Monitoring macular pigment changes in macular holes using fluorescence lifetime imaging ophthalmoscopy

FLUORESCENCE LIFETIME IMAGING OPHTHALMOSCOPY IN PATIENTS WITH MACULAR TELANGIECTASIA TYPE 2 WITH AND WITHOUT DIABETES

PURPOSE

Macular telangiectasia type 2 (MacTel) is a vision-altering retinal disease with a high prevalence of diabetes. Differences between patients with MacTel with and without diabetes were investigated using fluorescence lifetime imaging ophthalmoscopy (FLIO).

METHODS

Eighty-six patients with MacTel (59 ± 12 years) were included. 40 patients (46%) did not have diabetes, 16 patients (19%) were prediabetic, and 30 patients (35%) were diabetic. Of these, seven had diabetic retinopathy. 18 diabetic patients without MacTel and 42 age-matched healthy controls were included. FLIO lifetimes (FLTs) were obtained in short (SSC, 498-560 nm) and long (LSC, 560-720 nm) spectral channels from different areas of interest using a Heidelberg Engineering FLIO.

RESULTS

Fundus autofluorescece lifetimes did not show significant differences when comparing diabetic with nondiabetic MacTel eyes (MacTel zone, SSC, diabetic: 243 ± 65 ps; nondiabetic: 232 ± 51 ps; P = 1.0; LSC, diabetic: 327 ± 66 ps; nondiabetic: 309 ± 54 ps; P = 0.582). Longitudinal changes were similarly unrelated to diabetes status. A nonsignificant trend of increased FLT progression with higher body mass index was found. Fundus autofluorescece lifetimes in diabetic patients without MacTel were significantly shorter within the MacTel zone and longer in the periphery compared with diabetic patients with MacTel.

CONCLUSION

Although MacTel has a high prevalence of diabetes, FLTs from the MacTel zone are unrelated to diabetes. Fluorescence lifetime imaging ophthalmoscopy retains diagnostic abilities in patients with MacTel even in the presence of prediabetes, diabetes, and advanced diabetic retinopathy. The lack of diabetic FLT changes in the periphery of diabetic patients with MacTel is an interesting finding that needs further investigation.

Combining fluorescence lifetime with spectral information in fluorescence lifetime imaging ophthalmoscopy (FLIO)

Fluorescence lifetime imaging ophthalmoscopy (FLIO) provides information on fluorescence lifetimes in two spectral channels as well as the peak emission wavelength (PEW) of the fluorescence. Here, we combine these measures in an integral three-dimensional lifetime-PEW metric vector and determine a normal range for this vector from measurements in young healthy subjects. While for these control subjects 97 (±8) % (median (interquartile range)) of all para-macular pixels were covered by this normal vector range, it was 67 (±55) % for the elderly healthy, 38 (±43) % for age-related macular degeneration (AMD)-suspect subjects, and only 6 (±4) % for AMD patients. The vectors were significantly different for retinal pigment epithelium (RPE) lesions in AMD patients from that of non-affected tissue (p < 0.001). Lifetime- PEW plots allowed to identify possibly pathologic fundus areas by fluorescence parameters outside a 95% quantile per subject. In a patient follow-up, changes in fluorescence parameters could be traced in the lifetime-PEW metric, showing their change over disease progression.

The Development and Clinical Application of Innovative Optical Ophthalmic Imaging Techniques

The field of ophthalmic imaging has grown substantially over the last years. Massive improvements in image processing and computer hardware have allowed the emergence of multiple imaging techniques of the eye that can transform patient care. The purpose of this review is to describe the most recent advances in eye imaging and explain how new technologies and imaging methods can be utilized in a clinical setting. The introduction of optical coherence tomography (OCT) was a revolution in eye imaging and has since become the standard of care for a plethora of conditions. Its most recent iterations, OCT angiography, and visible light OCT, as well as imaging modalities, such as fluorescent lifetime imaging ophthalmoscopy, would allow a more thorough evaluation of patients and provide additional information on disease processes. Toward that goal, the application of adaptive optics (AO) and full-field scanning to a variety of eye imaging techniques has further allowed the histologic study of single cells in the retina and anterior segment. Toward the goal of remote eye care and more accessible eye imaging, methods such as handheld OCT devices and imaging through smartphones, have emerged. Finally, incorporating artificial intelligence (AI) in eye images has the potential to become a new milestone for eye imaging while also contributing in social aspects of eye care.

Adaptive optics two-photon excited fluorescence lifetime imaging ophthalmoscopy of photoreceptors and retinal pigment epithelium in the living non-human primate eye

Fluorescence lifetime imaging has demonstrated promise as a quantitative measure of cell health. Adaptive optics two-photon excited fluorescence (TPEF) ophthalmoscopy enables excitation of intrinsic retinal fluorophores involved in cellular metabolism and the visual cycle, providing in vivo visualization of retinal structure and function at the cellular scale. Combining these technologies revealed that macaque cones had a significantly longer mean TPEF lifetime than rods at 730 nm excitation. At 900 nm excitation, macaque photoreceptors had a significantly longer mean TPEF lifetime than the retinal pigment epithelium layer. AOFLIO can measure the fluorescence lifetime of intrinsic retinal fluorophores on a cellular scale, revealing differences in lifetime between retinal cell classes.

