AIM: To investigate the physical principle that suggests that a large globe offers less resistance to applanation than a small one. METHODS: 400eyes of 200 adults were included in this study. All patients were randomly selected from patients scheduled for cataract surgery at Benha Faculty of medicine hospital. Preoperatively, all patients had their intraocular pressure (IOP) measured and their axial length was also measured and recorded. Data collected was examined using a regression analysis . RESULTS: There was a statistically significant negative correlation where it was found that for every 1.0 mm increase in axial length the tonometry value was 0.28 units lower (P= 0.0002) CONCLUSION: The size of the globe may influence the applanation tonometry readings. Thus when clinical findings do not fit the tonometry readings, axial length measurement may give a clue.