RETINA LASERS

In principle, a laser is a very strongly concentrated source of light that, depending on physical properties, triggers a certain effect when it hits tissue. In the case of the retina laser, the laser penetrates the anterior sections of the eye without having an effect. When it reaches the retina, it has a primarily thermal reaction. This leads to intentional burning effect. In the case of microsecond pulsing laser therapy, in which the laser beam is pulsed very briefly onto the retina, the tissue is “heated”, but not burned.

A laser is an instrument that produces a pure, high-intensity beam of light energy. The laser light can be focused onto the retina, selectively treating the desired area while leaving the surrounding tissues untouched. The absorbed energy creates a microscopic spot to destroy lesions or weld tissues together

Effect of laser on the retina

A retina laser system concentrates the light on the retina – at a point that normally only measures a tenth of a millimetre. This heats the tissue at this spot, and leads to coagulation of the protein components. The tissue “burns.” This burning, known as coagulation can positively affect the course of a retinal disease. For one, this re-seals leaking vessels. In addition, it inactivates diseased areas that no longer receive circulation. Both of these things lead to an improvement in the supply to still-functioning areas of the retina, and therefore to its preservation. In addition, it is assumed that this “burning” triggers the production of messenger substances, which has a positive impact on the healing of the disease itself.

Indications of laser surgery

Lasers were first widely used to treat eye diseases in the early 1970’s and have become the standard of care for previously untreatable disorders. For many patients, laser can preserve or prevent vision loss if given in a timely fashion.

Your eye will almost always look and feel normal with retinal diseases, even when there is haemorrhaging and leakage in the back of your eye. Your sight may also be normal for a while despite the presence of potentially blinding eye problems.

The only way to tell if you need laser surgery is to have a careful, dilated retinal examination, often followed by special testing including OCT scanning and fluorescein angiography. Lasers are commonly used to treat the following eye conditions:

1. 1. Diabetic retinopathy.

Diabetes causes circulation problems throughout the body, including the eyes, nerves, and kidneys. The retinal blood vessels are usually like pipes, bringing blood into and out of the back of the eye. In diabetes, however, the vessels may leak, causing the retina to swell and not work properly (diabetic macular oedema). Vision is affected when the swelling involves the central vision area. Laser surgery can seal the leaks, thereby preventing further vision loss.

Some patients will have new retinal blood vessels grow to replace some which have closed from the diabetes (proliferative diabetic retinopathy). While this sounds helpful, these new blood vessels can cause blindness from bleeding and scarring. Laser treatment can often prevent severe vision loss by making these new vessels disappear.

Argon green (514 nm) or double frequency NdYAG (532 nm) are the preferred laser wavelengths for treatment of diabetic retinopathy.

1. 1. Retinal vein occlusions.

The small blood vessels that drain blood from the retina (retinal veins) can sometime become blocked as part of the aging process. This is more common in patients with diabetes or high blood pressure. A retinal vein occlusion can cause the retina to swell with fluid and blood, blurring central and peripheral vision. Other times, new blood vessels may grow and cause pain with very high pressure inside the eye (neovascular glaucoma). Laser treatment can help reduce this swelling or cause the new blood vessels to disappear.

1. 1. Age-related macular degeneration.

Some people will develop aging changes in the macula, the portion of the retina responsible for our central reading vision. Most will experience the less harmful dry type, which usually causes minimal visual changes. The more severe, or wet type, causes the macula to swell with fluid and blood. Symptoms of wet macular degeneration include painless blurred or distorted vision. Urgent treatment can often prevent or delay vision loss in some patients with this wet type.

1. 1. Ocular histoplasmosis.

Most people in the Kentuckiana area have been exposed to histoplasmosis, a tiny plant-like organism (fungus) that causes an asymptomatic or viral-type illness early in life. There are often scars left behind in the eye and lungs that usually cause no symptoms. Some patients will develop new blood vessels adjacent to an old macular histoplasmosis scar. These vessels usually cause painless blurring or distortion. Urgent treatment can control these leaking vessels, often preserving central vision.

1. 1. Retinal breaks and detachment.

The retina lines the back of the eye like wallpaper. Retinal tears or holes can occur from congenital retinal thinning, as part of aging, or following cataract surgery or eye injury. Patients will often see cobweb-like floaters or light flashes when a retinal break develops. Liquid that normally fills the central portion of the eye (the vitreous) can leak beneath the break, lifting the retina away from the eyewall. This is called a retinal detachment, which can cause blindness if left untreated. Laser surgery around retinal tears is often able to weld the retina to the underlying eyewall. This can prevent or limit retinal detachment.

1. 1. Central serous retinopathy.

