While the annual meeting of the American Society of Cataract and Refractive Surgeons (ASCRS) mainly deals in anterior segment topics, there’s a small section on the posterior segment too. Here are some of the highlights of the retina posters at the recent ASCRS 2019 in San Diego that caught our attention . . .
Vitreolysis lasers need to be cool too!
“Using a laser system equipped with an active air-cooling module would be advantageous when performing procedures that require a large number of shots, such as laser-based floater treatment of YAG laser vitreolysis.” – Dr. Paul Singh
Pulsed Nd:YAG lasers feature a solid-state cavity design that is precisely tuned. A key element of pulsed Nd:YAG laser’s cavity design is the establishment of precisely aligned internal mirrors – and this is where maintaining consistent cavity temperature becomes critical.
At the recent ASCRS 2019 San Diego, Dr. Paul Singh shared key insights into important considerations related to thermoregulation and stability of energy delivery during vitreolysis. According to Dr. Singh, vitreolysis treatment requires multiple laser shots, causing the heat of the flash lamp to be absorbed into the metal and glass components of the solid-state cavity. This leads to a slight change in the alignment and characteristics of the laser pulse emitted by the cavity.
In order to moderate the negative effects associated with heat buildup, traditional pulsed cavity design relies on ambient cooling and a limited assumption of shots required in a given time frame. This ambient cooling method of heat dissipation in turn puts a limit on treatment effectiveness, cavity longevity and treatment stability – all of which come with inherent risks to treatment outcomes.
An active air-cooled cavity adds a closed loop cooling system to the flash lamp, and this dissipates the heat before it has an opportunity to soak into the solid-state cavity. In addition, this method allows more rapid shot placement, reduced treatment times, increased system stability and arguably, increases cavity longevity. Each of these benefits adds to the safety and efficacy of selective laser trabeculoplasty (SLT) and vitreolysis treatments.
Vitreolysis requires a higher number of shots than a YAG capsulotomy. Previous studies by Dr. Singh and colleagues demonstrated that average number of laser shots to sufficiently vaporize floaters amorphous clouds was 568.
With so many shots fired Dr. Singh asked: “Does the delivery of energy stay the same throughout the entire procedure? Will the laser need to cool down during the procedure to stabilize the delivery of energy?”
Dr. Singh then evaluated if the air-cooling cavity reduces and/or stabilizes the delivery of energy emitted over a few hundred shots from a newly designed Q -Switched Nd:YAG laser.
A test system was set-up using a 1064nm, Q-Switched Nd:YAG laser with an air-cooling module (Ultra Q Reflex, Ellex, Adelaide, South Australia). The system was set to deliver 2.0mJ per shot and 300 shots fired with the air-cooling enabled. Next, the system was turned off for 30 minutes, the air-cooling module was disabled, and a second round of 300 shots was fired. Actual energy delivered with each shot was recorded.
With the active air-cooling enabled and 300 shots fired at 1 shot per second, the range of energy recorded was 1.99-2.44mJ, with a standard mean deviation of 3.53%. However, with the active air-cooling disabled, 300 shots fired at 2.0mJ, the energy range increased to 1.85-2.93 mJ with a standard mean deviation of 10.05%.
Dr. Singh observed: “With active air-cooling disabled in the Ultra Q Reflex laser, the actual energy delivered increased up to 46.5% from the selected 2.0mJ to 2.93mJ. This increase was well outside standard safety tolerances.”
Dr Singh concluded that active air-cooling of the laser cavity can help to maintain a stable range of energy delivery over hundreds of shots. In addition, he emphasized that using a laser system equipped with an active air-cooling module would be advantageous when performing procedures that require a large number of shots, such as laser-based floater treatment of YAG laser vitreolysis.
Ocular syphilis and HIV: Here’s what you need to know
““With proper identification and adequate treatment with IV penicillin, ocular syphilis can have equivalent visual outcomes regardless of the severity of the concomitant HIV.” – Dr. Mariam Mathai
Syphilis is out there. It’s sexually transmitted and caused by the spirochete bacterium Treponema pallidum. Lately, there’s been an upsurge in the incidence of syphilis in the United States, particularly among HIV positive patients. Ocular syphilis is rare, and it typically occurs with secondary or tertiary syphilis. Studies have shown that the progression of syphilis to more advanced stages is faster among patients with HIV infection.
