BOSU (British Ophthalmic Surveillance Unit) Study on Essential Infantile Esotropia

last updated: 06/11/18

This page is to inform on a British Ophthalmic Surveillance Unit study that is being led by Welsh Ophthalmology Doctors (Mr.Damien Yeo, Mr.Ryan Davies) under the guidance of Consultant Ophthalmologist Mr.Patrick Watts.


This study is a national (United Kingdom) prospective study done under the guidance of BOSU and data collection will take place from October 2017 to November 2018 in all eye units that receive a BOSU notification card.

We are looking to study all cases that fit this description:

A constant, non-accommodative esotropia, greater than or equal to 20 prism dioptres with an onset less than 12 months old in a neurologically normal child with no ocular abnormalities.

For clinical professionals:

If you are an orthoptist or ophthalmologist in the UK working with children, we would love for you to download this pdf file below to print and display in your clinical workspace.

Frequently Asked Questions:

1. I am an orthoptist in the UK, how may I participate in the study?

We would love to recruit any patients that are seen by orthoptists. If you work in a NHS department, the consultant paediatric ophthalmologist should receive a yellow BOSU card every month. If you see a child that fits the criteria, please let the named consultant know you've seen one and they can report the case on the card. The questionnaire can then be sent to either the consultant or the orthoptist in charge. Alternatively, if you have already seen the case and would prefer to fill in the questionnaire earlier, email me at and I can post a questionnaire and some details direct to you within 24 hours. 

2. What if I operated/gave botulism to a patient before October 2017 and am seeing them for a follow up now? Are these cases to be included?

With this BOSU study, we are looking for new cases only between October 2017 to November 2018. If the child developed the esotropia before that time period(ie when they were a few months old), but is diagnosed by a clinician in your team within October 2017 to November 2018, then they would qualify. If a clinician gives them a diagnosis before the 1st October 2017 inclusive then technically they were diagnosed before that time period so they do not qualify even if a majority of their care will take place in the study period.

If you gave them a procedure before October 2017, that means that they would have received their diagnosis way before that and therefore do not qualify.

3. What if a child has not had the diagnosis formally before (ie. never presented to an eye department before) but has an esotropia fitting the description and an onset <12 months old but is now only being seen for the first time at an older age (anything >12m old)? Does that still make them a "new" case?

Although technically this is a new case to the department, for a case to be confirmed, the patient had to have been examined by a  orthoptist, or an ophthalmologist (with an interest in strabismus) while they were still under 12 months old. So the above case can be excluded.

The actual onset of the condition is written as per the history (when was the squint first noticed?) from the parents/carer (eg from birth, 2 months old, 7 months old) but for confirmation of an infantile esotropia, the child has to be less than 12 months old when the squint is confirmed for the first time. If they were examined by a clinician elsewhere (eg: community orthoptist, ophthalmologist in another unit) before they were 12 months old and a squint is confirmed then, then that is accepted.

This means that even though a child has a clear typical history (eg 2 months old onset) but never had the squint confirmed by an orthoptist/ophthalmologist till they were >12 months old, they will not be included.

4. What if a child was seen by the orthoptist and then the optometrist before seeing a doctor? 

We appreciate that every department runs their service differently and it may be a few different clinics before the child sees an ophthalmologist. In the majority of centres, all infants with a large-angled squint would be seen by a doctor quite early on. However, an orthoptic/optometrist team is more than capable of diagnosing an infantile esotropia and this would not affect the inclusion criteria.

The issue here might be what to fill in in the questionnaire with respect to specific questions on date of diagnosis etc. Every case might be different - so feel free to email us on or and we can discuss the finer details.

5. The definition states that the esotropia has to be non-accommodative. However, we have not had time to give them a trial of glasses before confirming if it is indeed non-accommodative. 

Please still include these cases for now. This is relevant in the young age group (6 to 18 months old). Often, it can be easy to identify those with a non-accommodative element as the hypermetropia is low (+2.50 or less). Also, if they are really young, there might be some hesitation among practitioners in prescribing small amounts of hypermetropia.  

6. If the definition of onset of essential infantile esotropia is <6 months old, why have you set your definition of an onset <12 months old?

This is because the esotropia sometimes may have been present for a longer time than reported (esp when you look back at older photos). It can be difficult to date it to exactly <6 months but very easy to date it to <12 months old.

For the public:

The letter below is a notice for the general public if you think this study may apply to your child. Feel free to contact us or for any enquiries.

Link to BOSU website:

Link to Health Research Authority:


Lastly, all information on this page "BOSU (British Ophthalmic Surveillance Unit) Study on Essential Infantile Esotropia" has been independently written by Mr.Damien Yeo. For all enquiries, please use the email

The study itself is not sponsored by but we would like to thank them for the webspace to host this page.