Objective survey of the prescription of occlusion therapy for amblyopia
- First Online:
- Cite this article as:
- Loudon, S.E., Polling, J., Simonsz, B. et al. Graefe's Arch Clin Exp Ophthalmol (2004) 242: 736. doi:10.1007/s00417-004-0896-9
- 54 Views
To identify the variation within and consistency amongst orthoptists when prescribing occlusion therapy for amblyopia in an objective survey.
A questionnaire was designed with five case examples of amblyopic children and distributed at annual meetings of orthoptists in the Netherlands and Germany. It was filled in simultaneously within 15 min in complete silence to avoid any exchange of opinions between orthoptists that would reduce variability. For each case the orthoptists were asked to give their prescription of hours or days of occlusion.
The questionnaire was filled in by 177 Dutch orthoptists and 227 German orthoptists. Their prescriptions of occlusion therapy were classified into five main regimens: part-time; part-time not every day; full-time; also occluding the amblyopic eye; alternating; and no occlusion therapy. The variation was large: the standard deviation was half the average prescribed hours of occlusion for each regimen in each of the five cases. All orthoptists were assigned a rank number for each of the five cases depending on whether their prescription was above or below average. These five rank numbers were not consistently above or consistently below average value per case.
The number of prescribed hours of occlusion varied widely per regimen per case. Orthoptists were not consistently strict or lenient in their prescription of occlusion therapy.
Treatment for amblyopia with occlusion of the better eye dates back to at least the early eighteenth century. Charles de Saint-Yves first described occlusion of the dominant eye to promote use of the squinting eye in 1722 . After that, Allen in 1730 and Compte de Buffon in 1743 recommended occlusion of the good eye to straighten the squinting one [1, 2]. Javal (1896) in France and Worth (1901) in England advocated the use of occlusion for amblyopia [4, 11].
Despite the fact that occlusion therapy dates back to the eighteenth century, there are still few guidelines for prescribing occlusion hours. This is in contrast to the prescription of antibiotics or other drug medication, which is done according to protocol and to scientifically derived standard measures. Age, visual acuity and to a lesser extent diagnosis seem to be the most important determinants when prescribing a number of hours of occlusion therapy. Mein and Trimble stated that the lazy eye should be occluded full-time in the case of strabismic amblyopia and part-time in the case of anisometropic amblyopia followed by full-time occlusion if the acuity does not improve sufficiently . According to Haase the good eye should be occluded for a number of days per week corresponding to with the age of the child in years, followed by 1 day of occlusion of the amblyopic eye . Von Noorden and Campos stated that the good eye should be occluded full-time when there is a difference in visual acuity between the two eyes .
As there is no consensus amongst orthoptists, different orthoptists may prescribe very different hours of occlusion for the same patient. This can lead to confusion amongst parents seeking second opinions and result in non-compliance with the therapy .
A questionnaire was developed with five case examples of children diagnosed with amblyopia in order to try and identify these variations in prescription of occlusion hours amongst orthoptists, their consistency and their main determinants.
The questionnaire containing the five sample amblyopic cases. The following instructions were given: Please enter below the number of hours of occlusion therapy you would prescribe in each case. Do not consider the prescription of glasses. Please do not discuss the cases with your neighbour, lest we measure less variability!
3 years old
2 years old
5 years old
6 months old
3 years old
Esotropia first noticed 6 months earlier
Microstrabismus, untreated amblyopia
20° Right esotropia
Slight left esotropia
15° Left esotropia
Large right esotropia, no DVD / NL
Slight left esotropia
Marked esotropia, alternating, NL, DVD unclear
Large (30 cm) / moderate (5 m) left esotropia
Titmus Fly +, animals ABC +
Titmus Fly −
Central / Central
Nasal / Central
Central / Eccentric nasal
Visual acuity RE/LE
5/10 & 5/5 Pictures
Cannot maintain fixation, saccadic pursuit, some protest when occluding left eye
1.0 / 0.2 E-Chart
5/6 & 5/15 Pictures
+3.5 / +2
+2 / +2
S+1.0=C-0.5axis180 / S+1.5=C-1.75axis50
+1 / +1
+4 / +4
Hours per day
Days per week
Cases 1, 2, and 5 were common amblyopic cases with a clear difference in acuity between the two eyes. Case 1 was a 3-year-old with an anisometropia and visual acuity of 5/10 and 5/5 as measured with a Children’s Picture Chart. Case 2 was a 2-year-old with esotropia of the right eye first noticed 6 months earlier. Case 3 was a 5-year-old diagnosed with slight esotropia of the left eye with eccentric fixation of this eye and mild anisometropia. Case 4 was a 6-month-old baby with infantile esotropia of 30° alternating freely. Case 5 was a 3-year-old with hypermetropia combined with esotropia of the left eye, eccentric fixation and a clear difference in the visual acuity between the two eyes. Case 2, 3, 4 and 5 were children with strabismic amblyopia, case 1 was a child with anisometropic amblyopia.
