We gratefully acknowledge support by the Harold and Pauline Price Chair in Ophthalmology and the Jules Stein Eye Institute to MBG, the NEI Core grant (EY00331-43) to SN. Research was supported in part by a generous gift from the Sakaria family to SN and MGB, and from an unrestricted grant from the Research to Prevent Blindness to the Department of Ophthalmology. We thank Charlotte Yiyi Wang at Berkeley School of Optometry for obtaining initial OCT images of subretinal injections.

Animals: Wild type C57Bl/6J mice bred at the University of California at Los Angeles (UCLA). All animals were between 11 - 17 weeks old, and included male and female mice. All mice were group-housed, maintained in a 12:12 light/dark cycle with food and water ad libitum. All experiments were performed in accordance with the institutional guidelines of UCLA and the Association for Research in Vision and Ophthalmology Statement for the Use of Animals in Ophthalmic and Vision Research.
NOTE: All drugs and injectable agents are United States Pharmacopeia (USP) grade.
1. Surgical Preparation
<ol>
	<li>Anesthetize the mouse with an intraperitoneal injection of 100 mg/kg ketamine and 8 mg/kg xylazine in a saline mix. Administer anesthesia to a depth such that the mouse has no toe pinch or corneal touch reflexes.</li>
	<li>Maintain body temperature at 37.0 &#176;C with a circulating water pad.</li>
	<li>Dilate pupils with 2.5% phenylephrine eye drops and trim whiskers to facilitate visualization. Whiskers provide significant sensory input to the mouse, therefore, whisker trimming should remove only the portion that blocks clear access to the eye, and not to the base of the whisker. In our experience, mice show normal recovery after this procedure.&#160;Apply methylcellulose eye drops to prevent dryness and minimize anesthetic induced transient cataracts13.</li>
	<li>Sterilize instruments prior to surgery (i.e., betadine and ethanol or hot beads).</li>
	<li>Prepare diluted fluorescein (0.01% using 0.9% saline) in a sterile environment (i.e., biosafety cabinet) if visualization will be performed (see section 3 below).</li>
</ol>
2. Injection Site Preparation
<ol>
	<li>Prepare a syringe (e.g., 5 &#181;l syringe) with the appropriate injection volume (e.g., 0.3 to 1.0 &#181;l).</li>
	<li>Position the mouse so the eye is facing up and clearly visible in the dissecting microscope.</li>
	<li>Gently pinch the temporal conjunctiva with fine tipped forceps. Make a circumferential incision of approximately 90 degrees using curved Vannas scissors.</li>
	<li>Repeat step 2.3 with the underlying Tenon&#39;s capsule.</li>
	<li>Resect the surrounding connective tissue with fine tipped forceps while rotating the globe nasally. Work towards the injection site approximately 0.5 mm temporal to the optic nerve. Use great care to avoid disrupting the retro-orbital sinus.</li>
</ol>
3. Sclerotomy and Subretinal Injection
NOTE: It is recommended that the injection of 0.01% fluorescein in 0.9% Saline be used to assist with visualization while learning this procedure. The topographic distribution of fluorescein can be effectively documented with fundus imaging (see section 4 below).
<ol>
	<li>Make a small scleral incision at the injection site by gently scratching the eyecup with a 22.5-degree ophthalmic blade. This incision should only be large enough to allow the tip of the needle to pass through the sclera.</li>
	<li>Insert the beveled 33 G needle (angled 5 - 10&#176; into the sclerotomy with the bevel facing and angled parallel to the retina. Inject desired volume (e.g., 0.3 to 1.0 &#181;l of 0.01% Fluorescein for learning purposes). 
	NOTE: Maintain sterility of the syringe by thoroughly cleaning with successive washes of a suitable solvent and DI water before each injection.</li>
	<li>Depress the plunger slowly (over ~ 3 sec) without moving the needle and with even pressure. 
	NOTE: When the needle is in the subretinal space, a slight resistance will be felt while depressing the plunger. There will be no to minimal resistance if the needle punctures the retina, and high resistance if the needle does not penetrate the sclera or RPE.</li>
	<li>Wait several seconds before withdrawing the needle to minimize backflow.</li>
	<li>Rinse the eye with sterile buffered saline and ensure the eye has rotated back to its normal position.</li>
</ol>
4. Assessment of Retinal Detachment by OCT and Fundus Imaging
<ol>
	<li>Perform OCT imaging immediately after injection to evaluate the quality of the injection and at appropriate time points post-injection as needed to evaluate retinal structure. 
