An in-depth look at monocular vision & ocular prostheses

Would l ever be able to climb a flight of stairs again? Would I be able to cross the street with a reasonable expectation of reaching the other side alive? Would I be able to drive a car again? Would I be able to just sit down and read a book? These are arguably some of the most common concerns of people who have to face life with monocular vision. Defined as having vision in only one eye, monocular vision comes about due the loss of vision in one eye, due to either natural causes (e.g. a congenital disease leading to blindness) or external trauma (e.g. damage sustained to the eye as a result of a car accident). A person who had suffered the loss of vision in one eye needs to adapt to two new realities – the reality of going through life being blind in one eye, and, provided he or she can afford it, the reality having to wear on ocular (or orbital) prosthesis.

The physiology and psychology of seeing with only one eye

Jackie Heatlie, an ocularist at the Pretoria Eye Institute and one of the directors of the Ocularist Association of South Africa (OASA), says the psychological trauma involved in both of these situations can be great. “Support and counselling before and after an eye procedure is very important. The trauma can be a very difficult experience to come to terms with,” she says. “Pre-surgery counselling is the responsibility of the ophthalmologist (eye specialist) and a psychologist, while post-surgery counselling and support is provided by the ocularist.” A person whose loss of sight has been gradual will obviously adapt easier to monocular vision since the unaffected eye will have had time to get accustomed to an increased ‘workload’.

Having lost the use of my right eye due to a retina detachment I can certainly attest to the fact that life with monocular vision presents quite a few challenges. I was very fortunate in the sense that the loss of vision in my right eye occurred over a gradual period of time, and as such the adaptation to a life of monocular vision was relatively smooth. In many ways, I look upon my condition as more of a nuisance than an outright disability. A positive mind-set is obviously key here, and it is important to keep in mind that monocular vision is not blindness (in the same way that walking with a limp is not tantamount to being paralysed). Even so, there are a few unavoidable facts that needed to be faced.

Edwina Vos, a senior theatre nurse and someone who has been involved in most of my surgeries, says the loss of sight in one eye affects the patient in three main ways: (i) the horizontal field of vision is narrowed, (ii) depth perception is impaired and (iii) the overall visual system (the relationship between the eyes, the brain and the body) is thrown off balance. “Each eye has a visual field of about 180 degrees, or a half circle. Those with monocular vision lose about 20% on the affected side, which is not really that much,” she says. With regards to depth perception (the distance and spatial relationship of objects) Vos stresses that those with monocular vision often have difficulty in judging the distance of objects. “In the same sense that those who are deaf in one ear have difficulty establishing the direction of sounds, those with sight in only one eye have difficulty in terms of establishing distance,” she says.

Having gradually lost the use of my right eye over a period of time had enabled me to adapt to these unavoidable changes in terms of the way I see, or do not see, things. In the same way that a person with sore teeth or gum problems on the one side of his or her mouth will subconsciously and automatically chew foods with the teeth on the unaffected side, so too will the person with monocular vision simply start viewing the world with his or her unaffected side. With one eye blinded, the brain will automatically “cancel” that eye out and rely only on the unaffected eye. This is important to note since many people have fears about constantly being aware of a “black block” on the one side of their visual field. The brain simply cancels the blinded side out. Vos agrees, but adds that if the dominant eye is the one affected there might be occasional complications. “If the brain is used to relying predominantly on receiving information from the right eye, and that eye is then blinded, the brain will still try to receive information from that eye,” she says. I can certainly attest to this, as this phenomena becomes most obvious when reading a book – I will find myself reading the words on a page and then suddenly realise that my vision had become blurred. This is as a result of the brain trying to use the right (blinded) eye to read. This is a minor inconvenience, however, since a few blinks of the eyes will “reset” the visual system, for want of a better term.

The most obvious challenge presented by monocular vision, however, is not impaired depth perception or the brain ‘forgetting’ that the one eye cannot see, but the fact that 20% of the visual field is now effectively a blind spot (this could increase to 40% if the unaffected eye tries to look in the affected direction’s side, since it will be obstructed by the bridge of the nose – see Figure 1). This loss of peripheral vision could lead to a lot of collisions with objects or people. Frank B. Brady, author of the semi-autobiographical A Singular Vision – The Art of Seeing with One Eye, notes the hyper-awareness necessitated by the loss of one eye, stating that “Any loss of visual perception was more than offset by the enforced – and often excruciating – increase in alertness.” This is something I can intimately relate to, as I find myself using my neck and hearing in a heretofore unprecedented way in an effort to pick up as much visual and sonic stimuli as possible so as to prevent me from unintentionally bumping into people and objects. Still, some awkward bumps are unavoidable.