In March 2001, at the national Spring Meeting of the Union for Dutch Orthoptists in Utrecht, the questionnaire was put to Dutch orthoptists representing almost all practicing orthoptists in the Netherlands. In October 2001, at the annual meeting of the Union for German Orthoptists in Warnemünde, the questionnaire was put to the German orthoptists present. They were asked to determine their prescription of hours of occlusion (hours per day or days per week) for each of the five cases within 15 min. Additional instructions for filling in the questionnaire included the statement that the prescription of glasses was not to be considered. They were not allowed to discuss or copy the cases and were under strict supervision from the four researchers present to prevent any exchange of views that might lessen variability. As a result the questionnaires were completed in silence. After 15 min the completed questionnaires were collected, also under strict supervision.
A database was created which consisted of four primary items: (1) the number of hours prescribed per day, (2) the number of days of occlusion per week, (3) the period of occlusion and (4) the total number of occlusion hours prescribed per week. Both eyes were itemized this way. The prescriptions given by each orthoptist were recorded on a case-by-case basis in the database. All the variations in the prescriptions of occlusion therapy could be stored into one database. From there it was possible to translate them into different regimens of prescribing occlusion therapy. For the statistical analysis of the database we used non-parametric tests (Mann–Whitney).
To determine whether orthoptists prescribed their hours of occlusion consistently above average or consistently below average, all orthoptists were ranked according to their number of prescribed hours of occlusion per case. From these rank numbers percentiles were derived and the standard deviation (SD) of the percentiles was calculated. On statistical considerations this SD of percentiles could not exceed 28.87%. If occlusion hours were completely randomly prescribed with a uniform distribution of the percentiles between 0% and 100%, the SD of the percentiles would be √1/12(100%–0%)2=28.87%. The SD would be 0% if orthoptists prescribed consistently above or consistently below average, i.e. if the strictest orthoptist prescribed the most hours of occlusion for each of the five cases and the most lenient orthoptist prescribed the least hours of occlusion for each of the five cases.
177 Dutch and 227 German orthoptists filled in the questionnaire. Seven (4%) of the Dutch orthoptists and four (2%) of the German orthoptists failed to complete the questionnaire properly, but in these cases only one of the five cases on the questionnaire had been left unanswered; therefore, they were included in our analysis. The orthoptists wrote no negative comments on the forms regarding the sample cases.
Definitions of the five prescribed occlusion regimens
Part-time occlusion, i.e. the non-amblyopic eye is occluded the same number of hours every day of the week
Part-time occlusion not every day of the week, i.e. the non-amblyopic eye is occluded for the same number of hours, followed by days of both eyes open
Full-time occlusion, i.e. the non-amblyopic eye is occluded for all waking hours every day of the week or the non-amblyopic occluded for all waking hours followed by days when both eyes are open
Also occluding the amblyopic eye, i.e. the amblyopic eye is also occluded for any period of time (either part-time or full-time) in addition to the occlusion of the non-amblyopic eye for any period of time
Alternating occlusion therapy, i.e. both eyes are occluded alternately for the same number of hours every day, part-time as well as full-time
No occlusion therapy of either eye
Pair of spectacles, foil, exercise, more complex regimes
There was an occasional prescription of a pair of spectacles, foil, inverse occlusion only or of even more complex regimens. Regimens prescribed by fewer than 12 orthoptists were excluded from analysis.
Because of the different ages of the sample cases, and in order to permit comparison of the actual hours of occlusion that had been prescribed, the time spent awake by a 6-month-old baby were estimated to be 6 h per day, a 2-year-old child, 10 h per day and a 3-year-old and 5-year-old child, 12 h per day. In this way the prescriptions of days per week were converted to hours per week.
Dutch and German orthoptists’ prescribing behaviour
The median of the prescribed hours of occlusion for the non-amblyopic eye per day distributed over the five regimens per case. In brackets are the percentages of Dutch and German orthoptists prescribing that regimen
Case 1: Anisometropia, 3 years
Case 2: Esotropia, 2 years
Case 3: Microstrabismus,5 years
Case 4: Alternating, 6 months
Case 5: Accommodative esotropia, 3 years
Orthoptists prescribed significantly more hours of occlusion when prescribing FTO than when prescribing PTO or PTONED (P<0.005).
In cases 1, 2, 3 and 5, orthoptists who prescribed PTO prescribed significantly more hours per week than orthoptists who prescribed PTONED. This difference was significant in cases 1, 2, and 5 (P<0.002).
