni"f, n"t now become the lowest point. On seating the patient at the slit lamp, thereafter, the aggregated microfilariae start falling by gravity again. tt is at this point in time that the microfilariae in the anterior chamber of ine eye are counted. Thisprocedure ensures standardized microfilarial counts. - He presents the form of the first patient, correctly identified, to the ophthalmologist and seats the patient at the slit lamp after the first patient has bent down his head for at least 2 minutes. - It is important that the assistant checks that the identity of each patient is correct. To identify a patient correctly, the assistant calls out the name of the patient as appears on the individual form. He then proceeds to check that the tàmporary number the patient is carrying plastered on his right wrist, tallies with that on theindividual form. The ophthalmologist, on his part-, checks whether the age and sex recorded on the form correspond to the patient. Occasionally, the patËnt might have lost the number plastered on his wrist. It is then partièularly important to ensure that the identification of the patient is correctly established. 9-2.1.1 count of microfileriae in the anterior chamber of the eye (MFAC). - The ophthalmologist starts the examination by counting the microfilariae present in the anterior chamber, first of the right eye, then the left using the slit lamp magnification x 16.Instruction for coding the count is given by "Record description to form 56ô'1M,, annex 2. - The search for microfilariae in the anterior chamber is straight forward but the counting becomes more and more inaccurate as the numbir of microfilariae exceeds 30. Also when only a few microfilariae are present in the anterior chamber, say I - 3, they may occasionally be difficult to find and the anterior chamber may need to be scanned carefully. If I or 2 microfilariae are found in theleft anterior chamber when none had been found previously in the right, another look at the right anterior chamber may be indicated to ensure that there is really no microfilaria in the anterior chamber of the right eye. 9.2.1.2 Count of dead microfllariae in the cornea, (DMFC). - Dead microfilariae in the cornea is counted using x l6 magnification of the slit lamp, first in the right then in the left cornea. - Dead microfilariae are usually found at 3 and 9 o'clock positions of the cornealperiphery but may be fairly evenly distributed in the cornea when they are many. They are usually found in the anterior I /3 of the cornea. Counting of dLad corneal _ l0_ t.' microfilariae is an accurate procedure when the patient is co-operative. When the microfilariae are many, the count may be facilitated by dividing the cornea into sectors and counting the microfilariae in a sector at a time. The coding of the result is similar to that of MFAC, see annex 2. 9.2.1.3 Count of Oncho Punctete Opaclty: - The counting of oncho punctate opacities of the cornea is done with x l6 magnification of the slit lamp. - Corneal punctate opacities or fluffy opacities are about 0.5 mm in diameter and liein the anterior layer of the cornea and the names describe their appearance. They are also known as snow flake or cotton wool opacities. They may or may not contain dead microfilariae, either in part or as a whole in théir miAOte. lwtrendead microfilariae are present in oncho corneal opacities, the microfilariae are counted and added to the count of the dead microfilariae made previously). Onchopunctate opacities are often found at the nasal or temporal periphery but may be anywhere in the cornea. Coding of the results is found in thô'Recorâ descripiion of form S60lM', annex 2. 9.2.1.4 Sclerosing keratitis (SK) - The search for sclerosing keratitis is done with x l6 magnification of the slit lamp. The codingfollows the instructions in the'Record description oifor. s60lM, - Sclerosing keratitis is a diffuse opacification of the cornea resulting from theinvasion of numerous microfilariae therein. The diagnosis of i-he typicat onchocercal sclerosing keratitis is straightforward. Horrerer, often, itsdifferentiation from other non-onchocercai corneal lesions ."y noi be easy, inparticular, when microfilariae are not found in the cornea. Sclerosing keratitis may appear atypical in the course of the regression of the lesion during càntrol andpose a problem in the diagnosis. This anomaly is well described in the "Recorddescription of form 560lM'. annex 2. The additional codes 4, 5,6 are provisional.They are designed to determine the validity of the association of the iesions with oncho sclerosing keratitis. 