What is the significance of near point vision

The RNPR is designed such that the cheek rest cannot advance closer than 5. Maples et al. Several authors have assessed NPC between subjects with normal binocular vision and convergence insufficiency and suggested a clinical cutoff value of 5 and 7 cm for the NPC break and NPC recovery, respectively 5 , 20 , Furthermore, recent studies have used NPC of six or less as a criterion for the diagnosis of convergence insufficiency 27 - To overcome the drawback of the RNPR to accurately measure less than 5.

RNPR is an accommodative target, and it can be less sensitive to evaluate NPC for the diagnosis of convergence insufficiency.

The study by Pang et al. Thus, the credibility and reliability of RNPR become questionable. Adler et al. They concluded that NPC determined with targets in free space would be more accurate as it correlates with the real world scenario Similarly, Siderov et al.

The touch gives a proprioceptive feedback which might indicate that the target is closer than its actual distance and provides a stimulus to cease convergence and accommodation early, resulting in a more remote NPC Several studies have reported that the NPC break point would differ from the recovery point 17 , 20 , The relative difference is important in making the diagnosis of convergence insufficiency; the use of the RNPL rule makes it difficult to diagnose the borderline cases of convergence insufficiency There are also no recent studies to validate the use of RNPR and the design of the instrument has remained unchanged since its introduction in the mids.

Nevertheless, clinicians still choose to use the RNPR. Moreover, it is expected that if targets are used in free space, the chances of errors are high if the subject or the clinician moves or is not steady.

Another possible reason could be that most of the clinicians are not aware of the drawbacks of the RNPR. Though the RNPR has a few advantages; there is no enough evidence to validate its use.

The author would like to thank Prof. Monica Chaudhry and Associate Prof. An SE refraction worse than 0. Individuals with a history of eye surgery and those with a diagnosis of tropia or amblyopia were excluded from the present study. Linear regression was used to explore the relationship of these indices with age and sex. Analysis of variance was used to determine the differences between these indices by using refractive errors. Finally, the relationship between each of these indices with age, sex, and refractive errors was examined in a multiple linear regression model.

In this model, refractive errors were entered into the model by considering individuals with emmetropia as the reference group. The cluster effect was considered for more accurate estimation of the standard error.

A significance level of 0. Given the higher participation of female students, weighting for sex was applied. Of the 1, selected individuals, 1, participated in the study After applying the exclusion criteria history of surgery, heterotropia, and amblyopia , a total of 1, individuals were analyzed in this study; of these, 1, The age of the included students ranged from 18 to 39 years, and the mean age was Table 1 shows the mean NPC by age and sex.

The findings of the present study showed that the mean NPC for all the students was 7. As shown in Table 1, the NPC increased from 6. Linear regression showed that a 1-year increase in age was associated with a 0. The mean NPC in the emmetropic, myopic, and hyperopic groups was 7. In the multiple linear regression model, after entering the variables of age, sex, and refractive error in the model, only age maintained a significant relationship with the NPC.

The NPA was measured separately in each eye. The mean NPA in the present population was 9. The NPA increased from 9. The near point of accommodation in different refractive errors. SE, spherical equivalent. This study evaluated the AA and convergence in a young-to-middle-aged student population in a southern city.

According to the findings of this study, the mean NPC is approximately similar to the values reported by Ostadimoghaddam et al [ 15 ] for the 20—29 years age range 7. However, it is more proximal than the levels reported for the 19—30 years age group in other studies. Ovenseri-Ogbomo et al [ 2 ] and Yekta et al [ 14 ] reached the values of 6 and 5.

Table 2 summarizes the NPC values reported in the different studies. These different results can be attributed to several factors, including the type of target used in the NPC measurement, differences in the characteristics of the studied populations, and variations in the source and method of measurement.

In their study, the NPC was defined as the distance between the break point and the plane of the lateral canthus, while in our study, the measured distance was from the break point to the spectacle plane. Considering a 12 to 15 mm vertex distance for the glasses, a 22 mm difference between the results is reasonable. The type of target is also an important factor in NPC evaluation. Therefore, attention to clarity may interfere with convergence and may lead to a more proximal NPC.