	NOTE: Examples of the use of OCT in similar studies has been previously described7,14.
	<ol>
		<li>Adjust and align the OCT image to target the site of injection. The injection site should be midline and 0.5 mm temporal to the optic nerve head. Repeat as needed if the detachment is out of frame or not optimally centered.</li>
	</ol>
	</li>
	<li>Visualize retinal detachment and dye injection area with en-face fundus imaging7,14. 
	NOTE: If an OCT imaging system is not available, injection of a small amount of fluorescein with a vector for practice will allow visualization with any fundus camera that performs fluorescein angiography using the same excitation wavelengths and blocking filters. Localized areas of hyper-fluorescence will appear underneath the vasculature and the vasculature will have sharp and distinct boundaries if the subretinal space is targeted correctly. The edge of the bleb from the injection will be demarcated by the transition from hyper- to hypo- fluorescence. Several instruments provide this capability for the mouse; the instrumentation used here is described elsewhere14.</li>
</ol>
5. Post-operative Care
<ol>
	<li>Apply a thick coat of triple antibiotic ophthalmic cream to the corneal surface of the injected eye.</li>
	<li>Place mice in clean solitary cages for recovery. Do not combine mice that have undergone surgery until they are fully recovered.</li>
	<li>Monitor respiration and temperature during anesthesia recovery. Monitor animals until they can maintain sternal recumbency.</li>
	<li>Perform additional appropriate post-operative monitoring and treatment, including a sub-cutaneous injection of carprofen (5 mg/kg) for post-surgical pain management.</li>
</ol>
6. Assessment of Retinal Function by Electroretinography (ERG)
<ol>
	<li>Perform ERG analysis pre-injection and at appropriate times post-injection as needed to evaluate retinal function. If the injection was made into the subretinal space, the retinal detachment should resolve within 72 hr.
	<ol>
		<li>Use standard ERG techniques to evaluate retinal function before and after injection as previously described14,15.</li>
	</ol>
	</li>
</ol>
7. 3D Reconstruction and Bleb Volume Quantification
NOTE: OCT scans with high contrast encompassing the entire detachment within the frame of view are optimal for use. ImageJ/Fiji17,18 and Imaris were used, but other software can be used.
<ol>
	<li>Export the b-scan of interest, import to ImageJ/Fiji and crop (Image &#62; Crop) the portion of the OCT scan to be modeled using the rectangular selection tool.
	<ol>
		<li>Adjust contrast (Image &#62; Adjust &#62; Brightness/Contrast) and delineate any missing boundaries by connecting two sections with a line.</li>
		<li>Draw a straight line with the line tool (holding shift) that spans the RPE to the photoreceptor layer. Measure (Analyze &#62; Measure) the length of the line to obtain size of maximum detachment for step 7.8.</li>
	</ol>
	</li>
	<li>Import cropped frames to the 3D-reconstruction software (See Table of Materials) using the &#34;RGB to Gray&#34; plugin and MATLAB Compiler Runtime.</li>
	<li>Set the voxel size (under Image Properties) using the calibration parameters from the OCT scan (x,y,z).</li>
	<li>Execute the &#34;RGB to Gray&#34; plugin (under Image Properties), with equal weighting to each channel, to create a fourth channel. Delete original Red-Green-Blue channels.</li>
	<li>Invert the gray channel using contrast change. Store Image.</li>
	<li>Click the &#34;add a new surface&#34; button in the 3D-View tab, and begin the guided 4 step process of creating the surface.
	<ol>
		<li>Set the surface level detail (step 1 of 4). 
		NOTE: In our experience 8.0 to 12.0 was the most effective range.</li>
		<li>Set the maximum sphere size (under Background Selection) to slightly less than the maximum detachment size measured in 7.1.2. Create the surface and undo gray channel inversion (step 2 of 4).</li>
		<li>Set the threshold to the maximum value so the surface of the negative spaces outside of the retina and the detachment do not come in contact (step 3 of 4).</li>
		<li>Set the filter type to the number of voxels and isolate the negative space in the detachment site by size. Finish the surface (step 4 of 4). 
		NOTE: The volume of the detachment surface is located under volume in the statistics tab.</li>
	</ol>
	</li>
</ol>

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None of the authors have any commercial disclosures.