Central serous consists of one or more “blisters” of fluid (serous detachment) beneath the macula. It can cause central blurriness, distortion, abnormal colour vision, blind spots, and temporary farsightedness. Although the vast majority of cases will resolve spontaneously, laser photocoagulation is sometimes necessary for persistent lesions.

1. 1. Ocular tumours.

Some patients will have non-cancerous leaking vascular tumours that can cause the retina to swell and not function properly. Laser surgery can destroy these tumours and allow the swelling to go away.

Different Lasers of Retina

Broadly speaking, there are two types of retina lasers – the conventional, slit lamp based laser, and the modern, navigated laser system. Both types of laser systems primarily differ in terms of the type of application – i.e. how precisely the laser is positioned on the retina.

Conventional slit lamp laser

The conventional slit lamp laser has been used on the retina since around 1965. After initial experiments with sunlight, lasers have been used as a source of light for treatment. Because ophthalmologists already own slit lamps – they are used as a diagnostic tool – it’s easy for them to use it for this new application. Despite numerous further developments on the effectiveness of the laser itself, the application concept with the slit lamp has always remained the same.

 Treatments with the conventional slit lamp laser

Advantages of the conventional laser:

• Very long tradition of use
• Cost-effective system
• Popular

Disadvantages:

• Limited field of view through slit lamp
• Manual control without advanced planning
• No digital documentation

Navigated Laser System 

These days, we could scarcely do without the navigation and assistance systems in cars which bring us reliably and safely to our destination. This technology has also found a place in ophthalmology, for example to correct defective vision. Nowadays, the more advanced laser system facilitates more precise and secure application than conventional systems, thanks to modern eye-tracking technology.

Treatment with the navigated laser

Advantages of the Laser System:

• Excellent precision and safety
• More comfortable and less painful than conventional lasers^2. 6
• Fewer subsequent treatments

Disadvantages:

• Higher costs for advanced technology

Forms of laser therapy

Different forms of retinal laser treatment are used depending on the retinal disease in question. The treating doctor makes the decision based on the stage and cause of the disease.

Focal laser therapy

Focal laser therapy is generally used for swelling of the macula, known as macular oedema. Leaking vessels near the location of sharpest vision are sealed up in a very targeted way. At the same time, the targeted sealing of vision cells increases the activity of the pigment layer, which leads to a reduction in macular swelling.

With this treatment, the eye-tracking and navigation only available leads to:

• Great safety by protecting sensitive areas
• Fewer subsequent laser treatments through more thorough planning
• Less painful use due to no need of using treatment contact lenses

Panretinal laser treatment

Panretinal laser coagulation is carried out on the fringes of the field of view. The number of photoreceptor cells is reduced in an even manner. For one thing, this leads to a decrease in the need for oxygen. In addition, the resulting scarring of the retina activates messenger substances, which reduces the growth of diseased vessels

The more advanced laser systems available today, has a pre-planning mode and an adhoc pattern mode, in which short laser pulses are applied to the retina in very rapid succession, thus minimizing the sensation of pain as well as the time required.

In this form of treatment, the eye-tracking and navigation technology leads to:

• Less pain
• Shorter treatment time

Tissue-sparing therapy

In a new procedure, which is called microsecond pulsing therapy, the laser beam is applied in repeated, short pulses of less than one thousandth of a second. This warms the tissue, but it cools again in the pause between the laser pulses. In certain diseases, this can start the healing process without demonstrably damaging the tissue. This procedure therefore exploits the positive effect of the laser without destroying photoreceptors (vision cells). Your doctor can explain to you whether navigated microsecond pulsing therapy could be a potential, gentle option for you.

The eye-tracking and navigation technology available in the more advanced laser system results in:

• Transparent treatment documentation
• Complete treatment planning
• No need to use treatment contact lenses

What are the risks of laser treatment?

In conventional laser treatment, the effect is always achieved through the destruction of a small area and therefore always leads to the impairment of small areas of the retina. In general, this is not consciously perceived by the patient, as the damaged parts of the retina usually only have a small diameter of approx. 0.1 mm. In certain cases, vision may deteriorate, however.

Many patients find it uncomfortable to put on a special contact lens for laser treatment. Sometimes, this treatment contact lens can cause pain after the treatment. However, this generally subsides relatively quickly. Nevertheless, the treatment duration and the glare of the laser can lead to unpleasant sensations for the patient. Very rarely, bleeding and an increase in intraocular pressure may occur.

Lasers in Current Retina Practice

Recent updates bode well for the relevance of laser therapy in retina.

