BLOG: Using indirect ophthalmoscopy lenses for retinal laser applications
Click Here to Manage Email Alerts
We are all familiar with and routinely utilize condensing and aspheric lenses at the slit lamp during comprehensive eye exams. The lenses produce a magnified, inverted image to optimize visualization of retinal structures. Once we master the technique, these “accessory” lenses are a great assist while performing retinal laser applications to treat pathology such as diabetic retinopathy through a slit lamp.
Every lens has different characteristics, and choosing which lens to use is a personal decision. What you use will depend on the desired magnification, the spot size on the eye and how that relates to the actual micron spot size on a laser.
We can break lenses down into two categories: high-magnification lenses used to visualize details and wide-angle lenses for a large field of view (FOV). Field of view refers to the diameter of the image visible through the lens. These two parameters are the most important when determining which lens to use for specific pathology. Unfortunately, physics dictates a trade-off between higher magnification and a large FOV, and we cannot get a lot of both. Magnification is inversely proportional to lens power, whereas FOV is directly proportional to lens power. A lens with great magnification may have such a small FOV that we could miss what we are there to treat.
How to choose a lens
When I choose a lens, I start with my magnification requirements. When performing panretinal photocoagulation with MicroPulse (Iridex), I prefer a high-resolution lens and frequently use the HR Wide Field (Volk) lens because it provides a nice balance between magnification and FOV. I get a wide FOV with an essentially 1:1 magnification ratio for spot size. The advantages of this lens include better image quality at the extreme periphery of the lens view; a wide FOV and treatment area to the ora serrata; and the elimination of distortion at the extreme periphery due to the superior, high-grade, low-dispersion glass design. Additionally, it is easier to manipulate within the eye orbit due to its small size, which is particularly helpful in patients with a large brow or deep-set eyes. For me, this lens provides ideal magnification with the wide FOV that I prefer when performing MicroPulse laser therapy.
The Centralis lens (Volk) is also an excellent choice, particularly for focal and grid laser therapy. Some pros about this lens include better image quality and stereopsis at the extreme of the lens view; enhanced double aspheric design that eliminates distortion and improves stereopsis to the periphery of the view; and a superior, high-grade, low-dispersion glass delivering unsurpassed resolution. The Centralis provides improved capability on patients with pupils as small as 4 mm, and it also has a small size, which assists with manipulation inside the orbit.
We are fortunate to have a variety of options to choose from, each with a distinct set of pros and cons. Ultimately, the best lens for you to use during laser therapy procedures comes down to personal preference. Select lenses that provide you with the best ratio of magnification to FOV based on your technique.
Disclosure: Luo reports he is a consultant for AbbVie, Alimera, Allergan, Genentech, Iridex and Lumenis and receives research grands from Allergan and Lumenis.