9.2.1.5 Other corneal signs: - After the search for the typical onchocercal signs of the cornea, a search for any other cornealpathology is made and the results recorded using the applicable code. See under other corneal signs in 'Record description of form 560lM,, anne* j.- 9.2.1.6 Iridocyclitis. Next, the signs of iridocyclitis, viz, flare, cells, KP's, circumcorneal injection, iris changes andfinally pupillary form and pupil reaction to light aie looked for and coded accordinfto the 'Record description of form 560lM,, annex 2. 9.2.1.7 ConJunctivr/lld signs: - A search is made for signs of conjunctival and lid pathology and coded as applicable accordingto the 'Record description of form 560lM,, annex 2. - The assistant now instills two drops of mydriatic in the eyes of the patient and helps him or her out of the mobile clinic. He then seats the next patient for examination at the siit lamp after correctly identifying him or her and handing over his or her record form to the ophthalmologist. I - ll - - Meanwhile the ophthalmologist records his findings by filling the appropriate codes on form 560lM, annex l, belonging to the patient just examined. 9.2.2 Poslerior segment examinetion - The second leg of the examination requires a well dilated pupil. It therefore starts after about one hour of slit lamp examination which entails some 20 - 30 patients. - The assistant calls the first 6-E patients again. This time the patients sit down normally. - The first patient is seated at the slit lamp and his form, checked to be correct, is handed overto the ophthalmologist. 9.2.2.1 Lens/ceteract: - The ophthalmologist examines first the lens with the slit lamp to look for the presence of lens opacities or lens luxation and codes the results according to "Record desciiption of form560lM,'annex 2. - Occasionally, dead microfilariae are found attached to the posterior lens capsule. Fundus examination: (This is done with the clirect and/or indirect ophthalmoscope). 9.2.2.2 Optic disc: - The examination of the optic disc is done with the direct ophthalmoscope to look for changes such as pallor of the disc, changes at the disc margins, iheathing of central retinal blood vessels, signs of papillitis and cupping of the disc. These are coded-according to the ,Recorddescription of form 560lM,, annex 2. 9.2.2.3 Oncho Choroido-retinitis: - The ophthalmoloqist looks for the presence and the distribution of the typical oncho signs ofthe choroido-retina, viz. atrophy of the retinal pigment epittrôtium, atrophy of choriocapillaries, grey discs and subretinal fibrosis. The search is made with the direct andif necessary the indirect ophthalmoscope, and the results are coded according to the "Recorddescription of form S60lM", annex 2. 9.2.2.4 Other choroido-retinal slgns of possible oncho origln: - The non-typical oncho choroido-retinal signs viz. pigment hyperplasia, pseudo-drusen andpseudo-grey discs are coded according to "Record description of form S6ôtU,, annex 2. - This portion of the record of the results of the ophthalmological examination is designed to testthe probable association of pseudo-drusen, pigment hypeiplasia and pseudo-greÿ disc wittr oncho and should be viewed as provisional. 9.2.2.5 Other fundus signs: Other signs of non-oncho choroido retinal pathology are looked for and coded according to 'Record description of form 560lM,, annex 2. 9.3 Yisual fields: All patients with onchocercal lesions of the fundus affecting the optic nerve or choroid-retina, will require visual field test and the ophthalmologist must rèquest it. The test is carried out bythe ophthalmic nurse who has been trained especially to conduct it, using the Bjerrum t"ngani screen and also the Freedman's analyzer if possible as a check for accuràcy. -12- Tbe procedure of the test is detailed in annex 10. The results of the visual field test are recorded according to "Record description of form 560lM', see annex 2. 