Subretinal injections are the method of choice for the delivery of viral vectors and stem cell-derived therapy for manipulating photoreceptors and the RPE in both basic research and clinical treatment. In patients, subretinal injections are typically done with an anterior sclerotomy at the pars plana, a posterior core vitrectomy and penetration of the retina by the needle with direct visualization. As with most vitrectomy procedures, it is common for cataract formation to occur prematurely unless the eye is already pseud...

Subretinal injections are the primary means of delivering cellular and viral agents to the retinas of mice to study their effects on photoreceptors and the underlying RPE1,2. Most subretinal injection protocols in mice use a transcorneal or a transcleral injection site anterior to the equator (Figure 1). This approach can result in inherent collateral damage that includes nicking and resultant clouding of the lens, disruption of the integrity of the vitreous, penetration of the neurosensory retina and iris, retinal hemorrhage, substantial retinal detachments and lasting subretinal edema 3-9. Experimental manipulations must overcome these effects in order to evaluate the effects of therapeutic interventions3,7,10,11. This study provides a detailed description and validation of a posterior transcleral injection method that avoids these complications, minimizes trauma and has a high success rate of targeting the subretinal space.
Injections targeting the subretinal space in mice are often very difficult to perform and most investigators encounter a high frequency of failed attempts in which the vector is delivered to an incorrect location or there is significant retinal damage, for example in a complete retinal detachment6. The number of eyes excluded from analysis because of injection complications is typically not reported in mouse studies, but in our own experience and in discussion with other investigators, the number of failed injections can be as high as 50% and vary dependent on the experience and capabilities of the investigator who is performing the injections. The success of the injection is typically assessed by direct fundus imaging and/or optical coherence tomography (OCT)7,9. An easily mastered method with high success rates for subretinal injections in mice can hasten experimentation and reduce the cost of preclinical studies of treatments for retinal diseases that are major causes of blindness in the United States.
The posterior, transcleral subretinal injection technique described here is an adaptation from clinical and preclinical protocols9,12. The noninvasive diagnostic assessments performed in injected mice demonstrate mild and highly localized damage and lack additional collateral lens, retinal and RPE injury. Furthermore, with relatively little practice, an experimenter can achieve these results with a high success rate (80 - 90% or better), thereby reducing the costs associated with such studies. This procedure can be used to deliver cellular, viral, or pharmacological therapeutic interventions to photoreceptors and/or RPE in preclinical studies and to easily evaluate experimental interventions.

<table><tbody><tr><td>Hamilton Model 62 RN SYR</td><td>Hamilton</td><td>87942</td><td>Syringe x 1</td></tr><tr><td>Hamilton Needle 33 G, 1.0&quot;, 20 DEG, point 3 (304 stainless steel)</td><td>Hamilton</td><td>7803-05</td><td>Needles x 6</td></tr><tr><td>Vannas Curved Scissors</td><td>Ted Pella, INC.</td><td>1347</td><td>5 mm Blade</td></tr><tr><td>22.5 Degree Microsurgery Knife</td><td>Wilson Ophthalmic Corp.</td><td>91204</td><td></td></tr><tr><td>Ketaject&amp;nbsp;</td><td>Phoenix</td><td>NDC 57319-609-02</td><td>Ketamine</td></tr><tr><td>Anased</td><td>Lloyd Laboratories</td><td>NDC 61311-482-10</td><td>Xylazine</td></tr><tr><td>Fluorescein 10% AK-Fluor</td><td>Akorn</td><td>NDC 17478-253-10</td><td>100 mg/ml</td></tr><tr><td>0.9% Saline USP</td><td>Hospira</td><td>NDC 0409-4888-50</td><td>0.9% NaCl</td></tr><tr><td>Antibiotic Ointment</td><td>Akorn</td><td>NDC 17478-235-35</td><td>Ophthalmic</td></tr><tr><td>Water Circulating Pump</td><td>Gaymar</td><td>TP-500 T/Pump&amp;nbsp;</td><td>P/N 07999-000</td></tr><tr><td>sd-OCT</td><td>Bioptigen</td><td>R-Series</td><td>Commercial</td></tr><tr><td>Fundus Camera</td><td>Phoenix Research Laboratories</td><td>MICRON III</td><td></td></tr><tr><td>Tweezers Type 3</td><td>Ted Pella, INC.</td><td>5385-3SU</td><td></td></tr><tr><td>2.5% Phenylephrine</td><td>Paragon BioTeck</td><td>NDC 42702-102-15</td><td>Ophthalmic</td></tr><tr><td>IMARIS8</td><td>Bitplane</td><td></td><td>Version 8.1.2</td></tr><tr><td>ImageJ</td><td>NIH</td><td></td><td>V1.8.0_77</td></tr><tr><td>Hypromellose&amp;nbsp;2.5%</td><td>Goniovisc</td><td>AX0401</td><td>Methylcellulose</td></tr><tr><td>Eye Drops (Rinse)</td><td>Bausch &amp;amp; Lomb</td><td></td><td>Saline Solution</td></tr><tr><td>Microscope</td><td>Zeiss</td><td>Stemi 2000</td><td>Microscope</td></tr><tr><td>Light source</td><td>Fostec</td><td>P/N 20520</td><td>Light source</td></tr></tbody></table>

