Prism in the Control of Hidden Internal Strabismus Myopia – A Study of Reading Additional Lens Cai Yan, Ophthalmology, PLA 474 Hospital
Xu Yuan, Ophthalmology, Xijing Hospital, Fourth Military Medical University
0. Introduction
Myopia, a phenomenon that has kept pace with human civilization, has caused many inconveniences to people. Myopia is also a product of human adaptation to nature, and low myopia has some advantages in many aspects that are incomparable to orthopia, such as the convenience of near eye use after old vision. Myopia that has been stable, wearing a pair of glasses is not a big deal. However, the continued increase in myopia has caused many people to develop many complications without realizing it. These complications lead to low vision and blindness, second only to glaucoma and cataracts in China. As the incidence of myopia continues to grow in China and as this myopic population continues to age, the number of people whose complications cause permanent visual impairment is likely to increase dramatically, potentially becoming the number one killer of vision. The social burden of increased myopia can be imagined as the demand for prescription glasses will become higher and the difficulty of various surgeries will increase, in addition to the cost of frequent replacement of glasses. Effective control of myopia development has become an urgent expectation of myopic patients and many parents of children with myopia, and an unavoidable responsibility of optometrists. To this end, we have made some attempts to design a reading add-on mirror using the refractive effect of the trigeminal prism and the relaxing effect of the orthospheric mirror, which has a better control effect on myopic patients with internal obliquity. The results of the study are as follows.
1.Literature review
The hypothesis of regulatory tension, based on studies of myopic regulation in students in the 1960s, suggests that excessive near-eye work during near vision can cause regulatory fatigue, loss of flexibility of the ciliary muscles, and insufficient relaxation of the ciliary muscles during distance vision, hence the appearance of pseudomyopia; and notes that myopia is temporarily shifted to the far point after sustained near-eye work, i.e., myopia is aggravated[1] . In recent years, more international studies have been conducted on this phenomenon, confirming that transient myopia occurs after sustained near-eye work. For example, Ciuffreda (1998) found that myopia can be induced after 10 min of sustained near-eye work (equivalent to 5 D of regulatory load) with myopia of -0.35 D, which gradually disappears after 1 to 2 min. This phenomenon was not observed in orthoptic eyes [2]. This finding has been confirmed by reports from this century. For example, Vera-Diaz (2002) reported that temporary myopia induced by 10 min of use of 4 D regulation exceeded resting myopia and orthopia in progressive myopia.3 Ciuffreda (2002) found that continuous reading for 4 h also induced a tendency for temporary refractive conversion to myopia in myopia, but not in hyperopia.4 Wolffsohn (2003) found that this phenomenon was more pronounced in yellow individuals with a high prevalence of myopia[5] . This phenomenon is more pronounced in progressive myopia and late-onset myopia than in resting myopia and early-onset myopia (where genetic factors may be more important). This study is direct evidence that conditioning factors can induce myopia in humans and suggests that some individuals may be more sensitive to conditioning load, i.e., susceptible to myopia.
In the past 30 years, myopia research has focused on animal studies, while clinical studies have not received the attention they deserve, and to some extent, the differences between experimental animals and humans have been ignored, and the results obtained from animal experiments have been applied to clinical practice without analysis. But in fact, the results of animal experiments have practical significance only when they are confirmed in clinical studies. Functional studies (e.g., transient myopia due to persistent myopia), optical index analysis, biochemical tests, and pathological studies (including ultrastructure, immunohistochemistry, molecular pathology, etc.) will be the main directions of myopia research [6].
