Advances in Ophthalmic Epigenetics and Implications for Epigenetic Therapies: A Review

The epigenome represents a vast molecular apparatus that writes, reads, and erases chemical modifications to the DNA and histone code without changing the DNA base-pair sequence itself. Recent advances in molecular sequencing technology have revealed that epigenetic chromatin marks directly mediate critical events in retinal development, aging, and degeneration. Epigenetic signaling regulates retinal progenitor (RPC) cell cycle exit during retinal laminar development, giving rise to retinal ganglion cells (RGCs), amacrine cells, horizontal cells, bipolar cells, photoreceptors, and Müller glia. Age-related epigenetic changes such as DNA methylation in the retina and optic nerve are accelerated in pathogenic conditions such as glaucoma and macular degeneration, but reversing these epigenetic marks may represent a novel therapeutic target. Epigenetic writers also integrate environmental signals such as hypoxia, inflammation, and hyperglycemia in complex retinal conditions such as diabetic retinopathy (DR) and choroidal neovascularization (CNV). Histone deacetylase (HDAC) inhibitors protect against apoptosis and photoreceptor degeneration in animal models of retinitis pigmentosa (RP). The epigenome represents an intriguing therapeutic target for age-, genetic-, and neovascular-related retinal diseases, though more work is needed before advancement to clinical trials.

Intraocular Methotrexate for the Treatment and Prevention of Proliferative Vitreoretinopathy: A Review

Purpose:

To review the current literature on the use of intravitreal methotrexate (IVT MTX) for the treatment and prevention of proliferative vitreoretinopathy (PVR).

Methods:

All reports of IVT MTX to treat and prevent PVR published in PubMed, Google Scholar, and EBSCOhost were reviewed. The relevant current studies are included in this report.

Results:

The literature search yielded 32 articles describing the use of MTX in PVR. These included preclinical studies, 1 case report, and several case series. Early studies found that IVT MTX is a promising medication for the treatment and prevention of PVR. MTX works as a potent anti-inflammatory agent through a new mechanism of action different from that of other medications for use in PVR. Few side effects have been reported and were mostly limited to mild reversible corneal keratopathy. There are 2 current ongoing randomized controlled clinical trials to further evaluate the efficacy of MTX for PVR.

Conclusions:

MTX is a safe and potentially efficacious medication for the treatment and prevention of PVR. Additional clinical trials are needed to further establish this effect.

MR Imaging Characteristics of Intraocular Perfluoro-n-Octane

We describe the unique MR imaging characteristics of intraocular perfluoro-n-octane, a liquid used for intraoperative and postoperative tamponade in the context of complex retinal detachment repair, and contrast it with other intraocular pathologies. Because trace amounts of perfluoro-n-octane may be left in the globe postoperatively, it may be confused for other abnormalities, such as foreign bodies or tumors.

Epiretinal membrane: optical coherence tomography-based diagnosis and classification

Epiretinal membrane (ERM) is a disorder of the vitreomacular interface characterized by symptoms of decreased visual acuity and metamorphopsia. The diagnosis and classification of ERM has traditionally been based on clinical examination findings. However, modern optical coherence tomography (OCT) has proven to be more sensitive than clinical examination for the diagnosis of ERM. Furthermore, OCT-derived findings, such as central foveal thickness and inner segment ellipsoid band integrity, have shown clinical relevance in the setting of ERM. To date, no OCT-based ERM classification scheme has been widely accepted for use in clinical practice and investigation. Herein, we review the pathogenesis, diagnosis, and classification of ERMs and propose an OCT-based ERM classification system.

Ocriplasmin: who is the best candidate?

Enzymatic vitreolysis is currently the focus of attention around the world for treating vitreomacular traction and full-thickness macular hole. Induction of posterior vitreous detachment is an active area of developmental clinical and basic research. Despite exerting an incompletely elucidated physiological effect, ocriplasmin (also known as microplasmin) has been recognized to serve as a well-tolerated intravitreal injection for the treatment of vitreomacular traction and full-thickness macular hole. There are several unexplored areas of intervention where enzymatic vitreolysis could potentially be used (ie, diabetic macular edema). Recent promising studies have included combinations of enzymatic approaches and new synthetic molecules that induce complete posterior vitreous detachment as well as antiangiogenesis. Although no guidelines have been proposed for the use of ocriplasmin, this review attempts to aid physicians in answering the most important question, "Who is the best candidate?"

Serum levels of intravitreal bevacizumab after vitrectomy, lensectomy and non-surgical controls

PURPOSE

To determine serum level differences of intravitreally-placed bevacizumab after vitrectomy and lensectomy-vitrectomy and to compare these with non-operated eyes in a rabbit model.

