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College of Optometry Theses, Dissertations and Capstone Projects

5-17-1998

Myopic progression throughout the pre-presbyopic adult years Myopic progression throughout the pre-presbyopic adult years

Brandt Dennehy Pacific University Chris Heetland Pacific University

Recommended Citation Recommended Citation

Dennehy, Brandt and Heetland, Chris, "Myopic progression throughout the pre-presbyopic adult years"

(1998). College of Optometry. 34.

https://commons.pacificu.edu/opt/34

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Myopic progression throughout the pre-presbyopic adult years Myopic progression throughout the pre-presbyopic adult years

Abstract Abstract

The documentation of the trends and progression of myopia has been a topic of many previous studies.

This retrospective study was designed to track and analyze myopic progression in the pre-presbyopic adult years. Records of seventy-seven non-RGP/ PMMA subjects between 20-40 years of age were reviewed and then grouped by decade and gender for further data comparisons. Statistical analyses showed significant myopic progression, but there was no significant difference in levels of myopic progression between males and females or the 20-30 vs. the 30-40 year age ranges. Results show the need for further studies that will take into account additional data such as the subjects' occupation, level of education, race, axial length, and keratometry readings.

Degree Type Degree Type Thesis

Degree Name Degree Name

Master of Science in Vision Science Committee Chair

Committee Chair Karl Citek

Subject Categories Subject Categories Optometry

This thesis is available at CommonKnowledge: https://commons.pacificu.edu/opt/34

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MYOPIC PROGRESSION

THROUGHOUT THE PRE-PRESBYOPIC ADULT YEARS

By

BRANDT DENNEHY and

CHRIS HEETLAND

A thesis submitted to the faculty of the College of Optometry

Pacific University Forest Grove, Oregon

for the degree of Doctor of Optometry

May 17, 1998

Adviser:

Karl Citek, O.D., Ph.D., FAAO

Biography

Brandt Thomas Dennehy

I was born on July 10, 1972 in Missoula, MT. I was raised in Butte, MT, and graduated from Butte High School in 1990. After high school, I attended Carroll College (in Helena, MT) and received my Bachelor of Arts in Biology at the end of May, 1994. My optometric education began in the Fall of 1994 at Pacific University (in Forest Grove, OR). Upon graduation (in May 1998), I plan to move back to Montana (near home) and practice as an employee or associate at some optometric practice.

Christopher Grant Heetland

I was born on December 10, 1970 in Platte, SD. In 1977 my family and I moved to Valley City, ND where I spent my childhood years, graduating from high school in 1989. I attended both North Dakota State and Moorhead State Universities before receiving my Bachelor of Arts in Psychology in May, 1994 at Concordia College, Moorhead, MN. I was married that same summer and then moved to Forest Grove, OR to pursue my optometric degree. I plan to graduate from Pacific University College of Optometry in May of 1998 and become an associate of an optometric practice somewhere in the southwest.

Br~-

cl~ w ^f.L-ttwo~

Christopher G. Heetland

Karl Citek, O.D., Ph.D., FAAO

Acknowledgments

Patrick Caroline, C.O.T., F.A.A.O., for giving us a topic that led us to pursue myopic progression.

Dale Heaston, O.D., for providing us with all ofthe patient files and organizing them into a data base for easier analysis.

Abstract

The documentation of the trends and progression of myopia has been a topic of many previous studies. This retrospective study was designed to track and analyze myopic progression in the pre-presbyopic adult years. Records of seventy-seven non-RGP/

PMMA subjects between 20-40 years of age were reviewed and then grouped by decade and gender for further data comparisons. Statistical analyses showed significant myopic progression, but there was no significant difference in levels of myopic progression between males and females or the 20-30 vs. the 30-40 year age ranges. Results show the need for further studies that will take into account additional data such as the subjects' occupation, level of education, race, axial length, and keratometry readings.