Spectral fundus autofluorescence peak emission wavelength in ageing and AMD

PURPOSE

To investigate the spectral characteristics of fundus autofluorescence (FAF) in AMD patients and controls.

METHODS

Fundus autofluorescence spectral characteristics was described by the peak emission wavelength (PEW) of the spectra. Peak emission wavelength (PEW) was derived from the ratio of FAF recordings in two spectral channels at 500-560 nm and 560-720 nm by fluorescence lifetime imaging ophthalmoscopy. The ratio of FAF intensity in both channels was related to PEW by a calibration procedure. Peak emission wavelength (PEW) measurements were done in 44 young (mean age: 24.0 ± 3.8 years) and 18 elderly (mean age: 67.5 ± 10.2 years) healthy subjects as well as 63 patients with AMD (mean age: 74.0 ± 7.3 years) in each pixel of a 30° imaging field. The values were averaged over the central area, the inner and the outer ring of the ETDRS grid.

RESULTS

There was no significant difference between PEW in young and elderly controls. However, PEW was significantly shorter in AMD patients (ETDRS grid centre: 571 ± 26 nm versus 599 ± 17 nm for elderly controls, inner ring: 596 ± 17 nm versus 611 ± 11 nm, outer ring: 602 ± 16 nm versus 614 ± 11 nm). After a mean follow-up time of 50.8 ± 10.8 months, the PEW in the patients decreased significantly by 9 ± 19 nm in the inner ring of the grid. Patients, showing progression to atrophic AMD in the follow up, had significantly (p ≤ 0.018) shorter PEW at baseline than non-progressing patients.

CONCLUSIONS

Peak emission wavelength (PEW) is related to AMD pathology and might be a diagnostic marker in AMD. Possibly, a short PEW can predict progression to retinal and/or pigment epithelium atrophy.

FLUORESCENCE LIFETIME IMAGING OPHTHALMOSCOPY: Findings After Surgical Reattachment of Macula-Off Rhegmatogenous Retinal Detachment

This study confirms that fluorescence lifetime imaging ophthalmoscopy is able to identify and quantify macular alterations after surgical reattachment of macula-off rhegmatogenous retinal detachment that relate to visual acuity. Fluorescence lifetime imaging ophthalmoscopy could be a useful noninvasive diagnostic tool to assess eyes after rhegmatogenous retinal detachment repair.

Purpose:

The purpose of this study was to investigate fluorescence lifetime imaging ophthalmoscopy lifetimes after macula-off rhegmatogenous retinal detachment (RRD) repair.

Methods:

Fifty-eight patients with successful macula-off RRD reattachment surgery were included. Retinal autofluorescence was excited with 470 nm, and amplitude-weighted mean fluorescence lifetimes (Tm) were measured in a short spectral channel (SSC, 498–560 nm) and a long spectral channel (LSC, 560–720 nm). Tm were obtained within a standardized Early Treatment Diabetic Retinopathy Study grid and correlated with Tm. The unaffected fellow eye served as control.

Results:

Fifty-eight patients (age: 65 ± 1.6 years, 11 women) were imaged at median 1.5 months postoperatively. Tm were significantly prolongxxxed within areas of previously detached retina in the long spectral channel and particularly in the central subfield in the short spectral channel. Short lifetimes in the center of the Early Treatment Diabetic Retinopathy Study grid correlated with better visual acuity (short spectral channel; r² = 0.18, P = 0.001, long spectral channel; r² = 0.08, P = 0.03). Areas of residual subretinal fluid pockets in four RRD eyes displayed short fluorescence lifetimes.

Conclusion:

Areas of previously detached retina exhibit significant fluorescence lifetime changes. We found a significant correlation of fluorescence lifetimes within the fovea with visual acuity after successful RRD repair. Our data suggests that the prolongation of fluorescence lifetimes in the fovea is mainly driven by loss of macular pigment. Therefore, fluorescence lifetime imaging ophthalmoscopy may be useful in the prediction of long-term functional outcomes after macula-off RRD surgery.

LONGITUDINAL FLUORESCENCE LIFETIME IMAGING OPHTHALMOSCOPY ANALYSIS IN PATIENTS WITH MACULAR TELANGIECTASIA TYPE 2 (MacTel)

PURPOSE

Fluorescence lifetime imaging ophthalmoscopy (FLIO) shows characteristic patterns in macular telangiectasia Type 2 (MacTel). This study investigates FLIO changes over time to better understand disease progression.

METHODS

Thirty-three patients with MacTel (age 60 ± 15 years) were followed at the Moran Eye Center with a prototype Heidelberg Engineering FLIO. The mean follow-up time was 19 ± 8 months (range 6-34 months). Fundus autofluorescence was excited at 473 nm, and FLIO lifetimes were recorded in in short (498-560 nm) and long (560-720 nm) spectral wavelengths channels.