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Figure 1. Graphic illustration of the visual field of a person with monocular vision. © Juan Garcia and Craig Luce

As has been pointed out, the psychological reaction to losing the use of one eye varies from person to person. Some see it as a mere nuisance, while others look upon it as a debilitating disability. With proper psychological counselling and care the more adverse effects of monocular vision can be mitigated to a significant extent. Karlien Erasmus is a practising psychologist who often works with patients who had suffered some or other kind of trauma. She says it is imperative that such individuals receive proper psychological assistance in order to help them come to terms with whatever trauma they had suffered and to help adjust them to the reality of wearing prosthetic appliances. “The eyes are the windows to the soul and we communicate a lot of our emotions with our eyes when we are in conversation with others. If someone is experiencing problems with his or her eyes, or eye prosthesis, it will certainly affect that person’s self-esteem […] it is of course possible that a person’s eye prosthesis will closely resemble a real eye, but it also might not. If so, the person with the prosthesis will feel self-conscious and might be inclined to withdraw from social interaction.”

Once it has been established that the affected eye is beyond repair, the focus shifts to a more aesthetically-oriented issue: orbital or ocular prostheses. Depending on the severity of the trauma that had rendered the eye blind, be it as a result of external trauma or a congenital condition, one will have either an orbital or an ocular prosthesis custom made for oneself. The difference between an orbital and an ocular prosthesis will be discussed below, as well as the specific types of surgical procedures that are often performed in advance in order to prepare the eye and eye socket for the insertion of a prosthesis.

Pre-prosthesis surgery

Depending on the severity of external trauma or the effects of congenital disease, the ophthalmologist most commonly will perform either enucleation of the eye, exenteration of the eye or carry out what is known as a ‘conjunctival flap’. Enucleation involves surgical removal of the eyeball, exenteration involves the surgical removal of most of the tissue in the orbital socket (eye socket) while a conjunctival flap procedure keeps the eye intact but numbs it by having layers of the conjunctiva (the invisible layer covering most of the eye) stretched over the front part and then sown shut.

The most drastic procedure of the three, ophthalmologists generally opt only to enucleate the eye in cases of extreme trauma (e.g. if the eye had been badly disfigured as the result of a car accident), though it may also be performed to eliminate a pain caused in the affected eye due to disease. According to Carrie Morris, MD and Julie Woodward MD of EyeNet Magazine, therapeutic enucleations have been performed since the 16th century, but the procedure has only been optimally performed from the 20th century onwards due to the advent of new technologies that have enabled surgeons to keep the eyelids and orbital volume intact. As Edwina Vos explains, enucleation is performed in order to lessen pain, remove a disfigured eye, aid in terms of cosmesis (the aesthetic dimension of the eyes) and to restore the loss of volume in the orbital socket.

According to Vos, enucleation involves the ophthalmologist performing a 360 degree periotomy (severing the outer conjunctiva), severing Tenon’s fascia (the membrane attached to the inner layer of the conjunctiva and envelops the eye from the limbus to the optic nerve in the back of the eye socket). After this membrane had been dissected, the six extraocular eye muscles (see Figure 2) that effectively hold the eye in place are severed (these being the Superior Oblique, Medial Rectus, Inferior Oblique, Superior Rectus, Lateral Rectus and Inferior Rectus). Any remaining fatty tissue is then cleared away before the optic nerve is severed and the globe (eye ball) is removed from the orbital socket. Extreme care should be taken to preserve the integrity of the six extraocular muscles since these will be reattached to the silicone or coral implant, so as to aid in mobility of the implant. Once the implant has been placed, it is wrapped in the remaining sclera (white part of the eye) and conjunctiva, after which the extraocular muscles are reattached. The entire procedure is carried out under general anaesthesia.

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Figure 2. Graphic illustration of the six extraocular eye muscles. © Juan Garcia and Craig Luce.