Introduction

The documentation of the trends and progression of myopia has been the topic of many previous studies. The overwhelming majority of these studies, however, pertain only to the early years of myopia -- through the teens. The lack of research covering myopic trends beyond the age of 19, and especially between the ages of20 and 40, is likely due to the presumed notion that, in general, this age period is one of refractive stability, coinciding with the cessation of normal ocular growth during the late teenage years (Fledelius, 1995). Gosset al (1985), for example, concluded that myopia

stabilization was the predominant trend in 108 young adult myopes. Information

regarding the trends of myopia after the age of 40 is also more plentiful than the preceding 20 years. The abundance of clinical data available for this age group which is free from the problem of self selection may explain this. Epidemiology studies on refractive error which utilize the clinical data of younger populations would likely be skewed in the myopic direction, but in the "40 and over" population, the inevitability of presbyopia will nullify the issue. This paper examines the myopic trends occurring between the ages of 20 and 40 and analyzes male versus female results.

Conclusions regarding the incidence and progression of early myopia have thus been well established through analysis of the fmdings of many authors. The benchmark study by Glasscock and Cook ( 1951 ), for example, has been confirmed by numerous other studies since then. The results from 375 cycloplegic retinoscopy fmdings on full term newborns indicate that 25% of all neonates are myopic, where the overall average refractive error is +2.07 D of hyperopia. By age 6, however, according to the work of

Kempf and Collins (1928), most of these myopes have disappeared, and the hyperopes, too, have gravitated toward the middle, producing an over-all mean refractive error of + 1.06 D of hyperopia. The prevalence of myopia then begins to increase again after age 6, with the incidence peaking at around puberty (Hirsch, 1963). Goss and Cox (1985) report that the average rate of childhood myopia increases at a rate of 0.4 D/year, although there is considerable individual variation, with girls typically progressing earlier and faster than boys, and thereby reaching higher degrees of myopia and stabilizing at an earlier age (Braun et al, 1996; Parssinen and Lyyra, 1993). Environmental factors have also been implicated in the progression of myopia. The study by Parssinen and Lyyra (1993) found that while time spent on sports and outdoor activities correlated with decreased myopic progression, time spent on reading and close work correlated with increased myopic progression. Reading distance was also found to be a significant variable in this study.

Interestingly, one of the most predominant and consistent conclusions made from previous research on myopia pertains to the age at which the myopia begins, with an earlier onset being associated with a higher myopic refractive error end result (Braun et al,

1996; Gosset al, 1985; Parssinen and Lyyra, 1993). Grosvenor (1987), in an effort to create a more practical and verifiable classification for myopia uses this age of onset as the distinguishing feature. Grosvenor's classification utilizes four different stages: congenital- -born with myopia; youth--onset from age 6 through the teens; early adult--onset from age 20 through 40; and late adult--onset after age 40. While congenital and late adult onset myopia are associated with prematurity and cataractous changes, respectively, youth and early adult onset myopia have more complex proposed etiologies involving genetic predisposition, race, near work, educational level, and sex. Due to the many possible

variables contributing to myopic progression in the adult years, the trends are not as clearly defmed as during the youth years. The prevalence of late onset myopia, for example, is still debatable. The recent study in Copenhagen, Denmark (Fledelius, 1985) suggests that adult onset myopia appears more frequently than evident from textbooks, placing the estimate at 25-30% of all adult age myopia, with males accounting for the majority. One explanation for the relatively high estimate may simply be due to the recency of the study. Undoubtedly, modem generations incur far more near work than in the earlier generations which many textbooks are likely based upon.