Epidemiological surveys have confirmed that the occurrence of myopia is related to near-eye work. The prevalence of myopia is higher in those with high near-eye workloads[7, 8, 9] . This phenomenon persisted after adjusting for family history[7, 9] . The higher prevalence of myopia in the cohort survey was found in those with higher education levels, which may be related to high near-eye workload[10, 11] . The high prevalence of myopia among high-income individuals may be due to the association between their income and educational level [10, 11]. The difference in myopia prevalence between urban and rural children may also be related to the higher near-eye workload in urban areas [12]. The United Nations Health Organization conducted population-based surveys in China, Chile, and Nepal. The prevalence of myopia in a district of Beijing was found to increase annually from age 5 to 15 years, more than in Chile and much more than in Nepal[13] . A 2-year follow-up confirmed that this trend persists[14] . In recent years, the prevalence of myopia has been increasing among the Asian yellow population (China, Japan, and Singapore), with the prevalence of myopia in the Japanese and Singaporean adult populations exceeding that of the European and American populations [10, 11]. In contrast, the prevalence of myopia in Europe and the United States has remained relatively stable[15] . The majority of scholars now accept that myopia is genetically and environmentally related [16]. The mode of inheritance is also considered to be polygeneic, i.e., each group of genes acts in a micro-effective and cumulative manner[16] . In recent years, myopia genetic indices calculated from twin studies or family aggregation analysis are higher in Western countries, but the role of environmental factors is still recognized, especially in Eastern countries.16 Work in this field in the 21st century has mainly validated the phenomena observed in the 20th century. New and unknown environmental factors were rarely explored [6].
In the last century, experimental animal studies confirmed the role of environmental factors in the development of myopia, emphasized myopia-causing changes dominated by retinal signals, and discovered many biochemical substances that influence the development of myopia, which strongly contributed to the study of the pathogenesis of myopia. However, when applying the results to clinical practice, researchers have not been aware of the species differences between humans and experimental animals (especially between chickens and mammals) and the age differences (experimental animals are mostly juveniles, while the age of myopia in humans is high in adolescence); they have not understood the differences between the two types of myopia, which are fundamentally different (form deprivation myopia is extremely rare in humans, and is only occasionally seen in individuals with high lid ptosis and refractive media in early childhood; the vast majority of humans have myopia. The vast majority of human myopia is closer to out-of-focus myopia), which has also led to some misconceptions. In the past, studies on the mechanism of myopia development denied the role of accommodation in myopia development because of the observation that form-deprived myopia could still occur in chickens after severing the optic nerve, destroying the Edinger-Westphal nucleus, and severing the ciliary and choroidal nerves. However, in fact: (1) most human myopia is out-of-focus myopia. Cutting the optic nerve in experimental animals had an inhibitory effect on out-of-focus myopia, indicating the importance of the center in myopia development. (2) The fact that myopia can still occur in experimental animals after disruption of the Edinger-Westphal nucleus only suggests that regulation is not the only mechanism of myopia, but does not mean that regulation does not play a role in myopia development under normal conditions. After cutting the ciliary nerve and the choroidal nerve, myopia still occurred in chickens, but myopic refraction was significantly reduced, suggesting that the efferent nerve still plays a role in myopia development[16] . In recent years, it has been found in experimental animals that accommodation plays a role in refractive changes caused by double visual planes[17] , and in clinical studies, transient myopia caused by persistent near vision has been found[18-21] , all of which have reawakened the attention of researchers to the mechanisms of accommodation.
A recent classification system for myopia is based on age-related myopia prevalence and age of onset. Early onset myopia (EOM) is the most common type of myopia, with onset around 6 to 15 years of age, and once it occurs, myopia continues to increase until it reaches 20 years of age before stabilizing. Myopia mostly stops developing at the age of 16 or 17, when overall physical development has also basically stopped.
There are two types of myopia caused by continuous near work: temporary myopia and permanent myopia. Transient myopia is a refractive state that resembles myopia due to a temporary shift in the distance, while a ciliary muscle paralysis examination will reveal a true refractive state of hyperopia or orthopia. Many studies of permanent myopia have demonstrated a strong association with proximity work, and Zadnik et al. suggested that the best model for predicting refractive error should take into account not only the parents’ history of refractive error but also the child’s own proximity work. It is also of great interest to study myopia in college students and proximity workers, as such studies reveal that a large amount of proximity work is directly related to the development of adult myopia. Because myopia development in the LOM is closely related to the near-visual environment, studies of persons with myopia caused by proximal work may offer the possibility of investigating the ocular components and oculomotor mechanisms that contribute to myopia development. Because proximity work includes enhanced amounts of accommodation and vergence, it is particularly important and logical to investigate the role of accommodation and vergence and the oculomotor system as a whole in the development of myopia.
