INTRODUCTION
The eyes are the first features of the face to be noted. The unfortunate loss or absence of an eye may be caused by a congenital defect, irreparable trauma, or tumors. The disfigurement due to the loss of an eye can cause significant physical and emotional problems.[1] Therefore providing an artificial substitute to restore the form and functions is the mandatory reason for such disability. Prosthodontic rehabilitation of such patients has therefore become the treatment option to restore esthetics and comfort and also elevate the psychological status of such patients.[2]
In terms of anatomy, the iris is the muscular, pigmented curtain that covers the area in front of the eye between the cornea and the lens and is punctured by the pupil. The iris is situated behind the cornea and in front of the lens and ciliary body. Iris positioning in a prosthetic eye is critical as the complete success of maxillofacial prosthesis depends on the esthetics offered, which in turn lifts the patient's quality of life. The esthetics mainly depends on positioning the iris along with proper shade selection and contouring. Various factors affecting iris positioning are the appropriate selection of shape, size, contour, and color of the iris.[3]
Many methods for the precise positioning of the iris have been described in the literature, such as an ocular locator, fixed calipers, grids, dividers, inverted anatomic tracings, and visual assessment.[4] The present literature review aims to highlight all the proposed techniques for iris positioning in a prosthetic eye with their pros and cons. This study will help the maxillofacial prosthodontist select the appropriate iris positioning technique to enhance the prosthetic eye's esthetics.
METHODOLOGY
The present narrative review used the Preferred Reporting Items For Systematic Review and Meta-Analyses guidelines for the literature search, including all the relevant articles. The search strategy is in Table 1 with an assessment based on the Population, Intervention, control, and outcomes study criteria.
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Table 1: Systematic search strategy
LITERATURE SEARCH
The dental literature in English was searched electronically to find scientific articles that applied to the methods of iris positioning in patients with ocular and orbital defects. The following index word searches were used in PubMed, Google Scholar, and Cochrane: Iris positioning and patients with ocular and orbital defects. The publication year ranged from January 1969 to February 2022, allowing the quest to encompass all of the papers in that database. The abstracts were read first, followed by the full-text documents that had been preselected.
Articles with full text were collected and reviewed further for research that met the inclusion criterion. The inclusion criteria include all the case reports, which are in the English language from 1969 to February 2022. The titles and abstracts of all screened papers were evaluated and checked for appropriateness. Finally, a manual search was conducted to enhance the electronic search, which included the citations of the documents that were eventually retrieved. Newcastle–Ottawa Quality Assessment scale was used for assessing the risk of bias in prospective studies. AXIS tool was used for bias assessment of cross-sectional studies. Examples of times in the AXIS tool include assessing the appropriateness of the study design for the stated aims, sample size justification, the reliability of survey instruments, and evaluating whether the response rate raises concerns.
RESULT OF LITERATURE SEARCH
The electronic search in the GoogleScholar and PubMed databases provided a total of 25 articles that were considered potentially relevant. The text found using the “and“ Boolean operator in between the search words: Positioning, Iris, and ocular Prosthesis were 25. In the second phase of article selection, one article was excluded as it was not found to be in the English language. Another 1 article was excluded as the complete text was not found. After reading the full text, 24 articles were selected for the present review. After reading the full text out of 24 articles, three articles were excluded due to duplication of method and material. A total of 21 articles were selected for the narrative review, as described in Figures 1 and 2. The Newcastle–Ottawa Scale and AXIS Tool showed that the study design was appropriate, with a proper selection of articles for generating the best results.
Figure 1: Inclusion of articles from Google Scholar Search
Figure 2: Inclusion of articles from PubMed Search
RESULT OF INCLUDED ARTICLES
The methods and techniques involved for iris positioning in an ocular prosthesis that were included in this review were pupillometers by Roberts,[5] facial measurements using anatomic landmarks by Brown,[6] window light by Joneja et al.,[7] visual assessment by James et al.,[8] ocular locator by McArthur,[9] inverted anatomic tracings by Nusinov et al.,[10] graph grid method by Guttal et al.,[11] Boleys gauge by Manvi et al.,[12] grid cutouts placed on spectacle frame by Pai et al.,[13] customized scale computer-aided designing/computer-aided manufacturing (CAD/CAM) by Gupta et al.,[14] modified Hanau wide-view spring bow by Shetty et al.,[15] customized frame spring bow assembly by Chamaria et al.,[16] pupillary distance (PD) ruler by Bhochhibhoya et al.,[17] digital photograph by Dasgupta et al.,[18] and optical Vernier interpupillary distance (IPD) ruler by Chicago and Syafrinani,[19] a laser pointer technique by Belkhode et al.[20] and digital imaging by Lanzara et al.,[21] and Naes' ruler by Atwal et al.[22] were included in the present review.