an alternative and validated injection method for accessing the subretinal space via a transcleral posterior approach

Subretinal injections have been successfully used in both humans and rodents to deliver therapeutic interventions of proteins, viral agents, and cells to the interphotoreceptor/subretinal compartment that has direct exposure to photoreceptors and the retinal pigment epithelium (RPE). Subretinal injections of plasminogen as well as recent preclinical and clinical trials have demonstrated safety and/or efficacy of delivering viral vectors and stem cells to individuals with advanced retinal disease. Mouse models of retinal disease, particularly hereditary retinal dystrophies, are essential for testing these therapies. The most common injection procedure in rodents is to use small transcorneal or transcleral incisions with an anterior approach to the retina. With this approach, the injection needle penetrates the neurosensory retina disrupting the underlying RPE and on insertion can easily nick the lens, causing lens opacification and impairment of noninvasive imaging. Accessing the subretinal space via a transcleral, posterior approach avoids these problems: the needle crosses the sclera approximately 0.5 mm from the optic nerve, without retinal penetration and avoids disrupting the vitreous. Collateral damage is limited to that associated with the focal sclerotomy and the effects of a transient, serous retinal detachment. The simplicity of the method minimizes ocular injury, ensures rapid retinal reattachment and recovery, and has a low failure rate. The minimal damage to the retina and RPE allows for clear assessment of the efficacy and direct effects of the therapeutic agents themselves. This manuscript describes a novel subretinal injection technique that can be used to target viral vectors, pharmacological agents, stem cells or induced pluripotent stem (iPS) cells to the subretinal space in mice with high efficacy, minimal damage, and fast recovery.

Posterior approach transcleral subretinal injections were performed on 31 healthy eyes from 16 wild type mice with injections of 0.3 &#181;l (n = 18), 0.5 &#181;l (n = 8) and 1.0 &#181;l (n = 5) of 0.01% fluorescein. One eye was excluded from injection due to a pre-existing corneal opacity that prevented structural and functional analysis. Every injected eye is included in this report. No unintended retinal detachments, punctures of the neurosensory retina, or leakage into the vitreous we...

Watch this Scientific Journal Video about An Alternative and Validated Injection Method for Accessing the Subretinal Space via a Transcleral Posterior Approach at JoVE.com

An Alternative and Validated Injection Method for Accessing the Subretinal Space via a Transcleral Posterior Approach

Subretinal injections are the most common technique for delivering large therapeutic agents such as proteins and viral vectors to photoreceptors and the retinal pigment epithelium. An alternative method in mice that successfully targets the subretinal space with minimal collateral damage and fast recovery times is described here.

An Alternative and Validated Injection Method for Accessing the Subretinal Space via a Transcleral Posterior Approach

Subretinal injections have been successfully used in both humans and rodents to deliver therapeutic interventions of proteins, viral agents, and cells to ...

an-alternative-validated-injection-method-for-accessing-subretinal

Research

JoVE Journal

Neuroscience

13.1K Views.  University of California, Los Angeles. Subretinal injections are the most common technique for delivering large therapeutic agents such as proteins and viral vectors to photoreceptors and the retinal pigment epithelium. An alternative method in mice that successfully targets the subretinal space with minimal collateral damage and fast recovery times is described here.