Time spent on computers and the paper work required to meet today's stringent educational demands are two readily apparent examples of the ever increasing near stress placed on our visual systems. In agreement with this, one's education level , occupation, and income have all been repeatedly connected to the progression of myopia, the inherent near work involved implicated as the most likely causative factor. The nation wide study by Rosner and Belkin (1987) employed 157,748 males and found that years of schooling and intelligence weigh equally in their relationship with myopia. One survey of 447 optometry students reveals a remarkable deviation in the prevalence of myopia in this specific population at 75% (Septon, 1984). In contrast, the National Health and

Nutritional Study (1972), comprising a similarly aged population, suggests a 25% myopic prevalence.

The mechanism involved in this myopic progression in adulthood, whether originating during youth or early adult years, has been largely attributed to the axial elongation of the eye, with males accounting for the large majority of the cases (Fledelius, 1995; Grosvenor and Scott, 1993; McBrien and Adams, 1997; Simensen and Thorud,

1994). However, reports do exist that state otherwise. The study by Gosset al (1985) not only indicates that most myopes do not progress in the years from 20 to 25, but for those individuals who do undergo myopic progression, the corneal power change is a major determinant. Perhaps this is the very reason for the empirical use of rigid gas permeable lenses in the effort to control myopic progression in certain individuals-- the reduction of corneal curvature steepening. For, although a review of available literature on the subject will yield conflicting opinions and conclusions (Kerns, 1981), there is, nonetheless, ample research which indicates much efficacy in the control of myopia

through such measures (Grosvenor etal, 1991; Perrigin etal, 1990). The exact mechanism, however, behind the retarding of myopia progression through RGP wear is definitely not understood; as the very studies that validate RGP use also suggest that the induced flattening of the cornea is only part of the RGP effect as measured by keratometry

changes. This suggests an additional unknown mechanism involved and/or the possibility that keratometry readings do not perfectly correlate with the actual corneal curvature at the apex.

The purpose of the present study is to track the myopic progression of a randomly selected clinical population with the intent of gaining additional understanding of the progression of myopia in adulthood and any differences which may exist between men and women. Specific questions this study will attempt to answer are 1) Is there a tendency for myopia to progress in the pre-presbyopic adult years? 2) Are males more likely to have myopia progression through the adult years than females, as some previous research suggests? Or is this a fmding of the past when females generally spent less time in the educational system and thus performed less near work? 3) Does myopia progress faster in

females versus males as it does in the pre-adulthood years? 4) How does the 20 to 30 age group compare to the 30 to 40 age group? To insure the attainment of valid answers to such questions, certain criteria are used to screen this study's population base. One such criterion is the absence of any previous RGP or PMMA contact lens wear, which could otherwise be a significant source of data contamination.

Implications

By answering the above questions, the present study will provide valuable insight on myopia progression in adults. Such knowledge has direct application for refractive surgery, which has become increasingly popular in recent years. Determining an approximate age at which myopic progression stabilizes may benefit both the refractive surgeon and the referring optometrist in distinguishing a good surgical candidate from a poor one. Additionally, due to the increased near work demands of modern society, it is plausible to expect myopia to progress later into adulthood and to a greater extent than previously thought. If the current study's results support this hypothesis, they will be a source of validation for the near point stress theory of myopic progression.

Methods

This retrospective study involves the evaluation for myopic progression between the ages of 20 and 40. Seventy-seven patient records were taken randomly from an

optometric practice in the state of Washington, and only non-RGP/ PMMA wearers were used in order to not influence normal corneal curvature fluctuations. The subjects were divided into a 20-30 age range and a 30-40 age range, based upon age at the initial presentation, so that the results could be analyzed by decade. The study utilized 31 subjects who started in the 20-30 year age range and 46 subjects who started in the 30-40 year age range. All subjects had three refractive exams in their records, which spanned anywhere from a two to eight year period. Every subject also began the study with between zero and seven diopters of spherical equivalent myopia. Astigmatic levels were all converted into spherical equivalents because little astigmatic fluctuations were noted throughout the evaluation period.