DISCUSSION
A prosthetic eye is frequently used to replace an eye lost or removed due to a congenital deformity, accident, or malignancy. The physical and psychological effects of evisceration, enucleation, or exenteration of an eye influence the patient's quality of life. In such unhappy individuals, rehabilitation in the form of a prosthetic eye reestablishes shape, improves psychological status, and restores esthetics and comforts.[232425]
The most critical stage in creating a prosthetic eye is positioning the iris. A correctly positioned iris gives the patient's face realism and symmetry. The exact location of the iris has been widely established in the literature using a variety of approaches and procedures.[26] Subjective and objective techniques can be used to classify these methods. Ocular locator, fixed calipers, grids, divisions, inverted anatomic tracings, and visual evaluation are examples of subjective procedures. They manipulate the operator's perception for the iris to be precisely positioned. The list of subjective and objective techniques used for iris positioning is listed in Table 2. Objective techniques were developed and published to solve the issues associated with subjective methods. Table 3 lists the advantages and disadvantages of objective procedures over subjective ones.
Table 2: List of objective and subjective techniques of iris positioning
Table 3: Pros of objective methods over subjective methods
In 1968, Roberts developed a device consisting of cylindrical tubes with parallel axes, each with a positive lens.[5] The instrument was created with the pupil as a fixation point, with two plastic rotating discs with scale marks sitting on the bridge of the nose. The Pupillometer was designed to be utilized during the wax-up stage of construction. This pupil segment is aligned in the wax sclera for prosthetic eye replacement alone, without replacement of the surrounding orbital region. The Pupillometer was found helpful in identifying the precise location of the artificial eye in the whole prosthesis when the prosthetic eye was to be put in an orbital prosthesis. This is true for both types of applicators. The Pupillometer is used to provide a natural esthetic effect by providing an exact final registration of the position and alignment of an eye prosthesis.[5]
Brown recommended moving measurements from the normal contralateral eye to the problem location in the 1970 publication.[6] This was utilized to mimic the size and form of a typical anatomical eye. To orient the iris in the prosthetic globe, Brown proposed collecting the facial measurements of several facial anatomic features concerning the relationship of the normal eye with the neighboring anatomic structures.[6]
In a 1976 publication, Joneja et al. presented a verification procedure for appropriate iris placement.[7] He stated that the measurements should be taken such that the pupil's center is at the same distance from the bridge of the nose as a normal eye. The patient is next instructed to stare straight ahead in the direction of a well-lit window. The picture of window glass may be observed symmetrically in both eyes if the eyes are correctly aligned. To obtain appropriate alignment, the location of the acrylic resin eye may be changed. The “Window Light Technique“ is the name given to this technique.[7]
In a 1976 study published in Glasgow, James et al. described a method including a wax replica of the prosthesis into which a plastic disc was placed to show the location of the iris and pupil.[8] The artificial eye's primary body is made to fit the wax model perfectly. After adding vascular and other marks to the sclera, a circular hole is drilled onto its anterior surface to receive a painted plastic disc mimicking the iris. Then, a clear acrylic cornea is put anteriorly (lensing). Then a clear acrylic cornea is put anteriorly (lensing). While the transfer of information between the fitter and manufacturer often results in a sufficient prosthesis, there are inherent issues in adequately interpreting the fitting's instructions and the regularly utilized production procedures.[8]
With his novel Ocular Locator, McArthur devised a grid approach. An X and Y-axis and a mirror image of the axes were drawn on graph paper with a grid side of 1 mm × 1 mm.[9] The division and subdivision pattern was repeated for all intervals on the X-axis. The Y-axis was labeled 1 through 9 and split and subdivided in the same way as the X-axis was divided and subdivided. The black-and-white film was used to photograph the grid. The negative was reproduced and expanded to the exact size of the original grid on photographic film. The finished device consisted of a black grid on a transparent backdrop between two sheets of 1/8th-inch Plexiglas with a nose aperture in the center. A line was scribed into the Plexiglas from top to bottom along the middle of the grid, splitting the right set of coordinates from their mirror copy on the left. A pair of horizontal lines were also scribed into the Plexiglas, one at the top and one at the bottom of the grid. The distance between the two horizontal scribed lines was reproduced using a stiff caliper. The scribe midline and intersecting set of horizontal lines on the ocular locator are superimposed over the marks on the patient's face when the locator is put on the patient's face. The ocular locator is applied to the stone moulage as it was to the patient's face. Before the prosthesis is processed, all indirectly produced facial prostheses must be directly verified on the patient's face.[9]
Nusinov et al. suggest a technique termed “Inverted Anatomic Tracings“ for iris location and centricity in this study.[10] On a 5 × 5-inch acetate sheet (0.020 inches thick), trace the orbital architecture of the remaining eye and the orientation lines with a wax pencil. Making the tracing when the patient is staring straight ahead in a conversational gaze is critical. To ensure that all orientation lines are overlaid, invert the anatomic tracing over the surgical defect.[10]