Regulation and vergence are fundamental elements of the oculomotor system’s mechanism of near work, and their combination produces a clear monocular image in the binocular state. Based on Westheimer’s pioneering research, feedback control theory was used to develop models that describe the static and dynamic responses of the accommodation and vergence system. The basic feature of all models is that regulation initiated by fuzzy imaging and vergence initiated by lavish opening are controlled by two negative feedback loops, and the interaction between the two is represented by the crossover of the two feedbacks at the control output. In this way, modulation control can trigger a convergence response (modulated convergence or AC), and conversely, convergence control can trigger a modulation response (convergence modulation or CA). The acquisition of AC or CA is represented by AC/A or CA/C, respectively. Either the modulation system or the vergence system can be separated by opening the feedback loop, e.g., covering a glance can open the vergence feedback loop, or using a pinhole pupil to open the modulation feedback loop. The control of the convergence system (VCG) can be estimated from the amplitude of the stimulus/response function in the open-loop convergence state, and the control of the convergence system (VCG) can be estimated from the open-loop regulation state of the gaze lavage opening curve; while regulation and convergence measured in the dark is the physiological resting state.
Temporary myopia caused by near work is considered to be a temporary shift of the far point after sustained near eye use. This myopia is considered to be the first stage of refractive error. Unlike true myopia, pseudomyopia is a temporary myopia in which the far point is continuously shifted closer, and pseudomyopia is a myopic refractive error when examined without ciliary muscle paralysis. However, pseudomyopia is reversible because the refraction of pseudomyopia is orthoopic when examined after ciliary muscle paralysis, suggesting that the temporary myopia is caused by an adjustment spasm or ciliary muscle spasm.
Temporary myopia due to close work has been extensively studied in the laboratory. Since 1960-1970, when the dark focus was identified as a marker of regulatory rest, a preliminary approach to speculate on the oculomotor/ocular component was proposed: a person with a dark focus that is too far away (low refraction) will exert more oculomotor force to focus on the myopic marker during near work than a person with a close dark focus. However, similar studies have had different results, with some finding that the dark focus of the LOM is significantly more distant than that of the ortho-optic eye, while others have concluded that there is no significant difference between the two. a single study by Gilinartin and Bullimore highlights the diversity of findings. In their study, the dark focus values were the same in the orthoptic and late myopic groups, and the results appear to be such that although the dark focus of an individual is relatively stable, inward proximity work causes an inward shift of the dark focus that persists for some time after the proximity work has ceased, a shift that is referred to as modulation adaptation or modulation lag. Since modulation hysteresis refers to a prolonged and sustained increase in ciliary muscle tone, it is conceivable that this hysteresis is associated with myopia triggered by near work. However, studies of accommodation between refractive groups have shown different results. McBrien and Millodot, Woung and Strang et al. reported that the late-myopic group showed greater accommodation than other types of refractive groups, but other studies did not find differences between the orthoptic and late-myopic groups. Although all of these studies were designed to identify differences in dark focus across refractive groups, because they were cross-sectional or retrospective, it is not possible to determine whether the differences in dark focus observed from these subjects were the cause of myopia occurrence or a consequence of myopia production. The same problem exists with the comparison of differences in oculomotor parameters between refractive groups cited in the following paragraphs, where Jiang conducted a longitudinal study and found lower dark focus values in LOM than in orthoptic eyes. However, this low dark focus was altered when a person developed myopia to permanent myopia. Instead, orthoptics with high dark focus values were at risk of developing myopia. It is clear that a distant dark focus is evidence of a spasm or lag in accommodation and can lead to the development of myopia.
