Single-spot lasers used in photocoagulation usually deliver about 100 milliseconds of laser energy in a single burn. Although effective, they can cause peripheral visual field loss affecting the patient’s ability to drive.
Patients treated with multispot laser panretinal photocoagulation (PRP) for proliferative diabetic retinopathy can see well enough to pass driving tests, researchers said.
âThis study demonstrates that at six months after bilateral PRP delivered using a multispot laser, a visual field compatible with driving in the UK is preserved in most patients,â wrote Mala Subash, BM, FRCOphth, of the National Institute for Health Research Biomedical Research Centre at Moorfields Eye Hospital in London, England, and colleagues.
The finding, published in JAMA Ophthalmology, could indicate a safer alternative to conventional single-spot photocoagulation, the researchers said.
Panretinal photocoagulation has been the standard treatment for proliferative diabetic retinopathy since 1975, they wrote.
Single-spot lasers used in photocoagulation usually deliver about 100 milliseconds of laser energy in a single burn. Although effective, they can cause peripheral visual field loss affecting the patientâs ability to drive. The authors cited estimates that within 6 months of treatment, 11% to 50% of patients suffer visual field defects sufficient to stop them from driving.
By contrast, multispot laser panretinal photocoagulation delivers its energy in pulses lasting 20 to 50 milliseconds, combined with a rapid raster scan application of multiple spots. With similar power levels and spot sizes, the overall fluence (power multiplied by time and divided by area) is reduced, the researchers said.
In theory, this could limit collateral retinal damage and reduce the subsequent expansion in laser spot size. The researchers wanted to know whether these lasers have a different effect on the visual field than single-spot lasers.
They recruited 43 patients to participate in a study of a multi-spot laser from June 27, 2012 through October 14, 2013. They excluded everyone with coexistent ocular or systemic conditions that might have affected their visual field, those with a visual acuity of less than 20/200 that might affect the accuracy of visual field testing, and those with vitreous haemorrhages or planned intraocular surgery.
The group consisted of 17 men and 26 women with a mean age of 46.6 years. None had an IOP greater than 21 mm Hg, were receiving glaucoma medication, or had undergone vitrectomy. Eight right eyes and 11 left eyes were pseudophakic at the start of the study, and none of the patients had visually significant cataracts.
Sixteen had diabetes mellitus type 1 and 27 had type 2. The mean duration of their diabetes was 16.3 years, and on average it was poorly controlled. Their average haemoglobin A1c level was 9.5%. Twenty-nine had hypertension, two had renal impairment, 26 had hypercholesterolemia, and eight had peripheral neuropathy.
The patients all underwent the following functional assessments and imaging:
Â· Binocular Esterman visual field test for driving on the Humphrey field analyzer (Carl Zeiss Meditec)
Â· Monocular and binocular full-field static perimetry and on the Octopus 900 (Haag-Streit Diagnostics)
Â· Goldmann monocular kinetic testing, microperimetry on the Nidek MP-1 (Nidek Technologies)
Â· Mass of Activity Inventory questionnaire (which quantifies the difficulty of performing certain tasks)
Â· Ultrawide-field colour and fundus fluorescein angiography
Â· Spectral-domain optical coherence tomography
Forty-one participants met the UK standards for driving on the Esterman visual field test.
After this testing, the patients received treatment with the Valon TT multispot laser system (Valon Lasers). This began with two initial treatment sessions of up to 1200 burns per eye per session, separated by two weeks.
The retinal spots were 400 Î¼m and they were separated by 1 burn width. The pulse duration was 20 ms. The power was sufficient to achieve "blanching" (a greyish white lesion) of the retina without producing visible necrosis.
The patients returned for review every six weeks, or more frequently if needed. If their retinopathy remained active, they received a further 800-1200 burns.
After six months, the researchers called in the participants to repeat the visual function testing. Two never responded, two had moved abroad and one was no longer believed to be ineligible for the inclusion criteria.
Of the 38 who showed up, 31 showed evidence of clinical efficacy. Three failed to meet the UK standards for driving on the Esterman visual field test, including the two who had failed at baseline.
Among those patients whose retinal sensitivity tests the researchers considered reliable at both baseline and follow-up, they found a mean reduction of -1.4 (3.7) db OD and -2.4 (2.9) db OS. They found a binocular reduction of -1.4 (3.6) dB. They considered this a ârelative preservation of global mean retinal sensitivity.â
They found a similar reduction with Goldmann monocular kinetic testing, though there was a greater reduction in left eyes, possibly because they tested the right eye first.
Microperimetry revealed relative preservation of macular function for 12Â° and 4Â° areas, with a reduction in mean retinal sensitivity of 3.0 (5.2) db OD and 2.6 (5.4) db OS at the central 4Â° area.
The researchers also modeled the entire hill of vision (HOV) for the full-field static perimeter data set, allowing comparison of the magnitude and extent of change. This revealed a ârelatively minorâ 10%-20% loss of retinal function.
âVisual fields after multispot laser panretinal photocoagulation for proliferative diabetic retinopathy are likely sufficient to pass standards for driving in the United Kingdom,â the researchers concluded.