In cases 2 (n=23), 3 (n=18) and 5 (n=19) some German orthoptists also prescribed occlusion of the amblyopic eye for a period of time. In these cases the non-amblyopic eye was occluded for significantly more hours than it was by orthoptists who prescribed PTO, PTONED or FTO (P<0.005).
Consistency in prescription of occlusion hours
To calculate whether orthoptists prescribed their hours of occlusion consistently above average or consistently below average, each orthoptist was assigned a rank number according to number of prescribed hours per case. From these rank numbers the five percentiles, their average and their SD were derived. The average SD of the percentiles for all orthoptists was 21%. It would have been 28.87% if occlusion hours had been prescribed completely at random and 0% if they had been prescribed consistently above or below average (see above, Data analysis).
By distributing our questionnaire at annual meetings for orthoptists and preventing exchange of opinions we were able to gain an objective insight in the prescriptions of occlusion therapy for amblyopia.
Whilst analysing the data we were taken aback not only by the amount of variation in the number of prescribed hours of occlusion, but also by the diversity in the ways of prescribing occlusion therapy. The number of occlusion hours was neither normally nor log-normally distributed in any of the five example cases. However, during the analysis on a case-by-case basis it became apparent that certain ways of prescribing occlusion therapy, i.e. certain regimens, were more prevalent (Table 2). Within these regimens the SD was half of the average prescribed hours of occlusion. This applied to each of the five sample amblyopic children.
The five sample amblyopic cases were chosen in order to make the difference in the prescribed hours of occlusion by orthoptists more easily transparent. Cases 1, 2 and 5 were common amblyopic cases, while cases 3 and 4 were more controversial. The largest variation in the prescription was found in case 3, representing a 5-year-old child with microstrabismus and untreated amblyopia. To improve visual acuity long periods of occlusion could have been thought necessary, although the outcome of the treatment was uncertain. That may have been the reason why some orthoptists decided not to occlude at all, whereas others prescribed long periods of occlusion.
Case 4, a baby with alternating fixation, may not have required any occlusion therapy as there was no real evidence of amblyopia. However, some orthoptists prescribed ALT with a median of 1 h every day of the week. This decision to commence with alternating occlusion therapy may well have been prompted by the desire to prevent the development of an amblyopic eye. It may also have been influenced by the uncertainty of the diagnosis.
Orthoptists who prescribed FTO prescribed significantly more hours of occlusion in the same case than orthoptists who prescribed PTO and PTONED. This tendency can be partly explained by orthoptists opting for the FTO regimen when they wanted to prescribe longer periods of occlusion. Orthoptists wanting rapid success would select FTO rather than prescribing PTO or PTONED and waiting patiently. The same difference is seen between PTO and PTONED: orthoptists who chose PTO prescribed significantly more hours of occlusion in the same case than those who prescribed PTONED. It can also be partly explained by the assumption that orthoptists wanting to prescribe shorter periods of occlusion would opt for reducing the number of days per week rather than reducing the number of hours per day.
Orthoptists who prescribed an AOA regimen prescribed significantly more hours of occlusion than orthoptists who prescribed only occlusion of the non-amblyopic eye, possibly to compensate for the hours the amblyopic eye was patched.
In our questionnaire orthoptists were asked to make their prescription on the basis of the main determinants: age, visual acuity and diagnosis. Not included were further determinants that may have influenced the results, such as personal experience, the perceived domestic situation, the possible interference with homework or the waiting time for a follow-up appointment. The personal attitude of the orthoptists towards the success of the treatment was also not taken into account when designing the questionnaire.
Based on traditional and educational differences we expected a difference in occlusion prescriptions between Dutch and German orthoptists. Indeed, German orthoptists did tend to prescribe slightly longer hours of occlusion and to prescribe to FTO more often than Dutch orthoptists. However, the amount of variation in prescribed hours of occlusion was equal in the Dutch and German orthoptists (Table 3).
Neither consistently strict nor consistently lenient orthoptists of either nationality could be identified.
This study clearly emphasises the need for prospective studies investigating the relationship between prescribed occlusion hours and actual occlusion time carried out by the parents . Secondly, the relationship between the patched hours and the child’s acuity increase should be established . The findings of such investigations might lead to the development of validated guidelines or protocols for prescribing occlusion therapy.
If consensus and uniformity could be achieved among orthoptists and ophthalmologists as to the prescription of occlusion therapy, this would go a long way towards convincing the parent that a specific regimen of occlusion is the best therapy for the amblyopic eye, thus promoting compliance.
We thank the 404 orthoptists for their hospitality and for filling in the questionnaire. We acknowledge René Eijkemans and Caspar Looman for their help with the statistical analysis.