Contents
Dysphotopias:
It is an aberrant phenomenon which usually occurs after a cataract surgery (implantation of an intraocular lens). It is divided into two categories which are positive dysphotopia (PD) and negative dysphotopia.
Photopia is a subjective perception of flashes of light or luminous rays. So, dysphotopias are visual perceptions that occur when there is absence of light. Before dysphotopia was not known to many, but later on it became a major problem which is complained by majority of patients who have undergone a successful surgery. But unfortunately, there are no ways to prevent or treat this side effect effectively.
Positive Dysphotopia:
The patient in this condition see extra and unwanted images. This can be caused by scintillating vision or arcs. The arcs are seen by the patient which is usually the edge of the intraocular lens when the pupil dilates during night time. Flashes are also seen, when the peripheral rays get reflected at the edge of the intraocular lens. When multifocal intraocular lens are used, then haloes and rings are formed and due to high refractive index and intraocular lens reflection , glares are formed.
Causes:
The causes of positive dysphotopia are
- High refractive index
- Square edge
- Unequal design of bi-convex
- Intraocular lens is decentered.
Other causes are since acrylic lens usage is increased and some other factors that are favorable, the patients are suffering with dysphotopia condition. These usually occur with use of hydrophobic acrylic lens. As we know that there is no possible way to treat dysphotopia completely, but use of PMMA lenses helps in reducing the chances of getting dysphotopia because this condition was virtually unknown. Use of high refractive indices cause symptoms of dysphotopia by concentrating the large amount of light which is reflected from the posterior surface of the intraocular lens on to the small area of retina.
A square edge of an ovoid lens produces stray light and concentration of light into an arc on the retina, causes dysphotopia symptoms. An intraocular lens that is decentered causes change in reflection angle and positive dysphotopia in the edge of the intraocular lens.
Unequal bi-convex lens produces more concentrated images inside the eye which produces the internal reflections which are much more focused than normal lens. This increases the chances of getting a positive dysphotopia.
Negative Dysphotopia:
This condition is less understood and is more debilitating than positive dysphotopia. In this, the patient sees a dark shadow/ crescent which gives an impression of shade over the temporal region in the vision of the patient.
It was first understood as the “horseblinders”, this was the term given by James Davison for temporal darkness. The light scattering from the nasal edge of the intraocular lens, gives a dark area over the retina.
Causes:
The causes of negative dysphotopia are classified into primary and secondary. The factors which are primary are small pupil, increased distance between the back of iris and intraocular lens and extension of anterior functional nasal retina.
The shadow of the negative dysphotopia is seen through constricted pupils as constriction of pupils leads to increase in contrast between the rays (which similar in size of a pinhole) and shadow. Negative dysphotopia are usually caused mainly by acrylic lens due to higher distance.
Secondary factors are increase in angles which causes the turning of eye that results in temporary formation of negative dysphotopia. High plus lenses and idiosyncrasy in predisposition. Cataract and a shallow orbit of the eye causes negative dysphotopia.
Since the retina reaches farther in the anterior nasal quadrants, more than the temporal ones. Hence, this is the reason why shadow is temporal in the eye. The flat edge is seen as it is reflected from the periphery when the light enters the eye.
The positive dysphotopia and negative dysphotopia are some what different in their causes as well as in their symptoms. But in a crossover, the rays from the positive dysphotopia on the temporal retina from the edge would be absent in refracted image of the glare source (light image). The patient can suffer with both of them at same time i.e, both the conditions can co-exist together.
There are stages in negative dysphotopia which shows different severity in different stages. In duration of 2 weeks, the negative dysphotopia is said to be transient which is due to hydration of a clear corneal incision which is placed temporarily and gradually subsides in a few weeks as the dehydration of incision area.
In the next span from six weeks to six months, there is a temporary negative dysphotopia which is caused by penumbra of the intraocular lens which is square edged on the nasal retina. This condition can gradually decrease it’s time, by opacification of peripheral capsule.
The third stage is namely, persistent stage which annoys patients and causes frustration to both patients as well as to doctors.
Conclusion:
Therefore, it is necessary to understand the problems faced by the patient. The dysphotopia condition, especially in positive dysphotopia, it can be chalked superficially up to a posterior capsular opacification. The patient must check for negative dysphotopia, because it is nearly impossible for the exchange of lens after the surgery.
Even after the patient is given a few weeks for neuroadaptation, the exchange of intraocular lens becomes more and more difficult with time. Some doctors would like to take the risk of such a challenge after almost six months, in which the patient education shows that exchange of intraocular lens has a higher level of risk in procedure than the initial cataract extraction.
In recognizing the symptoms or condition inside the eye, optometrists play a pivotal role in postoperative care.
Educating the patients with the transient nature of dysphotopia and it’s symptoms which have a strange approach, so that the patients can have a pharmacological intervention in order to treat their problems. And the surgery is performed for the patients who are not completely satisfied by the outcome.
Hence, if a patient undergoes a surgery using a high refractive lenses or any other sharp edged lenses that cause internal reflections in such a manner that it is concentrated in the small area of retina or formation of dark shadows in the retina causes positive and negative dysphotopia conditions.
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