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Demystifying Dysphotopsia After Cataract Surgery

2 CPD in Australia | TBC in New Zealand | 1 June 2019

 

By Dr Alex Ioannidis

Although we do not fully understand the aetiology of pseudophakic dysphotopsia, we do know that most cases resolve on their own without invasive intervention. Reassuring patients of successful surgical outcomes, and counselling them about the risks and likely benefits of treatment if required, is important.

LEARNING OBJECTIVES

  1. To understand the nature of dysphotopsia after routine cataract surgery,
  2. To differentiate the various types of dysphotopsia from other common ophthalmic conditions, and
  3. To look at the various treatment options to manage patients that present with dysphotopsia after cataract surgery.

A patient walks in three days after routine cataract surgery and complains of a peripheral shadow in his vision. He was seen on day one following surgery and all was well on the first postoperative visit. He is obviously worried that there is a complication with his operation. His vision is 6/5 unaided and the examination reveals no abnormality. This scenario is not uncommon and occurs fairly often somewhere around the world. This patient has dysphotopsia – not an uncommon complaint after routine cataract surgery.

Cataract surgery remains the most common ophthalmic surgical procedure. Over 20 million cataract surgeries are performed world wide each year and this is projected to rise to 30 million cases by 2020.1 The prevalence of dysphotopsia after routine surgery is difficult to ascertain as most cases are likely to be transient and patients may not report symptoms to their surgeon.

Dysphotopsia can be defined as unwanted patterns of light or shadowing on the retina. There are essentially two types of dysphotopsia: positive and negative.2

Positive dysphotopsia first appeared in the literature in 1993 and is better understood than its counterpart as it is represented by light patterns typically in the peripheral retina.3 Patients typically report peripheral halos, glare and flickering, which are never seen in the dark. The effect is transient and cannot be easily replicated in the clinic on examination.

Negative dysphotopsia can be more disconcerting as patients typically describe a shadow effect often in the far periphery of the visual field. It is often described as a semi-circle that “is always there” and “was not there before the operation”. One characteristic feature of negative dysphotopsia is that the visual field examination is normal on presentation and the described field defect cannot be mapped on formal perimetry.

Theories on Positive Dysphotopsia

The cause of positive dysphotopsia remains essentially elusive and a number of hypotheses have been put forward by a number of authors.2 Factors that have been implicated relate to the intraocular lens (IOL) material, IOL shape, the relationship between the IOL and the peripheral retina, and IOL handling at the time of implantation or IOL damage. One very plausible hypothesis relates to the square-edge design of modern IOLs creating refracted light patterns into the peripheral retina. A number of clinical studies have confirmed that such IOL design increases the risk of positive dysphotopsia.4,5 The square-edge was devised by most IOL companies to reduce the risk of developing posterior capsular opacification as the sharp edge is thought to impede the migration of lens epithelial cells behind the IOL (Figure 1).

Figure 1. Typical IOL designs. A ’sharp edge‘ design (top row) and a ‘rounded edge’ design (bottom).

 

Another factor in the development of dysphotopsia is the IOL material and the high index of refraction of modern IOL materials. It has been suggested that high refractive IOLs are associated with higher rates of positive dysphotopsia, and that this finding may be related to both the material and radius of curvature.6 A new type of dysphotopsia has been attributed to a new implantantable contact lens design (ICL) which has a central hole in the implant – this dysphotopsia is described as a bright ring of light in the central vision.7

Theories on Negative Dysphotopsia

Unlike positive dysphotopsia, negative dysphotopsia has been described with various types of IOLs.4 The cause of negative dysphotopsia is multifactorial, which makes assessment and treatment particularly difficult. It is also said that negative dysphotopsia is less well tolerated and can be more disconcerting for patients. When negative dysphotopsia was first introduced by Davidson in 2000, the first theory of its cause was the high refractive index and edge design of the acrylic IOLs as opposed to the silicone IOLs.8 A number of silicone IOL designs have more rounded edges and it is thought that this helps to disperse the light rays, resulting in reduced rates of dysphotopsia with that particular IOL material and design.