Vos says while enucleation is generally an effective proactive measure against the possible onset of sympathetic ophthalmia (a syndrome in which the unaffected eye develops a sympathetic reaction to the affected eye) and intraocular tumours (tumours inside the eye), the procedure is not without possible complications. “Before surgery the ophthalmologist should explain to the patient that certain complications may arise after the eye had been enucleated, including some impairment ofintraocular muscle function, infection of the eye socket, visual hallucinations and sagging of the eyelid (ptosis).” She explains that it is for these reasons that exenteration is also sometimes viewed as an alternative to enucleation since the former preserves some of the internal tissue and nerves. See Figure 3 for a simple illustration of the difference between enucleation and exenteration.

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Figure 3. Graphic illustration showing the difference between an enucleated and exenterated orbit. © Juan Garcia and Craig Luce.

As explained in the My Story post, the conjunctival flap is the least intrusive and traumatic of these procedures. A conjunctival flap is most often performed on patients who have a blinded and sometimes pain-ridden eye, but where the eye itself has not been disfigured and is not afflicted by intraocular disease. This is the procedure that I underwent at the beginning of 2013. As detailed in the abovementioned section, a conjunctival flap involves the ophthalmologist severing parts of the conjunctiva around the back of the eye and stretching it over the front part of the eye (that being the sclera, iris, cornea and pupil), and then sewing it shut. The aim of this procedure is to numb the eye by covering any sensitive parts with the invisible conjunctival layer. The eye itself remains intact, and after it has healed an ocular prosthesis (scleral shell) is placed over the eye in the same way that a contact lens fits over the eye. If all goes well, the difference between the prosthesis and the unaffected eye will hardly be visible to those not aware of your situation. Of course it was not always this easy. Let us take a look at the evolution of, and technology behind what is commonly referred to as an artificial eye.

The Ocular Prosthesis

 According to Brady, the first artificial eyes started appearing around the time of Shakespeare. These primitive prostheses were usually made of gold or silver and worn over the eyelids, basically resembling a monocle with an arm that fit around the back of the head. These were known as ekblepharon eye prostheses. (See Figure 4). By the time of the Venetians the ekblepharon prosthesis had evolved into lens-like implants that were worn over damaged or shrunken eyes (enucleation had been around since the 1500s but really only became standard medical practice around the 1800s).

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Figure 4. Graphic illustration of a Renaissance era ekblepharon eye prosthesis. © Juan Garcia and Craig Luce.

Jackie Heatlie says the prostheses that were developed around the 19th century resembled marbles and were often made from enamel or cryolite glass. “They [prostheses] had a thick rounded shape and were mainly imported from Germany, due to the Germans’ superior glass blowing techniques.” She adds that these crude glass eyes were later replaced with acrylic eyes, or ‘stock eyes’. “During or just after the Second World War, the USA started producing their own artificial eyes from acrylic as it was more affordable for the general public. These acrylic eyes were mass produced and called ‘stock eyes’. These ‘stock eyes’ were imported and fitted by eye specialists or nurses at government hospitals in South Africa in the 1900s and often did not appear natural. Optometrists later started fitting the stock eyes in their practices.”

She says many laypeople and would-be prosthesis wearers are still under the impression that an eye prosthesis resembles the marble-shaped or stock eyes of yore. This is perhaps due to the fact that some people still wear ‘glass eyes’, coupled with the fact that the modern-day prosthesis (i.e. the modern scleral shell) was only introduced in the 1970s from the United Kingdom.

Since the 1970s there have been many technological innovations in the fields of ocular implants and ocular prosthesis. Heatlie says before the advent of silicone implants those who have had an eye enucleated often had bulky enamel implants fitted into the empty orbit. Because these enamel implants were not as malleable as silicone they were fitted on a “best fit” basis, and the thickness of the implants often resulted in pathological problems to the patient’s facial features (build-up of intra-orbital pressure, sagging etc). With the introduction of silicone implants, the ophthalmologist’s and ocularist’s jobs became much easier. Due to its malleability, silicone could be custom fit into an empty orbit, was better at accommodating intra-orbital pressure and its relative lightness meant that sagging of facial features in and around the orbit became less prominent. Coral implants were even more helpful in this regard. Vos says another added benefit was that the extraocular muscles could be easier attached to a silicone opr coral implant than a glass or enamel one, thus aiding in mobility of the implant (and, by default, the scleral shell placed over the implant).