Siderov et al [ 29 ] measured the NPC in 20—85 years old subjects using several types of targets and found that the NPC results were influenced by the target type only in younger individuals but not in presbyopic individuals. Thus, we can conclude that the NPC is related to accommodation. This is not unexpected because in NPC measurement, in fact, the absolute convergence is being evaluated, which is the combination of tonic, accommodative, proximal, and reflexive convergences.

Therefore, stimulating accommodation increases the total amount of absolute convergence by increasing accommodative convergence, and ultimately, the measured NPC is underestimated; however, this does not occur with non-accommodative targets. Regarding the measurement method, it has been suggested that targets that are mounted on a rule provide a higher estimated NPC than targets that are moved manually and freely.

The findings of the present study indicate an increase in the NPC values with age. Larsson et al [ 24 ] and Yekta et al [ 12 ] observed lower NPC values in children younger ages. Studies have also shown that the NPC recedes with aging. However, in our study, the mean NPC in men was 0. Given the students' greater need for vision, especially near vision, [ 1 ] the AA is a key factor in the rate of ocular symptoms resulting from prolonged near work.

Studies have shown that the AA decreases with age, [ 13 , 14 , 26 ] and our results concur with their findings. Table 3 summarizes the AAs in different studies. Most studies evaluated the AA in people under 18 years of age and reported higher values more proximal NPA than in the present study. The estimation of Abraham et al [ 13 ] in 19—year-old Indians was 1. Rambo and Sangal [ 31 ] posited the possible effect of geographic region on the AA and suggested that people residing in tropical climates tended to have a lower AA than the Europeans.

However, it must be noted that their population sample was presbyopic. A comparison of the AA in this study with the calculated values based on the Hofstetter formula shows that the latter is not an accurate predictor for the adult Iranian population. As demonstrated in Figure 3, the mean AA in our younger age groups was lower than the mean estimated by Hofstetter [ 32 ] and was significantly higher in the older age groups, especially after 30 years of age.

This formula fits the studied population best at the age of 30 years; therefore, Hofstetter's formulas, which are widely used in the diagnosis of AI, may lead to false negative results in individuals under 30 years of age and false positive results in individuals over 30 years of age. The mean and minimum amplitudes of accommodation calculated by Hofstetter's formula according to age and mean amplitude of accommodation measured in the present study.

Results regarding the relationship between the AA and sex are inconsistent. In agreement with the study by Castagno et al, [ 33 ] our study did not show a significant difference in the NPA between women and men. However, Hashemi et al [ 26 ] showed that the AA in year-old girls was higher than that of boys in the same age group. They attributed the difference to factors such as education and nutrition. Yekta et al, who studied presbyopic individuals, estimated a higher AA in women and suggested that hormonal factors might have a role, especially in post-menopausal women.

While some studies state that refractive errors do not correlate with the AA, [ 23 ] Abraham et al [ 20 ] reported higher AAs in myopes. This difference was observed in 35—year-old individuals, and no difference was observed between the types of refractive error after the age of 44 years. Maheshwari et al reported similar results. Investigating the relationship between the NPA and refractive errors in the present study showed a low level of NPA in the hyperopic group.

Despite the greater accommodation demand with hyperopic spectacle correction than with myopic and emmetropic correction, we found a lower NPA in hyperopic patients. There are several possible reasons for this finding. First, hyperopes may go without glasses, especially at younger ages. Therefore, they use their accommodation for near work and even far vision more than emmetropic and myopic individuals do.

This is similar to orthoptic reinforcement exercises that increase the amplitude with repeated accommodation, [ 36 , 37 ] which occurs naturally in hyperopic eyes. Another reason may be the magnification effect of glasses. The blur caused by defocus is understood much later in the larger retinal images because the details in a larger image are more recognizable than those in a smaller one. Thus, the patients may report the blur much later. This study reports normative values in large university students using a valid method; however, it has some limitations.

Cycloplegic refraction was not performed. In addition, similar to other studies, refractive errors were measured based on SE that may affect the interpretation of results in some cases such as mixed astigmatism.

Moreover, the age range of participants was relatively wide. The NPC values were lower than those reported in most other studies on this age group. Clinicians should be aware of the impact of age and sex during the evaluation of CI symptoms and other binocular vision dysfunctions.

The discord with the Hofstetter formula also should be considered in the diagnosis of AI. National Center for Biotechnology Information , U. J Ophthalmic Vis Res. Near point and far point of accommodation.

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