Anatomic Variables

Specific anatomic variables have been implicated in the development of dysphotopsia. Osher et al. has suggested that some patients with prominent globes and shallow orbits are more likely to report dysphotopsia.9 The explanation given is that such eyes allow more incident light to reach the nasal retina as the eye is more exposed to temporal incident light rays. Another anatomical consideration is variable retinal sensitivity, whereby the nasal retina is more sensitive to incident light than the temporal retina. Angle kappa has also been described as a cause of dysphotopsia in some patients. Angle kappa is the angle between the visual axis and the pupillary axis. The association between angle kappa and diverse photic phenomena, where higher angle kappa may produce a shadow consistent with negative dysphotopsia, has been described.10

Corneal wound location during cataract surgery is another anatomic variable that can result in negative dysphotopsia. In some cases patients report a temporal shadow and this relates to the presence of the temporal wound in the cornea – casting a shadow across the pupil. It is unclear why some patients are able to detect this, while others remain oblivious and do not report an issue to the surgeon. Pupil size has also been reported as a cause of dysphotopsia, with smaller pupil sizes increasing the risk of negative dysphotopsia in some cases.

Challenges in Evaluating Dysphotopic Symptoms

One of the challenges in the evaluation of dysphotopsia is that patients will not necessarily report symptoms unless they are severe and impact their daily lives. In some cases, patients will not report an issue unless they are asked directly by the ophthalmologist. The subjective nature of the condition is also a factor that makes diagnosis difficult. A number of devices have been used to allow patients to best describe what they see, including questionnaires and halometers. The latter use visual screen aids that allow patients to see patterns of stray light on a computer screen or a tablet. These aids are helpful in cases of positive dysphotopsia but it is more difficult to describe a scotoma and represent this on a computer screen. In cases of negative dysphotopsia the Goldmann perimeter has been used with some success to help map the negative defect.

Case Presentation One

A 64 year old man walked into the eye clinic complaining of a ‘flicker’ in his vision after his routine cataract surgery. He had been seen on day one after surgery and his vision was recorded as 6/6 with minimal post operative inflammation. The operation notes were recorded as a ‘routine case’. His examination was unremarkable apart from a small refractile area nasally on the IOL (Figure 2.) The patient was informed that there was something unusual about the IOL and that an IOL exchange was recommended. The IOL was exchanged within two weeks of presentation and inspection revealed a small defect on the body of the IOL. With the new IOL implanted, the dysphotopic symptoms resolved. In this case dysphotopsia was attributed to a flaw in the actual IOL which may have been a manufacturing flaw or due to poor handling of the IOL at the time of implantation.

Figure 2. The small refractile area represents a defect in the IOL. The patient presented complaining of a bright light coming from the side.

 

Case Presentation Two

A 68 year old man presented at the eye clinic complaining of a crescentic shadow in his vision. This had been present for several months after his last refractive cataract surgery. His VA was 6/5 unaided and he had had previous LASIK surgery, a clear lens extraction and a secondary IOL (Figure 3). His retinal examination was unremarkable. He also underwent Humphrey Visual Field testing and this was normal. The patient was counselled about management options of negative dysphotopsia including conservative and surgical options. In the end, the patient decided against further surgery in view of his excellent refractive outcome from previous cataract and IOL surgeries – he was in fact prepared to ‘live with it’. A suggestion was made to use a drop of brimonidine to cause a mild pharmacological miosis. This intervention proved effective and his dysphotopsia was minimised. On further review several months later, the patient stated that the symptoms had almost resolved and he wished to be discharged from the clinic. The use of brimonidine has been described as a means to reduce the pupil size and minimise the effects of dysphotopsia in some patients.11

Figure 3. A dropped IOL in case two. In this case, the patient opted not to have further surgery as his refractive outcome was good from previous surgery. He was prepared to live with some dysphotopsia.

 

Multifocal IOLs and Dysphotopsia

Multifocal IOLs (MFIOLs) provide excellent refractive outcomes and reduce dependency on glasses after cataract surgery. They are, however, associated with an increased incidence of dysphotopsiae and decreased contrast sensitivity.12,13 This is a consequence of the design that confers multifocality as these lenses have typical diffraction pattern designs inbuilt into the IOL surface. These patterns produce photic phenomena which are often described as ‘rings of light’ or ‘halos’ around bright pinpoint light sources such as car headlights or street lamps (Figure 4).

Figure 4. A typical diffractive multifocal IOL. These lenses can lead to reports of post-operative dysphotopsia due to their design characteristics.

 

Monaco et al. initiated an interventional study aiming to compare trifocal, extended range of vision, and monofocal IOLs. Their findings showed that visual acuity was significantly better in the trifocal group compared with the extended range of vision group, and both multifocal groups were superior to the monofocal group in both visual acuity and spectacle independence.

