Navigated panretinal photocoagulation vs conventional pattern laser for PDR

Take-home message: An interventional trial recently compared standard and navigated pattern PRP techniques. In this article, Dr Kozak explains how continuous prepositioning and stabilisation of the aiming beam with navigated PRP, enables pattern application of the more effective longer pulse durations while reducing treatment times and broadens therapeutic options in proliferative diabetic retinopathy.

By Dr Igor Kozak, MD, PhD

Laser panretinal photocoagulation (PRP) is the standard of care of ischemic retinopathies such as proliferative diabetic retinopathy (PDR). The landmark Diabetic Retinopathy Study (DRS)1 and the Early Treatment Diabetic Retinopathy Study (ETDRS)2 established standardised treatment with parameters of 200 to 500 µm spot size, pulse duration of 100-200 milliseconds (ms) and power adjusted to produce moderate-intensity burns.

Glaucoma therapy: What if a PGA isn't enough?

In 2006, pattern scanning laser photocoagulation technique was introduced with a reduction in pulse duration of each laser spot.3 This minimised the time needed to apply multiple laser treatment spots in a pre-selected, fixed pattern during which the eye can move. The introduction of pattern scanning laser systems, where the treating ophthalmologist only positions a regular pattern of laser spots, significantly reduced the treatment time as well as the patient’s pain perception.4 However, this improvement required the reduction of the pulse duration to 20-30 milliseconds, representing a change from the ETDRS protocol.

Navigated laser photocoagulation technique was introduced in 2009 initially for focal laser treatment, with an ability to perform color, infrared and fluorescence angiography imaging, digital treatment planning of desired treatment location based on fundus images and subsequent focal laser treatment to compensate eye movements.5 The navigation functions offered by this laser for focal treatment such as laser pre-positioning by computer assistance has been studied extensively. Retinal navigation has shown significant increase in treatment accuracy compared to all currently existing laser systems6 and a significant reduction in need of laser retreatments.7 Also, two studies demonstrate a significant reduction in anti-VEGF injections after navigated laser treatment.8,9

Next: Panretinal photocoagulation: a novel approach

A novel technique of navigated panretinal photocoagulation (nPRP) allows imaging and the positioning of a single and multi-spot laser patterns up to far periphery with continuous prepositioning of the laser beam relative to eye movements (Figure 1).

The panel addresses questions during the "Getting to New Horizons: FDA Panel Discussion" session. The panel included (from left) Stuart Abelson, MBA, of ORA Inc., Wiley A. Chambers, MD, of the FDA, Kuldev Singh, MD, Malvina B. Eydelman, MD, also of the FDA, and Eugene de Juan, Jr., MD.As a result of stabilisation of the laser onto the retina, multi-spot treatment patterns may now be applied with the well-established, longer pulse durations such as 100 milliseconds and above. This makes following the ETDRS protocol possible even with pattern laser photocoagulation technique. Furthermore, navigated laser treatment minimises patient light exposure by using continuous infrared imaging.

Technique comparison

Recently, standard and navigated pattern PRP techniques for PDR were compared in a randomised interventional trial performed simultaneously at two centres: the King Khaled Eye Specialist Hospital in Riyadh, Saudi Arabia and LV Prasad Eye Institute in Hyderabad, India. Patients were consecutively enrolled and equally randomised into group 1: navigated PRP with short pulse (20-30ms) duration patterns; group 2: conventional PRP with short pulse (20-30ms) duration patterns; group 3: navigated pattern laser with long pulse (100-200ms) duration; group 4: conventional single spot laser with long pulse (100-200ms) duration. The authors analysed characteristics of laser burns after both PASCAL (Topcon Medical Laser Systems, Inc. Tokyo, Japan) and NAVILAS (OD-OS GmbH, Teltow, Germany) laser systems8 as well as their clinical efficacy.9 The analysis included assessment of laser burn area and shape/ellipticity, treatment time and pain score and measures of clinical efficacy in PRP such as regression/development of neovascularisation and need for additional laser session.

Laser Burn Area

The study has shown that short pulse treatments with both techniques produce smaller laser burn areas. The variation of the laser burn area among the different techniques was not significant except for the smaller variation of laser burns with navigated laser using 100 ms compared with the laser burn variation with conventional laser using single shot 100-ms laser spots (P < 0.01). Similar analysis was performed to assess the variation of laser burn area between retinal areas proximal to the arcades and areas close to the equator. The variation of the laser burn area near the arcades for navigated pattern laser and for the conventional pattern laser was 29% and 22%, respectively (P < 0.01). In the area closer to the equator, laser burns from the navigated laser showed variation of 15% compared with 25% with laser burns applied with the conventional laser system (P< 0.005).