Since not every refraction was performed on a yearly basis, the average dioptric change per year was calculated by dividing the dioptric change per exam by the number of years between each refractive exam. These results were then compiled onto a database so that all of the average dioptric changes could be added together and divided by the number of subjects involved during that year span. The total average dioptric change between 20-30 and 30-40 years of age was calculated as the sum of the average yearly progression. The database was designed so that the results can compare myopic progression between men and women separately or as a whole.

Results

This study showed myopic progression in both the 20-30 year and 30-40 year age groups. The total average myopic progression of the subjects between 20-30 years old was -0.807 diopters (D). The average myopic progression of the subjects between 30-40 years of age was -0.562 D. Although the amount of myopic progression per year varied, the average was -0.081 D per year (D/yr), standard deviation (S.D.)=0.0298 D/yr.

between 20-30 years and -0.056 D/yr., S.D.=0.0467 D/yr. between 30-40 years of age.

These are significantly different from zero at the 0.001 and 0.01levels, respectively.

Males progressed a total average of -0.874 D between 20-30, whereas females progressed -0.731 D. For this age group, the average myopic increase per year was -0.087 D/yr., S.D.=0.0413 D for males and -0.073 D/yr., S.D.=0.0387 D for females, both groups between 20-30 years of age. This difference between males and females is not significant at the 0.05 level, t(9)=0.78.

For the 30-40 year age group, males progressed an average of -0.828 D between 30- 40, while females progressed only -0.231 D. The average myopic increase per year was -

-0.083 D/yr., S.D.=0.0757 D for males and -0.023 D/yr., S.D.=0.057 D for females. Once again, this difference is not significant at the 0.05 level, t(9)=1.97.

Discussion

As expected, the results indicate a significant myopic progression between the ages of twenty and forty. Either an increase in corneal power or axial length accounts for this myopic progression, but this study does not differentiate between the two.

At the initial exam for the patients placed into the 20-30 year age group, males averaged -1.26 diopters (D) of myopia with a standard deviation (S.D.) of 1.55 D, and females averaged -1.07D with a S.D.=l.33D. In the 30-40 year age group, males averaged -2.47 D of myopia with a S.D.=l.90 D, and females -1.69 D of myopia with a S.D.=l.75 D. These high standard deviations show that there was no significant

difference in spherical equivalents of myopia between males and females in these age ranges.

It is also evident that myopic progression amongst males is not significantly different than with females. Even though the trend of the mean would appear to show that myopia progresses more in males than females, statistical analysis shows otherwise, due to the large standard deviations. For males vs. females in the 20-30 age range t(9)=0.78 and for the 30-40 year age range t(9)=1.97. Neither of these are significant at the 0.05 level.

Although the myopic progression is faster and has an earlier onset in females during the adolescent years (Braun et al, 1996; Parssinen and Lyyra, 1993), our results show that this dichotomy between males and females does not continue through the adult years

The trend of the mean also appears to show that myopic progression in the 20-30 year vs. the 30-40 year age range is faster, but statistical analysis shows that this difference is not significant at the 0.05 level, t(9)=1.94. Contrary to Goss (1985), we found that there is no difference between males and females and no difference between age groups.

Data including occupation, education level, and race, along with periodic axial length measurements and keratometry readings were not available in our data. Future studies should take those factors and methods into account in order to pinpoint the exact mechanism that causes the myopic progression though these adult years.

Appendix A

(raw data)

This appendix contains all of the raw patient records. The patients not used in this study have a line drawn through them

Patient Name.

Birthdate:· 12-15-62

Exam Date: - 6, uncorrected VA 20/400 right 201400

r._...~," right 20/20 left, RX -4.~0 OD, -3.75 OS

Patient Name:

Bithdate: 10-9-70

Exam Date: 7-10-92. uncorrected VA 20/400 right 201400 left, corrected VA 20J20 right 20J20 left, RX -4.00 OD. -4.25 OS

Exam Date: 1-6-9~. uncorrected VA 20/400 right 20/400 left, corrected VA 20120 right 20/20 left, RX -4.00 00. -4.50 OS

Exam Date: 5-20-96, uncorrected VA 20/400 right 20/400 left, corrected VA 20120 right 20/20 left, RX -4.00 00. -4.75 OS

, r Patlenl Name: ·

f

Birhtoale: .3=24.:61

t .