METHODS

Five Dutch-belted rabbits underwent pars plana vitrectomy (PPV), five rabbits underwent pars plana lensectomy (PPL) and five rabbits served as non-surgical controls. Twelve days following the surgical procedures, each operated eye underwent an intravitreal injection consisting of 1.25 mg/0.05 mL bevacizumab. Serum levels from each rabbit were drawn on days 2, 4, 7, 10, 14, 21, 28 and 35 and were measured with ELISA immunoassay.

RESULTS

The average peak serum concentration (Cmax) was highest for the PPL group (11.33 μg ± 3.48 mL), and was similar between the PPV (5.35 μg ± 2.69 mL) and non-surgical control groups (5.35 μg ± 0.69 mL). The average time to maximal plasma concentration (Tmax) in days was earliest for the PPL group (2.8 ± 0.47), followed by the PPV (5.6 ± 0.84) and non-surgical control groups (6.4 ± 0.71). The PPL group had higher serum levels than the other two groups until day 7 that was significant only at day 2 (p < 0.0001). After day 4, there were no significant differences or trends between any of the three groups. The half-life (T1/2) was fastest for the PPL group (1.41 ± 0.21 d) followed by the PPV (2.80 ± 3.35 d) and non-surgical control groups (6.69 ± 10.4 d).

CONCLUSIONS

Serum bevacizumab levels were initially elevated following lensectomy and vitrectomy compared to non-surgical eyes following intravitreal injection. The half-life of bevacizumab was prolonged in non-surgical eyes presumably due to a slower release from the vitreous cavity.

The effect of intravitreal bevacizumab and ranibizumab on cutaneous tensile strength during wound healing

Purpose

To investigate the effect of intravitreal bevacizumab and ranibizumab on wound tension and by histopathology during cutaneous wound healing in a rabbit model and to compare this effect to placebo intravitreal saline controls 1 and 2 weeks following intravitreal injection.

Methods

A total of 120 New Zealand white rabbits were randomly assigned to one of three treatment groups each consisting of 40 rabbits. Each group received intravitreal injections of bevacizumab, ranibizumab, or normal saline. Immediately afterwards, each rabbit underwent four 6 mm full-thickness dermatologic punch biopsies. Twenty rabbits from each agent group underwent wound harvesting on day 7 or day 14. The skin samples were stained for CD34 for vascular endothelial cells on day 7, and maximal wound tensile load was measured on days 7 and 14. Quantitative assessment of mean neovascularization (MNV) scores was obtained from 10 contiguous biopsy margin 400× fields of CD34-stained sections by two independent observers.

Results

Wound tension reading means (N) with standard error and adjusted P-values on day 7 were: saline placebos, 7.46 ± 0.87; bevacizumab, 4.50 ± 0.88 (P = 0.041); and ranibizumab, 4.67 ± 0.84 (P = 0.025). On day 14 these were: saline placebos, 7.34 ± 0.55; bevacizumab, 6.05 ± 0.54 (P = 0.18); and ranibizumab 7.99 ± 0.54 (P = 0.40). MNV scores in CD34 stained sections were: saline controls, 18.31 ± 0.43; bevacizumab, 11.02 ± 0.45 (P < 0.0001); and ranibizumab, 13.55 ± 0.43 (P < 0.0001). The interobserver correlation coefficient was 0.928.

Conclusion

At day 7, both anti–vascular endothelial growth factor (anti-VEGF) agents had significantly suppressed MNV scores and exerted a significant reduction of cutaneous wound tensile strength compared with saline controls. At day 14, neither agent produced a significant effect on tensile wound strength. Since angiogenesis is an integral component of the proliferative phase of wound healing, we encourage clinicians to be aware of their patients’ recent surgical history during intravitreal anti-VEGF therapy and to consider refraining from their use during the perioperative period.

Pharmacokinetic properties of intravitreal I-124-aflibercept in a rabbit model using PET/CT

PURPOSE

To determine the anatomic characteristics and pharmacokinetic properties of intravitreally-placed aflibercept in a rabbit model.

MATERIALS AND METHODS

Four Dutch-belted rabbits underwent intravitreal injection with I-124-aflibercept. Serial imaging with PET/CT imaging was performed on days 0, 2, 5, 7, 14, 21, 28 and 35. Measured radioactivity emission in becquerels/mL was used to calculate the half-lives for aflibercept.