Video: An Alternative and Validated Injection Method for Accessing the Subretinal Space via a Transcleral Posterior Approach

Subretinal Injection of Gene Therapy Vectors and Stem Cells in the Perinatal Mouse Eye

The loss of sight affects approximately 3.4 million people in the United States and is expected to increase in the upcoming years.1 Recently, gene therapy and stem cell transplantations have become key therapeutic tools for treating blindness resulting from retinal degenerative diseases. Several forms of autologous transplantation for age-related macular degeneration (AMD), such as iris pigment epithelial cell transplantation, have generated encouraging results, and human clinical trials have begun for other forms of gene and stem cell therapies.2 These include RPE65 gene replacement therapy in patients with Leber's congenital amaurosis and an RPE cell transplantation using human embryonic stem (ES) cells in Stargardt's disease.3-4 Now that there are gene therapy vectors and stem cells available for treating patients with retinal diseases, it is important to verify these potential therapies in animal models before applying them in human studies. The mouse has become an important scientific model for testing the therapeutic efficacy of gene therapy vectors and stem cell transplantation in the eye.5-8 In this video article, we present a technique to inject gene therapy vectors or stem cells into the subretinal space of the mouse eye while minimizing damage to the surrounding tissue.

This surgical technique illustrates the injection of gene therapy vectors and stem cells into the subretinal space of the mouse eye.

The loss of sight affects approximately 3.4 million people in the United States and is expected to increase in the upcoming years.1 Recently, gene therapy ...

Medicine

Performing Subretinal Injections in Rodents to Deliver Retinal Pigment Epithelium Cells in Suspension

The conversion of light into electrical impulses occurs in the outer retina and is accomplished largely by rod and cone photoreceptors and retinal pigment epithelium (RPE) cells. RPE provide critical support for photoreceptors and death or dysfunction of RPE cells is characteristic of age-related macular degeneration (AMD), the leading cause of permanent vision loss in people age 55 and older. While no cure for AMD has been identified, implantation of healthy RPE in diseased eyes may prove to be an effective treatment, and large numbers of RPE cells can be readily generated from pluripotent stem cells. Several interesting questions regarding the safety and efficacy of RPE cell delivery can still be examined in animal models, and well-accepted protocols used to inject RPE have been developed. The technique described here has been used by multiple groups in various studies and involves first creating a hole in the eye with a sharp needle. Then a syringe with a blunt needle loaded with cells is inserted through the hole and passed through the vitreous until it gently touches the RPE. Using this injection method, which is relatively simple and requires minimal equipment, we achieve consistent and efficient integration of stem cell-derived RPE cells in between the host RPE that prevents significant amount of photoreceptor degeneration in animal models. While not part of the actual protocol, we also describe how to determine the extent of the trauma induced by the injection, and how to verify that the cells were injected into the subretinal space using in vivo imaging modalities. Finally, the use of this protocol is not limited to RPE cells; it may be used to inject any compound or cell into the subretinal space.

Here we present a community accepted protocol in multimedia format for subretinally injecting a bolus of RPE cells in rats and mice. This approach can be used for determining rescue potentials, safety profiles, and survival capacities of grafted RPE cells upon implantation in animal models of retinal degeneration.

The conversion of light into electrical impulses occurs in the outer retina and is accomplished largely by rod and cone photoreceptors and retinal pigment ...

Limbal Approach-Subretinal Injection of Viral Vectors for Gene Therapy in Mice Retinal Pigment Epithelium

The eye is a small and enclosed organ which makes it an ideal target for gene therapy. Recently various strategies have been applied to gene therapy in retinopathies using non-viral and viral gene delivery to the retina and retinal pigment epithelium (RPE). Subretinal injection is the best approach to deliver viral vectors directly to RPE cells. Before the clinical trial of a gene therapy, it is inevitable to validate the efficacy of the therapy in animal models of various retinopathies. Thus, subretinal injection in mice becomes a fundamental technique for an ocular gene therapy. In this protocol, we provide the easy and replicable technique for subretinal injection of viral vectors to experimental mice. This technique is modified from the intravitreal injection, which is widely used technique in ophthalmology clinics. The representative results of RPE/choroid/scleral complex flat-mount will help to understand the efficacy of this technique and adjust the volume and titer of viral vectors for the extent of gene transduction.

Subretinal injection is a surgical technique for effective gene delivery to retinal pigment epithelium in the mouse eye. Here we describe an easy and replicable method for subretinal injection of viral vectors to retinal pigment epithelium in experimental mice.

The eye is a small and enclosed organ which makes it an ideal target for gene therapy. Recently various strategies have been applied to gene therapy in ...