Exam Date: 3-3-92, uncorrected VA 20/400 right 20/400 left, corrected VA 20/20 right 20/20 left. RX -4.25 00, -3.00 OS

Exam Date: 11-22-94. uncorrected VA 20/400 right 20/400 left. corrected VA 20/20 rlghl20/20 lett, RX -4.50 00, -3.50 OS

Exam Date: 6-7-96, uncorrected VA 201400 right 20/300 left, corrected VA 20120 right 20/20 left. RX -5,00 OD, -3 75 OS

P.1:5

-M

1- , uncorrected VA-20/300 right 20/400 e , 20 left, RX -4.25 OD, -3.25 OS

Patient Name:

Birthdate: 2-3-59

t-1\

Exam Date: 2-27-96, uncorrected VA 20/400 righl20/400 left. corrected VA 20/20 right 20/20 left, RX ·5.25 00, -4.25 OS

Exam Date: 4-H-96. uncorrected VA 20/400 right 20/400 left, corrected VA 20120 right 20/20 left. RX -5.00 OD, -3.75 OS

Exam Date: 4-2·1-97, uncorrected VA 20/400 right 20/400 left, corrected VA 20120 right 20/20 left, RX -5.00 OD, -4.00 OS

Patient Name: I

M

Birthdate: 5-8-5/

Exam Date: 4-9-92, uncorrected VA 20/500 right 201500 left. corrected VA 20/20 right 20/20 left. RX -5.50 OD, ·5.75 0$

Exam Date: 5-31-94, uncorrected VA 20/400 right 20/400 left. corrected VA 20/20 right 20/20 left, RX ·5.50 00, -5.50 OS

Exam Date: 5-30-96, uncorrected VA 20/400 right 20/400 left. corrected VA 20/20 right 20/20 left, RX ·6.25 00, -6.00 OS

Patient Name:

Birthdate: 11·15-62

M

Exam Date: 10-22-92, uncorrected VA 20/400 right 20/400 lett, correcled VA 20/20 right 20/20 left R.X ·5.25 OD, -5.75 OS

i:P ' 2 cs ! i i i ! PIJL! ?PJQP! 2 ^ISS

Exam Date: 11-15-93, uncorrected VA 20/400 right 20/400 left, corrected VA 20/20 right 20120 left RX -5.25 OD -5.75 OS

Exam Date: 3-13-96, uncorrected VA 21400 right 20/400 !eft. corrected VA 20120 right 20/20 left RX -5.50 OD, -6.00 OS

Birthdate: 1-30-58

... 3 .1. b

Exam Date: 6-16-94, uncorrected VA 20/600 right 20/700 left, corrected VA 20/20 right 20/20 left RX -7.00 OD, -1.75 OS

~illtt~~ ·.

^{Exam Date:} 5-7-96, uncorrected VA 201600 right 20noo left. corrected VA

&'U\~~- 20/20 right 20/20 left RX-7 .00 00, -1 . 7 5 OS

am~

Exam Date: 5-8-97, uncorrected VA 20/600 right 201700 left. corrected VA 20/20 right 20/20 left, RX -7.00 OD. -1.75 OS

Pattent Name:

Sirthdate: -21-61

·""

.

.

.W :

Exam Date: - , uncorrected VA 20 20/20 rig 0120 left. RX -3.50 00, -4.00 OS

Patient Name: f

.at~p_ .. --;,~.-~. Blrthdate: 7-19

Exam Date: - . uncorrected VA 201400 rig 2012 20125 left, RX -5.50 OD. -6.00 OS

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