They use LED (light-emitting diode) technology to measure cataracts at a molecular level.
This gives clinicians a better idea of whether patients need to have surgery.
About 10 million cataract removal operations are performed globally each year, and in the UK more than half of people who are over 65 have cataracts in one or both eyes.
In the later stages of cataract formation, patients commonly experience cloudy vision prior to treatment. It is also a recognised complication of Type 1 and Type 2 diabetes.
Heriot-Watt has been working with Edinburgh Biosciences Ltd and experts from Edinburgh University and organisations in Sweden and Denmark to develop the LED technique.
It allows clinicians to monitor a florescence signal from proteins in the eye lens and document changes during cataract formation.
Prof Rory Duncan from Heriot-Watt University said: "Rather than waiting for the condition to appear, it could be possible to diagnose and monitor a cataract before it forms, allowing preventative measures to be taken where possible.
'While this stage is not a cure for cataracts, we believe it could have wide-reaching benefits such as limiting the symptoms experienced by our increasingly-ageing population and those living with diabetes. It could significantly diminish the pressure on our health service."
He added: "We believe that the diagnostic also allows us to determine a patient's 'true age' as opposed to the age on their birth certificate.
"The technology identifies how much oxidative damage lens proteins have accumulated through lifestyle or environmental factors. This accumulated damage may be important in determining risk factors for a number of age-related conditions."
Prof Des Smith, one of the co-founders of the research, said: "This research brings us one step closer to developing a non-invasive treatment for cataracts."
The team will now conduct further studies in pigs to validate the findings, demonstrate safety in humans and explore whether non-invasive treatment is feasible.
Scientists at Heriot-Watt University have developed a new way to diagnose cataracts.