Since prolonged near work causes a near shift of the dark focus, its effect on the regulatory stimulus/response function has been a hot topic of research. pigion and Miller reported that in 20 orthoptic youths, there was no significant difference in the preadaptation and postadaptation regulatory responses, regardless of whether they looked near (3.3D) or far (0.16D). Ebenholtz and Zander measured the far point versus the near point after sustained near vision in 17 orthoptic youths and found that the near point shifted closer while the far point did not change significantly. ehrlich found that after accommodative adaptation, the accommodative response became closer when looking far, but he did not measure the response under other accommodative demands in his experiment with 15 subjects with refraction of +1D to -5D. Owens and Wolf-kelly used 28 college students as subjects and measured the regulatory values at four target distances between 0D and 4D before and after adaptation; their refractive values were not reported and the regulatory response shifted closer on average by 0.35 D after adaptation. jiang and White used Hung and Semmlow’s static model to predict that the change in the regulatory response after adaptation should be (1-K)×ΔDF, where K is the slope of the modulated stimulus/response function and ΔDF is the magnitude of the shift of the dark focus after adaptation. The experimental data they derived with orthoptic eyes and LOM are consistent with the above equation calculation. Also, the differences in the results of the studies by Owens and Wolf-kelly, Digion and Miller, and Jiang and White can be explained by this equation. The difference in the slope of the conditioning stimulus/response function in these studies determines the different effects of dark focus shifting on the conditioning response. Persistent eye use in environments with poor illumination or low contrast is thought to be an environmental factor that contributes to the development of myopia. We know that the slope of the regulatory stimulus/response is lower in these environments, so dark focus shifting does help reduce the regulatory lag caused by myopic labeling, but as previous studies have shown, persistent dark focus shifting will eventually affect the ocular dynamics by altering refractive error. McBrien and Millodot recorded dark focus regression after sustained near work in both the ortho- and LOM groups. They were unable to determine the rate of regression in the ortho-group because there was little change in dark focus after near work in these subjects, whereas the LOM group showed a significant dark focus shift after near work and no significant dark focus regression within 15 minutes of the end of near work. Rosenfield and Gilmartin found no significant difference between the ortho- and LOM groups after relatively short periods (15, 30, and 45 seconds) of near-visual marker (3D) fixation, but Gilmartin and Bullimore reported that the dark focus regression rate was significantly lower in the LOM group than in the ortho-visual group after 20 minutes of fixation on the same near-visual marker, and that if the near Strang et al. also showed that the LOM group had slower dark focus regression after adaptation. In conclusion, all of these studies suggest that the time constant for dark focus regression after adaptation is longer in the LOM group than in the ortho-optic group when sustained near work or in situations requiring high accommodation. It is possible that the vagal inhibition of the ciliary muscle was weaker in the LOM group than in the orthoptic group. If this phenomenon existed before the emergence of myopia, it would be a precursor to the triggering of accommodation hysteresis in near working conditions [22].
Data suggest that as early as the 1960s, studies have suggested that reducing myopia or increasing hyperopia during near reading can effectively prevent myopia onset or slow myopia progression, but past research data have some design flaws, such as reasonable control group design, adequate longitudinal observations, standardization of standardized and uniform testing instruments or standardization of testing devices, etc. There is no conclusive information to prove that this There is no conclusive data to prove that this method can prevent myopia or slow down its progression, but it is worthy of further study as it can relax the regulation of near reading and is based on the “regulation theory” of myopia occurrence and development.
2. Clinical practice
In a large number of clinical practices, we have taken different compensatory measures for each patient’s different eye position, different refractive status and different gaze habits. Adding a near-use additional lens on top of the original glasses significantly improved the fatigue symptoms of myopic eyes and received good results in controlling the progression of myopia.
The first is used for hyperacuity. Under normal conditions, the process from the point of gaze from far to near, the adjustment of both eyes increases, while both eyes turn inward. Correct pooling is a prerequisite for maintaining normal visual function in both eyes. People with hyperconjugation have more symptoms, such as eye discomfort and headache after a short period of reading, and occasional blurred or double vision when working at close distances. The characteristics of hyperconjugation are basically no occlusion at distance gaze, but internal occlusion at near gaze and increased AC/A ratio (usually greater than 6△). Reading add-on (+1.50Ds) can drastically change the focus and alleviate the symptoms caused by hyperconcentration. A significant reduction in myopic progression was also observed with this add-on, which is the most desirable effect.
For most myopic eyes that exhibit exotropia, the adoption of a bottom-facing nasal-side trigeminal plus +1.50Ds additional lens not only improved the fatigue symptoms that many myopic eyes are prone to after prolonged reading, but the myopic progression also improved, but the long-term results were still less than ideal. Here, the suspicion is raised whether occult exotropia is a result or a cause of myopia. The trigeminal lens may be only a stop-gap measure for exotropia, and the effects after its removal have to be considered. The lack of long term effect is considered to have this cause.
