Abstract
Purpose: :
Break up time (BUT) measurement is a method for detection of a possibly dry eye. BUT detection is typically performed by measuring the time from the last blinking to the time where dry spots on the cornea surface appear. BUT is determined at a slit lamp using blue light and a previous application of fluoresceine. Typical BUTs for dry eyes are less than 10 seconds. Video topography may be capable to detect BUT without using fluoresceine.
Methods: :
A commercial available topography system (OphthaTOP from OphthaSWISS, Switzerland) is modified to capture and store 4 video images per second. Also the brightness of the system (normally 1800 Lux) is adjustable to analyse the influence to BUT. The measuring time is limited to 30 sec as the patient has to keep open the eye over that time period. 112 Eyes with dry eye syndrome of 57 Patients were investigated. Mean age of the patients was 47 years. Measured is the time from the last blinking to the time when variations like deformation or decrease of brightness of the projected placido rings on the cornea could be visually detected.
Results: :
BUT is measured to be less than 10 sec in 86 % of the dry eyes. In 93 % of the eyes the time was less than 15 sec and in 98 % it was less than 20 sec. In comparison normal eyes always shows BUTs of more than 30 sec (often there was no BUT measurable). The video image of the topography allows also the analysis of the location where break up (BU) started. In 88.1 % of the eyes it was in the inferior 2 quadrants of the cornea. In 65 % of the eyes the BU is located nasally. There was no correlation to the sex of the patients. Variation of light intensity (between 600 and 1800 Lux) shows minor influence to BUT.
Conclusions: :
BUT determination performed with a video topography system shows comparable results to measurements at the slit lamp using fluoresceine. The advantage is a contact free measurement, no use of any drugs. Another advantage is the possibility to measure BUT and local position on the corneal surface. This may help to classify dry eyes. The BUT measuring done visually so far may be automated inside the topography system for future applications.
Keywords: cornea: tears/tear film/dry eye • topography • refractive surgery: corneal topography