RESULTS

Autofluorescence lifetimes imaging ophthalmoscopy lifetimes from the MacTel area prolonged significantly over time (subfield T1, baseline: short spectral channel 210 ± 54 ps, long spectral channel 269 ± 58 ps; follow-up: short spectral channel 225 ± 59 ps, P < 0.001, long spectral channel 282 ± 64 ps, P < 0.01). The average 12-months prolongation of FLIO lifetimes was 9 ps (short spectral channel) and 8 ps (long spectral channel). Autofluorescence lifetimes changes correlated positively with ellipsoid zone loss and negatively with changes in retinal thickness.

CONCLUSION

Autofluorescence lifetimes in MacTel slowly prolong over time, and temporal patterns progress to full rings. Detailed knowledge about FLIO changes will aid in understanding disease development and progression.

Fluorescence lifetime imaging ophthalmoscopy: autofluorescence imaging and beyond

Fluorescence lifetime imaging ophthalmoscopy, FLIO, has gained large interest in the scientific community in the recent years. It is a noninvasive imaging modality that has been shown to provide additional information to conventional imaging modalities. The FLIO device is based on a Heidelberg Engineering Spectralis system. Autofluorescence lifetimes are excited at 473 nm and recorded in two spectral wavelength channels, a short spectral channel (SSC, 498-560 nm) and a long spectral channel (LSC, 560-720 nm). Typically, mean autofluorescence lifetimes in a 30° retinal field are investigated. FLIO shows a clear benefit for imaging different retinal diseases. For example, in age-related macular degeneration (AMD), ring patterns of prolonged FLIO lifetimes 1.5-3.0 mm from the fovea can be appreciated. Macular telangiectasia type 2 (MacTel) shows a different pattern, with prolonged FLIO lifetimes within the typical MacTel zone. In Stargardt disease, retinal flecks can be appreciated even before they are visible with other imaging modalities. Early hydroxychloroquine toxicity appears to be detectable with FLIO. This technique has more potential that has yet to be discovered. This review article focuses on current knowledge as well as pitfalls of this technology. It highlights clinical benefits of FLIO imaging in different ophthalmic and systemic diseases, and provides an outlook with perspectives from the authors.

Comparison of algorithms to suppress artifacts from the natural lens in fluorescence lifetime imaging ophthalmoscopy (FLIO)

Fluorescence lifetime imaging ophthalmoscopy (FLIO) has developed as a new diagnostic tool in ophthalmology. FLIO measurements are taken from 30° retinal fields in two spectral channels (short spectral channel (SSC): 498-560 nm, long spectral channel (LSC): 560-720 nm). Because of the layered structure of the eye, the detected signal is an interaction of the fluorescence decay of the anterior part and of the fundus. By comparing FLIO measurements before and after cataract surgery, the impact of the natural lens was proven, despite the application of a confocal laser scanning (cSLO) technique. The goal of this work was to determine the best algorithmic solution to isolate the sole fundus fluorescence lifetime from the measured signal, suppressing artifacts from the natural lens. Three principles based on a tri-exponential model were investigated: a tailfit, a layer-based approach with a temporally shifted component, and the inclusion of a separately measured fluorescence decay of the natural lens. The mean fluorescence lifetime τ_m,12 is calculated using only the shortest and the intermediate exponential component. τ_m,all is calculated using all three exponential components. The results of tri-exponential tailfit after cataract surgery were considered as a reference, because the implanted artificial lens can be assumed as non-fluorescent. In SSC, the best accordance of τ_m,all of the reference was determined with τ_m,12 of the tailfit before surgery. If high-quality natural lens measurements are available, the correspondence of τ_m,12 is best with τ_m,all of the reference. In LSC, there is a good accordance for all models between τ_m,12 before and after surgery. To study the pure fundus fluorescence decay in eyes with natural lenses, we advise to utilize fluorescence lifetime τ_m,12 of a triple-exponential tailfit, as it corresponds well with the mean fluorescence lifetime τ_m,all of eyes with fluorescence-less artificial intraocular lenses.

Fluorescence Lifetime Imaging Ophthalmoscopy (FLIO) in Patients with Choroideremia

Purpose

To provide a detailed characterization of choroideremia (CHM) using fluorescence lifetime imaging ophthalmoscopy (FLIO) and to provide a deeper understanding of disease-related changes and progression.

Methods

Twenty-eight eyes of 14 patients with genetically confirmed CHM (mean age, 28 ± 14 years) and 14 age-matched healthy subjects were investigated in this study. FLIO images of a 30° retinal field were collected at the Moran Eye Center using a Heidelberg Engineering FLIO device. FLIO lifetimes were recorded in short spectral channels (SSC; 498-560 nm) and long spectral channels (LSC; 560-720 nm), and mean autofluorescence lifetimes (τm) were calculated. Optical coherence tomography (OCT) scans were recorded for each patient. Three patients were re-imaged after a year.

Results

Patients with CHM exhibit specific FLIO lifetime patterns. Prolonged FLIO lifetimes (around 600-700 ps) were found in the peripheral macula corresponding to atrophy in OCT imaging. In the central macula, τm was unrelated to autofluorescence intensity. Some areas of persistent retinal pigment epithelial islands had prolonged FLIO lifetimes, whereas other areas of hypofluorescence had short FLIO lifetimes. At 1-year follow-up, FLIO lifetimes were significantly prolonged within atrophic areas (P < 0.05).