RESULTS

I-124 aflibercept was confined within the vitreous cavity for the duration of the study. I-124 aflibercept could be detected in the vitreous cavity until day 28 and the average retention time with standard error after correction for radioactive decay was 4.58 ± 0.07 days.

CONCLUSIONS

I-124 aflibercept was only visible in the vitreous cavity by PET/CT imaging following intravitreal injection. The retention properties were found to be comparable to those measured by other reported methods.

Histopathology of optic nerve pit-associated maculopathy

Purpose

To describe the histopathologic findings of an eye bank specimen containing an optic nerve pit with associated serous elevation of the macula and cavernous atrophy of the optic nerve.

Methods

An eye bank specimen found to have an optic nerve pit with serous elevation of the macula was grossly examined and photographed. The globe was processed for both light and scanning electron microscopy.

Results

The scanning electron microscopic study of this eye with an optic nerve pit revealed holes in the diaphanous membrane overlying the nerve at the edge of the optic pit. Serial histopathology sections revealed a connection between the holes overlying the optic pit and the subretinal space via a schisis-like cavity in the retina.

Conclusion

The discovery of an optic nerve pit with coexisting serous detachment of the macula in an eye bank eye and subsequent pathological evaluation provides support for current theories into the mechanism of the visual loss in this condition. Our finding supports syneretic vitreous to be the source of the subretinal fluid.

Cytomegalovirus retinitis after central retinal vein occlusion in a patient on systemic immunosuppression: does venooclusive disease predispose to cytomegalovirus retinitis in patients already at risk?

Cytomegalovirus (CMV) retinitis remains the most common opportunistic ocular infection in immunocompromised patients. Patients with immunocompromising diseases, such as acquired immunodeficiency syndrome, inherited immunodeficiency states, malignancies, and those on systemic immunosuppressive therapy, are known to be at risk. Recently, it has been suggested that patients undergoing intravitreal injection of immunosuppressive agents may also be predisposed. One previous case report speculated that there may be an additional risk for CMV retinitis in acquired immunodeficiency syndrome patients with venoocclusive disease. This case study presents a case of CMV retinitis following central retinal vein occlusion in a patient on systemic immunosuppressants.

PET/CT imaging of I-124-radiolabeled bevacizumab and ranibizumab after intravitreal injection in a rabbit model

PURPOSE

To determine whether bevacizumab and ranibizumab remain confined within the vitreous cavity after intravitreal injection and to determine the pharmacokinetic properties of these agents within the vitreous cavity.

METHODS

Radiolabeling with I-124 was completed using a modified Iodogen method. After testing for radiochemical purity, three anesthetized Dutch-belted rabbits underwent intravitreal injection with I-124 bevacizumab, and three underwent it with I-124 ranibizumab. All rabbits were imaged with a Micro PET-CT scanner on days 0, 2, 5, 7, 14, 21, 28, and 35.

RESULTS

The intravitreally placed radiolabeled agents were found to be contained within the vitreous cavity for the duration of the study with no extravasation into the central nervous system or elsewhere. I-124 bevacizumab was detectable until day 28, whereas I-124 ranibizumab was detectable until day 21. The kinetic model appears to represent a two-compartment model, and the average retention times for bevacizumab and ranibizumab after correction for radioactive decay were found to be 4.2 days and 2.8 days, respectively.

CONCLUSIONS

There was no significant escape of bevacizumab and ranibizumab from the vitreous cavity after intravitreal injection. After correction for radioactive decay, both agents remained detectable until 28 and 21 days, respectively, with retention properties that validated those methods reported in previous studies.

