Macular Retinal Thickness and Retinal Nerve Fiber Layer Thickness Measured in Amblyopia, an OCT study.

Amblyopia is defined as a unilateral or bilateral decrease of visual acuity
caused by pattern vision deprivation or abnormal binocular interaction during
the critical period of visual development for which no optical or organic
origin can be detected (von Noorden 1996). Amblyopia can be seen as a
developmental disorder; the same causal factors that cause amblyopia during
infancy or early childhood have no lasting effect on vision when these occur in
adulthood.
Retinal involvement accompanying amblyopia is however controversial. In the
normal developing retina a process of postnatal ganglion cell reduction occurs
(referentie). In amblyopia this process is thought to be disrupted due to
unequal or unfocussed images, projected on the retina.
Optical Coherence Tomography (OCT) is a relatively new imaging technique,
similar to ultrasonography, which uses near-infrared light waves, instead of
ultrasound, to obtain a reflectivity profile of the retina (Huang et al.,
1991). OCT is widely used for imaging the vitreoretinal interface, for
monitoring macular edema and retinal thickness, retinal nerve fiber layer
(RNFL) thickness and optic nerve head parameters in a wide variety of patients.
The OCT technique currently available in clinical practice is also referred to
as time-domain OCT (TDOCT). Only recently, major advances in imaging speed,
sensitivity and image resolution have been achieved with the introduction of
spectral-domain OCT (SDOCT) (Nassif et al.2004; Wojtkowski et al., 2004).
Moreover, OCT is a non-invasive, non-contact, and was found to be well
tolerated and easy to undergo by children (Shields et al. 2006). .
Yen et al. ( 2004) studied the retinal thickness using OCT in two groups of
amblyopes, one group contained strabismic amblyopes while the other contained
anisometropic amblyopes. They found a significant thicker RNFL in anisometropic
amblyopes, compared to the fellow eyes. This was not the case in the group of
strabismic amblyopes. These study outcomes are refuted by Repka et al. who
studied a similar population of patients and found no clinical difference in
OCT measured RNFL thickness. Huynh et al. (2007) investigated the macular and
peripapillary RNFL thickness in amblyopia. They found an increased foveal
minimum thickness in amblyopic eyes compared to the normal fellow eye and
compared to eyes of non-amblyopic children. Children who had untreated
unilateral amblyopia had a significantly increased inter-ocular difference in
central macular thickness. No differences in peripapillary RNFL thickness were
found in amblyopic eyes compared to normal eyes.
Retinal involvement remains controversial in strabismic and anisometropic
amblyopes. Therefore the topic of this study is to investigate the macular
retinal thickness and the RNFL thickness in both strabismic and anisometropic
amblyopic patients, using both TDOCT and SDOCT, and compare them with a control
group of normal subjects. We hypothesize that there is a correlation between
the causal factors of amblyopia and a normal postnatal reduction of the inner
neuroretinal layers in the development of the visual pathway. One would expect
a thicker macular and RNFL thickness in amblyopic eyes compared to healthy
subjects, but this is still poorly investigated.

1.To investigate the relationship between amblyopia and the development of the
neurosensory retina:
Measurements: Central / foveal retinal thickness
RNFL
Inner retinal layer thickness thru segmentation algorithms
2.To investigate the differences in macular retinal and/or RNFL thickness
between strabismic and anisometropic amblyopes

This study is designed as a prospective, cross sectional case-control study.
Our control group consist of healthy children with no ophthalmic or orthoptic
diagnosis. In theory the non amblyopic eye could be used as a control. This is
however questionable because it is unknown what the effect of the amblyopic eye
will have on development of the normal eye. By choosing normal, healthy
subjects as a control group this issue is avoided.

The patient will undergo a single IOL and OCT measurement during 35 minutes,
directly afterwards the normal orthopthic examination.
OCT and IOL master use very low levels of energie, so the patient (eye) is not
at any risk. Moreover, OCT is a non-invasive, non-contact, and was found to be
well tolerated and easy to undergo by children (Shields et al. 2006).

Time table per patient: outlined in appendix C, page 9 of the protocol.