Aims: The aims of this study are as follows: (1) to describe a standardised methodology for the ice test, and where necessary a heat test; (2) to determine the effects of local cooling vs. heating on ptosis in myasthenia gravis (MG) patients. Methods: Twenty-three MG patients with ptosis were identified from a tertiary referral neuroimmunology clinic, seventeen with significant ptosis ≥2 mm. Latex party balloons were filled with ice and cold tap water for the ice test, or with water heated to 45 °C for the heat test. Each test was performed for 2 min, with ruler measurement and photographs taken of the palpebral aperture before and immediately after each test. Results: This standardised method was efficient in a clinical setting while maintaining efficacy. In all 23 patients, the mean improvements in ptosis with the ice, rest, and heat tests were 2.3 (±1.5) mm, 1.3 (±1.1) mm, and 0.33 (±1.4) mm respectively. In the 17 patients with significant ptosis, the mean improvements in ptosis with the ice, rest, and heat tests were 2.9 (±1.2) mm, 1.8 (±0.92) mm, and 0.83 (±1.4) mm, respectively. In these 17 patients, the ice test improved ptosis by 1.3 mm more than rest (p < 0.0001). The heat test improved ptosis by 1.1 mm less than rest (p = 0.0013). The ice test improved ptosis by 2.3 mm more than the heat test (p < 0.0001). Conclusions: The standardised methodology of ice and heat testing was safe, easily reproducible and effective. We confirm that temperature had a significant effect on ptosis in MG, and therefore refute the notion that measured changes are purely due to the associated rest.