In myopic internal obliquity, wearing ordinary negative spherical lenses improves the refractive state of each eye and creates a clear image on the retina, but also increases the regulation of close reading, and this regulation increases the collection. In the case of internal obliquity, even in the absence of these effects of increased accommodation, there will be excessive accommodation at close and sustained gaze, which will be more pronounced with lenses. The excessive pooling will cause the retinal image to change its correspondence after transmission to the visual center, resulting in a blurred image in the visual center due to mutual interference of binocular imaging. The human eye is unable to distinguish between this central cause of visual quality loss and retinal imaging ambiguity, and habitually tries to obtain a change by increasing accommodation. However, regulation once again increases the pooling, and this cycle gradually intensifies, causing not only visual fatigue but also the logical development of myopia. By reducing the near accommodation by adding +1.50 Ds of progressive lenses or +1.50 Ds of additional lenses for near use, the cycle is interrupted, the symptoms are relieved, and the development of myopia is slowed. This has been proven in practice and must still be explored theoretically.
In the case of myopic emmetropia, it is worthwhile to consider the question of the causal relationship between emmetropia and myopia. Myopic eyes do not need to use regulation when looking at the near, and after the relaxation of regulation, the lack of pooling impulses may induce emmetropia; after the appearance of emmetropia, the requirement of the visual center to fuse the image increases the pooling impulses, which also increases the impulses of regulation, and myopia may also develop, which may be the main way of myopia development. In myopia, 30% to 80% of myopes have varying degrees of exotropia, and the use of accommodation alone makes the pooling impulse less, but makes the exotropia worse. The use of the method of relieving the adjustment plus helping the collection, that is, ortho-spheres plus trigeminal lenses with the bottom facing the nasal side, can relieve the symptoms, and some can also improve the naked eye vision in the near future, but the long-term effect is not satisfactory, probably related to the inability to completely improve the eye position.
The distant gaze plus pooling training, a great attempt in the 1970s in the former Soviet Union, was an effective intervention for myopia development (the incidence of high myopia after 5 years was more than 20 times different from that of the control group), and the recognition of this result at that time was that this training could relax regulation. What is the pathway through which this training acts as a control? The mechanism of action is still inconclusive and is considered to be related to an increase in binocular coordination. However, it is clearly not justified to adopt this training for myopic patients with internal obliquity.
3. Opportunity
A chance attempt led us to another role of the trigeminal lens. This was during a trial of near-use lenses on a patient who was experiencing visual fatigue after reading and whose chief complaint was that he needed to elevate his books a bit after wearing the lenses in order to read comfortably. He then added a pair of bottom-facing trigeminal lenses to his trial frame, and the visual fatigue was relieved, and he has been responding well to this prescription. This led us to think of patients with developing myopia, and whether the use of bottom-facing trigeminal lenses could play a role in controlling the development of myopia.
4. Theoretical analysis
When sitting at a table to read and write, in addition to the head-down movement, the downward turning of the eyeballs is an essential auxiliary movement, as shown in Figure 1.
Figure 1
There are three factors to consider for the occurrence of visual fatigue when gazing downward.
First, the pressure of the eyelids.
When the human eye is gazing horizontally, the pressure on the optical center of the cornea is balanced up and down. In lower gaze, the pressure of the lower lid on the cornea deforms the lower cornea, increasing the refractive power in this area. This change facilitates reduced accommodation. A superficial example: from time to time, I see some elderly people who look up and down when looking at small things without glasses, and this solves part of the problem by taking advantage of the law of increased local curvature below. However, when this phenomenon occurs, it may create another difficult problem, which is aberration. It may be manifested as a kind of upper concave lower convex higher-order aberration, long time in this environment reading, visual fatigue will certainly appear, an unclear imaging is more likely to cause myopia increasing. This is certainly related to conventional astigmatism.
Second, the impact of the lower and inner rectus muscles of both eyes.
When the eyes gaze downward, the inferior rectus muscles have an inward retracting effect in addition to the downward rotation. The impulse of the internal rectus muscle matches the impulse of the regulation, which will undoubtedly affect the regulation. The overuse of the extraocular and intraocular muscles is the basis for the occurrence of visual fatigue; at the same time, the internal retraction action also creates the opportunity for microstrabismus to appear in patients with internal obliquity when they look close. When microstrabismus is present, binocular vision is affected and the imaging of the target that both eyes are looking at at the same time produces blurring in the visual center. The nucleus involved in the regulation may send abnormal impulses, again exacerbating microstrabismus. This may also account for the faster progression of myopia in the presence of internal strabismus. Thus, it seems that reading add-on lenses are more suitable for myopic eyes with occult internal strabismus.