9.4 Fecultative examination: - These examinations are done for special studies only. 9.4.1 Count of llving mlcrofllerlee ln thc corner, (LMFC) - The counting of living microfilariae in the cornea is conducted with x 25 magnification of the slit lamp. Coding of the results is similar to that of DMFC and MFAC, see ànnex 2. - Living microfilariae lie usually coiled over themselves in the anterior cornea. On continued observation, they may be found to uncoil and recoil themselves. They are transparent and are usually difficult to see by the untrained observer. Retro- illumination technique facilitates the viewing of living microfilariae in the cornea. Similar to dead microfilariae, they are located at 3 or 9 o'clock position of the corneal periphery when they are only a few. When many, they are distributed fairly evenly in the cornea. If this facultative examination is envisaged it is recommended to carry it out after the count of dead microfilariae, see (9.2.1.2). 9.4.2 Meesurlng of Intre-ocular pressure, (IOp): Intra-ocular pressure should be measured when there are signs of glaucoma or the existence of glaucoma is suspected. Intra-ocular pressure is generally not measured as a routine. The IOP is entered as exact value on form S60lM. 9.4.3 Gonioscopy: - When done the result is coded according to the "Record description of form 560IM'. annex 2. 9.4.4 Fluorescein engiogrephy: - This is done only in special studies and can be coded if necessary according to the "Record description of form 360lM', annex 2. 9.4.5 Eye photography: - Photos may be made of oncho lesions of the anterior segment of the eye or the posterior segment using the fundus camera. The coding of eye photography is given by the "Record description of form 560lM', annex 2. - These photos are for documenting and recording changes that have occurred during follow-up surveys. 9.4.6 Observetion: - The space "observation" on form 560lM is provided for recording any extra information that has no provision for coding and should be used freely. 9.5 Main cause of visual lmpairment: - This gives a summary diagnosis of the eye examination and is coded according to the'Record description of form 560lM", annex 2. - 13 - t Finel verification - After filling in the form 560lM, the ophthalmologist must check to ensure that all spaces on the form are correctly filled in and that there are no apparent discrepancies. 10 DATA ORGANIZATION. - At the end of the survey in the village the ophthalmic assistants set out to organize the data collected by age and sex in a summary table on a special form provided, annex I I. - This enables the ophthalmologist to prepare a preliminary analysis of the results of the survey of the village. - He is thus able to brief the local authorities on the level of or the changes in the severity of ocular onchocerciasis in the village and therefore in the area as a whole, when he pays them the usual courtesy visit at the end of the survey. 11 DEPARTURE FROM THE VILLAGE: - Before leaving the village, the village authorities should be thanked for the co-operation exhibited in the course of the survey. They are also given a brief account of the results of the survey. - A small packet of drugs - nivaquine, aspirine and vitamins - is left with the village chief to be put in the village first-aid box, a useful public relations gesture. 12 DATA ENTRY AND PROCESSING - Back in Ouagadougou, the census clerk checks that all the individual forms have been correctly completed. Any mistakes or omissions found on the individual forms are corrected with the help of the ophthalmologist concerned. The reviewed forms are then handed over to the datà entry clerks. - There are two data entry clerks who have been trained specially to process the data received from the census clerk. Their work starts with a careful sorting of the forms. First of all individuals are arranged in the family forms, to enable the detection of those who might otherwise have been omitted. Next, the data of the present passage are compared with thôse of the previous passage (if there had been one) i.e. verification. Finally new individuals are allocated numbers. - The data are entered twice, first by one clerk (the entry clerk) and then by the other (the verifier). This double entry of the same data by two different persons minimises typing errors and ensures correct data entry. - After the entry of the data and the manual verification, the clerks carry out programme validation and correction (if errors had been observed). The validation is focused mainly on: - a probable transposition of sex; - too Sreat an age difference compared to that between the two evaluation dates; - an abnormal transfer of an individual from one family to ànother; - a conclusive incompatibility of the registration codes; - the possibility of detecting, through the examination code, dead individuals (or those having left the village for good) who may have been recorded as present. -t4- - To facilitate the data analysis, three additional codes (5 = not yet born; 6 = notyet registered; 7 = dead or emigrated earlier) have been added tô trre registration codes. These codes are not filled in directly on the entry forms but add;d duringthe validation process as the case may be. - once the data have be-en correctly validated, one embarks on the creation (updating of the databanks) of operation files, commonly called analysis files. These files constitute entries forprogrammes for printing the results on the printei or on other disks or diskettes for future usewith special programmes. - All the programmes for data entry, validation, correction, rerun, updating, analysis andprinting have been developed in gÀstc languagl. irre taure riles tïi, geneial and commoninformation which change rarely and slowlyl rulh ., " iiuu, basin, a country, etc.) and thoseconcerning the data (information on the inàividual) "i. in a random access iayout, while theindex files (file annexed to that of the data, for betier management) are in ASCII layout. I3 DATA ANALYSIS - The proS'rammes for analysis are grouped together into two main categories: analysis of onepassage (cross-sectional) or between at least t*o p"ss"ges (longitudi""il] - The detailed statistical analyses in BAsIC are executed with a statistical software, spss. Todo that' AscII files are first of all created from the .r".si."r analysis files. Next, these files aresubjected to sPSS procedures for their transformation .nJproduction of frequencies and tables. An example of data analysis by recoding the different types of resions, i.e., sclerosing keratitisand iridocyclitis, lesions of the anterior seg,ment of the éye, and optic atrophy and choroïdo-retinitis lesions, lesions of the posterior segment, is shown in annex 12. These lesions are recoded 'no le-s.ion' meaning absence of a lesion, 'iarly iesion,, ',Rdvanced lesions. "na ',no-uiuni..t-î;;classification facilitates the analysis anâ allows rapio interpretation of the different codes. Inaddition, it makes it possible to follow more easilythe trenàs in onchocercal eye lesions. I rhe different grades of these lesions are defined as follows: (i) Sclerosing keratitis. (a) An early sclerosing keratitis is a corneal opacity limited to the nasalor temporal periphery or both. (b) An advanced sclerosirig keratitis is a ôorneal opacity moreextensive than the former, presenting as an inferior semi-1inar opacity but which could extendto cover the pupil area. (ii) Iridocyclitis' (a). An early iridocyclitis is the condition in the acute or chronic stage butwithout synechiae. (b) An advanced iridocyclitis exists *rr"n in addition to the signs of the earlystage either anterior or posterior synechiae has aerretopeJ.--- (iii) choroldo-retlnitis' (a) An early choroido-retinitis is recognised by the presence of retinalpigment epithelial atrophy, typicalü located temporal to the macular area (b) An advancedchoroido-retinitis exists when atrophy of-chorio-ffir"iis, crroroido-retinal scarring or sub-retinal fibrosis can be seen in addition to the atropny of reiinat pigment epithelium. (iv) optic atrophy' (a) An early optic atrophy comprises the early pallor of the disc or the acuteor chronic optic neuritis. (b) An advanced optic airoptry is the frank optic atrophy, presentingas post-neuritic optic atrophy, often associatéo wittr rh.âtr,ing of the central retinal vessels andincreased peri-papillary pigmentation or the secondary optic atrophy consecutive to retinaldisease. Acknowledgements: We are grateful to members of thc 'Expert Advisory Committee' of the Onchocerciasis Control Programme who com-mented on and gave helpful suggestions on the manual at various times duringits preparation. we thank Dr B. A. Boatin for invaruable editorial help. rile also thank Mr T. A. Millsfor translation of the manual into French and Dr o. Ba for thc translation of ccrtain nnncxes. Wc aregrateful to Drs G. oussa and M. Banla for helpful criticisms on the French version of the manual. We thank Dr G. De Sole for the review of the earlier drafts. We arè gratefuI to Mr E. Soumbey-Alley and Mr M. S. N'Gadjaga for contributing thc part of the manual de-ali"g with data entry proccssÉg and analysis. Finally, lve are indebted to Dr E. M. Samba, DirectJr of the programme whoi continued supPort and encouragement made the preparation of the manual possible. a