Description of the first instance of retinal photocoagulation, albeit not with a laser, dates back to 400 B.C., when Socrates first described burns of the retina during a solar eclipse. German ophthalmologist Meyer-Schwickerath in 1940 developed the first solar photocoagulator using a carbon arc light source. Schwickerath and Littman subsequently devised the xenon arc photocoagulator.

AT A GLANCE

• Since the introduction of anti-VEGF therapy, laser photocoagulation has taken a back seat in the management of some retinal diseases.
• Nonetheless, lasers as a modality of treatment for a number of vitreoretinal disorders continue to evolve in terms of management protocol, innovations, and ever-expanding indications.
• With the advent of micropulse and nanopulse laser technologies, laser therapy may be regaining importance.

Gas (argon, krypton) and liquid (tunable dye) lasers were subsequently introduced, but these did not remain practical options due to the bulky nature of the equipment and the expense of upkeep. Semiconductor lasers were introduced in the 1960s, but early versions were purely infrared and had limited applications. These devices did not gain popularity until recently, when visible light wavelength lasers were introduced.

Conventionally, the mechanism of action of lasers for retinal applications has been retinal photocoagulation, wherein light energy is converted to heat at the level of the retina, leading to protein denaturation. Several mechanisms have been proposed for how laser photocoagulation works in the retina: first, from direct action on the vessels, leading to closure and reduced leakage; and second, from reduced oxygen demand and increased oxygenation of the inner retina following scarring and burns at the level of the retinal pigment epithelium (RPE) and photoreceptors. A third theory is that RPE activation following photocoagulation injury leads to cytokine production, and ultimately to reduction of VEGF load and, thus, oedema. This theory is of most interest today, as it suggests the possibility of nondamaging laser treatment that promotes retinal rejuvenation.

The ETDRS established laser photocoagulation as standard of care for management of diabetic retinopathy. Since the introduction of anti-VEGF therapy, laser photocoagulation has taken a back seat in management of diabetic macular oedema (DME). However, laser photocoagulation still has a significant role in the treatment of a number of retinal diseases and can be considered a standard of care.

In this article we describe current indications for laser photocoagulation and recent updates in this field.

INDICATIONS FOR LASERS

Proliferative Diabetic Retinopathy

Panretinal photocoagulation (PRP) reduces the hypoxic load and promotes inner retinal oxygenation. The efficacy of PRP was demonstrated in the ETDRS and the Diabetic Retinopathy Study. Treatment of proliferative diabetic retinopathy (PDR) remains the most common indication for photocoagulation to date. Recently, the Diabetic Retinopathy Clinical Research Network (DRCR.net) Protocol S found anti-VEGF monotherapy to be as effective as conventional PRP. However, clinical and economic advantages still make PRP the preferred treatment choice in many real-life situations.

Limited literature is available on the use of micropulse laser as retinal rejuvenation therapy for stimulating the RPE and thus decreasing the chance of visual field loss, increased traction, and ultimately irreversible damage secondary to conventional laser.

Diabetic Macular Oedema

Anti-VEGF therapy may be the preferred choice for centre-involving DME; however, focal laser photocoagulation is still useful in the treatment of extrafoveal oedema. In addition, focal laser targeting leaking microaneurysms or grid laser targeting areas of diffuse leakage on the retina can be useful to reduce the need for repeated anti-VEGF injections and also to reduce the burden on health care systems.

Subthreshold micropulse laser has been shown to be as effective as focal laser in reducing oedema and subsequently reducing the need for frequent injections.

Vascular Occlusion

The Branch Vein Occlusion Study showed the efficacy of grid laser in macular oedema secondary to branch retinal vein occlusion (BRVO), and the Central Vein Occlusion Study showed the benefit of scatter photocoagulation in the management of neovascularization in central retinal vein occlusion (CRVO) for prevention of glaucoma. Anti-VEGF therapy has since become the first choice of treatment for these indications. However, macular or peripheral laser to ischemic areas may still have a role in recalcitrant cases.

Central Serous Chorioretinopathy

Lasers have long been used for management of focal leaks in the treatment of persistent cases of nonresolving central serous chorioretinopathy (CSCR). The introduction of micropulse laser has allowed clinicians to manage not only extrafoveal leaks but also subfoveal leaks, along with areas of diffuse RPE dysfunction, quite successfully. Micropulse laser can be considered an alternative to photodynamic therapy in eyes with chronic CSCR with or without subfoveal leaks.

Retinal Breaks

Retinopexy around retinal breaks is performed by promoting chorioretinal adhesion secondary to laser photocoagulation and sealing the area surrounding the break. This plays a key role in prevention of retinal detachments.

Exudative Retinal Vascular Disorders

In exudative retinal vascular disorders such as Coats disease, retinal capillary haemangioma, or retinal artery macroaneurysms, laser photocoagulation can be used to directly close the leaking vessels by promoting thrombosis.