Conclusions

FLIO shows distinct patterns in patients with CHM, indicating lesions of atrophy and areas of preserved function in the presence or absence of findings in fundus autofluorescence intensity images. FLIO may provide differentiated knowledge about pathophysiology and atrophy progression in CHM compared to conventional imaging modalities.

Translational Relevance

FLIO shows distinctive lifetime patterns that potentially identify areas of function, atrophy, and disease progression in patients with CHM.

Autofluorescence Lifetimes Measured with Fluorescence Lifetime Imaging Ophthalmoscopy (FLIO) Are Affected by Age, but Not by Pigmentation or Gender

Purpose

Fluorescence lifetime imaging ophthalmoscopy (FLIO) is a novel modality to investigate the human retina. This study aims to characterize the effects of age, pigmentation, and gender in FLIO.

Methods

A total of 97 eyes from 97 healthy subjects (mean age 37 ± 18 years, range 9-85 years) were investigated in this study. This study included 47 (49%) females and 50 males. The pigmentation analysis was a substudy including 64 subjects aged 18 to 40 years (mean age 29 ± 6 years). These were categorized in groups A (darkly pigmented, 8), B (medium pigmented, 20), and C (lightly pigmented, 36). Subjects received Heidelberg Engineering FLIO and optical coherence tomography imaging. Retinal autofluorescence lifetimes were detected in two spectral channels (short spectral channel [SSC]: 498-560 nm; long spectral channel [LSC]: 560-720 nm), and amplitude-weighted mean fluorescence lifetimes (τ_m) were calculated. Additionally, autofluorescence lifetimes of melanin were measured in a cuvette.

Results

Age significantly affected FLIO lifetimes, and age-related FLIO changes in the SSC start at approximately age 35 years, whereas the LSC shows a consistent prolongation with age from childhood. There were no gender- or pigmentation-specific significant differences of autofluorescence lifetimes.

Conclusions

This study confirms age-effects in FLIO but shows that the two channels are affected differently. The LSC appears to show the lifelong accumulation of lipofuscin. Furthermore, it is important to know that neither gender nor pigmentation significantly affect FLIO lifetimes.

Translational Relevance

This study helps to understand the FLIO technology better, which will aid in conducting future clinical studies.

Influence of Lens Fluorescence on Fluorescence Lifetime Imaging Ophthalmoscopy (FLIO) Fundus Imaging and Strategies for Its Compensation

Purpose

To explore the contribution of crystalline lens fluorescence to fluorescence lifetimes measured with fluorescence lifetime imaging ophthalmoscopy (FLIO) and to propose a computational model to reduce the lens influence.

Methods

FLIO, which detects autofluorescence decay over time in a short-wavelength spectral channel (SSC, 498–560 nm) and a long-wavelength spectral channel (LSC, 560–720 nm), was performed on 32 patients before and after cataract extraction. The mean autofluorescence lifetime (τ_m) of the fundus was determined from a three-exponential fit of the postoperative fluorescence decays. The preoperative measurements were fit with series of exponential functions in which one fluorescence component was time-shifted in order to represent lens fluorescence.

Results

Postoperatively, τ_m was 185 ± 22 ps in the SSC and 209 ± 34 ps in the LSC at the posterior pole. These values were best reproduced by fitting the postoperative measurements with a three-exponential model with a time-shifted third fluorescence component (SSC, 203 ± 45 ps; LSC, 215 ± 29 ps), whereas disregarding time-shifted lens fluorescence resulted in significantly (P < 0.001) longer τ_m values (SSC, 474 ± 206 ps; LSC, 215 ± 29 ps). The fluorescence of the cataract lens contributed to the total fluorescence by 54.2 ± 10.6% (SSC) and 29.5 ± 9.9% (LSC).

Conclusions

Cataract lens fluorescence greatly alters fluorescence lifetimes measured at the fundus by FLIO, resulting in an overestimation of the lifetimes; however, this may be compensated for considerably by taking lens influence into account in the fitting model.

Translational Relevance

This study investigates cataract fluorescence in FLIO and a mathematical model for compensation of this influence.

The future of retinal imaging

PURPOSE OF REVIEW

This article reviews emerging technologies in retinal imaging, including their scientific background, clinical implications and future directions.

RECENT FINDINGS

Fluorescence lifetime imaging ophthalmoscopy is a technology that will reveal biochemical and metabolic changes of the retina at the cellular level. Optical coherence tomography is evolving exponentially toward higher resolution, faster speed, increased portability and more cost effective. Adaptive optics scanning laser ophthalmoscopy fluorescein angiography will provide unprecedented detail of the retinal vasculature down to the level of capillaries, enabling earlier and more sensitive detection of retinal vascular diseases.

SUMMARY

Continued developments in retinal imaging focus on improved resolution, faster speed and noninvasiveness, while providing new information on the structure-function relationship of the retina inclusive of metabolic activity at the cellular level.

FLUORESCENCE LIFETIME IMAGING OPHTHALMOSCOPY (FLIO) PATTERNS IN CLINICALLY UNAFFECTED CHILDREN OF MACULAR TELANGIECTASIA TYPE 2 (MACTEL) PATIENTS

PURPOSE

Macular telangiectasia Type 2 (MacTel) is an inherited retinal disease following an autosomal dominant pattern with late onset and reduced penetrance. Fluorescence lifetime imaging ophthalmoscopy (FLIO) enhances diagnosis by showing distinct changes in MacTel. This study investigates FLIO-associated changes in clinically unaffected family members.

