[Research Progress of the Effects of Monocular Visual Impairment on Binocular Vision]

Binocular vision refers to a progress of analysing and integrating the binocular visual signals into a whole and three-dimensional sensory perception by higher nerve centre. In this process, the interac- tion between the two eyes results in the changes of output signal, which is called binocular interaction. Through a series of subjective and objective experiments, it can be concluded that binocular interaction can be divided into three types： facilitation, summation and suppression, and the forms of binocular interaction in different visual states are different. In general, the visual signal is processed by binocular interaction, so that there are some differences between binocular vision and monocular vision. The extent of the difference can be affected by the damage of monocular vision and then affects the binocular vision. Thus, it is necessary for forensic scientists to further study the effects of the monocular visual impairment on visual function. Based on relevant data, this paper reviews the mechanism of the monocular visual impairment in binocular vision, the research methods and the application prospect in forensic science.

Do we really know the prevalence of accomodative and nonstrabismic binocular dysfunctions?

Purpose

To determine the scientific evidence about the prevalence of accommodative and nonstrabismic binocular anomalies.

Methods

We carried out a systematic review of studies published between 1986 and 2009, analysing the MEDLINE, CINAHL, FRANCIS and PsycINFO databases. We considered admitting those papers related to prevalence in paediatric and adult populations. We identified 660 articles and 10 papers met the inclusion criteria.

Results

There is a wide range of prevalence, particularly for accommodative insufficiency (2–61,7 %) and convergence insufficiency (2.25–33 %). More studies are available for children (7) compared with adults (3). Most of studies examine clinical population (5 studies) with 3 assessed at schools and 1 at University with samples that vary from 65 to 2048 patients. There is great variability regarding the number of diagnostic signs ranging from 1 to 5 clinical signs. We found a relation between the number of clinical signs used and prevalence values for convergence insufficiency although this relationship cannot be confirmed for other conditions.

Conclusion

There is a lack of proper epidemiological studies about the prevalence of accommodative and nonstrabismic binocular anomalies. Studies reviewed examine consecutive or selected patients in clinical settings and schools but in any case they are randomized and representative of their populations with no data for general population. The wide discrepancies in prevalence figures are due to both sample population and the lack of uniformity in diagnostic criteria so that it makes difficult to compile results. Biases and limitations of reports determine that prevalence rates offered are only estimations from selected populations.