In 2007, Guttal et al. employed the Graph grid approach to locate the iris.[11] Anatomical landmarks such as the midline (passing through the forehead crease, glabella, tip of the nose, and chin), medial canthus, lateral canthus, and the horizontal lines referring to the center, inferior, and superior limits of the iris were marked on the patient's face with an indelible pencil in this method. The clear grid template was used to transfer the markings. The iris was affixed to the wax pattern after the marks were put onto the sculpted scleral wax pattern.[11]
Manvi et al. proposed a mechanism for accurately verifying iris location in a study.[12] The ocular prosthesis was adjusted to mimic the healthy eye's location, with the patient gazing at a distant point immediately ahead. A reference mark was placed at the midline, and the mediolateral location was confirmed using a Boley gauge. The prosthesis was precisely positioned mediolaterally, anteroposteriorly, and inferosuperiorly to mirror the location of the native eye.[12]
Pai et al. employed grid cut on spectacle frames to position the iris in 2010.[13] On the lens of the glass eyeglasses, two grid cuts of identical size were put. The patient was told to maintain a normal conversational gaze by looking forward. An indelible ink marker was used to outline and trace the iris. This grid is removed and put on the inner surface of the afflicted eye's eyeglasses lens, aligning with the horizontal and vertical lines of the affected eye's grid cuts. On the glassware's afflicted side, the iris's image is reflected on the grid cutout on the outside surface of the lens.[13]
In 2013, Guptal et al. used a customized scale to locate the iris.[14] From left to right at the top and right to left at the bottom, the custom scale was marked from 0 to 4 cm. The iris was placed mediolaterally, superior-inferiorly, and anteroposteriorly using this bespoke scale. As a reference point, the vertical line on the customized scale was aligned with the medial canthus of the eye. The mediolateral dimension of the iris and the distance from the medial outline of the natural iris to the medial canthus of the eye were measured using a bespoke scale. The measured distance was transferred to the scleral wax pattern using the tailored scale after the wax pattern was placed.[14] The patients were requested to sit up straight and maintain a normal expression, and their facial morphology was evaluated. The 3D facial models were then aligned to the standard head position. The healthy side of the mirrored model covered the fault region in the original model, which was mirrored according to the midplane. The prosthetic margin was designed to encompass the defect area's boundary, with the red circle as a guide. After the nonessential parts of the mirrored model were eliminated, a preliminary simulated prosthetic pattern was developed. The final prosthesis might be manufactured directly and swiftly using a CAD/CAM negative mold. The orbital defect was rebuilt precisely, and the ocular prosthesis was placed correctly.
In 2017, Shetty et al. employed a Modified Hanau wide-view spring bow to place the iris.[15] The orbital pointer is supported on the bottom border of the ala of the nose by the Hanau wide-view spring bow's frame, which has been inverted. The edentulous facebow fork was joined to the reversed frame with the transfer clamp assembly. With double-sided tape, a metal-graded scale measuring the width of the fork is affixed horizontally to the fork. Two paper clips were placed on the scale to measure the mediolateral breadth of the eye.[15]
Chamaria et al. used a customized frame spring bow assembly to place the iris in 2017.[16] This device consisted of a heat-cure acrylic resin frame on which a graph grid with equal lines on either side of the scale's midline was affixed. Ballpoint pen caps were used to fasten the scale to the spring bow. A Hanau Spring bow was used to attach this frame. The spring bow's graph grid and assigned scale aided in the proper alignment of the iris.[16]
In 2018, Chicago et al. employed an Optical Vernier IPD to locate the iris. The millimeter-scale optical Vernier IPD ruler has a moveable frame to adjust and record the distance between the eyes.[19]
In 2019, Bhochhibhoya et al. utilized a PD ruler to place the iris.[17] The instrument was composed of graded scales positioned in a horizontal plane relative to the patient's nose's axis. The notch on the bridge of the nose is utilized to situate the instrument in the patient, and the eye is then inserted into the ocular opening. The patient is instructed to grasp their eye in a conversational look, and the graduated scale is used to record the measurements. The sculpted scleral wax pattern is then transferred using these measurements.[17]
For iris placement, Dasgupta et al. in 2019 employed digital images and spectacles gridded with an mm scale.[18] A DSLR camera was used to get a shot of the entire face for digital photography. The patient was told to sit up straight without using a headrest. The patient was requested to stare straight and at eye level while the image was being taken, and the lens was held such that the flashlight's reflection was visible in the middle of the pupil. An indelible pencil was used to transfer all of the anatomical markers from the pictures on the patient's face. Both subjective and objective verification is used in this strategy.[18]
He also advocated a gridded spectacle approach by adding a gridded translucent paper to the front parallel acrylic glasses to create custom-made eyeglasses. The face marks were produced using this gridded spectacle to identify the natural eye's pupil location and corneal plane. The faulty site was then marked with these markers. The installation of a transparent grid boosted patient participation.