Age related macular degeneration and visual disability

Age-related macular degeneration (AMD) is the leading cause of central blindness or low vision among the elderly in industrialized countries. AMD is caused by a combination of genetic and environmental factors. Among modifiable environmental risk factors, cigarette smoking has been associated with both the dry and wet forms of AMD and may increase the likelihood of worsening pre-existing AMD. Despite advances, the treatment of AMD has limitations and affected patients are often referred for low vision rehabilitation to help them cope with their remaining eyesight. The characteristic visual impairment for both forms of AMD is loss of central vision (central scotoma). This loss results in severe difficulties with reading that may be only partly compensated by magnifying glasses or screen-projection devices. The loss of central vision associated with the disease has a profound impact on patient quality of life. With progressive central visual loss, patients lose their ability to perform the more complex activities of daily living. Common vision aids include low vision filters, magnifiers, telescopes and electronic aids. Low vision rehabilitation (LVR) is a new subspecialty emerging from the traditional fields of ophthalmology, optometry, occupational therapy, and sociology, with an ever-increasing impact on the usual concepts of research, education, and services for visually impaired patients. Relatively few ophthalmologists practise LVR and fewer still routinely use prismatic image relocation (IR) in AMD patients. IR is a method of stabilizing oculomotor functions with the purpose of promoting better function of preferred retinal loci (PRLs). The aim of vision rehabilitation therapy consists in the achievement of techniques designed to improve PRL usage. The use of PRLs to compensate for diseased foveae has offered hope to these patients in regaining some function. However, in a recently published meta-analysis, prism spectacles were found to be unlikely to be of substantial benefit in people with age-related macular degeneration. Prescription filters are one of the most beneficial visual aids that people with macular degeneration. In principle, one aims both at reducing short-wavelength light to reduce glare and at identifying light with specific wavelengths (colours) preferred by the patient for viewing. In both instances, such interventions result in apparent improved contrast sensitivity and better visual acuity. Although specific tests are performed to determine the best colour, tint, lens material, and type of frame for the patient's need, no scientific protocol has been developed so far to assist in prescribing tinted or selective transmission lenses . Magnifying optical lenses are available in a wide range of dioptric powers and are made from materials that correct for weight (plastic), thickness (high index), spherical aberrations (aspherical), and variable light intensities (photochromatic). These lenses can be used as loose lenses, mounted on optical frames, or used with a wide variety of attachments. As the dioptric power of plus lenses increases, the viewing distance of the target decreases, hence their usefulness mainly for tasks requiring near resolution acuity, like reading. Magnification can also be achieved with the use of telescopic devices that are built of two or more plus and (or) minus (minifying) optical lenses. Normal resolution acuity levels can be achieved with these devices for all viewing distances. Therefore, all telescopic devices are useful only for stationary patient tasks that do not require mobility and orientation. Electronic magnification has the great advantage over plus lenses of producing an acuity reserve enabling reading skills for almost all levels of visual acuity. The additional benefit provided is preservation of binocularity, even at high levels of visual disparity between the two eyes. Vision rehabilitation can help patients to maximize their remaining vision and adapt to activities of daily living. The support of the patient's social network is critical to patient's well-being as patients adjust to being partially sighted.

Volume of visual field assessed with kinetic perimetry and its application to static perimetry

Background:

The purpose of this study was to quantify the volume of the kinetic visual field with a single unit that accounts for visual field area and differential luminance sensitivity.

Methods:

Kinetic visual field perimetry was performed with a Goldmann perimeter using I4e, I3e, I2e, and I1e targets. The visual fields of 25 normal volunteers (17 women, eight men) of mean age 33.9 ± 10.1 (range 17–64) years were obtained and digitized. Isopter areas were measured with a method devised to correct cartographic distortion due to polar projection inherent in perimetry and are expressed in steradians. The third dimension of each isopter represents sensitivity to target luminance and was calculated as log (target luminance⁻¹). If luminance is expressed in cd/m², the values for the third dimension are 0.5 for I4e, 1.0 for I3e, 1.5 for I2e, and 2.0 for I1e. The resulting unit is a steradian (log 10³ (cd/m²)⁻¹ which is referred to as a Goldmann. In addition, the visual fields of four patients with representative visual defect patterns were examined and compared with normal subjects.

Results:

Mean isopter areas for normal subjects were 3.092 ± 0.242 steradians for I4e, 2.349 ± 0.280 steradians for I3e, 1.242 ± 0.263 steradians for I2e, and 0.251 ± 0.114 steradians for the I1e target. Isopter volumes were 1.546 ± 0.121 Goldmanns for the I4e target, 1.174 ± 0.140 Goldmanns for I3e, 0.621 ± 0.131 Goldmanns for I2e, and 0.126 ± 0.057 Goldmanns for I1e. The total mean visual field volume in our study for the I target was 3.467 ± 0.371 Goldmanns.

Conclusion:

The volume of the island of vision may be used to quantify a visual field with a single value which contains information about both visual field extension and differential luminance sensitivity. This technique may be used to assess the progression or stability of visual field defects over time. A similar method may be applied to static perimetry.

Histology of retina overlying bacterial subretinal abscess and implications for treatment

PURPOSE

To evaluate the state of the retina overlying a subretinal abscess and its contents by histopathologic analysis and electron microscopy (EM) and to determine implications for treatment.

METHODS

Case report of a patient with a subretinal abscess secondary to Klebsiella pneumoniae infection who underwent pars plana vitrectomy, PPL, endolaser, retinectomy, abscess drainage, and retinal biopsy. The retinal biopsy was analyzed histologically using special stains, and EM of the abscess contents was performed.

