Análisis de los programas específicos de apoyo al sector migrante retornado

Surveillance was undertaken independently through two national schemes: one, a newly devised, disorder-specific scheme in ophthalmology, and the other, an existing UK scheme in paediatrics covering a range o f disorders. Ophthalmic respondents were less compliant with the notification system than their paediatric counterparts but reported a higher proportion o f all eligible cases, as well as fewer ineligible cases. Using capture-recapture analysis, it was estimated that overall 92% o f infants were ascertained, with the level o f ascertainment being higher in the ophthalmic than the paediatric scheme (85% and 45% respectively).

5.1.2 Case definition.

In the absence o f an appropriate existing definition, a new clinical case definition for congenital and infantile was adopted for this study. This was intended to encompass children with visually significant cataract o f infantile onset, who form a clinically relevant group, distinct from other children with c a t a r a c t . I t s validity was assumed in this study, in the absence o f a ‘gold standard’ against which to evaluate it formally.

The case definition adopted had been agreed, before the study commenced, with ophthalmologists participating in the surveillance scheme. The majority o f cases

were reported by a small number o f these respondents with particular expertise in the management o f young children with cataract. Only 2% o f cases notified by ophthalmologists were ineligible because they did not meet the case definition. Thus it is reasonable to assume that the case definition was reliably applied by ophthalmic respondents. This assumption is supported indirectly by published evaluations o f inter-observer variation in large epidemiological studies which have shown that m ost ophthalmic diagnoses made clinically are reliable.^'^

Ease o f application o f the case definition is recognised to be an important factor in successful s u r v e i l l a n c e . T h e r e f o r e a simplified case definition was adopted for the paediatric scheme, to minimise under-reporting o f cases in which the aetiology or age at onset o f cataract were unknown to the reporting

paediatrician. O f cases reported by paediatricians which did not meet the case definition, two thirds were ineligible because they were prevalent cases and only one child with acquired cataract was notified. This suggests that the use o f a broader case definition did not adversely affect specificity o f reporting by paediatricians.

The eligibility o f all notified cases was carefully assessed from the details provided. As discussed in the preceding chapter (section 4.6.2), there was evidence supporting infantile onset in those cases detected outside infancy. This included morphology, associated congenital ocular anomalies, nystagmus and established amblyopia. Thus they were included in the study as they were

considered to be valid cases o f cataract o f congenital or infantile onset.

5.1.3 Completeness of the reporting bases o f the surveillance schemes. Surveillance has not previously been used widely in ophthalmology.*^^’’^^’’^’’’*^ At the time the research reported in this thesis was initiated, a national surveillance scheme in ophthalmology did not exist. Therefore it was necessary to establish a new disorder-specific scheme.

The management o f congenital and infantile cataract is recognised to be a highly specialised area o f ophthalmic p r a c t i c e . E i g h t ophthalmologists in the UK known to have particular expertise in this area were specifically approached to establish the surveillance scheme: they subsequently reported more than half o f all eligible cases.

Most other respondents were identified through the survey o f self-reported

practice as a result o f which, 87% o f replying eligible ophthalmologists joined the reporting base. However, in the absence o f appropriate census data about

ophthalmic practice in the UK, formal validation o f the ophthalmic reporting base was not conducted. Although it is possible that there was biased recruitment o f respondents to the reporting base, a higher than expected number o f

ophthalmologists reported managing infants with cataract and it is likely that most eligible respondents were included. Evidence to support this comes from the

finding that only 7 (3%) eligible cases were under the care o f an ophthalmologist outside the scheme.

An ocular disorder has not previously been included in the BPSU surveillance s c h e m e . T h e composition o f the paediatric reporting base, comprising over

1300 respondents,'^* was not within the control o f this study. The surgical

(ophthalmic) management o f infants with cataract is more highly specialised than the detection o f affected children by screening or their general (paediatric)

assessment. Therefore it is likely that many o f the respondents on the paediatric reporting base would have been involved, in some way, in the management o f children with congenital and infantile cataract. However the findings of one study to validate the paediatric reporting base suggest some previous under­

representation o f neonatologists, community paediatricians and paediatric neurologists,^'" some o f whom might be responsible for the care o f infants with cataract. The effect o f this potential bias is discussed further in the context of ascertainment by the paediatric scheme.( Section 5.1.6, page 175)

Surveillance through the paediatric scheme was undertaken to minimise under­ representation o f children with lethal or systemic diseases or multiple disabilities, or those in whom surgery was not undertaken for any reason, as well as to allow ascertainment to be estimated. That paediatricians notified two children who died before ophthalmic assessment could take place was evidence that this aim was likely to have been realised.