Belkhode et al. employed laser pointer equipment to locate the iris in 2020.[20] This device comprises an occlusal plane analyzer, web camera, laser pointer, and software. An “L”-the shaped metal frame was attached to the horizontal plate to the side of the typical eye to shift the occlusal plane analyzer. The laser pointer and web camera were attached to the “L“ plate through holes. The horizontal plate was fastened by one more moveable vertical plate. The iris distances were measured using this adjustable vertical metal plate and a laser pointer. The web camera was connected to the laptop. It used the program “laser range finder“ to precisely measure the distances between the iris and the corner of the eyes. These measurements were taken from the healthy eyewear and then repeated on the damaged eye.[20] The installation of a transparent grid boosted patient participation.
Lanzara et al. used photoshop software to locate the iris on a digital image in 2019.[21] The iris of a typical eye was photographed digitally. After that, the image was transferred to Photoshop software and printed on high-quality photo paper. To preserve the image of the scleral blank from the staining impact of acrylic resin, it was then veneered with a laminating bag. On the afflicted side, the scleral blank was modified and altered.[21]
Nae's ruler is a flexible ruler made of plastic, consisting of a notch for a nasal bridge and two eye boxes one on each side of the notch. The eye boxes are placed equidistant from the nasal notch bridge center. The labeling of 30 in each of the two boxes created an interpupillary distance (IPD) of 60mm, which lies in the average range of the Indian Population for both gender. On the opposite side of the ruler, there are measurements for the iris and pupil size, which helps to choose the right iris for a particular patient. Due to the flexibility of this multifunctional ruler, measurements of the iris and IPD may be done with ease. It is not complicated like other systems and provides several readings on a single ruler while being user-friendly.[22]
Newer objective techniques have overcome the shortcomings of prior subjective procedures. None of the documented techniques of iris positioning is free of lacunae. They do have some pros and cons that are listed in Tables 4 and 5. A comment on the lifespan in terms of the outcome of the various procedures for iris centering can barely be made due to a lack of well-structured and long-term prospective research. The different commonly used techniques are the Guttal et al.'s Grid method,[11] the Reverse anatomic tracing method by Nusinov et al.[10] and the laser pointer method by Belkhode et al.,[20] etc. The other techniques which are seldom used are the pupilometer by Roberts,[5] Ocular Locator by McArthur et al.[10] and Naev's ruler[22] because of the unavailability of their instruments.
Table 4: Pros and Cons of subjective techniques of iris positioning
Table 5: Pros and Cons of objective techniques of iris positioning
SUMMARY
The success of an ocular prosthesis largely depends on the precise orientation of the iris. An attempt is made to call attention to the published articles on iris positioning. It can be concluded that the objective techniques for iris positioning making use of a simple armamentarium, without the need for patient cooperation and assistance that best suits the case, should be opted to get the best esthetic results such as techniques given by Dasgupta et al., Lanzara et al., and Pai et al. It depends on the proper knowledge of all the techniques with future advancements. The void for the availability of a recent theoretical review on iris positioning techniques has been filled with the compilation of all the available literature. The digital approach, such as digital photography, offers an advantage over traditional methods for iris location. However, well-structured and long-term prospective studies are recommended to comment on the longevity in terms of the outcome of the various techniques for iris positioning.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
Acknowledgment
The authors would like to acknowledge the help and support of all the teaching and nonteaching staff of the Department of Prosthodontics, Sharad Pawar Dental College and Hospital.
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