RESULTS

Postoperatively, the retina remained attached, and the patient regained visual acuity of 20/60. Culture of the vitrectomy specimen yielded K. pneumoniae. Retinal biopsy revealed a partially intact inner retina with destruction of the outer retinal layers in the setting of acute inflammation. Results of gram, Grocott-Gomori methenamine-silver nitrate, and acid-fast staining of the retinal biopsy specimen were negative. EM of the abscess contents revealed cellular debris with scattered inflammatory cells but no bacteria.

CONCLUSION

This case demonstrates that aggressive surgical management of a subretinal abscess due to K. pneumoniae in an eye can result in useful vision. Management included retinectomy of the retina overlying the abscess that revealed photoreceptor destruction with intraretinal inflammation. Drainage of a subretinal abscess without removal of the overlying retina may limit treatment effectiveness and spare retina that is not functional.

In vivo redirection of retinal blood flow into borosilicate micro-cannulas in rabbits

BACKGROUND

Microvascular manipulation is one application in the emerging field of retinal vascular surgery that could lead to new therapeutic approaches for retinal disease. Research in this field has largely focused on vessel cannulation and injection of vasoactive substances. This study expands on applications for retinal vessel manipulation by demonstrating that redirection of retinal blood flow in vivo can be achieved through retinal vessel cannulation in a rabbit model.

METHODS

Dutch-belted rabbits were anesthetized, and a sectoral peritomy and sclerotomy 1 mm from the superotemporal limbus were performed. Borosilicate glass microtips with external diameters of 10-20 mum were introduced into the vitreous through the sclerotomy site. Using an operating microscope and a direct contact lens for visualization, we cannulated the rabbits' retinal vessels, and blood flow was redirected through the microtips.

RESULTS

Retinal vessels approximately 30-60 mum in size were cannulated, and controlled blood flow through the microcannula was demonstrated with minimal or no vitreous hemorrhage. Though still achievable, flow after arterial cannulation was more difficult to demonstrate.

CONCLUSIONS

This study demonstrates that partial diversion of blood flow from a native vessel lumen could be successfully accomplished by retinal vessel cannulation. This early work indicates that more advanced retinal vascular procedures, such as vessel bypass around a thrombus or shunting blood towards an area of ischemic retina, may be feasible in the future.

In vivo rabbit eyecup preparation for use in retinal research

PURPOSE

To develop an in vivo rabbit eyecup preparation that preserves neuronal and vascular connections with normal posterior segment contour, permitting direct access to the retina and facilitating retinal microsurgical and neuroscience research.

METHODS

Cyanoacrylate glue was applied to the anterior sclera of six Dutch-belted rabbits before open-sky vitrectomy. The glue was used to harden the compliant scleral wall and to fix it to the surrounding periorbital tissues.

RESULTS

A normal contour of the posterior segment was retained in all cases. Vitrectomy under air was successfully accomplished and an extensive removal of the vitreous gel was achieved. Fluorescein angiography revealed normal vascular patency of the retinal vessels after vitrectomy.

CONCLUSIONS

The proposed modification of the rabbit eyecup retains the normal neurovascular connections and configuration of the retina, making it suitable for retinal microsurgical maneuvers or any procedures in which easy access to anatomically undisturbed retina is required.

CT characteristics of intraocular perfluoro-N-octane

Perfluoro-N-octane (PFO) is a heavy liquid that is used as an aid for complicated retinal surgical procedures. Although PFO is usually removed intraoperatively, the radiographic appearance of retained PFO may mimic an intraocular foreign body or vitreous hemorrhage. As the use of PFO in retinal procedures has become more widespread, recognition of its imaging appearance has become important in the differential diagnosis of intraocular foreign body and ocular trauma.

Resolution of leukemic retinopathy following treatment with imatinib mesylate for chronic myelogenous leukemia

PURPOSE

To report a case of leukemic retinopathy before and after treatment with imatinib mesylate (formerly STI-571) for chronic myelogenous leukemia (CML).

DESIGN

Interventional case report.

METHODS

A 58-year-old man diagnosed with stable phase CML (SP-CML) presented with blurry vision. Fundoscopy revealed several flame-shaped hemorrhages in the macular region in both eyes. One month after this initial visit, imatinib therapy was initiated.

RESULTS

: The patient noticed improvement in his visual as well as his medical symptoms; on repeat examination 6 months after the initial visit, the retinal hemorrhages had resolved and remained so after 18 months.

CONCLUSIONS

Imatinib appears to be an effective treatment for SP-CML, and the improvement in visual and medical symptoms in our case report correlates with this.