We hope as many women as possible will participate in this study but not all women will be suitable. Please read the sections below to make sure that the study is right for you.

You may be able to participate if

You are over 18yrs old

Have regular menstrual cycles that are within 25-35 days. By regular, we mean that your periods do not vary by more than 9 days in different cycles.

Please do not participate if any of the following apply to you:

You are pregnant or breast feeding

You are taking a progestogen contraceptive pill (Micronor, Noriday, Norgeston, Cerazette, Aizea, Cerelle, Feanolla)

You have a history of menorrhagia (heavy menstrual bleeding)

You are menopausal

You have diabetes

You have any mucopolysaccharide diseases

You are taking any medications which are known to affect vision

You have a drug or alcohol addiction

You are unable to provide informed consent

You have any eye diseases which are known to affect vision. This does not include short-sightedness, long-sightedness, and astigmatism and it is fine to participate in the research if you have these conditions and wear glasses or contact lenses.