Ophthalmic Imaging

Ophthalmic imagers often use a scanning technique with the pupil of the eye placed in the exit pupil of the scanning system [461]. This reduces image distortion and blurring due to the poor optical quality of the lens of the eye. Moreover, confocal detection can be used to suppress reflection, scattering, and fluorescence signals from the lens of the eye. 

Most ophthalmic scanners are designed for imaging the reflected tight. They contain a PMT that delivers an intensity-proportional signal of the light reflected at the eye background. The signal is amplified to a video-compatible level, combined with synchronisation pulses from the scanner, and displayed on a video monitor. 

A laser scanning ophthalmoscope can relatively easily be combined with the TCSPC scanning technique (see Sect. 3.4, page 37). The fluorescence light from the retina is split off by a dichroic mirror and detected by a second PMT. The detection wavelength of the PMTs is selected by filters, FI and F2. The photon pulses from the fluorescence channel PMT are fed into the start input of the TCSPC module. The stop pulses come from the diode laser. 

To build up lifetime images, the TCSPC module needs scan synchronisation pulses from the scanner. These can be either obtained directly from the scanner or separated from the video signal of the reflection channel. 

Because the excitation and the fluorescence light share the same optical path good blocking of scattered excitation light is essential. Moreover, fluorescence of materials in the excitation path must be carefully avoided. Especially fluorescence from epoxy can be very similar to autofluorescence of tissue, both in the spectram and the decay profile. Problems can also arise from the emission of LEDs used to control the pinhole wheel or the polygon mirror of the scanner. It may be necessary to place an NIR blocking filter in front of the detector. 

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Ophthalmic Services Guidance—Ophthalmic Imaging," Royal College of Ophthalmologists, Web. February 2009. 

Chan, A, Ko, TH, and Duker, JS, 2006. Ultrahigh-resolution optical coherence tomography of canthaxanthine retinal crystals. Ophthalmic Surg Lasers Imaging 37, 138-139. 

A 28-year-old medical student developed major depression and was given citalopram (20 mg/day) (14). After 12 days he described incapacitating diplopia which resolved when he closed one eye. Neurological and ophthalmic examination was normal and no structural lesion was detected with brain magnetic resonance imaging. The citalopram was withdrawn and the diplopia resolved within 3 days. 

Rosenfeld PJ, Fung AE, PuMafito CA. Optical coherence tomography findings after an intravitreal injection of bevacizumab (Avastin) for macular edema from central retinal vein occlusion. Ophthalmic Surg Lasers Imaging 2005 36 336. 

Bakri SJ, Beer PM. The effect of intravitreal triamcinolone acetonide on intraocular pressure. Ophthalmic Surg Lasers Imaging 2003 34 386. 

Gungor IU +, Ophthalmic Surg Lasers Imaging 36(4), 348 Glaucoma... 

Salvetti P, Rosen JM, Reichel E. Subthreshold infrared footprinting with indocyanine green for localizing low-intensity infrared photocoagulation. Ophthalmic Surg Lasers Imaging 2003 34 44 48. 

The application of an ophthalmic scanning TCSPC system to autofluorescence imaging at the fundus is described in [450, 451, 452, 453, 454]. A typical result is shown in Fig. 5.69. A double-exponential deconvolution was run on the complete pixel array. It delivered a fast lifetime component of the order of T = 400 ps and a... 

Acquisition times for TCSPC FLIM measurements can vary widely. In vivo lifetime measurements of the human ocular fundus in conjunction with an ophthalmic scanner delivered single exponential lifetimes for an array of 128 x 128 pixels within a few seconds [451, 452, 454]. High-quality double exponential lifetime images of microscopic samples were obtained within 10 seconds by a four-module TCSPC system (see Fig. 5.84) [39]. On the other hand, for the double exponential decay data of FRET measurements in live cells (see Fig. 5.87), acquisition times ranged from 5 to 30 minutes [32, 37]. In practice the acquisition time depends on the size and the photostability of the sample and the requirements for accuracy rather than on the counting capability of the TCSPC device. 

Aiming at medicinal apphcations, porphyrins have been intensively studied since the mid-1970s as photosensitizers (PS) in photodynamic therapy (PDT) of oncological, cardiovascular, dermatological, ophthalmic and infectious diseases [7-11], and in clinical trials as photomarkers in cancer diagnosis by fluorescence [ 12-14] and NMR imaging apphcations [15-18]. 

G.D. Kymionis, M.A. Grentzelos, A.E. Karavitaki, P. Zotta, S.H. Yoo, LG. PaUikaris, Combined comeal collagen cross-Unking and posterior chamber tone implantable collamer lens implantation for keratoconus. Ophthalmic Surg. Lasers Imaging 42 (2011) e22-e25. 

Schlottmann K, Fuchs-Koewel B, Demmler-Hackenberg M et al (2005a) High-frequency contrast-harmonic imaging of ophthalmic tumor perfusion. Am J Roentgenol 184 574-578... 

Denoyer A, Ossant F, Arbeille B, Fetissof F, Patat F, Pourcelot L, Pisella P-J. Very-high-frequency ultrasound comeal imaging as a new tool for early diagnosis of ocular surface toxicity in rabbits treated with a preserved glaucoma dmg. Ophthalm Res 2008 40 298-308. 

Leng T, Moshfeghi DM. Branch retinal artery occlusion after septoplasty. Ophthalmic Surg Lasers Imaging 2010 41 el-2. 

A common ophthalmic procedure is the radial keratotomy. With this procedure, fine laser cuts are made in a radial fashion around the cornea. These precision cuts can correct myopia (nearsightedness) and hyperopia (farsightedness). Laser is also used to treat a number of eye problems such as a detached retina (separation of the imaging surface of the retina from the back of the eye), glaucoma (increased pressure within the eyeball), and cataracts (clouding of the lens). 

Chen E, Ho AC, Garg SJ, Brown GC, Kaiser RS. Streptococcus mitis endophthalmitis presenting as frosted branch angiitis after intravitreal pegaptanib sodium injection. Ophthalmic Surg Lasers Imaging 2009 40 192-4. 

Kim SW, Oh J, Oh IK, Huh K. Retinal pigment epithelial tear after half fluence PDT for serous pigment epithelial detachment in central serous chorioretinopathy. Ophthalmic Surg Lasers Imaging 2009 40 300-3. 

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