Heatlie emphasises that the proliferation of conjunctival flaps was also significant since it ruled out the need to enucleate the eye completely. “Eye specialists also started performing ‘conjuntival flaps’ covering the blinded eye to decrease the sensitivity and to allow for successful haptic lens wearing,” she says, adding that the orbital volume presented by a natural eye meant that the shell that fits over a numbed eye could be thinner and thus less uncomfortable. Today custom-made ocular prostheses are made of high grade, high strength Acrylic–Poly Methyl Methacrylate (PMMA). “It is easily maintained, durable and is safe to use in the medical world,” she says.

The creation of an ocular prosthesis is quite an intricate procedure, even though it usually takes no more than a few hours to make. Heatlie describes the process as follows:

1. Depending on the orbital situation, an impression is made of the ocular/orbital cavity.

2. This impression is placed in a moulding flask filled with a moulding stone material similar to gypson.

3. The moulded shape is later filled with the soft clear acrylic and cured in a pressure oven.

4. When ready the mould is taken apart to reveal the now hard plastic model which is then shaped, polished and prepared for fitting.

5. This model is fitted to the socket and adjusted and shaped to achieve the right prominence, lid flow, opening and appearance. Measurements are made and a marker is placed in the exact spot where the pupil of the iris should be.

6. A second mould is poured and prepared for this model.

7. An exact replica of the iris colour is painted on a small ‘button’ and is later placed into the second mould with a white soft acrylic.

8. After curing it is cut down and the veins and tints are then hand painted onto the acrylic scleral surface.

9. The copied “eye” is prepared and again cured with a clear acrylic. After curing the final product is smoothed and polished and prepared for the fitting.

A brief video demonstration of how an ocular prosthesis is made can be found here.

Having undergone this exact procedure back in the beginning of 2013, I can personally attest to the skill and attention that go into the creation of an ocular prosthesis. Unaware of the fact that the prosthesis would be hand-painted, I was quite surprised, and more than a little apprehensive, when Heatlie sat down in front of me, inspected my unaffected eye meticulously and then started painting a replica of it (see Figure 5). How could the human hand create something that even remotely resembles an actual eye? Would she be able to capture all the little details and nuances of a natural eye? Needless to say, she did and I could not be happier.

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 Figure 5. Jackie Heatlie painting my ocular prosthesis. Photographer: Andrew Bwalya

Asked about this particular step of the process, Heatlie says it is not uncommon for the ocularist to also be an “eye painter” of sorts. “The ocularists in South Africa are all equipped with the skill to produce the whole eye, including the painting of the colour and the veins. Overseas they do have artists that only paint the colours and they would supply to the ocularists” she says. She was, however, quick to point out that some eye colours are more challenging to replicate than others. “The easiest colour to paint would be the brown coloured iris, the different shades of brown are quite easy to capture. The blue/green colours are a bit more difficult, but I would say painting a blue iris colour can become quite complicated. The colour can change quite significantly during the day, due to the lighting and the changing moods of the patient.”

Now that the ocular prosthesis has been created and custom fitted, it is important to take notice of the fact that great care should be taken in terms of the maintenance of the prosthesis. This should go without saying, as the average ocular prosthesis costs approximately R10 000. Routine removal and cleaning differs from patient to patient. Daily removal and/or too much handling of the prosthesis may cause irritation of the eye socket for some, while others may experience unsightly secretions if the prosthesis is removed and cleaned too seldom. “The material of which the prosthesis is manufactured is basically a hydrophobic material, meaning it does not allow water or tears to spread across its surface easily. This can cause the tearing to dry rapidly on the surface of the acrylic and result in severe protein deposit build-up,” says Heatlie. She also emphasises that an annual inspection of the socket by an ocularist with a maintenance procedure of polishing the ocular prosthesis is imperative as this maintains the health of the socket plus ensures that the fitting of the eye prosthesis is still correct.

While ocular prosthesis are expensive, with a starting cost of approximately R10 000 for a scleral shell (as mentioned above), they are an excellent means of restoring aesthetic balance to an affected person’s facial features. The continuous advances in technology means that ocularists are able to create a prostheses that push the limits of realism. The end result is extremely life-like and most people will never even notice the difference unless it is explicitly pointed out to them. The aesthetic and psychological benefits of a well-designed and well fitted prosthesis cannot be overstated. This particular aspect is discussed at length in the My Story post.

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