METHODS

Eighty-one patients with MacTel (61 ± 12 years), 33 clinically healthy children under age 40 years of these MacTel patients (MacTel-C; 31 ± 6 years), 27 other family members (children over age 40 years, siblings, and parents) and 30 controls were investigated with the Heidelberg FLIO. All subjects underwent multimodal conventional imaging, including optical coherence tomography, blue-light reflectance, fluorescein angiography, and macular pigment imaging.

RESULTS

All 81 patients with MacTel showed typical FLIO patterns. Of the 33 investigated MacTel-C with completely normal eye examinations and conventional imaging, 12 (36%) show FLIO patterns consistent with early MacTel.

CONCLUSION

Prolonged FLIO lifetimes in the parafoveal area within the short spectral channel, especially temporally, are MacTel-specific. Fluorescence lifetime imaging ophthalmoscopy detects these lifetime patterns in over one-third of clinically unaffected MacTel-C. Although further studies will be necessary to determine the specificity of FLIO, it may help diagnose MacTel before conventional imaging modalities show changes or patients experience visual disturbances. Early detection may facilitate future gene discovery studies and interventional trials.

Fluorescence Lifetime Imaging Ophthalmoscopy (FLIO) in Eyes With Pigment Epithelial Detachments Due to Age-Related Macular Degeneration

Purpose

To investigate fluorescence lifetime imaging ophthalmoscopy (FLIO) in neovascular AMD and pigment epithelial detachments (PEDs).

Methods

A total of 46 eyes with PEDs (>350 μm) as well as age-matched healthy controls were included in this study. We found 28 eyes showed neovascular AMD (nvAMD), and 17 had nonneovascular (dry) AMD (dAMD). The Heidelberg Engineering FLIO excited fluorescence at 473 nm. Fluorescence decays were detected in two spectral channels (498–560 nm; 560–720 nm) to determine fluorescence lifetimes of endogenous fluorophores in their specific spectral emission ranges. Mean fluorescence lifetimes (τ_m) were investigated. Multimodal imaging was reviewed by two ophthalmologists who circumscribed and classified PEDs as either serous (n = 4), hemorrhagic (n = 4), fibrovascular (n = 16), drusenoid (n = 17), or mixed (n = 5). Blood samples from a healthy subject and a patient with PED were investigated in a quartz cuvette.

Results

Eyes with nvAMD show similar FLIO patterns to dAMD: ring-shaped prolongations of τ_m 3 to 6 mm from the fovea. Different PED-forms show characteristic τ_m, while serous and hemorrhagic PEDs exhibit shortened τ_m, drusenoid PEDs show prolonged τ_m, and τ_m in fibrovascular PEDs is variable. Areas corresponding to sub-/intraretinal fluid display shortened τ_m. Ex vivo studies of blood also show short τ_m.

Conclusions

The previously described dAMD-related FLIO pattern is also present in nvAMD. Short τ_m in serous, fibrovascular, and hemorrhagic PEDs as well as sub/intraretinal fluid may disrupt this pattern. FLIO appears to differentiate between PEDs, hemorrhage, and fluid. Additionally, ex vivo studies of human blood help to better interpret FLIO images.

Fluorescence Lifetime Patterns of Retinal Pigment Epithelium Atrophy in Patients with Stargardt Disease and Age-Related Macular Degeneration

PURPOSE

To investigate whether autofluorescence lifetime patterns within retinal pigment epithelium (RPE) atrophy differ between age-related macular degeneration (AMD) and Stargardt disease (STGD).

METHODS

Mean retinal autofluorescence lifetimes were measured in a short and a long spectral channel (SSC: 498-560 nm; LSC: 560-720 nm). Mean retinal fluorescence lifetimes were analyzed with corresponding clinical features, fundus images, fundus autofluorescence intensity images, and optical coherence tomography. Mean fluorescence lifetime values of atrophic areas were compared between the two cohorts and within the same patient to adjacent nonatrophic regions.

RESULTS

Mean fluorescence lifetimes within areas with RPE atrophy of 13 patients with STGD (mean age ± SEM 43.7 ± 5 years) and 30 patients with geographic atrophy (mean age: 78 ± 2 years) were analyzed and compared to age-matched healthy participants. The mean area of RPE atrophy in STGD and AMD was 6.6 ± 2.3 mm2 (range: 0.66-33.17 mm2) and 17.5 ± 3.8 mm2 (range: 0.58-50.02 mm2), respectively. In patients with AMD, atrophic areas revealed significantly longer mean fluorescence lifetime values as compared with patients with STGD (SSC: 997 ± 60 vs. 363 ± 26 ps; LSC: 880 ± 46 vs. 393 ± 23 ps; p < 0.0001).

CONCLUSIONS

This study established that RPE atrophy in patients secondary to STGD and AMD display distinctive mean fluorescence lifetime characteristics. As retinal fluorescence lifetimes within areas of RPE atrophy were significantly longer in AMD patients, the analysis of specific lifetime patterns may provide additional insight into the disease processes and the pathogenetic mechanisms in the development of atrophic patches in AMD and STGD.