A Step by Step Protocol for Subretinal Surgery in Rabbits

Age related macular degeneration (AMD), retinitis pigmentosa, and other RPE related diseases are the most common causes for irreversible loss of vision in adults in industrially developed countries. RPE transplantation appears to be a promising therapy, as it may replace dysfunctional RPE, restore its function, and thereby vision.
Here we describe a method for transplanting a cultured RPE monolayer on a scaffold into the subretinal space (SRS) of rabbits. After vitrectomy xenotransplants were delivered into the SRS using a custom made shooter consisting of a 20-gauge metallic nozzle with a polytetrafluoroethylene (PTFE) coated plunger. The current technique evolved in over 150 rabbit surgeries over 6 years. Post-operative follow-up can be obtained using non-invasive and repetitive in vivo imaging such as spectral domain optical coherence tomography (SD-OCT) followed by perfusion-fixed histology.
The method has well-defined steps for easy learning and high success rate. Rabbits are considered a large eye animal model useful in preclinical studies for clinical translation. In this context rabbits are a cost-efficient and perhaps convenient alternative to other large eye animal models.

Retinal pigment epithelium (RPE) replacement strategies and gene-based therapy are considered for several retinal degenerative conditions. For clinical translation, large eye animal models are required to study surgical techniques applicable in patients. Here we present a rabbit model for subretinal surgery geared towards RPE transplantation, which is versatile and cost-efficient.

Age related macular degeneration (AMD), retinitis pigmentosa, and other RPE related diseases are the most common causes for irreversible loss of vision in ...

Development of a Refined Protocol for Trans-scleral Subretinal Transplantation of Human Retinal Pigment Epithelial Cells into Rat Eyes

Degenerative retinal diseases such as age-related macular degeneration (AMD) are the leading cause of irreversible vision loss worldwide. AMD is characterized by the degeneration of retinal pigment epithelial (RPE) cells, which are a monolayer of cells functionally supporting and anatomically wrapping around the neural retina. Current pharmacological treatments for the non-neovascular AMD (dry AMD) only slow down the disease progression but cannot restore vision, necessitating studies aimed at identifying novel therapeutic strategies. Replacing the degenerative RPE cells with healthy cells holds promise to treat dry AMD in the future. Extensive preclinical studies of stem cell replacement therapies for AMD involve the transplantation of stem cell-derived RPE cells into the subretinal space of animal models, in which the subretinal injection technique is applied. The approach most frequently used in these preclinical animal studies is through the trans-scleral route, which is made difficult by the lack of direct visualization of the needle end and can often result in retinal damage. An alternative approach through the vitreous allows for direct observation of the needle end position, but it carries a high risk of surgical traumas as more eye tissues are disturbed. We have developed a less risky and reproducible modified trans-scleral injection method that uses defined needle angles and depths to successfully and consistently deliver RPE cells into the rat subretinal space and avoid excessive retinal damage. Cells delivered in this manner have been previously demonstrated to be efficacious in the Royal College of Surgeons (RCS) rat for at least 2 months. This technique can be used not only for cell transplantation but also for delivery of small molecules or gene therapies.

Subretinal injection has been widely applied in preclinical studies of stem cell replacement therapy for age-related macular degeneration. In this visualized article, we describe a less risky, reproducible and precisely modified subretinal injection technique via the trans-scleral approach to deliver cells into rat eyes.

Degenerative retinal diseases such as age-related macular degeneration (AMD) are the leading cause of irreversible vision loss worldwide. AMD is ...

Retinal Pigment Epithelium Transplantation in a Non-human Primate Model for Degenerative Retinal Diseases

Retinal pigment epithelial (RPE) transplantation holds great promise for the treatment of inherited and acquired retinal degenerative diseases. These conditions include retinitis pigmentosa (RP) and advanced forms of age-related macular degeneration (AMD), such as geographic atrophy (GA). Together, these disorders represent a significant proportion of currently untreatable blindness globally. These unmet medical needs have generated heightened academic interest in developing methods of RPE replacement. Among the animal models commonly utilized for preclinical testing of therapeutics, the non-human primate (NHP) is the only animal model that has a macula. As it shares this anatomical similarity with the human eye, the NHP eye is an important and appropriate preclinical animal model for the development of advanced therapy medicinal products (ATMPs) such as RPE cell therapy.
This manuscript describes a method for the submacular transplantation of an RPE monolayer, cultured on a polyethylene terephthalate (PET) cell carrier, underneath the macula onto a surgically created RPE wound in immunosuppressed NHPs. The fovea-the central avascular portion of the macula-is the site of the greatest mechanical weakness during the transplantation. Foveal trauma will occur if the initial subretinal fluid injection generates an excessive force on the retina. Hence, slow injection under perfluorocarbon liquid (PFCL) vitreous tamponade is recommended with a dual-bore subretinal injection cannula at low intraocular pressure (IOP) settings to create a retinal bleb. 
Pretreatment with an intravitreal plasminogen injection to release parafoveal RPE-photoreceptor adhesions is also advised. These combined strategies can reduce the likelihood of foveal tears when compared to conventional techniques. The NHP is a key animal model in the preclinical phase of RPE cell therapy development. This protocol addresses the technical challenges associated with the delivery of RPE cellular therapy in the NHP eye.

