What are the advantages of an applanation tonometer?
Publish Time: 2025-10-11
As a core tool for measuring intraocular pressure in ophthalmology, the applanation tonometer's strengths lie primarily in four areas: measurement accuracy, interference immunity, clinical applicability, and device reliability. A detailed analysis is provided below:
1. Measurement Accuracy: Reliability of the International Gold Standard
Principle Advantage: Based on the Imbert-Fick law, intraocular pressure is indirectly estimated by applanating the central corneal region (3.06mm diameter), eliminating interference from the eyeball's hardness. For example, the Goldmann applanation tonometer, with a measurement error of only ±0.5 mmHg, is recognized as the international gold standard for intraocular pressure measurement.
Direct Data Reading: For example, the GT600 applanation tonometer utilizes a dual-prism applanation prism and fluorescein staining technology to directly display intraocular pressure values under a slit lamp microscope, eliminating the need for conversion and reducing human error.
Wide dynamic range: The measurement range covers 0-80 mmHg, accurately capturing elevated intraocular pressure (e.g., exceeding 50 mmHg) during acute glaucoma attacks. Non-contact tonometers are prone to failure in this range.
2. Interference immunity: Eliminates the influence of multiple factors.
Corneal thickness correction: For every 50 μm increase in central corneal thickness (CCT), the measured value may be 2-3 mmHg higher. Applanation tonometers use formulas (such as the Ehlers formula: ΔIOP = 0.071 × (CCT - 545)) to correct for this error, improving diagnostic accuracy.
Biomechanical stability: Compared to rebound tonometers (with an error of ±3 mmHg), the applanation design is less dependent on corneal biomechanical properties (e.g., elasticity and water content), resulting in more stable results.
Standardized operation: By fixing the applanation area (7.35 mm²) and vertical angle (15°), deviations caused by variations in probe angle or contact pressure are reduced.
Glaucoma Management: As a tool recommended by international diagnostic and treatment guidelines, it supports 24-hour intraocular pressure (IOP) monitoring, helping physicians adjust treatment plans. For example, Peking University Third Hospital uses the Goldmann tonometer to achieve stable IOP control and reduce the risk of optic nerve damage.
Suitable for Special Populations:
Decubital Examination: The Perkin handheld applanation tonometer can be used at the bedside or in the operating room, suitable for bedridden patients.
Children and Individuals with Movement Disabilities: The Icare rebound tonometer uses a tungsten steel probe for instant corneal contact (0.8ms). Anesthesia is not required, but repeated measurements can fluctuate by up to ±3 mmHg.
Preoperative Evaluation: Before cataract surgery, the risk of elevated IOP must be ruled out. The accuracy of the applanation tonometer can prevent misdiagnosis.
4. Device Reliability: Long-Term Use and Maintenance Advantages
Structural Stability: The GT600 tonometer has passed type evaluation by the China National Institute of Metrology and meets national mandatory metrological verification requirements. With annual maintenance costs accounting for 15% of the purchase price, it is suitable for long-term use in primary healthcare institutions.
Convenient Disinfection: Daily cleaning is performed with 70% isopropyl alcohol, followed by a 3% hydrogen peroxide soak for infectious disease risk. For frequent use, it is recommended that two people rotate the probe to reduce the risk of cross-infection.
Data Traceability: Some models automatically record the average and coefficient of variation of multiple measurements, facilitating long-term tracking of patient intraocular pressure changes.
Differentiation Compared to Other Tonometers
Applanation tonometers, with their precise measurement principle, anti-interference capabilities, adaptability to multiple scenarios, and long-term reliability, have become an indispensable tool in ophthalmic diagnosis and treatment. Although their operation requires specialized training and is not suitable for patients with corneal lesions, their performance far exceeds that of non-contact or rebound tonometers in key scenarios such as glaucoma management and preoperative evaluation. For medical institutions seeking diagnostic accuracy, applanation tonometers remain the preferred option.