In a paper presented at the recent ASCRS 2019 meeting, Dr. Mariam Mathai and colleagues at the MedStar Georgetown Washington Hospital Center, shared results of their study in which they evaluated whether uncontrolled HIV has an effect on visual outcomes in immunocompromised patients diagnosed with ocular syphilis.
The investigators conducted a retrospective chart review on patients diagnosed with ocular syphilis between August 2017 and June 2018.
Diagnosis of ocular syphilis was made via the clinical identification of uveitis, retinitis or optic neuritis on ocular exam, and was supported by laboratory serum RPR, FTA-Abs and/or CSF VDRL. Six patients (twelve eyes) were identified during this period, all of whom were found to be HIV positive. Visual acuities at presentation and after two weeks of treatment with intravenous (IV) penicillin were recorded.
The patients were then stratified based on absolute CD4 count (<200 cells/uL vs. >200 cells/uL) and HIV viral load (<500 copies/mL vs. >500 copies/mL). The data was analyzed using a Wilcoxon signed-rank test, comparing visual acuities at presentation and at the end of treatment between patients with controlled and uncontrolled CD4 count and viral loads.
Of the six patients in the cohort, three knew of their HIV positive status prior to presentation, and two of those patients were on antiretroviral therapy.
All patients were male with an average age of 28.8 years. Four identified as African American, one Hispanic and one Caucasian. Eighty-three percent (83%) reported their sexual orientation as men who have sex with men (MSM).
Dr. Mathai noted that all study patients presented to the clinic because of the development of ocular symptoms, and they did not have any other symptoms compatible with primary, secondary or tertiary syphilis. Additionally, 100% of eyes in this study had posterior segment involvement, emphasized Dr. Mathai. This tendency has been previously reported in literature. Visual recovery of at least one Snellen acuity line was seen in all affected eyes.
According to Dr. Mathai, there was no statistical difference in visual acuity at presentation or after treatment in patients with lower CD4 counts or higher viral loads, suggesting that “with proper identification and adequate treatment with IV penicillin, ocular syphilis can have equivalent visual outcomes regardless of the severity of the concomitant HIV”.
Catching DR early with fractal dimension and OCTA
“Fractal dimension is a useful method for differentiating diabetic retinopathy.” – Dr. Harrison Chiu
Diabetic retinopathy (DR) is a primary cause of visual impairment worldwide, and may be associated with ophthalmoscopically nonvisible neurovascular damage that progresses before the first clinical signs of DR appear. Therefore, there is an urgent need to develop highly sensitive screening tools.
Vascular abnormalities such as changes in the retinal vessel caliber and architectural indices have been investigated to evaluate the early stages of DR. Dr. Harrison Chiu and colleagues evaluated the effect of varying parameters in determining fractal dimensions (FD) of macular optical coherence tomography angiography (OCTA) images and its role in differentiating microvascular differences between normal and diabetic eyes. Their findings were presented at the recent ASCRS 2019 meeting.
The investigators conducted a retrospective study using OCTA images of 3x3mm and 6x6mm scans for superficial and deep capillary plexuses from 49 control eyes and 58 eyes with diabetic retinopathy.
ImageJ (a Java-based image processing program developed at the U.S. National Institutes of Health and the Laboratory for Optical and Computational Instrumentation or LOCI, University of Wisconsin), was used to standardize and binarize grayscale OCTA images with default, 20% and 40% thresholding of background pixel values. Fractalyse (a software developed by the research team
“Mobilities, city and transport” from the research center ThéMA) was used to determine FD and the correlation coefficient via the box-counting method, with an exponential factor of 2 and a circular mass-radius method centered at the barycenter.
Using the box-counting method, Dr. Chiu and colleagues found a significant difference between FD of control and diabetic eyes in the superficial 3x3mm scan and in the deep scans with default threshold; in the superficial and deep 3x3mm scans with 20% threshold; and deep 3x3mm scan with 40% threshold (p < 0.05). Similarly, with the mass-radius method, they discovered a significant difference between FD of control and diabetic eyes in superficial 3x3mm scan and deep 3x3mm scan for both default and 20% threshold (p < 0.05).
Therefore, the investigators concluded that fractal dimension is a useful method for differentiating diabetic retinopathy. However, they cautioned that “there are variations in FD based on thresholding, image resolution and method of estimation. The study provides evidence for the necessity of standardizing parameters such as OCT scan size and thresholding prior to fractal analysis.”
Editor’s Note: The ASCRS 2019 Annual Meeting was held in San Diego, California, USA, from May 3-7, 2019. Reporting for this story also took place at ASCRS 2019.