The non-human primate (NHP) is an ideal model for studying human retinal cellular therapeutics due to the anatomical and genetic similarities. This manuscript describes a method for submacular transplantation of retinal pigment epithelial cells in the NHP eye and strategies to prevent intraoperative complications associated with macular manipulation.

Retinal pigment epithelial (RPE) transplantation holds great promise for the treatment of inherited and acquired retinal degenerative diseases. These ...

Transpupillary-Guided Trans-Scleral Transplantation of Subretinal Grafts in a Retinal Degeneration Mouse Model

Transplantation of photoreceptor cells and retinal pigment&#160;epithelial (RPE) cells provide a potential therapy for retinal degeneration diseases. Subretinal transplantation of therapeutic donor cells into mouse recipients is challenging due to the limited surgical space allowed by the small volume of the mouse eye. We developed a trans-scleral surgical transplantation platform with direct transpupillary vision guidance to facilitate the subretinal delivery of exogenous cells in mouse recipients. The platform was tested using retinal cell suspensions and three-dimensional retinal sheets collected from rod-rich Rho::EGFP mice and cone-rich OPN1LW-EGFP;NRL-/- mice, respectively. Live/dead assay showed low cell mortality for both forms of donor cells. Retinal grafts were successfully delivered into the subretinal space of a mouse model of retinal degeneration, Rd1/NS, with minimum surgical complications as detected by multimodal confocal scanning laser ophthalmoscope (cSLO) imaging. Two months post-transplantation, histological staining demonstrated evidence of advanced maturation of the retinal grafts into &#39;adult&#39; rods and cones (by robust Rho::EGFP, S-opsin, and OPN1LW:EGFP expression, respectively) in the subretinal space. Here, we provide a surgical platform that can enable highly accurate subretinal delivery with a low rate of complications in mouse recipients. This technique offers precision and relative ease of skill acquisition. Furthermore, the technique could be used not only for studies of subretinal cell transplantation but also for other intraocular therapeutic studies including gene therapies.

This protocol presents a transpupillary vision-guided trans-scleral approach to safely and precisely deliver subretinal cellular grafts, with a low rate of surgical complications, in mouse recipients with or without retinal degeneration.

Transplantation of photoreceptor cells and retinal pigment&#160;epithelial (RPE) cells provide a potential therapy for retinal degeneration diseases. ...

Revitalizing Sight: Stem Cell Therapy for Retinal Degeneration

Sub-Retinal Delivery of Human Embryonic Stem Cell Derived Photoreceptor Progenitors in rd10 Mice

Regeneration of photoreceptor cells using human pluripotent stem cells is a promising therapy for the treatment of both hereditary and aging retinal diseases at advanced stages. We have shown human recombinant retina-specific laminin isoform matrix is able to support the differentiation of human embryonic stem cells (hESCs) to photoreceptor progenitors. In addition, sub-retinal injection of these cells has also shown partial restoration in the rd10 rodent and rabbit models. Sub-retinal injection is known to be an established method that has been used to deliver pharmaceutical compounds to the photoreceptor cells and retinal pigmented epithelial (RPE) layer of the eye due to its proximity to the target space. It has also been used to deliver adeno-associated viral vectors into the sub-retinal space to treat retinal diseases. The sub-retinal delivery of pharmaceutical compounds and cells in the murine model is challenging due to the constraint in the size of the murine eyeball. This protocol describes the detailed procedure for the preparation of hESC-derived photoreceptor progenitor cells for injection and the sub-retinal delivery technique of these cells in genetic retinitis pigmentosa mutant, rd10 mice. This approach allows cell therapy to the targeted area, in particular the outer nuclear layer of the retina, where diseases leading to photoreceptor degeneration occur.

