Yasuki Ito

Measuring the human retinal oxygenation response to a hyperoxic challenge using MRI: Eliminating blinking artifacts and demonstrating proof of concept

The retinal oxygenation response to a hyperoxic challenge measured using MRI appears to be an early and accurate marker of retinopathy risk in experimental models, with promising clinical potential. However, the application of this technique in humans is limited by blinking artifacts that can confound detection of subtle signal intensity changes. We asked subjects to refrain from blinking during a 12‐s fast low‐angle shot (FLASH) image, and to blink if needed during the following 3‐s rest period. This no‐blink blink cycle was repeated sequentially 20 times during either room‐air or 100% oxygen breathing. Significant change (P < 0.05) was detected for the first time from the resultant blinking‐artifact‐free images in the preretinal vitreous oxygen tension (upper limit of about 13 mm Hg (1.8 KPa, N = 3)) following a 10‐min hyperoxic inhalation challenge. These results provide the proof‐of‐concept data needed for future MRI evaluation of the retinal oxygenation response and human retinopathy, such as diabetic retinopathy. Magn Reson Med 46:412–416, 2001.

Risk factors for retention of subretinal perfluorocarbon liquid in vitreoretinal surgery

Purpose: To analyze factors that may lead to inadvertent subretinal retention of perfluorocarbon liquid (PFCL) after vitreoretinal surgery and compare surgical outcomes and complications associated with these events. Design: Consecutive retrospective study. Methods: The authors retrospectively reviewed the charts of 72 vitreoretinal surgeries using intraoperative PFCL and its removal through fluid–air exchange and subsequent tamponade. Indications for surgery included trauma, retinal detachment, giant retinal tear, and submacular hemorrhage. Most interventions studied had significant amounts of proliferative vitreoretinopathy and were required after failed or complicated previous vitreoretinal surgery. Main Outcome Measures: Analysis was focused on the occurrence of subretinal retention of PFCL during different surgical procedures and techniques, indications, anatomic and visual results, and complications. Results: At the last follow-up, the retina was completely attached in 97% of eyes treated with PFCL after 1 or 2 vitrectomies. Subretinal PFCL was found in 8 (11.1%) eyes. There was no statistical difference in the retention rate for perfluorodecalin and perfluoro-n-octane. The factor most significantly associated with subretinal retention of PFCL was the presence and large size of a peripheral retinotomy. All cases of subretinal PFCL had a retinotomy of 120° or larger. The average retinotomy size in these cases was 259°. Subretinal PFCL was found in 40% of eyes with a 360° retinotomy. Small and medium-sized retinal breaks were not associated with PFCL retention. Another surgical procedure that correlated significantly with subretinal PFCL was lack of saline rinse during fluid–air exchange. Only 1 of the 23 eyes that were rinsed had subretinal PFCL, although many had large retinotomies. Conclusion: Subretinal PFCL retention is most likely to occur in eyes with large peripheral retinotomies, especially if 360°. Saline rinse seems to be useful in the prevention of subretinal PFCL. The presence of subretinal PFCL does not seem to affect visual and anatomic success when located outside the macula, at least during an intermediate period of follow-up.

MR studies of retinal oxygenation.

In this paper, we summarize the development and application of two novel magnetic resonance based measurements of retinal oxygenation in experimental models of retinopathy, including diabetic retinopathy and retinopathy of prematurity. We use 19F-NMR and a small (microl) perfluorocarbon drop positioned in the preretinal vitreous space to make PO2 measurement of the inner retina. In addition, we use magnetic resonance imaging (MRI) to accurately and non-invasively measure the change in the preretinal PO2 (DeltaPO2) following the shift from breathing room air to a hyperoxic inhalation challenge. The advantages and disadvantages of each method are discussed. New applications of these techniques in the newborn rat and adult mouse are presented. We expect such studies to motivate future MRI oxygenation studies of human retinopathy, including diabetic retinopathy and retinopathy of prematurity.