Patients with MFIOLs have been shown to experience more side effects, such as dysphotopsia, compared with those with monofocal IOLs when measured by a Quality of Vision (QOV) questionnaire.14

It is important when considering MFIOL surgery to discuss dysphotopsia with patients and the concept of a trade-off between achieving spectacle free vision and the photic phenomena that may occur following surgery. Patients that have been counselled appropriately before surgery are likely to be more accepting of dysphotopsia and often state, “yes I can see the rings and I was expecting to see them as you told me I would”. This is not seen as a failure of surgery by the patient but rather a feature of current technology and its limitations.

Things That Don’t Appear to Cause Dysphotopsia

There are conditions that develop in the vicinity of the IOL and lens capsule that don’t appear to cause dysphotopsia. One example is posterior capsular opacification. Patients may report blurring of vision, dullness in the vision or haziness, but they do not typically report fixed semi-crescentic shadows or photic phenomena. The explanation for this is the diffuse nature of opacification of the capsule and the fact that it does not cause an ‘edge effect’. Conversely there are situations where anterior capsular opacification can result in negative dysphotopsia and cases have been reported and treated in the literature.15 Other conditions that don’t appear to cause dysphotopsias are iris root defects after trauma or large iridotomies. Patients may report glare in such instances but this is not true dysphotopsia per se. The explanation for this is that large defects do not create ‘edge effects’ as light enters the eye. Conversely small iridotomies have been associated with positive dysphotopsia symptoms and this is an effect of the lid position and tear film meniscus location near the iridotomy.16 In this instance, the dysphotopsia is described as a bright horizontal line associated with blinking. The line appears to move up and down on blinking in most cases. This effect can be minimised by creating the iriditomy at the three o’clock position, as opposed to the 12 o’clock position.

Figure 5. Incident light rays in a model IOL. As light enters at a greater angle away from the lens axis, intense light patterns are created in the far periphery.

 

Dysphotopsia and Differential Diagnoses

Patients can describe a number of visual phenomena after cataract surgery that may imply dysphotopsia due to the timing of presentation. There are several differential diagnoses that can be considered and some are important. Temporal flashes can be a manifestation of vitreous dynamics such as Moores Lightning Streaks due to vitreous syneresis and peripheral retinal stimulation. In such instances, it is important to perform a thorough retinal examination to exclude a pseudophakic retinal detachment or tear. Patients who describe flashes and associated headache may be having a migraine. Mobile shadows may reflect the presence of vitreous opacities or floaters. These are differentiated from true dysphotopsia by the fact that they are mobile and have a lag time with saccadic eye movements. Other entoptic phenomena include asteroid hyalosis and vitreous opacities from intra-vitreal injections that cast a shadow and become more prominent after cataract surgery. In all instances it is therefore important to perform a good examination of the posterior segment as patients may have an obvious explanation for their presenting symptoms after routine cataract surgery.

Management of Dysphotopsia

The management of dysphotopsia can be divided into the conservative and surgical. It is important to note that most cases do settle on their own, due to the fact most patients learn quickly to ignore transient photic phenomena and rationalise that the symptoms are non-noxious. This explains why most dysphotopsia is essentially under-reported.

Conservative approaches to management include appropriate counselling after a thorough examination to exclude serious pathology such as a retinal tear or detachment, and the use of miotics to reduce the pupil size and reduce the incident light striking the periphery of the retina and/or the IOL. Drugs with miotic effects on the pupil include brimonidine and pilocarpine. Brimonidine has been shown to induce a mild miosis of 1–2mm and often this is enough for patients to report an improvement in their symptoms. There is no concrete evidence that miotics work best in positive or negative dysphotopsia. In many cases, patients eventually cease the miotic as they forget the dysphotopsia and report this on subsequent visits to the specialist.

On the surgical front a number of options are available. Laser YAG capsulotomy has been described as a successful modality in cases where the capsule edge is thought to be causing a problem and casting a shadow. The laser essentially breaks the edge effect and in some cases micro-movements of the IOL after capsulotomy result in resolution of the dysphotopic symptoms.17

The advantage of the YAG laser is that it is the least invasive surgical intervention available to treat dysphotopic symptoms and in that respect it is worth a try before considering more invasive options.