Simplified approach to least-square fitting of fluorescence lifetime ophthalmoscopy (FLIO) data by fixating lifetimes

Fluorescence lifetime imaging ophthalmoscopy (FLIO) is a new imaging modality in ophthalmology. For clinical investigations, the amplitude-weighted mean of two or three lifetime components is usually analyzed. In this study, we investigated the effects of fixation of lifetime components. This resulted in slightly higher fit errors but mean lifetimes were highly correlated to those from fits with variable individual lifetimes. Furthermore, this approach resulted in a similarly good discrimination of diabetic retinopathy patients from controls, a reduction of the computational workload, a de-noising of the mean lifetime images and allows higher local resolution. Thus, fixation of lifetimes in the fit of FLIO data could be superior for clinical routine analysis of FLIO data.

Ocular Carotenoid Status in Health and Disease

Retinal carotenoids are dietary nutrients that uniquely protect the eye from light damage and various retinal pathologies. Their antioxidative properties protect the eye from many retinal diseases, such as age-related macular degeneration. As many retinal diseases are accompanied by low carotenoid levels, accurate noninvasive assessment of carotenoid status can help ophthalmologists identify the patients most likely to benefit from carotenoid supplementation. This review focuses on the different methods available to assess carotenoid status and highlights disease-related changes and potential nutritional interventions.

Fundus Autofluorescence Lifetime Patterns in Retinitis Pigmentosa

Purpose

We investigated whether fundus autofluorescence (FAF) lifetimes in patients with retinitis pigmentosa display a disease-specific lifetime pattern.

Methods

Fundus autofluorescence lifetime imaging ophthalmoscopy (FLIO) was performed in two spectral channels (498-560 and 560-720 nm) after excitation with a 473 nm pulsed laser in patients with retinitis pigmentosa and compared to healthy controls of a similar age range. Corresponding FAF intensity and spectral domain optical coherence tomography (OCT) data, as well as best corrected visual acuity (BCVA) were acquired and compared to fluorescence lifetime data.

Results

We investigated 43 eyes from 43 patients with retinitis pigmentosa (mean age 45 ± 15 years) and compared them to eyes of 13 age-matched healthy participants. Mean FAF lifetimes were prolonged in areas of photoreceptor atrophy with preserved retinal pigment epithelium (RPE) (P = 0.0036) and even longer in areas with total atrophy of photoreceptors and RPE (P = 0.0002). The prevalence of perifoveal ring structures characterized by prolonged fluorescence lifetimes in FLIO was higher (63% vs. 49%) and the rings were wider compared to the hyperautofluorescent rings in qualitative fundus autofluorescence intensity images. In the central fovea with intact retinal layer structure identified by OCT, fluorescence lifetimes were slightly prolonged compared to those of age-matched healthy controls (short spectral channel [SSC], P = 0.0044; long spectral channel [LSC], P = 0.0128). Short lifetimes within the macular center were negatively correlated with BCVA (R2 = 0.33, P < 0.0001) as well as the greatest diameter of the ellipsoid band in OCT.

Conclusions

FLIO in retinitis pigmentosa reveals characteristic patterns that allow identification of areas of photoreceptor atrophy, RPE atrophy, and remaining photoreceptor segments in areas of RPE atrophy. Fluorescence lifetimes can be used to identify ellipsoid zone loss that correlates with functional parameters.

Fundus autofluorescence beyond lipofuscin: lesson learned from ex vivo fluorescence lifetime imaging in porcine eyes

Fundus autofluorescence (FAF) imaging is a well-established method in ophthalmology; however, the fluorophores involved need more clarification. The FAF lifetimes of 20 post mortem porcine eyes were measured in two spectral channels using fluorescence lifetime imaging ophthalmoscopy (FLIO) and compared with clinical data from 44 healthy young subjects. The FAF intensity ratio of the short and the long wavelength emission (spectral ratio) was determined. Ex vivo porcine fundus fluorescence emission is generally less intense than that seen in human eyes. The porcine retina showed significantly (p<0.05) longer lifetimes than the retinal pigment epithelium (RPE): 584 ± 128 ps vs. 121 ± 55 ps 498-560 nm, 240 ± 42 ps vs. 125 ± 20 ps at 560-720 nm. Furthermore, the lifetimes of the porcine RPE were significantly shorter (121 ± 55 ps and 125 ± 20 ps) than those measured from human fundus in vivo (162 ± 14 ps and 179 ± 13 ps, respectively). The fluorescence emission of porcine retina was shifted towards a shorter wavelength compared to that of RPE and human FAF. This data shows the considerable contribution of fluorophores in the neural retina to total FAF intensity in porcine eyes.

Characterization of Retinitis Pigmentosa Using Fluorescence Lifetime Imaging Ophthalmoscopy (FLIO)

PURPOSE

We investigated fundus autofluorescence (FAF) lifetimes in patients with retinitis pigmentosa (RP) using fluorescence lifetime imaging ophthalmoscopy (FLIO).