Third, the direction of gaze off the visual axis produces coma.
When the human eye is gazing at the object below, it may also use the deviation of the visual axis to assist. Multifocal IOLs, take advantage of the fact that the visual axis can change this property. The presence of this assist when the eye is held downward for long periods of time may bring about a change in the optical performance of the human eye. Aberrations occur when the optical axis of a group of optical lenses deviates. Almost all aberrations may result in altered imaging clarity on the retina. This loss of imaging clarity, which cannot be resolved by accommodation, not only causes visual fatigue, but is also a trigger for increased myopia, as is the effect of eyelid pressure.
How can this set of problems caused by the downward rotation of the eye be addressed? The only consideration is to keep the eye from turning too far down. What is the best way to allow these readers to read without having their eyeballs turn down too much? The trigeminal lens provides a good helper for us.
As shown in Figure 2.
Figure 2
Without the addition of a trigeminal, as in Figure 1, the upper eyeball, which then needs to be turned downward, may appear in the three situations described above. If a bottom-facing prism is added, it is possible to achieve downward gaze without excessive downward turning. This patient, who needed to elevate his reading material to feel comfortable, confirmed this for us first.
Visual fatigue is more common in clinical practice, and the triggers that cause it are also factors that contribute to the development of myopia. Unclear imaging on the retina can lead to regulatory lag and regulatory disorders, and the mechanisms by which these phenomena lead to myopia progression are well established. We have been confused whether myopia progression leads to visual fatigue, or visual fatigue leads to myopia progression, or both are homologous. If they are homologous, solving the visual fatigue may also solve the continuous progression of myopia. For this reason, we have made the following design.
5. Design of additional lenses for reading
Add half a pair of glasses to the lower part of one spectacle for reading. Add this half pair of lenses when looking close. In the classroom, use the upper half to see far and the lower half to see close. The long-wearing glasses crossbars are equipped with a magnetic suction device. The removable half glasses are also equipped with a magnet on the bridge. The removable half glasses are equipped with a combination of spherical and prismatic lenses with +1.50Ds to +2.00Ds for spherical lenses and 4∆ to 5∆ for prisms with the prismatic base facing downward at 90° [24]. As shown in Figure 3.
Figure 3
6. use of reading add-on lenses
Patients with myopia with occult internal obliquity were screened by ophthalmologic examination and selected to wear reading add-on lenses. Using removable half lenses, the lower two layers of lenses were used when looking close. When looking at the blackboard in class use the upper portion of the original lens left in place. This half additional component can be removed when leaving the desk, without abnormal eye changes caused by wearing a temporarily unused prescription for a long time. Practice has confirmed that this solution solves the problems of irregular astigmatism aggravation caused by progressive multifocal lenses and loss of best corrected vision.
7. Reading add-on lens effect
We have observed 50 cases of myopia with internal obliquity, and have successively used near-use glasses with descending-1.50Ds, student progressive multifocal lenses, and reading add-on lenses for fitting. The shortest follow-up period was 4 months and the longest was 5 years. RESULTS: Patients with myopic intraocular obliquity had a rapid increase in myopia with regular glasses. The decrease -1.50Ds near with and student progressive lenses was the second, and the increase in myopia after wearing reading add-on lenses was the smallest, all with significant differences, and even a decrease in myopia in the short term. Patients who had experienced a decrease in best-corrected visual acuity after wearing student progressive multifocal lenses had to get their visual acuity back. There was also a significant difference in the degree of increase in columnar lenses compared to progressive multifocal lenses [25].
8. Outlook
In the study of the development of myopia, the regulation doctrine has undergone several rejections, each of which opened up new doctrines but also left open the possibility of the existence of a part of such factors. In practice, it has been seen that each of the different triggers may, under its specific conditions, produce a common effect – myopia deepening. If different measures can be taken to capture each of the different triggers, the effect of prevention and control will be more desirable. Addressing myopia with a hidden internal obliquity, as a specific type of myopia, at the first prescription is an ideal way to prevent and control myopia. Reading add-on lenses, which use a bottom-facing trigeminal lens to assist the downward rotation of both eyes, along with a convex lens to assist reading, are effective in controlling the development of this type of myopia. This will also open up a new avenue of research for myopia prevention and control.
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