In cases where dysphotopsia is persistent, other options include a piggyback IOL, or IOL exchange with a lens of different design or material. Piggyback lenses are typically implanted in the sulcus over a pre-existing IOL. The theory in dysphotopsia is that piggyback IOLs disrupt any aberrant light pathways that are casting a shadow or a ray of light in the peripheral retina.18 The secondary IOL acts in essence as a diffuser, and thus this approach has been shown to be effective in cases of positive and negative dysphotopsia.19 The main drawbacks of piggyback IOL implantation are an increased risk of pupillary block in eyes with shallow chambers, glaucoma, and lens decentralisation, either in the original or the secondary lens, resulting in refractive error.20

Another option available to treat the edge-effect of the anterior capsule is to reflect this capsule behind the implant body – a maneuover known as reverse optic capture. This has been shown to be effective in cases of dysphotopsia and has the advantage of being a relatively safe procedure to perform in theatre as the IOL is not explanted.21 This technique has been successfully attempted to reduce the risk of dysphotopsia in a contralateral eye that reported dysphotopsia in the first operated eye. More recently Alapati et al. reported a technique of IOL truncation to minimise the straight edge effect and thus reduce the risk of dysphotopsia in a selected group of patients. In this new technique, the nasal optic edge is amputated, which helps reduce optical impact at the nasal edge. They hypothesised that the resulting irregular edge increases light scattering, which successfully eliminates the shadow seen in negative dysphotopsia.22

The final option to treat dysphotopsia is the explantation of the IOL and its exchange. This decision is not taken lightly as patients need to understand that there are inherent risks of anterior chamber bleeding, corneal endothelial trauma, decompensation, glaucoma and a worse refractive outcome. Indeed IOL exchange has been reported to be effective in cases of both positive and negative dysphotopsia but there are also cases where this approach has failed to resolve the problem and the surgeon is left unclear about further management.23,24

As a general principle it is wise when contemplating IOL exchange to consider the implant of a different design and material. For instance, if an acrylic implant was used in the first operation, consider a silicone based IOL with a round edge and vice versa. This approach has had some reported success.

One other simple manoeuver that I have found useful prior to IOL exchange is to rotate the IOL so that the haptics are positioned along the horizontal meridian. This seems to  reduce  the edge effect that results in dysphotopsia and in some cases it has helped to ameliorate the symptoms described by the patient. It is also likely that minor adjustments on how the IOL sits in the eye have a positive contributing effect.

Often, despite using the ‘nuclear option’ of taking the patient back to theatre to explant and exchange an IOL, patients have continued to report dysphotopic symptoms, suggesting there are other factors at play besides IOL design and material that we don’t fully understand in causality of this condition.25

Emergent Technologies to Prevent Dysphotopsia

The development of new IOLs designed to prevent dysphotopsia is a promising area of research. A new oval-optic IOL was used in two patients with the expectation that its large optic size, mimicking the natural crystalline lens, would decrease the risk of negative dysphotopsia.26,27 Unfortunately, both patients developed positive dysphotopsia, and one of them potentially had both positive and negative dysphotopsia. This patient required an IOL exchange to resolve symptoms.

Another new implant incorporates a design inspired by reverse optic capture that is anticipated to prevent negative dysphotopsia.28 This new IOL has only been used in Europe in a small clinical trial, and it remains to be seen how it will fare when commercially available.

Conclusion

We have yet to fully understand the aetiology of pseudophakic dysphotopsia. Its true nature remains elusive despite several decades of investigation and review. It is also evident that there is still no clear answer for the treatment of this annoying condition that creates, on occasions, great distress to patients after routine cataract surgery. Better understanding of the cause of dysphotopsias will help us continue to develop better treatments and preventative techniques aimed at these causal factors. All suggested treatment modalities have generated their own challenges and it is always important to counsel patients appropriately about the risks and likely benefits of the suggested intervention.

It is comforting to note that in most cases, pseudophakic dysphotopsia resolves on its own without any further invasive interventions and most patients do well having been reassured that the actual operation was uneventful and no abnormal findings have been detected in the post-operative period.

 

Dr. Alex Ioannidis is a cataract and anterior segment specialist. He is Fellowship trained both in cornea and glaucoma. Dr. Ioannidis is able to offer his patients refractive cataract surgery and one of his many interests is cataract surgery in complex patients with other diseases of the anterior segment.

He works as a Visiting Medical Officer at the Royal Melbourne Hospital and consults privately at Vision Eye Institute in Melbourne.

 
References

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' One of the challenges in the evaluation of dysphotopsia is that patients will not necessarily report symptoms unless they are severe and impact their daily lives '