METHODS

A total of 33 patients (mean age, 40.0 ± 17.0 years) with RP and an age-matched healthy group were included. The Heidelberg FLIO was used to detect FAF decays in short (SSC; 498-560 nm) and long (LSC; 560-720 nm) spectral channels. We investigated a 30° retinal field and calculated the amplitude-weighted mean fluorescence lifetime (τm). Additionally, macular pigment measurements, macular optical coherence tomography (OCT) scans, fundus photographs, visual fields, and fluorescein angiograms were recorded. Genetic studies were performed on nearly all patients.

RESULTS

In RP, FLIO shows a typical pattern of prolonged τm in atrophic regions in the outer macula (SSC, 419 ± 195 ps; LSC, 401 ± 111 ps). Within the relatively preserved retina in the macular region, ring-shaped patterns were found, most distinctive in patients with autosomal dominant RP inheritance. Mean FAF lifetimes were shortened in rings in the LSC. Central areas remained relatively unaffected.

CONCLUSIONS

FLIO uniquely presents a distinct and specific signature in eyes affected with RP. The ring patterns show variations that indicate genetically determined pathologic processes. Shortening of FAF lifetimes in the LSC may indicate disease progression, as was previously demonstrated for Stargardt disease. Therefore, FLIO might be able to indicate disease progression in RP as well.

TRANSLATIONAL RELEVANCE

Hyperfluorescent FLIO rings with short FAF lifetimes may provide insight into the pathophysiologic disease status of RP-affected retinas potentially providing a more detailed assessment of disease progression.

Fluorescence Lifetime Imaging Ophthalmoscopy: A Novel Way to Assess Macular Telangiectasia Type 2

PURPOSE

Macular Telangiectasia Type 2 (MacTel) is an uncommon, late-onset complex retinal disease that leads to central vision loss. No causative gene(s) have been identified so far, resulting in a challenging clinical diagnostic dilemma because retinal changes of early stages are often subtle. The objective of this study was to investigate the benefit of fluorescence lifetime imaging ophthalmoscopy (FLIO) for retinal imaging in patients with MacTel.

DESIGN

Cross-sectional study from a tertiary-care retinal referral practice.

SUBJECTS AND CONTROLS

42 eyes of 21 patients (mean age 60.5±13.3 years) with MacTel as well as an age-matched healthy control group (42 eyes of 25 subjects, mean age 60.8±13.4 years).

METHODS

A 30° retinal field centered at the fovea was investigated using FLIO. This camera is based on a Heidelberg Engineering Spectralis system. Fundus autofluorescence (FAF) decays were detected in short (498-560 nm, SSC) and long (560-720 nm, LSC) spectral channels. The mean fluorescence lifetime, τm, was calculated from a 3-exponential approximation of the FAF decays. For MacTel patients, macular pigment (MP), OCT, blue light reflectance, fluorescein angiography, as well as fundus photography, were also recorded.

MAIN OUTCOME MEASURES

Mean FAF lifetime (τm) images.

RESULTS

FLIO of MacTel patients shows a unique pattern of prolonged τm at the temporal side of the fovea in patients with MacTel in the "MacTel area" within 5-6° of the foveal center. In early stages, this region appears crescent-shaped, while advanced stages show a ring-like pattern. This pattern corresponds well with other imaging modalities and gives an especially high contrast of the affected region even in minimally affected individuals. Additionally, FLIO provides a novel means to monitor the abnormal MP distribution. In one case, FLIO showed changes suggestive of MacTel within a clinically normal parent of two MacTel patients.

CONCLUSIONS

FLIO detects retinal changes in patients with MacTel with high contrast, presenting a distinctive signature that is a characteristic finding of the disease. The non-invasive properties of this novel imaging modality provide a valuable addition to clinical assessment of early changes in the disease that could lead to more accurate diagnosis of MacTel.

Fluorescence Lifetime Imaging Ophthalmoscopy (FLIO) of Macular Pigment

Purpose

To describe different patterns of macular pigment (MP) seen in fluorescence lifetime imaging ophthalmoscopy (FLIO) and to analyze ex vivo fluorescence characteristics of carotenoids.

Methods

A total of 31 eyes of young healthy subjects, 4 eyes from patients with albinism, 36 eyes with macular telangiectasia type 2 (MacTel), 24 eyes with retinitis pigmentosa, and 1 eye with a macular hole were included in this clinic-based, cross-sectional study. All subjects underwent Heidelberg Engineering FLIO and MP measurements (dual-wavelength autofluorescence). Fundus autofluorescence (FAF) lifetimes of a 30° retinal field were detected in two spectral channels (SSC: 498-560 nm; LSC: 560-720 nm), and amplitude-weighted mean fluorescence lifetimes (τm) were calculated. Additionally, autofluorescence lifetimes of known dilutions of lutein and zeaxanthin were measured in a cuvette in free- and protein-associated states.

Results

MP shows a significant inverse correlation to foveal FAF lifetimes measured with FLIO (SSC: r = -0.608; P < 0.001). Different distribution patterns can be assigned to specific disease-related changes. Two patients with albinism, who did not have MP, were found to be missing short FAF lifetimes. In solvent, lutein and zeaxanthin show very short autofluorescence lifetimes (∼50-60 ps; SSC), as do their respective binding proteins (∼40-50 ps; SSC). When combining carotenoids with their specific binding proteins, the decay times shift to longer means (∼70-90 ps; SSC).