Author Spotlight: Advancing Vision Restoration - Stem Cell-Based Therapy for Retinal Diseases 

We describe a detailed protocol for the preparation of post-cryopreserved hESC-derived photoreceptor progenitor cells and the sub-retinal delivery of these cells in rd10 mice.

Regeneration of photoreceptor cells using human pluripotent stem cells is a promising therapy for the treatment of both hereditary and aging retinal ...

Intraoperative Visualization of Subretinal Injection and Retinal Detachment in Rats

Subretinal injection, the delivery of a solution between the photoreceptors and the retinal pigment epithelium (RPE), creates a subretinal space where components are in direct contact with photoreceptors and RPE cells. This delivery method allows for targeted treatment of these cells. Therapeutics for subretinal injection have been developed and approved, particularly for inherited retinal diseases. In animals, subretinal injection procedures can be challenging due to the lens size, especially in rodents. This article describes methods for subretinal injection in rats, enabling intraoperative visualization and control of both the injection site and the size of the detached area, as performed in humans. The procedure is conducted under general and local anesthesia and requires pupil dilation. Using an ophthalmic microscope, the subretinal injection is performed through a 30 G scleral channel, with the cannula tip gently applied to the retina to create a retinotomy. Volumes ranging from 10-25 &#181;L can be delivered, corresponding to two-fifths to half of the rat retina. Immediate postoperative examinations using fundus photography and optical coherence tomography confirm successful delivery into the subretinal space with visible subretinal fluid. The major risks of this procedure include lens damage (cataract), detachment failure, intravitreal hemorrhage, subretinal hemorrhage, and postoperative keratitis. In addition to delivering therapeutics into the subretinal space, this technique is used to induce short-term or long-term retinal detachment using aqueous or viscous products, respectively. Unlike the transscleral approach, this method enables precise intraoperative positioning of the retinal detachment.

This article describes methods for subretinal injection in rats, utilizing intraoperative visualization to control both the injection site and the area of retinal detachment.

Subretinal injection, the delivery of a solution between the photoreceptors and the retinal pigment epithelium (RPE), creates a subretinal space where ...

Transconjunctival Approach for Injection into the Rat Optic Nerve

The rat serves as an important model for studying disorders of the optic nerve, including heritable, traumatic, neoplastic, and autoimmune conditions. Accessing the rat optic nerve for experimental manipulations and injections is challenging due to the small size of the orbit and the vascularity of the surrounding orbital tissues. Previous techniques have involved a cutaneous incision, which carries a higher risk of infection and requires wound closure. This study aims to describe a unique, less invasive, and potentially more efficient approach to accessing the rat optic nerve. A transconjunctival incision, along with a rat spinal cord hook, is used to isolate the optic nerve for experimental injections. In these experiments, an adenoviral vector is injected into the optic nerve with the goal of using this technique for direct gene therapy delivery in the future. This technique can also be applied by investigators requiring access to the rat optic nerve for other experimental studies, including drug delivery and optic nerve injury research.

This protocol describes a unique technique using a transconjunctival approach to access the rat optic nerve for injections.

The rat serves as an important model for studying disorders of the optic nerve, including heritable, traumatic, neoplastic, and autoimmune conditions. ...

An Alternative and Validated Injection Method for Accessing the Subretinal Space via a Transcleral Posterior Approach

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Chapters in this video

Subretinal Injection of Gene Therapy Vectors and Stem Cells in the Perinatal Mouse Eye

Performing Subretinal Injections in Rodents to Deliver Retinal Pigment Epithelium Cells in Suspension

Limbal Approach-Subretinal Injection of Viral Vectors for Gene Therapy in Mice Retinal Pigment Epithelium

A Step by Step Protocol for Subretinal Surgery in Rabbits

Development of a Refined Protocol for Trans-scleral Subretinal Transplantation of Human Retinal Pigment Epithelial Cells into Rat Eyes

Retinal Pigment Epithelium Transplantation in a Non-human Primate Model for Degenerative Retinal Diseases

Transpupillary-Guided Trans-Scleral Transplantation of Subretinal Grafts in a Retinal Degeneration Mouse Model

Sub-Retinal Delivery of Human Embryonic Stem Cell Derived Photoreceptor Progenitors in rd10 Mice

Intraoperative Visualization of Subretinal Injection and Retinal Detachment in Rats

Transconjunctival Approach for Injection into the Rat Optic Nerve