Introduction:

Fogging is a technique used during subjective refraction to enhance the accuracy of determining an individual's optimal refractive correction. By temporarily blurring the vision in the non-tested eye, fogging helps prevent accommodation and ensures a more precise assessment of the patient's refractive needs. This article aims to provide a comprehensive understanding of the principles and technique of fogging during subjective refraction.

Principles of Fogging:

Fogging works on the principle of creating a temporary blur in the non-tested eye, which helps relax the eye's focusing mechanism and prevent accommodation. The key principles of fogging are:

• Monocular fogging: The technique involves occluding or blurring the vision in one eye, usually the non-tested eye, to prevent the patient from fixating on the optotypes during subjective refraction. This eliminates any accommodation or binocular interaction that may affect the accuracy of the results.
• Inducing blur: By introducing a defocusing lens or adding plus power to the non-tested eye, the clarity of vision is reduced, creating a blurred image. This stimulates the patient's visual system to maintain clear focus, minimizing accommodation and allowing for a more accurate refraction.
• Maintaining awareness: The fogged eye allows the patient to remain aware of the presence of letters or images without clear visibility, ensuring their cooperation and active participation during the refraction process.

Technique of Fogging:

The technique of fogging involves several steps to effectively induce blur in the non-tested eye. These steps include:

• Occlusion or blurring: Use an occluder or a fogging lens to block or blur the vision in the non-tested eye while maintaining clear visibility in the tested eye.
• Starting point: Begin subjective refraction by presenting the optotypes or letters to the patient's tested eye, ensuring they are clear and visible.
• Fogging lens selection: Choose a fogging lens with appropriate power, usually +0.75 to +1.00 D, depending on the patient's age and accommodative ability. This lens should be placed in front of the non-tested eye.
• Adjusting fogging power: Increase the power of the fogging lens in small increments until the patient reports a noticeable blur. This ensures that the patient is unable to read the optotypes clearly, indicating successful fogging.
• Refinement: Fine-tune the fogging power by adding or reducing plus power to achieve a balance between sufficient blur and patient comfort. The goal is to create a blur that is noticeable but not excessive.
• Refraction of the tested eye: Proceed with the subjective refraction of the tested eye, using the fogging lens to maintain the blur in the non-tested eye. The patient's responses should be based solely on their perception of the optotypes presented to the tested eye.

Advantages and Considerations:

Fogging during subjective refraction offers several advantages and considerations, including:

• Accurate refraction: Fogging reduces accommodation and prevents binocular interaction, allowing for a more accurate and reliable determination of the patient's refractive needs.
• Minimized accommodation: By inducing blur in the non-tested eye, fogging reduces accommodation and helps identify the patient's true refractive error without accommodation-induced overcorrection.
• Patient cooperation: Fogging keeps the patient actively engaged and aware of the optotypes, facilitating their cooperation during the refraction process.
• Considerations: While fogging is generally effective, it may not be suitable for all patients, such as those with significant eye conditions or reduced visual acuity in the non-tested eye. In such cases, alternative techniques may be necessary.

Conclusion:

Fogging is a valuable technique during subjective refraction, helping to eliminate accommodation and optimize the accuracy of refractive correction. By understanding the principles and mastering the technique of fogging, eye care professionals can enhance the precision and reliability of subjective refraction, leading to better visual outcomes for their patients.

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