Conclusions

This study expands upon previous findings of an impact of MP on short FAF lifetimes by describing ex vivo autofluorescence lifetimes of carotenoids and different in vivo autofluorescence patterns that can be associated with certain diseases.

Monitoring foveal sparing in geographic atrophy with fluorescence lifetime imaging ophthalmoscopy - a novel approach

PURPOSE

To investigate fundus autofluorescence (FAF) lifetimes in geographic atrophy (GA) with a focus on macular pigment (MP) and foveal sparing.

METHODS

The study included 35 eyes from 28 patients (mean age 79.2 ± 8.0 years) with GA. A 30° retinal field, centred at the macula, was investigated using fluorescence lifetime imaging ophthalmoscopy (FLIO). The FLIO technology is based on a Heidelberg Engineering Spectralis system. Decays of FAF were detected in a short (498-560 nm, SSC) and long (560-720 nm, LSC) spectral channel. The mean fluorescence lifetime, τ_m , was calculated from a three-exponential approximation of the FAF decays. Macular optical coherence tomography (OCT) scans as well as fundus photography were recorded.

RESULTS

Review of FLIO data reveals specific patterns of significantly prolonged τ_m in regions of GA (SSC 616 ± 343 ps, LSC 615 ± 154 ps) as compared to non-atrophic regions. Large τ_m differences between the fovea and atrophic areas correlate with better visual acuity (VA). Shorter τ_m at the fovea than within other non-atrophic regions indicates sparing, which was identified in 16 eyes. Seventy per cent of patients treated with lutein supplementation showed foveal sparing, whereas the rate among non-supplemented patients was 22%.

CONCLUSION

Using FLIO, we present a novel way to detect foveal sparing, investigate MP, and analyse variability of τ_m in different foveal regions (including the prognostic valuable border region) in GA. These findings support the potential utility of FLIO in monitoring disease progression. The findings also highlight the possibly protective effect of lutein supplementation, with implication in recording the presence and distributional pattern of MP.

Patterns of Fundus Autofluorescence Lifetimes In Eyes of Individuals With Nonexudative Age-Related Macular Degeneration

Purpose

To investigate fundus autofluorescence (FAF) lifetimes in patients with nonexudative AMD.

Methods

A total of 150 eyes of 110 patients (mean age: 73.2 ± 10.7 years) with nonexudative AMD, as well as a healthy group of 57 eyes in 38 subjects (mean age: 66.5 ± 8.7 years), were included. Investigations were conducted at the University Eye Clinic in Jena, Germany, as well as the Moran Eye Center in Salt Lake City, Utah, USA, using the Heidelberg Engineering Spectralis-based fluorescence lifetime imaging ophthalmoscope (FLIO). A 30° retinal field centered at the fovea was investigated. FAF decays were detected in short (498-560 nm) and long (560-720 nm, LSC) spectral channels. The mean fluorescence lifetimes (τm) were calculated. Optical coherence tomography scans and fundus photographs were also recorded.

Results

In patients with nonexudative AMD, FLIO shows a ring-shaped pattern of prolonged τm in the LSC. This pattern occurs in all patients with AMD (including very early stages) and in one-third of the healthy controls. FAF lifetimes were longer with more advanced stages. The presence of drusen is associated with prolonged τm when compared with the healthy fundus, but drusen identification is difficult with FLIO only.

Conclusions

FLIO detects a clear pattern of changes within the fundus, which appears to be AMD-associated. These changes are already visible in early AMD stages and not masked by the presence of other coexisting retinal diseases. These findings may be useful for the early diagnosis of AMD and to distinguish AMD from other retinal diseases.

Fluorescence lifetime imaging ophthalmoscopy

Imaging techniques based on retinal autofluorescence have found broad applications in ophthalmology because they are extremely sensitive and noninvasive. Conventional fundus autofluorescence imaging measures fluorescence intensity of endogenous retinal fluorophores. It mainly derives its signal from lipofuscin at the level of the retinal pigment epithelium. Fundus autofluorescence, however, can not only be characterized by the spatial distribution of the fluorescence intensity or emission spectrum, but also by a characteristic fluorescence lifetime function. The fluorescence lifetime is the average amount of time a fluorophore remains in the excited state following excitation. Fluorescence lifetime imaging ophthalmoscopy (FLIO) is an emerging imaging modality for in vivo measurement of lifetimes of endogenous retinal fluorophores. Recent reports in this field have contributed to our understanding of the pathophysiology of various macular and retinal diseases. Within this review, the basic concept of fluorescence lifetime imaging is provided. It includes technical background information and correlation with in vitro measurements of individual retinal metabolites. In a second part, clinical applications of fluorescence lifetime imaging and fluorescence lifetime features of selected retinal diseases such as Stargardt disease, age-related macular degeneration, choroideremia, central serous chorioretinopathy, macular holes, diabetic retinopathy, and retinal artery occlusion are discussed. Potential areas of use for fluorescence lifetime imaging ophthalmoscopy will be outlined at the end of this review.