Retinochoroidal Neovascular Diseases

Retinochoroidal neovascular diseases, such as extrafoveal choroidal neovascular membrane, extrafoveal retinal angiomatous proliferation lesions, and polyps in polypoidal choroidal vasculopathy, can be addressed with thermal photocoagulation efficiently and with great results.

Peripheral Retinal Ischemic Retinopathies

In peripheral retinal ischemic retinopathies such as vasculitis, familial exudative vitreoretinopathy, and retinopathy of prematurity, laser can help to reduce the hypoxic load on the retina and prevent devastating complications.

Tumours

For vasoproliferative retinal tumours, angiomas, etc., laser photocoagulation can promote closure, much as described above for other neovascular complexes.

Foveoschisis Secondary to Optic Disc Pit

This condition can be addressed by laser prior to considering surgery.

Hyaloidotomy and Capsulotomy

Laser shock waves can be used in miscellaneous indications, such as to disrupt the hyaloid interface in eyes with subhyaloid haemorrhages or to clear the centre of the visual axis in dense posterior capsular opacifications.

INNOVATIONS IN TREATMENT PATTERNS

Endpoint Management

Endpoint Management is a program developed for the 577nm Pascal laser (Topcon) that allows mapping values of tissue damage based on computational modeling to a linear scale of laser energy, relative to a visible titration level. The titration algorithm for Endpoint Management begins by defining the laser power at 20 ms pulse duration to produce a barely visible burn within 3 seconds after the laser pulse. With this energy level defined as 100%, all other pulse energies are expressed as a percentage of this titration threshold. Although the coagulation threshold will vary from patient to patient, a 50% or 30% setting on Endpoint Management will always correspond to half or a third of the titration threshold energy.

Tissue damage at an energy level of 30% is limited to a single RPE cell in the center of the 200-µm spot. With Endpoint Management, some spots in a grid treatment pattern can be set at 100% (or above) to mark the location of the subvisble treatment with an immediately visible reference. This allows the user to adjust power to maintain the same ophthalmoscopic visibility grade throughout the fundus. It thus provides a fairly reproducible approach to subvisible retinal laser therapy, possibly resulting in reduced dependence on injections.

Micropulse Laser

Subthreshold micropulse laser is thought to limit damage to adjacent tissue. Rather than maintaining the same degree of energy throughout exposure time, laser energy is delivered in ultrashort (microseconds) pulses with adjustable on and off times. The length of these pulses must be shorter than the thermal relaxation time of the target tissue (the time required for heat to be transferred away from the irradiated tissue). Micropulse laser thereby induces a temperature rise insufficient to cause ancillary damage to surrounding retinal tissue.

This technology has been most extensively explored in the treatment of DME. It has been shown to minimize scarring to the extent that laser spots are generally undetectable on ophthalmic and angiographic examination. At the same time, it has been shown to stimulate the RPE and have a beneficial effect on its activation.

Nanopulse Laser

Retina Regeneration Therapy is a subthreshold laser modality using a 532-nm laser to produce 3-ns pulses. These nanosecond pulses are purported to stimulate renewal of the RPE. 2RT combines subthreshold with micropulse laser protocols. This nanosecond laser, using a speckle-beam profile, provides a wider therapeutic range of energies over which RPE treatment can be performed without damage to the apposed retina, as compared with conventional laser. The use of lower energy levels is meant to cause sublethal injury to targeted RPE, rather than destroying it and leading to cytokine release by recovering RPE cells.

Targeted Retinal Photocoagulation

Targeted retinal photocoagulation (TRP) is another concept in development. Targeted or selective therapy in general is any therapy aimed to block a specific target. Examples of targeted retinal therapy include feeder vessel photocoagulation in choroidal neovascularization, focal laser photocoagulation in the treatment of DME, and selective laser to areas of nonperfusion. The idea behind TRP is to selectively treat ischemic retinal areas and adjacent intermediate areas showing leakage on angiography while minimizing the risks and complications of conventional PRP. Muqit et al reported that TRP for PDR using 20-ms micropulses with the Pascal laser did not produce increased macular thickness; paradoxically, it improved central retinal thickness and visual field sensitivity with reasonable regression of neovascularization.

HOLDING STEADY

Lasers as a modality of management for retinal diseases continue to evolve in terms of management protocol, innovations, and ever-expanding indications. Laser therapy remains an integral component of conservative management in a number of vitreoretinal disorders. With the advent of micropulse and nanopulse laser technologies, laser therapy may be regaining its importance, with expanding indications in the management of many retinal diseases.