Next: Analyzing treatment

Ellipticity of Laser Burns

The ellipticity measurements were obtained by dividing the larger diameter by the smaller diameter of each laser burn. The navigated laser with 100-ms pulse durations showed significantly more circular spots than the conventional laser with 100-ms pulse duration. Both systems showed more circular spots when longer pulse duration was used. The laser spots from the conventional laser exhibited an increasing elliptical shape toward the periphery, whereas the navigated laser spots tended to be more uniform all over the retina.

Treatment time

Treatment time was consistently shorter in the groups that underwent navigated pattern treatment compared to groups using standard pattern treatment. And, naturally, treatment time was significantly shorter using the navigated long pulse pattern compared to a single spot for the long pulse duration groups (Figure 2).

(Figure 2) Comparison of treatment times to complete 100 laser spots using two instruments and two treatment protocols

Pain score

The pain score in the study was in trend lower in navigated short pulse group compared to conventional short pulse group (P = 0.1) and statistically significantly lower in navigated long pulse group compared to conventional long pulse group (P = 0.02). The experience of pain was statistically significantly different using the navigated pattern compared to a single spot for the long pulse duration groups (P < 0.001). It is believed that better comfort using infrared light illumination with navigated system contributes to less sensation of pain during treatments (Figure 3).

(Figure 3) Comparison of pain perception as self-reported by study patients using two instruments and two treatment protocols

Regression/Development of Neovascularisation

Treatment time was consistently shorter in the groups that underwent navigated pattern treatment compared to groups using standard pattern treatment. And, naturally, treatment time was significantly shorter using the navigated long pulse pattern compared to a single spot for the long pulse duration groups (Figure 2).

Next: Last takeaways

Need for Additional Treatment

One eye in navigated short pulse group and 1 eye in conventional short pulse group required vitreoretinal surgery due to non-clearing vitreous hemorrhage that spared the visual axis. None of the eyes in long pulse groups required additional surgery. These events were not statistically different between the short and long pulse duration groups (P = 0.98). Short pulse duration groups, however, required 22 procedures and long pulse duration groups required 12 procedures which represented a statistically significant difference (P < 0.05). A trend towards worse outcome (additional procedures) using short pulse duration treatments was expressed by slightly increased relative risk of 1.3 compared to the long pulse duration treatments.

Study conclusion

This prospective randomised interventional trial compared the efficacy of conventional and navigated pattern laser in panretinal photocoagulation treatment of proliferative diabetic retinopathy. It has shown laser tissue interaction in panretinal photocoagulation after use of both standard and navigated pattern lasers. It has also has demonstrated significantly reduced, almost halved, retreatment rates with 100ms pulse duration compared to 30ms treatments using either technology.

With continuous prepositioning and stabilsation of the aiming beam, navigated PRP, for the first time, enables pattern application of these more effective longer pulse durations while reducing treatment times. This ability combined with significantly reduced pain broadens therapeutic options in proliferative diabetic retinopathy

References

The Diabetic Retinopathy Study Research Group. Ophthalmology. 1981;88(7):583-600.

Early Treatment Diabetic Retinopathy Study Research Group. ETDRS report number 9. Ophthalmology. 1991;98(5):766-785.

M.S. Blumenkranz et al., Retina . 2006;26:370-376.

C. Sanghvi et al., Br. J. Ophthalmol. 2008;92:1061-1064.

B. Liesfeld et al., IFMBE Proceedings. 2009;25(11):243-246.

I. Kozak et al., Ophthalmology. 2011;118(6):1119-1124.

A.S. Neubauer et al., Clin. Ophthalmol. 2013;7:121-128.

G. Barteselli G et al., Br. J. Ophthalmol. 2014;98(8):1036-1041.

R. Liegl et al., PLoS One 2014;9(12):e113981.

J. Chhablani et al., Invest. Ophthalmol. Vis. Sci. 2014;55(6):3432-8.

J. Chhablani et al., Am. J. Ophthalmol. 2015;159(5):884-9.

Dr Igor Kozak, MD, PhD

e: ikozak@kkesh.med.sa

Dr Kozak is a Senior Academic Consultant at the Vitreoretinal Division of King Khaled Eye Specialist Hospital, Riyadh 11462, Kingdom of Saudi Arabia.

Dr Kozak is a medical advisory board member of OD-OS GmbH and works as a consultant for Beyer AG.