It was observed in the clinic that OSAHS patients often had anisometropia, and the
ipsilateral eye (the eye on the preferred sleeping side) had a significantly higher
myopic degree, compared with the contralateral eye (the other one). The influence
of sleeping position on anisometropia has not previously been reported. Therefore,
a study was performed on the clinical data of OSAHS patients to investigate the association
between sleeping position and anisometropia.
Our study indicates that anisometropia is more prevalent in patients in the OSAHS
group. The extent of anisometropia was greater in the OSA-S compared with the Nor-S
group, suggesting a role for sleep position.Of the 32 patients in the OSA-S group,
22 (68.8%) had anisometropia, with 20 of these patients having a higher myopic degree
of the eye on the preferred sleeping side, compared to the contralateral eye. These
findings suggest that OSAHS patients who sleep on one side are prone to developing anisometropia and myopia. Two possible reasons exist for
this finding: Firstly, OSAHS is characterized by chronic intermittent hypoxia, which can cause changes in
the metabolism, function and morphological structure of the ocular tissues [10,11].Increased degradation of collagen fibers in the cornea and sclera can alter the morphological
structure of the eyeballs.Another consideration is that patients with OSAHS have a
lower level of cortical arousal, so that , these do not turn over subconsciously when
the eyelids are subjected to high mechanical compression . The combination of these aspects likely increases the development of anisometropia
in patients with OSAHS who have a preferred sleeping side.
In 22 of the patients with anisometropia in the OSA-S group, anisometropia was diagnosed in 11 cases due to differences in spherical degree, while diagnosis in the remaining
11 cases was due to differences in cylinder degree. This suggests that OSAHS patients
who slept on one side may have different types of anisometropia due to changes in
the morphological structures of the cornea and sclera. The reason for this remains
unclear, but could be due to differences in mechanical compression in the eyes during
The results of the corneal topography revealed that the CYL, SRI and SAI of the eye
were greater on the preferred sleeping side in patients in the OSA-S group, while
the K value was similar in the ipsilateral and contralateral eyes. Furthermore, no
significant differences were found between the ipsilateral and contralateral eyes
in terms of the CYL, SRI, SAI and K values in the Nor-S group. These results indicate
that differences in spherical degree were not due to changes in the cornea. The CYL, SRI and SAI of the ipsilateral eye
were significantly higher than those of the contralateral eye in the OSA-S group,suggesting
that compression of the ipsilateral eye may cause changes in the morphological structure
of the cornea and increase the degree of corneal astigmatism.
The development of myopia is closely associated with the increased ocular axial length caused by scleral thinning and lengthening, leading to a higher spherical degree [13-19]. The ipsilateral
eye had a longer ocular axial length, compared with the contralateral eye in the OSA-S
group, suggesting that the increased ocular axial length of the ipsilateral eye is
associated with the sleeping position of OSAHS patients, and that the increase in
ocular axial length of the ipsilateral eye is in turn is correlated with the difference
in spherical degree. Researches has confirmed that OSA is closely related to FES and
keratoconus [20,21]. Donnenfeld  also noted that FES and keratoconus localized
to the side of sleeping preference, and hypothesis that eye rubbing maybe the casual
fator in KC and FES. Based on the results of our and others' researches, we boldly
speculate that when the ipsilateral eye is subjected to compression, it may cause
changes in the morphological structure of the sclera and increase the myopic degree,
leading to the development of anisometropia in OSAHS patients. Furthermore, fluid
retention plays a major role in OSA , recent investigations suggest that some
of the fluid retained in the legs during the day may redistribute rostrally when recumbent
[24,25].Therefore, we suspect that liquid may stay in the preferred sleeping side
of the eyelid, causing some mechanical stress on the eyeball and anisometropia.
The incidence of anisometropia was associated with the severity of OSAHS in our study..
Patients with severe OSAHS had a significantly higher incidence of anisometropia,
compared to patients with mild OSAHS. These data further confirms the association
between OSAHS and anisometropia. Patients with severe OSAHS are more prone to developing
floppy eyelid syndrome, have a higher degree of laxity, and increased expression of matrix metalloproteinases
may be the pathophysiological basis for the higher incidence of anisometropia .
The results of two patients in the OSA-S group who had a higher myopic degree in the
contralateral eye were not excluded from our analysis. It is possible that these patients
incorrectly recalled their sleeping positions, or that these patients had undiagnosed
anisometropia before the onset of OSAHS.
Although we have done many works in the research, it still has some limitations. (1)
OSHAS patients often have other diseases, such as diabetes, hypertension and obesity,
did not completely excluded in the study, which might influence the results. (2) There
is no more objective evaluation method for the patient's sleep posture, which may
cause certain errors. (3) The relevant data of FES were not collected in the study,
and may have some defects. In the future research, FES related data should be collected,
and the relationship between FES and anisometropia should be further studied.