A large spot diameter, typically between 8-10 mm, is recommended primarily to maximize the depth of laser penetration while minimizing surface damage. By reducing the scattering of laser light at the skin's surface, a larger spot size ensures that sufficient energy reaches pigment targets situated deep within the middle and lower dermis.
Core Insight: The "volume effect" dictates that a larger laser beam creates a more uniform column of energy deep within the tissue. This allows you to treat deep dermal pigments effectively using lower energy density (fluence), significantly increasing the safety profile of the procedure.
The Physics of Penetration
Overcoming Surface Scattering
When laser light hits the skin, it naturally scatters. A small spot size suffers significantly from this scattering, causing the beam's intensity to dissipate rapidly before it penetrates deep into the tissue.
The Volume Effect
A large spot diameter (8-10 mm) utilizes the volume effect. This physics principle ensures that a higher percentage of photons continue in a forward direction rather than scattering sideways, allowing the beam to maintain its integrity as it travels deeper.
Targeting the Lower Dermis
Dermal pigment lesions are located in the middle to lower layers of the dermis. Because of the reduced scattering, a large spot size is the only reliable way to deliver therapeutic heat to these deep targets.
Enhancing Safety and Efficacy
Lower Fluence Requirements
Because the large spot size transmits energy more efficiently to deep tissues, you do not need to use excessively high energy settings at the surface.
Protecting the Epidermis
Using a large spot allows for lower fluence (energy density) while still achieving the necessary clinical reaction at depth. This protects the epidermis (skin surface) from burns or unwanted texture changes that often occur when high energy is forced through a small spot.
Operational Efficiency
Faster Treatment Times
Beyond the physics of depth, a 10 mm spot size covers significantly more surface area per pulse than smaller diameters.
Treating Large Areas
For widespread lesions, such as those found in the sacral region, a larger spot size drastically reduces the operating time required for a full session.
Understanding the Trade-offs
System Power Requirements
While large spot sizes are advantageous, they require a laser system capable of generating high peak power. Delighting a large area with sufficient energy requires a robust machine; underpowered systems may not support high fluences at max spot sizes.
Precision vs. Coverage
Large spot sizes are excellent for area treatment and depth. However, for extremely minute, isolated superficial spots, a large diameter might treat unnecessary surrounding tissue, requiring a switch to a smaller optic for final detailing.
Making the Right Choice for Your Goal
When configuring your laser for dermal pigment lesions, consider your specific clinical objective:
- If your primary focus is Depth and Safety: Prioritize the largest spot size (8-10 mm) to reach the lower dermis with lower fluence, minimizing the risk of surface injury.
- If your primary focus is Speed: Use the maximum spot size available (10 mm) to treat broad lesion areas quickly and efficient.
Ultimately, the large spot size is the standard for dermal lesions because it aligns the physics of light transport with the anatomy of deep pigment.
Summary Table:
| Feature | Small Spot Size (2-4 mm) | Large Spot Size (8-10 mm) |
|---|---|---|
| Penetration Depth | Shallow (High scattering) | Deep (Volume effect) |
| Target Area | Epidermis / Superficial | Middle & Lower Dermis |
| Safety Profile | Higher risk of surface burns | Lower fluence, safer for epidermis |
| Treatment Speed | Slower for large areas | Rapid coverage |
| Clinical Focus | Precision detailing | Deep pigment lesions |
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References
- Suruchi Garg, Geeta Sharma. Advancements in Laser Therapies for Dermal Hyperpigmentation in Skin of Color: A Comprehensive Literature Review and Experience of Sequential Laser Treatments in a Cohort of 122 Indian Patients. DOI: 10.3390/jcm13072116
This article is also based on technical information from Belislaser Knowledge Base .
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